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Boundary Layer Transition: An Overview

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Presentation Slides from "BOUNDARY LAYER TRANSITIONS LECTURE SERIES" delivered at University of Calgary, Canada - Part 1

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Boundary Layer Transition: An Overview Mazharul Islam, PhD Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Boundary Layer Transition: An Overview Mazharul Islam, PhD University of Calgary, Canada March 20, 2015
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Main Contents 1 Objectives 2 Introduction 3 Brain Storming Session 4 Different Stages/Regions Related to BL Transitions 5 Instabilities & BL Transitions 6 Different Modes of Transitions 7 Important Parameters Affecting Transitions 8 Notable Experimental Investigations 9 Selected Models 10 Summary
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Objectives of This Presentation To learn about instabilities associated with boundary layer (BL) transition. To acquire knowledge about different modes of BL transition. To be informed about three classes of BL transition models.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Motivation Critical for computing the drag & skin friction coefficients reasonably for aerodynamic problems; Need for a useful model for the open-source/freely available CFD tools like OpenFOAM/foam-extend etc. Still challenging after many decades of research activities and there are scopes for further investigations; Quotes "... most important and probably the most difficult subject in boundary layer work..." (Schetz and Bowersox, 2010) Introduction, Chapter on "Transition To Turbulent Flow" “. . . predicting the onset of either natural or bypass transition is still more of an art than a science (see Savill, 1991 or Seiger et al. For examples).”(Mayle and Schulz, 1997)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Prominent Researchers Related to Instability/BL Transition L. Rayleigh (Instability) O. Reynolds (Pioneering experimentation in 1883) M.W.F Orr (Hydrodynamic Instability) A. Sommerfeld (Hydrodynamic Instability) L. Prandtl (concept of BL in 1904) G.I. Taylor (Instability) W. Tollmien (T-S Wave) H. Schlichting (T-S Wave) Klebanoff (K-type transition) A.M.O. Smith (original eN model) J.L. van Ingen (original eN model) M. V. Morkovin (Concept of Receptivity, Bypass transition) R.E. Mayle & A. Schulz (laminar kinetic energy equation) .... and many others
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Key Challenges related to BL Transition Different types; Affected by numerous parameters; Lack of experimental results of skin-friction coefficients around bodies of practical interests (like airfoils) at low Reynolds numbers (i.e. Re<500,000).
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Important Keywords Related to Boundary Layer Transition Critical Reynolds number (Recr ) Tollmien-Schlichting Wave Receptivity Transition onset Transition length Intermittency Relaminarization (or Reverse Transition) Λ-Vortices
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Brain Storming Session Importance of Boundary-Layer Transition Modeling; Ball-park critical Reynolds number for "pipe flow" (i.e. internal flow); Ball-park critical Reynolds number for "flat plate at zero incidence" (i.e. external flow) Available models or correlations for determining the transition onset and length;
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Brain Storming Session Commonly known Ball-Park Numbers According to Schlichting and Gersten (2000), For Pipe Flow (Eq. 1.11, pp 12): Recrit = 2100 (1) For Flat Plate at Zero Incidence (Eq. 1.12, pp 13) Recrit = 5.105 (2)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions BL transitions can be caused by different types of instabilities. "Some researchers identify as many as seven steps, going from instability through large three-dimensional disturbances and finally to turbulence." (Schetz and Bowersox, 2010)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Five Regions according to Schlichting (1979) Schlichting (1979) identified five regions which involves - 1 TS waves; 2 Spanwise vorticity; 3 Three-Dimensional breakdown; 4 Turbulent spots; and 5 Fully turbulent flow. Reproduced in Figure 2.1 in (Langtry, 2006)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Transition Region "The transition region is the region in which the boundary-layer flow changes from laminar to turbulent. The beginning of this region will be referred to as the "transition point" and will be considered to be the point at which the velocity near the surface begins to show an abnormal increase. The end of the transition region has been taken as the point at which the velocity near the surface has reached a maximum." (Silverstein and Becker, 1939)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Various Stages for a Flat Plate according to Narasimha Figure: Adapted from (Narasimha, 1990) Important Information from this figure: Breakdown zone Onset of Transition Intermittency Spot spread angle
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions "Onset of Transition", "Turbulent Spot" & "Intermittency" Onset of Transition: "The point of minimum skin friction is typically considered the start of transition" (Medida, 2014) Turbulent Spot: "... a turbulent spot is initiated when the maximum velocity fluctuation in the streamwise direction exceeds about one-fifth of the freestream velocity, almost independently of the Reynolds number [16]. " (Medida, 2014) Intermittency: "The intermittency factor was introduced [17] to quantify the rate of turbulent spot production and a relation between the transition Reynolds number and the intermittency factor was deduced. Once initiated, these intermittent turbulent spots grow in size and they travel downstream, until they merge into a fully turbulent boundary layer, thus completing the transition process." (Medida, 2014)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions BL transitions can be caused by different types of instabilities. "... instability and transition are not the same thing. Instability is merely the very early precursor of ultimate transition to turbulent flow, and knowing the conditions for instability alone is not of much use in predicting the subsequent conditions (Rex,trans) for transition." (Schetz and Bowersox, 2010) According to Kachanov (Kachanov, 2006), there are 3 types of BL instability: 1 Convective instability; 2 Absolute instability; 3 Global instability; Kachanov (2006) listed nine types of convective BL instabilities.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Three Types of Boundary-Layer Instability Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions What is Receptivity? According to Kachanov (2006) - "The term ’boundary-layer receptivity’ stands for various mechanisms of transformation of external (with respect to the boundary layer) perturbations into boundary-layer perturbations." "The receptivity process represents an initial stage of the transition process(see Fig. 2 and reviews in [3-5]), which starts, in fact, from the very leading edge, where the free stream just touches with a body." "Consequently, almost any laminar boundary layer can be regarded as a transitional boundary layer, at least when the Reynolds numbers are not too low."
