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- 2. IYPT 2012 Germany, National team of I. R. Iran2 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 3. Inspiration IYPT 2012 When a piece of thread (e.g., nylon) is whirled around with a small mass attached to its free end, a distinct noise is emitted. Study the origin of this noise and the relevant parameters. 3
- 4. approach What's sound? Vibration of the thread Transient pressure variation caused by the flow Investigated experimentally Doppler effect Microphone place FFT Result Transient pressure variation caused by the flow 4
- 6. Literature review Orselli1“Two and Three-Dimensional Simulation of Sound Generated by Flow Around a Circular Cylinder” Result : comparison different model od RANS in 2d and LES 3d Gloerfelt “Flow -induced Cylinder Formulated as a Diffraction Problem for Low Mach Numbers” Result : transient pressure because of flow in vibrating body Perot “Numerical Prediction of the Noise Radiated by a Cylinder Result : The acoustical results are dependence of the SPL on the correlation length is an open question 6
- 7. IYPT 2012 Germany, National team of I. R. Iran7 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 8. Background theory 1 Fluid Flow division according to Reynolds number 8
- 9. 9
- 10. Background theory Source ≡ Transient pressure variation caused by the flow Sound ≡ Pressure waves propagating in the acoustic medium 11
- 11. Analysis method Computational Aeroacoustics (CAA) Sometimes referred to as Direct Noise Computation (DNC) Sound sources and propagation solved in a single comprehensive model Segregated Source-Propagation Methods (SSPM) Variational Methods Boundary Element Methods Integral 12
- 12. CAA 13 aircraft noise heard on the ground Computationally expensive Large meshes Long transient computations Mesh needs to be carefully prepared to capture sources properly
- 13. Famous “Lighthill’s Acoustic Analogy” J.M. Lighthill’s theory (1952) completed by N. Curle in 1955 the mathematical foundation for connecting the source and propagation parts This theory highlights the quadrupolar property of sound sources induced by turbulence 14 Rippletank
- 14. Theory of SSPM Sound generation and propagation are independent phenomena in most cases Problem domain can be thought to be composed of two “layers” Flow field Governs sound generation Navier-Stokes equations Acoustic field Governs sound propagation Wave equation 15
- 15. Ffowcs-Williams Hawkins Based on a two step approach Simulate transient flow field accurately only around sources Propagate noise from source to receiver via analytical solution of wave equation 16
- 16. Advantages Need CFD solution only around source Less expense/improved accuracy Disadvantages Can’t account for reflection Can’t account for backward effect of sound on flow 17
- 17. Derivation of the Wave Equation Linearized Continuity Equation (For fluctuations) Linearized Momentum Equation (No convection, no body forces, no viscous stresses) Eliminate 18
- 18. Lighthill’sAcoustic Analogy Continuity Equation Momentum Equation (Convection included, but no viscous stresses) In a conservative form Eliminate 19
- 19. “Lighthill’sEquation” This is referred to as “Lighthill’stensor” 20
- 20. Lighthill’s equation can be thought of as a wave equation with a source term Wave Equation Lighthill’sEquation Lighthill’stensor representing the sound source can be calculated by solving Navier-Stokes equations using CFD 21
- 22. 23 Lighthill stress tensor the compressive stress tensor For a Stokesian fluid
- 23. Physical view 24
- 24. Solution using the free-space Green function ((g)=4r). The complete solution =>two surface integrals => one volume integral. 25
- 25. Integral solution surface integrals => monopole dipole partially quadrupole sources volume integrals => quadrupole outside the source surface volume integral becomes small flow is subsonic the source surface encloses a non-linear source in FLUENT, the volume integral is dropped (feri farasat solution) 26
- 26. IYPT 2012 Germany, National team of I. R. Iran27 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 27. DETAIL ON METHODOLOGY 2d and 3d CFD methodology Acoustic Methodology 28
