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Etc09 Id239

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Presented at ETC9 Istanbul, March 20-25 2011.

Presented at ETC9 Istanbul, March 20-25 2011.

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Etc09 Id239 Etc09 Id239 Presentation Transcript

  • Experimental aero-acoustic characterization of axial fan fittedwith shaped tip end-plates Stefano BIANCHI, Alessandro CORSINI A. G. SHEARD FMGroup @ DMA-URLS Fläkt Woods Ltd 9th European Conference on Turbomachinery, ETC9 Istabul, Turkey, March 25 2011
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Background motivations • Tip gap plays a detrimental role affecting axial flow rotor performance (Fukano and Takamatsu, 1986), (Furukawa et al., 1999) • A number of studies pointed out that the influence of tip leakage flow on rotor aero-acoustic signature is similar in low speed ventilating equipment as well as in high- bypass-ratio turbofan engines • Recognized tip noise generation mechanisms in axial decelerating turbomachines convection of the primary tip vortex producing tonal noise owing to vortex-stator interactions convection of large-scale fluctuations downwind the trailing edge producing scattering and broadband noise • Consequently there is a strong motivation to look for deliberate aerodynamic design to minimize the negative effects of tip gap • The target to tackle is to manage the tip-clearance flow in a manner that reduces the self-generated noise without sacrificing aerodynamic efficiency ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Aims • Recent studies investigated the application of end-plates of constant thickness to the blade tips of a family of industrial fans (Corsini et al., 2006 & 2007) Flakt Woods Ltd fan detail Amaral et al., GT2006-90345, 2006 • Aeroacoustic & aerodynamic analyses revealed for the family of tip featured rotors: i.  benefits in terms of aeroacoustic performance ii.  a diminution in aerodynamic performance in association with the occurrence of leakage vortex bursting over the tip end-plate • The goals of the present work are: to describe the evolution of a design concept for tip end-plate oriented to the implementation of passive flow control strategies e.g. leakage vortex swirl level to assess and validate through combined CFD&EFD the merit of the developed passive noise-by-flow control technologies ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Axial fan family • Family of commercially available cooling fans AC90/6 unswept rotor fan in ducted configuration in service experiences demonstrated good acoustics performance Design concept Arbitrary vortex with radially increasing work distribution AC90/6 blade profiles modified ARA-D Utip about 50 m/s
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Techniques and concepts for tip treatment, a first review (i) • Techniques appeared to date are generally designed to accomplish the goal by reducing the leakage flow, affecting the primary-secondary flow momentum transfer, or unloading the tip blade sections In the ambit of the so-called passive noise control approach, based on geometrical modifications of the rotor-casing, three concepts emerge • The use of swept blade stacking line in design methods (Wadia et al., 1998) is known to improve stall-free operating margin (Vad, 2001), (Corsini and Rispoli, 2004) • The use of casing treatments over the blade tip reported to improve stable flow range by weakening the tip leakage vortex e.g. grooves and slots (Takata and Tsukuda, 1977) (Smith and Cumpsty, 1984), or stepped tip gaps (Thompson et al., 1998). or in the ambit of fan technologies recirculating vanes, and annular rings have been proposed as anti-stall devices (Jensen, 1986) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Techniques and concepts for tip treatment, a first review (ii) • During the last decade have appeared several passive noise control concepts based on the blade tip modifications by means of anti-vortex appendages anti-vortex devices as end-plates at the tip originally inspired by the technique developed for the control of tip vortex and induced drag reduction in aircraft wings, also used as anti-vortex devices for catamaran hulls Karman end-plate Boeing, blended winglets F2005, rear winglets ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Conventional end-plate design • Base-line solution for the tip treatments, Corsini et al. (2006, 2007), defined a blade configuration with use of tip appendages to implement a control on leakage flow TF end-plate rotor AC90/6/TF tip blade section modified by an end-plate on pressure surface with square-tail trailing edge tip blade section is locally thickened of a factor 3:1 wrt maximum thickness at the tip of datum blade According to the theory behind the end-plate design, this dimension was chosen as the reference radial dimension of leakage vortex to be controlled approx. 