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Routes of BL Transition (Receptivity & Stability) Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Routes of BL Transition (Nonlinear Interactions & Formation of Vortical Structures) Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Classifications Classical / Conventional (Langtry, 2006) 1 Natural transition 2 Bypass transition 3 Separated flow transition 4 Wake induced transition 5 Reversed transition Mode-Based (Zaki and Durbin, 2005; Durbin and Wu, 2007) 1 Discrete Modes 2 Continuous Modes Secondary Instabilities due to Low-Amplitude Disturbances (Sayadi, 2012) 1 K-type 2 H-type
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Natural Transition Typical Turbulence Intensity (Tu) <1 %; “... the most common onset mechanism on transport aircraft in flight” (Medida, 2014) Associated with disturbances related to: 1 Viscous instability wave (commonly known as Tollmien-Schlichting or T-S wave) 2 Cross-flow instabilities (Two types - Stationary & traveling) “... well described by linear stability theory and the Orr-Sommerfeld equations ...” (Medida, 2014) Recent studies have also identified H- and K-type secondary instabilities due to low-amplitude disturbances.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Bypass Transition Typical Tu >1 Percent “it refers to many possible scenarios such as transition due to surface roughness, acoustic perturbations, or free-stream vortical disturbances.” (Zaki, 2005) "it is often argued that for bypass transition linear stability is irrelevant and to date no one has been able to detect Tollmien-Schlichting waves when the freestream turbulence level was greater than 1 percent (Mayle, 1991)" (Langtry, 2006) Quote "Bypass transition has been one of the most intriguing forms of boundary layer transition to turbulence." (Zaki, 2005)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Separated Flow Transition "When a laminar boundary layer separates, transition may occur in the shear layer of the separated flow as a result of the inviscid instability mechanism." (Langtry, 2006) “may or may not involve instability of the Tollmien-Schlichting type” (Mayle and Schulz, 1997) Examples are separation due to: 1 adverse pressure gradient; 2 trip wires; 3 airfoil leading edge which has a small radius; The shear layer may reattach and there can be formation of separation-bubble. Quotes "Of all the transition modes, there is none more crucial to compressor and low-pressure turbine design and none more neglected that this mode." (Mayle, 1991)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Wake Induced Transition A type of bypass transition; "Since the flow in a gas turbine is periodically unsteady, so is transition. The largest effect of unsteadiness on transition is caused by the periodic passing of wakes from upstream airfoils or obstructions and is called "wake-induced" transition (Mayle and Dullenkopt, 1989)." (Mayle, 1991) Quote "One very important instance of bypass transition arises in turbomachinery flows where the blade rows are subjected to periodically passing turbulent wakes." (Langtry, 2006)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Reversed Transition Also known as "relaminarization" "Transition from turbulent to laminar flow is possible if the flow is strongly accelerated." (Langtry, 2006) "... reverse transition involves a balance between convection, production, and dissipation of turbulent kinetic energy within the boundary layer." (Mayle, 1991) According to Mayle (1991), this type of transition is very important for the designer of gas turbines as accelerations are higher than that for which reverse transition occurs in the following locations: 1 On the pressure side of most airfoils near the trailing edge; 2 In the exit ducts of combustors; 3 On the suction side of turbine airfoil near the leading edge ;
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions H- & K-Type Transitions K-Type: Λ-vortices are formed due to non-linear interactions of 2D T-S wave with a set of oblique waves having the same frequency of the fundamental wave. This is a fundamental transition which is named after Klebanoff and known as K-type (Sayadi, 2012). According to Sayadi (2012) - “The Λ-vortices evolve and form hairpin-shaped loops that merge into turbulent spots (patches of localized incipient turbulence) leading to turbulence.” H-Type: Subharmonic transition which is named after Herbert (Sayadi, 2012). According to Sayadi (2012) - “This transition scenario is initiated from low-amplitude waves inside the boundary layer, and in this respect is similar to K-type transition. However, in this case no turbulent spots are observed.”
