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Rotorcraft Noise Prediction with Multi-disciplinary Coupling Methods Yi Liu NIA CFD Seminar, April 10, 2012 Outline Introduction and Background Multi-disciplinary Analysis Approaches Computational Fluid Dynamics Rotor Wake


  1. Rotorcraft Noise Prediction with Multi-disciplinary Coupling Methods Yi Liu NIA CFD Seminar, April 10, 2012

  2. Outline • Introduction and Background • Multi-disciplinary Analysis Approaches – Computational Fluid Dynamics – Rotor Wake Modeling Methods – Computational Structural Dynamics – CFD/CSD Coupling Procedure – Acoustic Analysis • Results for High speed impulsive noise prediction • Results for Blade vortex interaction noise prediction • Concluding remarks

  3. Introduction and Background • Complex interactional aerodynamics Dynamic Loads and Structure Dynamics Aeroelastic Response Acoustic Noise Flight Controlling System Engine/Drive Train Dynamics Leishman, ‘Principles of Helicopter Aerodynamics’

  4. Rotor Source Noise

  5. Lighthill’s Formulation

  6. Ffowcs Williams-Hawkings Formulation Numerical Solution to FW Numerical Solution to FW- -H equation H equation Numerical Solution to FW Numerical Solution to FW - - H equation H equation • � � � � � � � �� � − � � � � = ��� + �" # � + (' #,% ) ) � � �� �$ # �$ # �$ % • Three source terms: – � = +, - + + . - − , - thickness source (monopole) • Requires rotor blade geometry and kinematics – " # = / #,% - % + +. # . - − , - loading source (dipole) • Requires rotor blade geometry, kinematics and surface loading – ' #,% = +. # . % + / #,% − � � + − + 0 � #,% quadrupole source • Requires flow field around the rotor blade (volume integration)

  7. Noise prediction method • The noise standard became ever more stringent, and the cost of flight testing and wind tunnel experiments was increasing • Computational aero-acoustics gets more attention – Direct Numerical Method – Hybrid Numerical Method • High-speed impulsive (HSI) noise represents one of the most intense and annoying forms of noise generated by helicopter rotors in high-speed forward flight. • Blade Vortex Interaction (BVI) noise represents another type of intensive noise generated by helicopter rotor in low-speed decent flight close to ground.

  8. Approaches CAMRAD II, DYMORE Multi-body, Nonlinear Computational Structure Dynamics (CSD) Noise Propagation (WopWop, RNM) High-order Computational Fluid Dynamics (CFD) High-fidelity Wake Modeling (Particle-VTM) Shock Wave Blade-Vortex Boundary Layer Interaction FUN3D, OVERFLOW NASA RANS Flow Solver A systematic coupling approach among multiple disciplines to predict rotor noise

  9. Computational Fluid Dynamics TURNS ( Transonic Unsteady Rotor Navier-Stokes by Prof. Baeder ) – Compressible unsteady Reynolds Averaging Navier-Stokes (RANS) solver – Inviscid terms are computed using 3 rd MUSCL, and 5 th order WENO scheme – Viscous terms are computed using 2 nd central differencing – Second order time accuracy with Newton-type sub-iteration – Baldwin-Lomax and Spalart-Allmaras turbulence models – The low dispersion and dissipation Total Variation Diminishing (STVD) scheme developed by Helen Yee is implemented

  10. Rotorcraft Wake Modeling Methods • Free-wake module – Wake geometry is decided by potential flow based method – CFD calculates the wake effects with the inputted wake geometry – Heavily depend on empirical input • Overset grid methodology to capture wake directly – Physics based, high resolution wake capturing method – Grid dependency – Numerical dissipation diffuses the tip vortex too rapidly • Particle Vortex Transport Method (PVTM) (Dr. Phuriwat Anusonti-Inthra) – Solves the incompressible vortex transport equation using a Lagrangian (vortex particle) approach – Fully coupled with CFD • Uses CFD in near body to capture vortex generation • Uses PVTM in other domains for calculating vortex evolution

  11. Computational Structural Dynamics • CAMRAD II (Dr. Wayne Johnson) – Comprehensive Finite Element Analysis with Multi-body Dynamics – Forced periodic solutions for steady and level flight to get trim solutions – The structural dynamics response is very important for the rotor blade simulations in forward flight conditions

  12. CFD/CSD Coupling Procedure CAMRAD II • A loose coupling Lifting line aero with uniform inflow + “delta” force strategy based on a trimmed periodic rotor solution CAMRAD II trim solutions Forces and motions at quarter chord • The comprehensive airloads are replaced with CFD airloads with a ‘delta’ CAMRAD II Blade Motions force method Aero-loading • Use the lifting line TURNS / CFD Aero aerodynamics to trim and CSD to account for blade Aero-loading Difference ∆ F/M n+1 = (F/M cfd – F/M CII ) deformation in the CFD Surface Aero- + ∆ F/M n loading comprehensive analysis Check convergence