0.2 ÷ 0.1 blade span, (Inoue et al., 1986) (Corsini et al., 2004). ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Analysis on inner workings of TF end-plates, tip flow survey Corsini, Rispoli and Sheard, J. of Power and Energy, 221/5, (2007) datum rotor AC90/6/TF Helicity distributions and vortex core paths D operating pointTurbulence intensity evolution withinthe leakage flow regionD operating point datum rotor AC90/6/TF ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Analysis on inner workings of TF end-plates, tip leakage vortex bursting • This finding was in accordance with the existence of a vortex breakdown Criterion for VB detection based on vortex swirl analysis an interpretive criterion to detect the appearance of vortex breakdown makes use of the Rossby number (or inverse swirl parameter) (Ito et al., 1985) design point Ro Ro = V /(r Ω) for a confined vortex the scales are: r , radial distance from the vortex axis at which the swirl velocity was at its maximum in accord with characteristic viscous length scale Leibovich (1984) V = waTLV, was taken to be the axial velocity Ω, be the rotation rate in the wing-tip breakdown region vortices due to the solid body rotation-like structure (estimated near the vortex centre). fraction of chord ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates End-plates for tip leakage vortex swirl control, design goals • The present work is dedicated to sketch new concepts for the shaping (design) of the anti-vortex tip end-plate • The rationale is to designate a variation of end-plate thickness, in order to implement a manipulation of the chord-wise evolution of the leakage vortex swirl Visualization and Analytics Center for Enabling Technologies (VACET) DOE, USA Aircraft Vortex Manipulation, Manipulation of the blade vortex interaction of helicopters with nonplanar blade tips on the main rotor Institute of Aeronautics and Astronautics, Aachen, Germany • The aim is to promote an enhancement or a detriment of near-axis swirl by influencing the momentum transfer from the leakage flow and by inducing some waviness into the leakage vortex trajectory, as attempted in delta-wing platform design Srigrarom and Kurosaka (2000) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates I generation of end-plate Variable Thickness VTE. Design concept Corsini, A., Rispoli, F., Sheard, A. G., “Shaping of tip end-plate to control leakage vortex swirl in axial flow fans”, Transactions of ASME, Journal of Turbomachinery, vol. 132, 3, paper 031005, pp 1-9, 2010. The goal is to enhance near-axis swirl by reconfiguring the end-plate at the tip with a view to influencing the momentum transfer from the leakage flow The rationale was to compute the end-plate thickness distribution (tep(sc)) by combining a simplified law for the tip-gap pressure drop with a stability criterion of TLV by prescribing a safe chord-wise distribution of the vortex Rossby number The pressure losses within the tip gap at each AC90/6 fans chord-wise abscissa sc was modelled by studying datum the leakage flow as a two-dimensional flow orthogonal to the chord line The pressure drop could thus be expressed as a TF end-plate function of: -  gap geometry, (height & width) TFvte end-plate -  kinetic energy of the leakage flow -  friction factor which is itself a function of leakage flow Reynolds number, Regap ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Test evaluation of end-plate aerodynamics & aeroacoustics Ro TLV rotation number TF breakdown region fraction of chord TLV core paths TF TFvte datum FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Test evaluation of end-plate aerodynamics & aeroacoustics Δp(Pa) Ro TLV rotation number ηstat TF breakdown region fraction of chord volume flow (m3/s) TLV core paths TF TFvte datum FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates II generation of end-plate for Multiple Vortex Corsini A, Rispoli F & Sheard AG, A Meridional Fan, Patent granted No. GB 2452104, July Breakdown MVB, design goals (2009) The idea is to obtain an end-plate geometric able to combine the acoustic pay-off of TF related to the mixing