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Selected Video Links Animations Boundary Layer DNS/LES Data http://www.mech.kth.se/ pschlatt/DATA/ Transition http://engineering.jhu.edu/zaki/research/bypass-transition/ Bypass Transition http://www3.imperial.ac.uk/meflowscieng/projects/bypasstransition Separation-induced transition in a compressor passage http://www3.imperial.ac.uk/meflowscieng/projects/sit Lectures "Boundary Layer Transition by Discrete and Continuous Modes" by R. Durbin, 10 Sep 2008 http://sms.cam.ac.uk/media/17073 "Turbulent forcing and transient growth in boundary layers" by Tamer Zaki, 17 March 2009 http://sms.cam.ac.uk/media/538910
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Important Parameters Affecting Transition Transition is known to be affected by the following parameters: the free stream turbulence, the pressure gradient, Reynolds number, Mach number, acoustic radiation, surface roughness, surface temperature, surface curvature, the history of the above parameters. (Abu-Ghannam and Shaw, 1980) Some researchers have identified that vibration, leading edge sweep (Medida, 2014) also affects BL transition.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Notable Experimental Investigations Reynolds (1883) Silverstein and Becker (1939) Schubauer and Skramstad (1948) Schubauer and Klebanoff (1955) ERCOFTAC Database (1990)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Popular Choices Linear Stability Based (eN Types) Smith and Gamberoni (1956) van Ingen (1956) Jaffe et al. (1970) Drela and Giles (1987) Correlation-based Abu-Ghannam and Shaw (1980) Mayle (1991) γ − Reθ Model (Menter et al., 2004) γ − Reθ − SA Model (Medida, 2014) Phenomenological (Physics-based) Walters and Leylek (2004) Walters and Cokljat (2008)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Summary The process of BL transition is quite complex and yet to be fully understood even after significant amounts of research activities in different parts of the world; Different types of primary and secondary instability waves are associated with BL Transition; Modeling of BL transition, especially the bypass transition is quite challenging; Recent DNS-based studies are presenting more insights about the intricacies of BL transition for simple flows at low Reynolds numbers. Quote “The problem of laminar-turbulent transition and the origin of turbulence are after more than hundred years of scientific research still not fully understood today.” (Gersten, 2009)
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Suggested Readings Langtry, R. B. (2006). A Correlation-Based Transition Model using Local Variables for Unstructured Parallelized CFD Codes. PhD thesis, University of Stuttgart, Germany Sanders, D. D. (2009). CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers. Dissertation, Virginia Polytechnic Institute and State University, USA Medida, S. (2014). Correlation-based Transition Modeling for External Aerodynamic Flows. Dissertation, University of Maryland, USA
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Acknowledgment Preparation of the article was partly supported by the Canadian Natural Sciences and Engineering Research Council (NSERC) and the ENMAX Corporation under the Industrial Research Chairs program. Special thanks to Professor David Wood for his valuable suggestions and encouragements. I appreciate the kind permissions from Professor Peter Schmidt and Professor Yury S. Kachanov for allowing me to use images from their works.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References I Abu-Ghannam, B. J. and Shaw, R. (1980). Natural Transition Of Boundary Layers - The Effects Of Turbulence, Pressure Gradient, And Flow History. Journal of Mechanical Engineering Science, 22(5):213–228. Drela, M. and Giles, M. B. (1987). VISCOUS-INVISCID ANALYSIS OF TRANSONIC AND LOW REYNOLDS NUMBER AIRFOILS. Durbin, P. and Wu, X. (2007). Transition beneath vortical disturbances. Annual Review of Fluid Mechanics, 39:107–128. ERCOFTAC Database (1990). Flat Plate Transitional Boudary Layers. Gersten, K. (2009). Hermann Schlichting and the Boundary-Layer Theory. In Radespiel, R., Rossow, C.-C., and Brinkmann, B., editors, Hermann Schlichting – 100 Years SE - 2, volume 102 of Notes on Numerical Fluid Mechanics and Multidisciplinary Design, pages 3–17. Springer Berlin Heidelberg.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References II Jaffe, N. A., Okamura, T. T., and Smith, A. M. O. (1970). Determination of spatial amplification factors and their applicationto predicting transition. AIAA Journal, 8(2):301–308. Kachanov, Y. (2006). Routes of Boundary-Layer Transition. In Meier, G. E. A., Sreenivasan, K. R., and Heinemann, H.