- 28. DETAIL ON METHODOLOGY 2d cfd methodology Computational fluid dynamics (CFD) is used to obtain the unsteady flow field. Fluent 6.3 & Ansys/Fluent 14 Finite volume 2d LES and 3d LES 29
- 29. Turbulence Modeling 6-30 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory #002600 Training ManualLarge Eddy Simulation (LES) • Spectrum of turbulent eddies in the Navier-Stokes equations is filtered: – The filter is a function of grid size – Eddies smaller than the grid size are removed and modeled by a subgrid scale (SGS) model. – Larger eddies are directly solved numerically by the filtered transient NS equation Filtered N-S equation Filter, Δ Subgrid Scale Resolved Scale Instantaneous component (Subgrid scale Turbulent stress)
- 30. Turbulence Modeling 6-31 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory #002600 Training ManualLarge Eddy Simulation • Large Eddy Simulation (LES) – LES has been most successful for high-end applications where the RANS models fail to meet the needs. For example: • Combustion • Mixing • External Aerodynamics (flows around bluff bodies) • Implementations in FLUENT: – Subgrid scale (SGS) turbulent models: • Smagorinsky-Lilly model • Wall-Adapting Local Eddy-Viscosity (WALE) • Dynamic Smagorinsky-Lilly model • Dynamic Kinetic Energy Transport – Detached eddy simulation (DES) model • Choice of RANS in DES includes S-A, RKE, or SST • LES is compatible with all combustion models in FLUENT • Basic statistical tools are available: Time averaged and RMS values of solution variables, built-in fast Fourier transform (FFT). • Before running LES, consult guidelines in the “Best Practices For LES” (containing advice for meshing, subgrid model, numerics, BCs, and more)
- 31. Les resolves large scales better fidelity than RANS method models the smallest(and most expensive) scales Low computational cost for practical engineering systems 32
- 32. Sub grid scale the subgrid scale was modeled by the Dynamic Smagorinsky Model (DSM) 33
- 33. discretization The numerical discretization scheme employed for the pressure-velocity coupling was the PISO algorithm In order to avoid numerical diffusion in LES, the convective fluxes can be discretized by a non- dissipative central-differencing scheme (for momentum) Time => second order implicit => Non iterative time advancement 34
- 34. Condition Circular cylinder diameter = 0.019 m Ma = 0.2 Re= 90000 35
- 35. Mesh Structural mesh 22698 cell Left = 2D Right = 20D Up and down = 5D According to Orselli and kim suggestion 36
- 36. Boundary condition 37 Velocity inlet Pressure outlet symmetry
- 37. Structural mesh near cylinder 38
- 39. dt The time step size = time scale of the smallest eddies => CFL<1 Ferequency 40
- 40. IYPT 2012 Germany, National team of I. R. Iran41 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 41. Result Cfd result Acoustic result 42
- 42. Cfd result In order to obtain the acoustic far-field, the near-field unsteady flow results is used as an input data to the wave equations the noise prediction depends directly on the accuracy of the CFD results Camparison drag coeficcient lift coeficient strouhal number 43
- 43. CFL 44
- 47. 48
- 49. 50
- 50. 51
- 51. 52
- 53. Cfd result 54 Good Prediction of boundary layer
- 54. 35d 128 d 55
- 55. 56
- 57. IYPT 2012 Germany, National team of I. R. Iran58 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 58. Conclusion Most of sound causes by the distribution of dipoles (pressure surface vibration) Frequency is equal to frequency of von karman vortex shedding Ffowks hawking method has good agreement with experiment by using 2s LES 2D LES is better in computational cost in comparison to other Rans method and better match with experiment 59
- 59. Future work Cylinder with flixible body Rotationg circular cylinder Helholtz propulsion 60