enhancement effect induced by the vortex bursting the aerodynamic performance benefit of TFvte consequence of the healthier status of the flow in the annulus and in the wake The rationale was to profile the end-plate at the blade tip according to a prescribed chordwise distribution of the TLV Rossby number The design Rossby number distribution would drive the TLV to a sequence of critical condition able to induce the onset of vortex bursting fraction of chord ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates End-plate for Multiple Vortex Breakdown MVB Corsini A, Rispoli F & Sheard AG, A Meridional Fan, Patent granted No. GB 2452104, July concept rationale (2009) Rossby number definition for a confined vortex TLV rotational frequency and length measures datum given by Rain (1954) and Lakshminarayana (1970) AC90/6 fans Leakage flow modelled as a two-dimensional flow TF end-plate orthogonal to the chord line The TLV Rossby number could be TFvte end-plate expressed along the blade chord as a function of: -  gap geometry, (height & width) -  kinetic energy of the leakage flow MVB end-plate -  friction factor which is itself a function of leakage flow Reynolds number, Regap - local blade load conditions Ro(xc)=f [tip gap, blade load, leakage flow, end-plate thickness] ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB design concept, sensitivity analyses sensitivity on tip gap sensitivity on lift @ blade tip ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Investigation methodology, summary The experimental and computational investigation focused on the aerodynamic performance of the end-plate configurations, and provided an overview of the far-field acoustics The methodology that was adopted combined an accurate computational modelling of the leakage-flow phenomena (under design condition), with the measurement of the fan acoustic behaviours ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Numerical technique The authors solved the Reynolds-Averaged Navier-Stokes equations by an original parallel Multi-Grid Finite Element flow solver, using C++ technology and libMesh libraries The physics involved in the fluid dynamics of incompressible 3D turbulent flows in a rotating frame of reference is modelled with a non-linear k-ε model, here in its topology- free low-Reynolds variant. The Finite Element flow solver uses second-order accurate approximations in space for primary-turbulent variables. Concerning the solution strategy, the authors solved the Navier-Stokes and turbulence equations fully coupled. The linear solver uses a SOR preconditioned GMRES(5) technique. The mesh was built using a non-orthogonal body fitted coordinate system with block- structured topology. The mesh consists of about 0.6 million linear hexahedral elements. Standard boundary condition settings were adopted, as previously used in studies on high- performance fans ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates datum MVB tip leakage flow survey TLV detection helicity criterion (i) TF TFvte ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates datum MVB tip leakage flow survey TLV detection helicity criterion (i) MVB TF TFvte Identical TLV onset point wrt to datum and TF Vortex core path deformation according to the enhancement/detriment of swirl ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB tip leakage flow survey TLV helicity & 3D streamlines TLV streamlines (ii) datum TF TFvte swirl enhancement No evidences of helicity inversion swirl detriment No evidences of separation cores, TLV goes through the VB onset without actually bursting MVB ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB tip leakage flow survey, TKE & νt (iii) MVB Turbulent kinetic energy iso-surfaces 0.8 0.8 0.2 0.2 0.8 0.2 datum rotor AC90/6/TF AC90/6/TFvte MVB Normalized turbulent viscosity νt iso-surfaces ν _1 tνt_2: 102 νmol;νt_1: 5× 10 νmol νt_1 νt_1 νt_2 νt_1 νt_2 νt_2 datum rotor AC90/6/TF AC90/6/TFvte ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Experimental techniques, rig (i) Fan tested @ 8 – 6 m3/s Anechoic chamber BS848 p2 Noise measurements @ farfield: •  distance = 2 rotor D from the fan section •  six azimuthal positions Pressure measurements @ nearfield: •  distance d=15 mm from the trailing edge 2% of the chord •  spanwise traversing microphone in 14 positions (10% span each) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Techniques for near-field acoustic measurements, a review (i) • Coherence-based noise source identification techniques can be used in