-J., editors, IUTAM Symposium on One Hundred Years of Boundary Layer Research SE - 9, volume 129 of Solid mechanics and its applications, pages 95–104. Springer Netherlands. Langtry, R. B. (2006). A Correlation-Based Transition Model using Local Variables for Unstructured Parallelized CFD Codes. PhD thesis, University of Stuttgart, Germany. Mayle, R. E. (1991). The role of laminar-turbulent transition in gas turbine engines. Mayle, R. E. and Schulz, A. (1997). The Path to Predicting Bypass Transition. Journal of Turbomachinery, 119(3):405–411.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References III Medida, S. (2014). Correlation-based Transition Modeling for External Aerodynamic Flows. Dissertation, University of Maryland, USA. Menter, F. R., Langtry, R. B., Likki, S. R., Suzen, Y. B., Huang, P. G., and Völker, S. (2004). A Correlation-Based Transition Model Using Local Variables—Part I: Model Formulation. Journal of Turbomachinery, 128(3):413–422. Narasimha, R. (1990). Modelling the transitional boundary layer. Reynolds, O. (1883). An experimental investigation of the circumstances which determine whether the motion of water shall be direct or sinuous, and of the law of resistance in parallel channels. Proceedings of the royal society of London, 35(224-226):84–99. Sanders, D. D. (2009). CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers. Dissertation, Virginia Polytechnic Institute and State University, USA.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References IV Sayadi, T. (2012). Numerical simulation of controlled transition to developed turbulence in a zero-pressure-gradient flat-plate boundary layer. Dissertation, Stanford University, USA. Schetz, J. A. and Bowersox, R. D. W. (2010). Boundary Layer Analysis. American Institute of Aeronautics and Aeronautics. Schlichting, H. (1979). Boundary Layer Theory. McGraw-Hill, 7th editio edition. Schlichting, H. and Gersten, K. (2000). Boundary-layer theory. Springer. Schmid, P. (2014). Analysis of Fluid Systems: Stability, Receptivity, Sensitivity. Schubauer, G. B. and Klebanoff, P. S. (1955). Contributions on the mechanics of boundary-layer transition. National Advisory Committee for Aeronautics. Schubauer, G. B. and Skramstad, H. K. (1948). Laminar-boundary-layer oscillations and transition on a flat plate.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References V Silverstein, A. and Becker, J. V. (1939). Determination of Boundary-Layer Transition on Three Symmetrical Airfoils in the NACA Full-Scale Wind Tunnel. NACA, Wartime Report L, 637. Smith, A. M. O. and Gamberoni, N. (1956). Transition, pressure gradient and stability theory. Douglas Aircraft Company, El Segundo Division. van Ingen, J. (1956). A suggested semi-empirical method for the calculation of the boundary layer transition region. Technical report. Walters, D. K. and Cokljat, D. (2008). A Three-Equation Eddy-Viscosity Model for Reynolds-Averaged Navier–Stokes Simulations of Transitional Flow. Walters, D. K. and Leylek, J. H. (2004). A new model for boundary layer transition using a single-point RANS approach. Zaki, T. A. (2005). Continuous Mode Interaction and the Bypass Route to Transition. Dissertation, Stanford University, USA.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References VI Zaki, T. A. and Durbin, P. A. (2005). Mode interaction and the bypass route to transition. Journal of Fluid Mechanics, 531:85–111.
Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings T H A N K S F O R Y O U R P A R T I C I P A T I O N

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Boundary Layer Transition: An Overview

  • 1. Boundary Layer Transition: An Overview Mazharul Islam, PhD Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Boundary Layer Transition: An Overview Mazharul Islam, PhD University of Calgary, Canada March 20, 2015
  • 2. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Main Contents 1 Objectives 2 Introduction 3 Brain Storming Session 4 Different Stages/Regions Related to BL Transitions 5 Instabilities & BL Transitions 6 Different Modes of Transitions 7 Important Parameters Affecting Transitions 8 Notable Experimental Investigations 9 Selected Models 10 Summary
  • 3. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Objectives of This Presentation To learn about instabilities associated with boundary layer (BL) transition. To acquire knowledge about different modes of BL transition. To be informed about three classes of BL transition models.