- 60. References 1- Revell, J. D., Prydz, R. A. and Hays, A.P., “Experimental Study of Airframe Noise vs. Drag Relationship for Circular Cylinders”, Lockheed Report 28074, Final Report NASA Contract NAS1-14403, (1977). 2- Reinaldo M. Orselli1, Julio R. Meneghini2 and Fabio Saltara3 , “Two and Three-Dimensional Simulation of Sound Generated by Flow Around a Circular Cylinder” 15th AIAA/CEAS Aeroacoustics Conference (2009) 3- Gloerfelt, X., Perot, F., Bailly, C. and Juvé, D., “Flow-induced Cylinder Formulated as a Diffraction Problem for Low Mach Numbers”, J. Sound and Vibration, Vol. 287, 2005, pp. 129-151.(2005) 4- Perot, F., Auger, J., Giardi, H., Gloerfelt, X. and Bailly, C. “Numerical Prediction of the Noise Radiated by a Cylinder”.AIAA-2003-3240, 9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, SC, 12-14 May(2003). 5- Ffowcs Williams, J. E. and Hawkings, D. L., “Sound Generated by Turbulence and Surfaces in Arbritary Motion”,Philosophical Transactions of the Royal Society, Vol. A264, No. 1151, 1969, pp. 321-342.(1969) 6- Takashi, T., Miyazawa, M. and Kato, C., “A Computational Method of Evaluating Noncompact Sound Based on Vortex Sound Theory”, J. Acoust. Soc. Am., Vol. 121, No. 3, 2007, pp.1353-1361.(2007) 61
- 61. 7- Kato, C., Lida, A., Fujita, H. and Ikegawa, M., “Numerical Prediction of Aerodynamic Noise from Low Mach Number Turbulent Wake”, AIAA Paper 1993-0145, (1993). 8- Seo, J.H., Moon, Y.J., “Aerodynamic Noise Prediction for Long-Span Bodies”, J. Sound and Vibration, Vol. 306 (3-5), 2007, pp. 564-579.(2007) Pierre Sagaut,” Large Eddy Simulation for Incompressible Flows”, Springer, second Edition,(2005) 9- Versteeg, H. K., Malalasekera, W., An Introduction to Computational Fluid Dynamics, 2nd ed., Pearson Eductated Lt.,Harlow, England, 2007, Chaps. 3, 6.(2007) 10- Germano, M., Piomelli, U., Moin, P. and Cabot, W.H., “Dynamic Subgrid Scale Eddy Viscosity Model”, Physics of Fluids A, Vol. 3, No. 19, 1991, pp.1760- 1765.(1991) 11- Lilly, D. K., “Proposed Modification of the Germano Subgrid Scale Closure Method”, Physics of Fluids A, Vol. 4, 1992,pp. 633-635. (1992) 12- Kim. S. E. and Mohan, L. S., “Prediction of Unsteady Loading on a Circular Cylinder in High Reynolds Number Flows using Large Eddy Simulation”, Proceedings of 24th Int. Conf. Offshore Mech. and Artic Eng., OMAE 2005, Halkidiki, Greece, June 12-17, (2005). 13- Kim, S. E., “Large Eddy Simulation of Turbulent Flow Past a Circular Cylinder in Subcritical Regime”, AIAA 2006-1418, 44th AIAA Aerospace Science Meeting and Exhibit, Reno, NV, 9-12 Jan., (2006). 14- Norberg, C., “Fluctuating Lift on a Circular Cylinder: Review and New Measurements,” J. Fluids and Structures, Vol. 17,No. 1, 2002, pp.57-96.(2002) 15- Breuer, M., “A challenging Test Large for Large Eddy Simulation: High Reynolds number Circular Cylinder Flow”, Int. J.Heat and Fluid Flow, Vol. 21, 2000, pp. 648-654.(2007) 62
- 62. IYPT 2012 Germany, National team of I. R. Iran63 Main Approach Comprehension • Inspiration • Significant • Literature review Background theory • Flow around circular cylinder • sound generated aerodynamically • sound analysis methodologies (Lighthill acoustic analogy o … Our Project approach - Methodology cfd acoustic - results and graph Conclusion - comparison and conclusion - Future work - references
- 63. Thanks all for your attention 64
Editor's Notes
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- عدد ماخ پایین قابلیت تفکیک هست)) بگم چرا از این روش استفاده می کنیم و می شود تفکیک کردمثال صدای هواپیما روی زمین- اگر استاد بپرسه که چرا مدل می کنن خوب تو یک ناحیه کوچیک نوسانات فشار در بیاریم بعد اون رو اعمال کنیمبایذ بگم مثل اینکه تو خورشید بگیم تشعشع چقدره یا اینکه بگم باید به اندازه ای دور شد که از نوسانات جریان دور باشیم.
- بگم چرا از این روش استفاده می کنیم و می شود تفکیک کرد
- بگم چرا از این روش استفاده می کنیم و می شود تفکیک کرد
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- ,. In contrast, direct numerical simulation, which resolves every scale of the solution, is prohibitively expensive for nearly all systems with complex geometry or flow configurations.resolves large scales of the flow field solution better fidelity than alternative approaches such as Reynolds-Averaged Navier-Stokes(RANS)methods.models the smallest (and most expensive) scales of the solution, rather than resolving them as Direct Numerical Simulation(DNS)Lowcomputational cost for practical engineering systems with complex geometry or flow configurations (turbulent jets, pumps, vehicles, and landing gear)
- دو بعدی طول محاسباتی رو هم باید گفت
- فرمولای پرشر ولاسیتی کوپلینگ رو بیارمیک کم توضیح هر کدوم را بگمIn order to avoid numerical diffusion in LES, the convective fluxes can be discretized by a non-dissipative central-differencing scheme (for momentum)
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