identifying the contribution to the global far-field emission of the source distributed in the near-field • A number of techniques have appeared to date based on cross-correlation and coherence analysis mainly inspired by the early publication of the Mugridge and Morfey in 1972. • Previously published works in this area span from 1970 and 1980, (ie. Leggat and Siddon 1978) have been revised in more recent years for application in turbomachinery aeroacoustics (Holste and Neise, 1997), (Fehse and Neise, 1999), (Miles, 2006), subsonic jets (Laurendeau et al., 2007) and combustors (Bennett and Fitzpatrick, 2007) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Techniques for fan noise near-field measurements, a review (ii) • Leggat and Siddon (Journal of Acoustical Society of America (64), 1978): pressure-noise cross correlation to study the rotor-vortex in an axial fan. • Mongeau et al. (Journal of Sound and Vibration (181), 1995): near- and far-field cross correlation to isolate the aeroacoustic emissions a ducted centrifugal pump. • Kameier and Neise (Journal of Sound and Vibration (203), 1997 ): azimuthal cross correlation to investigate the rotating blade flow instability as a source of noise in axial high speed turbomachine. • J. H. Miles (NASA/TM-2006-214352, 2006): multiple microphone near- and far- field cross correlation to separate the correlated core noise from the uncorrelated noise in a PW 4098 turbofan engine. ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Experimental techniques, data post-processing (ii) Hypotesis: -  H(t,r) Linear throug the anechoic space - H(t,r) depends only from geometries tip Cross-correlation, between near- and far-field Auto&cross spectra GSS GNN GSN Coherence: hub H(t,r) N(t,r) Hsound(t,r) To far-field S(t,r) HpsdSound(t,r) D(t,r) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Experimental techniques, instrumentation (iii) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB rotor performance assessment aerodynamics (i) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB rotor performance assessment aeroacoustics (ii) operating point 8 m3/s narrow band (3 Hz) sound pressure level spectra sound power spectra in one-third octave band BPF motor signature ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates MVB rotor performance assessment aeroacoustics (iii) ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Norm Freq (ʄ = f/BPF) ʄ = 1 - 7 MVB rotor performance assessment Near-field aeroacoustic source dissection (i) Source characterization – Span wise Coherence map @ 30° AC90/6datum AC90/6/TF AC90/6/TFvte ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Norm Freq (ʄ = f/BPF) ʄ = 1 - 7 MVB rotor performance assessment Near-field aeroacoustic source dissection (i) Source characterization – Span wise Coherence map @ 30° AC90/6datum AC90/6/TF AC90/6/TFvte ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Norm Freq (ʄ = f/BPF) ʄ = 1 - 7 MVB rotor performance assessment Near-field aeroacoustic source dissection (ii) Source characterization – Span wise Coherence map @ 30° Norm Freq (ʄ = f/BPF) ʄ = 1 - 7 AC90/6/TFMVB ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • Experimental aero-acoustic characterization of axial fan fitted with shaped tip end-plates Conclusions• The passive control technique explored in the study was based on blade tips that had been modified by the addition of anti-vortex appendages as end-plates.• The end-plate configuration aimed to control the chord-wise evolution of the leakage vortex swirl level by preventing the occurrence of tip-leakage vortex bursting by the enhancement of near-axis swirl. • The leakage-flow survey has shown that the variable-thickness configuration MVB was able to exert control over near-axis leakage vortex swirl. As a result, although the critical Rossby number region is reached, the end-plate configuration provides effective control over leakage vortex bursting.• The comparative aerodynamic and aeroacoustic assessment, demonstrated the overall gain for the investigated end-plates was found to be a consequence of the implemented passive flow control concept acting on the tip leakage flow ETC9 – March 2011 FMGroup @ DMA-Sapienza
  • AcknowledgementThe present research was donein the context of the contractFW-DMA10-11, betweenFläkt Woods Ltd andDipartimento di IngegneriaMeccanica e Aerospaziale“Sapienza” University of Rome (Corsini A, Rispoli F & Sheard AG, A Meridional Fan, Patent granted No. GB 2452104, July 2009) ETC9 – March 2011 FMGroup @ DMA-Sapienza