  • 4. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Motivation Critical for computing the drag & skin friction coefficients reasonably for aerodynamic problems; Need for a useful model for the open-source/freely available CFD tools like OpenFOAM/foam-extend etc. Still challenging after many decades of research activities and there are scopes for further investigations; Quotes "... most important and probably the most difficult subject in boundary layer work..." (Schetz and Bowersox, 2010) Introduction, Chapter on "Transition To Turbulent Flow" “. . . predicting the onset of either natural or bypass transition is still more of an art than a science (see Savill, 1991 or Seiger et al. For examples).”(Mayle and Schulz, 1997)
  • 5. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Prominent Researchers Related to Instability/BL Transition L. Rayleigh (Instability) O. Reynolds (Pioneering experimentation in 1883) M.W.F Orr (Hydrodynamic Instability) A. Sommerfeld (Hydrodynamic Instability) L. Prandtl (concept of BL in 1904) G.I. Taylor (Instability) W. Tollmien (T-S Wave) H. Schlichting (T-S Wave) Klebanoff (K-type transition) A.M.O. Smith (original eN model) J.L. van Ingen (original eN model) M. V. Morkovin (Concept of Receptivity, Bypass transition) R.E. Mayle & A. Schulz (laminar kinetic energy equation) .... and many others
  • 6. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 7. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 8. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Figures Demonstrating BL Transition Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 9. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Key Challenges related to BL Transition Different types; Affected by numerous parameters; Lack of experimental results of skin-friction coefficients around bodies of practical interests (like airfoils) at low Reynolds numbers (i.e. Re<500,000).
  • 10. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Introduction Selected Important Keywords Related to Boundary Layer Transition Critical Reynolds number (Recr ) Tollmien-Schlichting Wave Receptivity Transition onset Transition length Intermittency Relaminarization (or Reverse Transition) Λ-Vortices
  • 11. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Brain Storming Session Importance of Boundary-Layer Transition Modeling; Ball-park critical Reynolds number for "pipe flow" (i.e. internal flow); Ball-park critical Reynolds number for "flat plate at zero incidence" (i.e. external flow) Available models or correlations for determining the transition onset and length;
  • 12. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Brain Storming Session Commonly known Ball-Park Numbers According to Schlichting and Gersten (2000), For Pipe Flow (Eq. 1.11, pp 12): Recrit = 2100 (1) For Flat Plate at Zero Incidence (Eq. 1.12, pp 13) Recrit = 5.105 (2)
  • 13. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions BL transitions can be caused by different types of instabilities. "Some researchers identify as many as seven steps, going from instability through large three-dimensional disturbances and finally to turbulence." (Schetz and Bowersox, 2010)
  • 14. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Five Regions according to Schlichting (1979) Schlichting (1979) identified five regions which involves - 1 TS waves; 2 Spanwise vorticity; 3 Three-Dimensional breakdown; 4 Turbulent spots; and 5 Fully turbulent flow. Reproduced in Figure 2.1 in (Langtry, 2006)
  • 15. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Transition Region "The transition region is the region in which the boundary-layer flow changes from laminar to turbulent. The beginning of this region will be referred to as the "transition point" and will be considered to be the point at which the velocity near the surface begins to show an abnormal increase. The end of the transition region has been taken as the point at which the velocity near the surface has reached a maximum." (Silverstein and Becker, 1939)
  • 16. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions Various Stages for a Flat Plate according to Narasimha Figure: Adapted from (Narasimha, 1990) Important Information from this figure: Breakdown zone Onset of Transition Intermittency Spot spread angle
  • 17. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Stages/Regions of BL Transitions "Onset of Transition", "Turbulent Spot" & "Intermittency" Onset of Transition: "The point of minimum skin friction is typically considered the start of transition" (Medida, 2014) Turbulent Spot: "... a turbulent spot is initiated when the maximum velocity fluctuation in the streamwise direction exceeds about one-fifth of the freestream velocity, almost independently of the Reynolds number [16]. " (Medida, 2014) Intermittency: "The intermittency factor was introduced [17] to quantify the rate of turbulent spot production and a relation between the transition Reynolds number and the intermittency factor was deduced. Once initiated, these intermittent turbulent spots grow in size and they travel downstream, until they merge into a fully turbulent boundary layer, thus completing the transition process." (Medida, 2014)
  • 18. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions BL transitions can be caused by different types of instabilities. "... instability and transition are not the same thing. Instability is merely the very early precursor of ultimate transition to turbulent flow, and knowing the conditions for instability alone is not of much use in predicting the subsequent conditions (Rex,trans) for transition." (Schetz and Bowersox, 2010) According to Kachanov (Kachanov, 2006), there are 3 types of BL instability: 1 Convective instability; 2 Absolute instability; 3 Global instability; Kachanov (2006) listed nine types of convective BL instabilities.