  13. Acoustic Analysis • PSU-WOPWOP (Prof. Brentner) – Solves Farassat’s retarded-time formulation 1A of the Ffowcs Williams-Hawkings (FW-H) equation – Propagate and compute the tone noises at any given observer locations – Impermeable surface method • Noise source based on the blade loadings or surface pressure predicted by CFD or comprehensive analysis • Thickness noise and loading noise – Permeable surface method • Noise source based on the flow field solutions provided by CFD on a specified surface around the rotor blade • Thickness noise, loading noise, high-speed impulsive noise

  14. High-order STVD scheme for Permeable Surface method • Implemented the low dispersion and low dissipation Symmetric Total Variation Physical Blade Surface Diminishing (STVD) scheme introduced by Permeable Surface Helen Yee into our surrounding the blade current CFD solver , or Acoustic Data Surface which replaces the original 2 nd order ROE High-order CFD scheme provides scheme inside the code sufficient spatial and temporal accuracy to propagate acoustic characteristic waves to the acoustic data surface

  15. High Speed Impulsive Noise Prediction with CFD+overset grid method • The DNW acoustic wind tunnel test is conducted in the large low-speed facility (LLF) at the Duits Nederlands Windtunnel (DNW) for a scaled model of the UH-60a helicopter main rotor • High speed forward flight case with advance ratio 0.3010 and the rotor tip Mach number of 0.8737 • CFD + overset background grid method coupled with CSD, with 10 million total grid points.

  16. Acoustic Experiments Set-up 3R Mic. 7 The acoustic predictions and 30 o measured sound pressure at Mic. 1 microphone 1 and microphone 7 are compared 3R Wind Top View Mic. 1 Mic. 7 3R Side View R

  17. Acoustic Experimental Measurements (Microphone 1) 100 EXP-Microphone 1 50 Sound Pressure (Pa) Noise due to vortex 0 -50 HSI Noise -100 0 0.25 0.5 0.75 1 Normalized Time

  18. Acoustic Experimental Measurements (Microphone 7) 100 EXP-Microphone 7 Noise due to vortex 50 Sound Pressure (Pa) 0 -50 HSI Noise -100 0 0.25 0.5 0.75 1 Normalized Time

  19. Impermeable Surface Method (Microphone 1) 30 20 10 0 Sound Pressure-Total -10 -20 -30 -40 -50 -60 Impermeable Surface Method EXP - Microphone 1 -70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No-dimension Time

  20. Impermeable Surface Method (Microphone 7) 40 20 0 Sound Pressure-Total -20 -40 -60 -80 Impermeable Surface Method EXP - Microphone 7 -100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No-dimension Time

  21. Permeable Surface Method: Acoustic Data Surface Red – Blade; Blue – Baseline Grid; Orange – New Grid

  22. Acoustic Predictions for Different Acoustic Data Surfaces 30 20 10 0 Sound Pressure-Total -10 Baseline Grid Grid No. 1 Grid No. 2 -20 Grid No. 3 EXP -30 -40 -50 -60 -70 0 0.01 0.02 0.03 0.04 Time

  23. Permeable Surface Method (Microphone 1) 30 20 10 0 Sound Pressure-Total -10 -20 -30 -40 -50 -60 Impermeable Surface Method Permeable Surface Method EXP - Microphone 1 -70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No-dimension Time

  24. Permeable Surface Method (Microphone 7) 40 20 0 Sound Pressure-Total -20 -40 -60 -80 Impermeable Surface Method Permeable Surface Method EXP - Microphone 7 -100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No-dimension Time

  25. Blade Vortex Interaction Noise Prediction with CFD+PVTM method Particle Vortex Transport Method: ω d 2 = ω ⋅ ∇ + ∇ ω + u v S L dt Coupled with CFD, where vortex source term come from RAN solution • First-principle method • Conserve vorticity • Gridless wake (No grid adaptation) Paper: Anusonti-Inthra, P. “Validations of Coupled CSD/CFD and Particle Vortex Transport Method for Rotorcraft Applications: Hover, Transition, and High Speed Flights” Proc. 66 th AHS Forum, Phoenix, AZ, 2010

  26. HART II – Baseline PVTM Set up • CAMRAD II – 5 beam elements • CFD grid – 1.5M cells × 4 blades – Boundaries (a) HART II CFD grid • 0.5c: downstream • 1.0c: other directions • Higher Harmonic Control • PVTM resolution Aeroacoustic Rotor Test – Fine: 0.5c (5R × 1.25R) (HARTII) performed in October – Medium: 1c(10R × 3.75R) 2001 in the Large Low-Speed – Coarse: 2c (15R × 6.25R) Facility (LLF) of the DNW Wind Tunnel • Flight Conditions: – Low speed decent flight – Advance ratio, µ = 0.15

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