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 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
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’
Rotor Source Noise
Lighthill’s Formulation
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)
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.
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
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
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
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
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
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
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
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.
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
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
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
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
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
Permeable Surface Method: Acoustic Data Surface Red – Blade; Blue – Baseline Grid; Orange – New Grid
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
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
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
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
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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