  • 19. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Three Types of Boundary-Layer Instability Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
  • 20. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions What is Receptivity? According to Kachanov (2006) - "The term ’boundary-layer receptivity’ stands for various mechanisms of transformation of external (with respect to the boundary layer) perturbations into boundary-layer perturbations." "The receptivity process represents an initial stage of the transition process(see Fig. 2 and reviews in [3-5]), which starts, in fact, from the very leading edge, where the free stream just touches with a body." "Consequently, almost any laminar boundary layer can be regarded as a transitional boundary layer, at least when the Reynolds numbers are not too low."
  • 21. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Routes of BL Transition (Receptivity & Stability) Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
  • 22. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Instabilities & BL Transitions Routes of BL Transition (Nonlinear Interactions & Formation of Vortical Structures) Figure: Adapted from (Kachanov, 2006), Courtesy of Professor Yury S. Kachanov, Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia.
  • 23. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Classifications Classical / Conventional (Langtry, 2006) 1 Natural transition 2 Bypass transition 3 Separated flow transition 4 Wake induced transition 5 Reversed transition Mode-Based (Zaki and Durbin, 2005; Durbin and Wu, 2007) 1 Discrete Modes 2 Continuous Modes Secondary Instabilities due to Low-Amplitude Disturbances (Sayadi, 2012) 1 K-type 2 H-type
  • 24. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Natural Transition Typical Turbulence Intensity (Tu) <1 %; “... the most common onset mechanism on transport aircraft in flight” (Medida, 2014) Associated with disturbances related to: 1 Viscous instability wave (commonly known as Tollmien-Schlichting or T-S wave) 2 Cross-flow instabilities (Two types - Stationary & traveling) “... well described by linear stability theory and the Orr-Sommerfeld equations ...” (Medida, 2014) Recent studies have also identified H- and K-type secondary instabilities due to low-amplitude disturbances.
  • 25. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Bypass Transition Typical Tu >1 Percent “it refers to many possible scenarios such as transition due to surface roughness, acoustic perturbations, or free-stream vortical disturbances.” (Zaki, 2005) "it is often argued that for bypass transition linear stability is irrelevant and to date no one has been able to detect Tollmien-Schlichting waves when the freestream turbulence level was greater than 1 percent (Mayle, 1991)" (Langtry, 2006) Quote "Bypass transition has been one of the most intriguing forms of boundary layer transition to turbulence." (Zaki, 2005)
  • 26. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Separated Flow Transition "When a laminar boundary layer separates, transition may occur in the shear layer of the separated flow as a result of the inviscid instability mechanism." (Langtry, 2006) “may or may not involve instability of the Tollmien-Schlichting type” (Mayle and Schulz, 1997) Examples are separation due to: 1 adverse pressure gradient; 2 trip wires; 3 airfoil leading edge which has a small radius; The shear layer may reattach and there can be formation of separation-bubble. Quotes "Of all the transition modes, there is none more crucial to compressor and low-pressure turbine design and none more neglected that this mode." (Mayle, 1991)
  • 27. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Wake Induced Transition A type of bypass transition; "Since the flow in a gas turbine is periodically unsteady, so is transition. The largest effect of unsteadiness on transition is caused by the periodic passing of wakes from upstream airfoils or obstructions and is called "wake-induced" transition (Mayle and Dullenkopt, 1989)." (Mayle, 1991) Quote "One very important instance of bypass transition arises in turbomachinery flows where the blade rows are subjected to periodically passing turbulent wakes." (Langtry, 2006)
  • 28. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Reversed Transition Also known as "relaminarization" "Transition from turbulent to laminar flow is possible if the flow is strongly accelerated." (Langtry, 2006) "... reverse transition involves a balance between convection, production, and dissipation of turbulent kinetic energy within the boundary layer." (Mayle, 1991) According to Mayle (1991), this type of transition is very important for the designer of gas turbines as accelerations are higher than that for which reverse transition occurs in the following locations: 1 On the pressure side of most airfoils near the trailing edge; 2 In the exit ducts of combustors; 3 On the suction side of turbine airfoil near the leading edge ;
  • 29. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions H- & K-Type Transitions K-Type: Λ-vortices are formed due to non-linear interactions of 2D T-S wave with a set of oblique waves having the same frequency of the fundamental wave. This is a fundamental transition which is named after Klebanoff and known as K-type (Sayadi, 2012). According to Sayadi (2012) - “The Λ-vortices evolve and form hairpin-shaped loops that merge into turbulent spots (patches of localized incipient turbulence) leading to turbulence.” H-Type: Subharmonic transition which is named after Herbert (Sayadi, 2012). According to Sayadi (2012) - “This transition scenario is initiated from low-amplitude waves inside the boundary layer, and in this respect is similar to K-type transition. However, in this case no turbulent spots are observed.”
  • 30. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Different Modes of Transitions Selected Video Links Animations Boundary Layer DNS/LES Data http://www.mech.kth.se/ pschlatt/DATA/ Transition http://engineering.jhu.edu/zaki/research/bypass-transition/ Bypass Transition http://www3.imperial.ac.uk/meflowscieng/projects/bypasstransition Separation-induced transition in a compressor passage http://www3.imperial.ac.uk/meflowscieng/projects/sit Lectures "Boundary Layer Transition by Discrete and Continuous Modes" by R. Durbin, 10 Sep 2008 http://sms.cam.ac.uk/media/17073 "Turbulent forcing and transient growth in boundary layers" by Tamer Zaki, 17 March 2009 http://sms.cam.ac.uk/media/538910
  • 31. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Important Parameters Affecting Transition Transition is known to be affected by the following parameters: the free stream turbulence, the pressure gradient, Reynolds number, Mach number, acoustic radiation, surface roughness, surface temperature, surface curvature, the history of the above parameters. (Abu-Ghannam and Shaw, 1980) Some researchers have identified that vibration, leading edge sweep (Medida, 2014) also affects BL transition.
  • 32. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Notable Experimental Investigations Reynolds (1883) Silverstein and Becker (1939) Schubauer and Skramstad (1948) Schubauer and Klebanoff (1955) ERCOFTAC Database (1990)
  • 33. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Popular Choices Linear Stability Based (eN Types) Smith and Gamberoni (1956) van Ingen (1956) Jaffe et al. (1970) Drela and Giles (1987) Correlation-based Abu-Ghannam and Shaw (1980) Mayle (1991) γ − Reθ Model (Menter et al., 2004) γ − Reθ − SA Model (Medida, 2014) Phenomenological (Physics-based) Walters and Leylek (2004) Walters and Cokljat (2008)
  • 34. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 35. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 36. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Prominent Correlations/Models for BL Transition Role of Laminar Stability Theory Figure: Adapted from (Schmid, 2014), Courtesy of Professor, Peter Schmidt, Imperial College, UK
  • 37. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Summary The process of BL transition is quite complex and yet to be fully understood even after significant amounts of research activities in different parts of the world; Different types of primary and secondary instability waves are associated with BL Transition; Modeling of BL transition, especially the bypass transition is quite challenging; Recent DNS-based studies are presenting more insights about the intricacies of BL transition for simple flows at low Reynolds numbers. Quote “The problem of laminar-turbulent transition and the origin of turbulence are after more than hundred years of scientific research still not fully understood today.” (Gersten, 2009)
  • 38. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Suggested Readings Langtry, R. B. (2006). A Correlation-Based Transition Model using Local Variables for Unstructured Parallelized CFD Codes. PhD thesis, University of Stuttgart, Germany Sanders, D. D. (2009). CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers. Dissertation, Virginia Polytechnic Institute and State University, USA Medida, S. (2014). Correlation-based Transition Modeling for External Aerodynamic Flows. Dissertation, University of Maryland, USA
  • 39. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings Acknowledgment Preparation of the article was partly supported by the Canadian Natural Sciences and Engineering Research Council (NSERC) and the ENMAX Corporation under the Industrial Research Chairs program. Special thanks to Professor David Wood for his valuable suggestions and encouragements. I appreciate the kind permissions from Professor Peter Schmidt and Professor Yury S. Kachanov for allowing me to use images from their works.
  • 40. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References I Abu-Ghannam, B. J. and Shaw, R. (1980). Natural Transition Of Boundary Layers - The Effects Of Turbulence, Pressure Gradient, And Flow History. Journal of Mechanical Engineering Science, 22(5):213–228. Drela, M. and Giles, M. B. (1987). VISCOUS-INVISCID ANALYSIS OF TRANSONIC AND LOW REYNOLDS NUMBER AIRFOILS. Durbin, P. and Wu, X. (2007). Transition beneath vortical disturbances. Annual Review of Fluid Mechanics, 39:107–128. ERCOFTAC Database (1990). Flat Plate Transitional Boudary Layers. Gersten, K. (2009). Hermann Schlichting and the Boundary-Layer Theory. In Radespiel, R., Rossow, C.-C., and Brinkmann, B., editors, Hermann Schlichting – 100 Years SE - 2, volume 102 of Notes on Numerical Fluid Mechanics and Multidisciplinary Design, pages 3–17. Springer Berlin Heidelberg.
  • 41. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References II Jaffe, N. A., Okamura, T. T., and Smith, A. M. O. (1970). Determination of spatial amplification factors and their applicationto predicting transition. AIAA Journal, 8(2):301–308. Kachanov, Y. (2006). Routes of Boundary-Layer Transition. In Meier, G. E. A., Sreenivasan, K. R., and Heinemann, H.-J., editors, IUTAM Symposium on One Hundred Years of Boundary Layer Research SE - 9, volume 129 of Solid mechanics and its applications, pages 95–104. Springer Netherlands. Langtry, R. B. (2006). A Correlation-Based Transition Model using Local Variables for Unstructured Parallelized CFD Codes. PhD thesis, University of Stuttgart, Germany. Mayle, R. E. (1991). The role of laminar-turbulent transition in gas turbine engines. Mayle, R. E. and Schulz, A. (1997). The Path to Predicting Bypass Transition. Journal of Turbomachinery, 119(3):405–411.
  • 42. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References III Medida, S. (2014). Correlation-based Transition Modeling for External Aerodynamic Flows. Dissertation, University of Maryland, USA. Menter, F. R., Langtry, R. B., Likki, S. R., Suzen, Y. B., Huang, P. G., and Völker, S. (2004). A Correlation-Based Transition Model Using Local Variables—Part I: Model Formulation. Journal of Turbomachinery, 128(3):413–422. Narasimha, R. (1990). Modelling the transitional boundary layer. Reynolds, O. (1883). An experimental investigation of the circumstances which determine whether the motion of water shall be direct or sinuous, and of the law of resistance in parallel channels. Proceedings of the royal society of London, 35(224-226):84–99. Sanders, D. D. (2009). CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers. Dissertation, Virginia Polytechnic Institute and State University, USA.
  • 43. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References IV Sayadi, T. (2012). Numerical simulation of controlled transition to developed turbulence in a zero-pressure-gradient flat-plate boundary layer. Dissertation, Stanford University, USA. Schetz, J. A. and Bowersox, R. D. W. (2010). Boundary Layer Analysis. American Institute of Aeronautics and Aeronautics. Schlichting, H. (1979). Boundary Layer Theory. McGraw-Hill, 7th editio edition. Schlichting, H. and Gersten, K. (2000). Boundary-layer theory. Springer. Schmid, P. (2014). Analysis of Fluid Systems: Stability, Receptivity, Sensitivity. Schubauer, G. B. and Klebanoff, P. S. (1955). Contributions on the mechanics of boundary-layer transition. National Advisory Committee for Aeronautics. Schubauer, G. B. and Skramstad, H. K. (1948). Laminar-boundary-layer oscillations and transition on a flat plate.
  • 44. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References V Silverstein, A. and Becker, J. V. (1939). Determination of Boundary-Layer Transition on Three Symmetrical Airfoils in the NACA Full-Scale Wind Tunnel. NACA, Wartime Report L, 637. Smith, A. M. O. and Gamberoni, N. (1956). Transition, pressure gradient and stability theory. Douglas Aircraft Company, El Segundo Division. van Ingen, J. (1956). A suggested semi-empirical method for the calculation of the boundary layer transition region. Technical report. Walters, D. K. and Cokljat, D. (2008). A Three-Equation Eddy-Viscosity Model for Reynolds-Averaged Navier–Stokes Simulations of Transitional Flow. Walters, D. K. and Leylek, J. H. (2004). A new model for boundary layer transition using a single-point RANS approach. Zaki, T. A. (2005). Continuous Mode Interaction and the Bypass Route to Transition. Dissertation, Stanford University, USA.
  • 45. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings References VI Zaki, T. A. and Durbin, P. A. (2005). Mode interaction and the bypass route to transition. Journal of Fluid Mechanics, 531:85–111.
  • 46. Boundary Layer Transition: An Overview Objectives Introduction Brain Storming Session Different Stages/Regions Related to BL Transitions Instabilities & BL Transitions Different Modes of Transitions Important Parameters Affecting Transitions Notable Experimental Investigations Selected Models Summary Suggested Readings T H A N K S F O R Y O U R P A R T I C I P A T I O N