Aero-Vibro Acoustics For Wind Noise Application David Roche and Ashok Khondge ANSYS, Inc.
Outline 1. Wind Noise 2. Problem Description 3. Simulation Methodology 4. Results 5. Summary Thursday, October 02, 2014 2014 Automotive Simulation World Congress 2
Aerodynamics Noise Generation Cavity Resonance A-Pillar Vortex Flow separation/ Vortex shading Cavity Resonance Flow separation/ vortex shading Flow separation/vortex shading Thursday, October 02, 2014 2014 Automotive Simulation World Congress 3
Wind Noise High Frequency (> 500 Hz) Noise generated by head wind and perceived inside automotive cabin @ highway driving speeds It is cost beneficial to address wind noise UPFRONT in Design Process 1. Highest degree of freedom to change exterior design causing wind noise 2. Avoids expensive late countermeasures [1] Thursday, October 02, 2014 2014 Automotive Simulation World Congress 4
Problem Description Demonstrate Aero-vibro-acoustics coupling to predict noise at the interior of the Hyundai simplified model [2] HSM Model Simplified model released by Hyundai Kia Motors for 2013 KSNVE Open Benchmark [2] Sound Source Transient Separated flow at A-pillar Transfer Path [Side glass, windshield] Receiver Ear of a driver Thursday, October 02, 2014 2014 Automotive Simulation World Congress 5
Simulation Methodology [1] Connection between Vibrating walls and Rigid walls A-pillar Mirror Turbulence Outer Walls (Rigid) Inflow Glass Mic. Interior Walls External CFD Model Transient Flow Vibrating Surfaces (Side Glass, Windshield) Acoustics Model (Car Interior) CFD modeling Vibroacoustics Modeling Thursday, October 02, 2014 2014 Automotive Simulation World Congress 6
Simulation Methodology [2] Solve Transient CFD Time Freq. domain transform Mapping Freq. Domain Pressure Loading Solve Vibro- Acoustics Model Thursday, October 02, 2014 2014 Automotive Simulation World Congress 7
Workflow Studied Strong Vibroacoustic Coupling ANSYS Fluent Pressure Mapping after FFT Harmonic Strongly Coupled Vibro-acoustic One Way Vibroacoustic Coupling ANSYS Fluent Pressure Mapping after FFT Harmonic Structural Velocity Mapping Harmonic Acoustic Thursday, October 02, 2014 2014 Automotive Simulation World Congress 8
Test Measurement Points 90mm 1000mm 200mm 650mm Interior Microphone Locations Accelerometers mounted on LH Side Glass Thursday, October 02, 2014 2014 Automotive Simulation World Congress 9
Transient CFD Modeling CFD Domain consists of External HSM surfaces, side glasses and windshield & wind tunnel boundaries Configuration Studied : HSM 0 deg. Yaw Nozzle Inlet : Velocity Inlet : 130 kmph [Profile] Tunnel Outlet : Pressure Outlet (Gauge Pressure = 0 Pa) Tunnel Inlet : Pressure Inlet (Gauge Tot. Pressure = 0 Pa) Tunnel Top, floor, side, wall BC (No-Slip) CFD Domain Inlet Vel. Profile Boundary Conditions Thursday, October 02, 2014 2014 Automotive Simulation World Congress 10
Mesh Details Total Cell Count = 45 Million Prims Cell Count = 23 Million No of Prism Layers = 12 First Prism Layer Height = 0.05 mm Surface Mesh Size : A-pillar 1.5 to 2.0 mm, Side glasses, windshield = 2.0 to 3.0 mm Thursday, October 02, 2014 2014 Automotive Simulation World Congress 11
Solver Settings : Transient CFD Simulation 1. Solver : ANSYS Fluent, Pressure Based, Double Precision, Transient, Gradient Green Gauss Node Based 2. Transient Formulation : 2 nd Order Implicit, Time Step Size = 2e-5 s 3. Material - Air as Ideal Gas 4. Turbulence Model Steady State : SST K-Omega 5. Turbulence Model Transient : DDES SST K-Omega 6. Pressure Velocity Coupling SIMPLEC 7. Spatial Discretization Pressure : Second Order, Density : Second Order Upwind Momentum : Bounded Central Differencing TKE & Specific Dissipation Rate : Second Order Upwind Energy : Second Order Upwind Thursday, October 02, 2014 2014 Automotive Simulation World Congress 12
Solution Procedure 1. Run Steady State Simulation using SST K-Omega Turbulence Model 2. Steady State Simulation Solver Settings Pressure Based Coupled Solver 3. Switch to Transient Simulation, Use Second Order Temporal Discretization 4. Switch to DDES SST K-Omega Turbulence Model 5. Run initial transient simulation to achieve dynamic steady state 6. Run Final transient simulation [time step size 2e-5, no. of iterations per time step = 8] 7. Export the ASD Data on Wind-shield, side-glass surfaces at every time step 8. Perform Surface Acoustics FFT to transform source data into Frequency Domain Thursday, October 02, 2014 2014 Automotive Simulation World Congress 13
Transient Flow Field Velocity Contours at Z = 0.5 m Pressure Contours at Z = 0.5 m Iso-surface of Q-Criterion colored by velocity magnitude Thursday, October 02, 2014 2014 Automotive Simulation World Congress 14
Source Data : Transformation Time Frequency Domain Acoustic Source FFT is a Beta Feature in R 16.0 1 3 2 1. Set Modes (Real /Img.) 2. Octave (SPL) 3. 1/3 rd Octave (SPL) 4. Constant Band (SPL) 5 4 Thursday, October 02, 2014 2014 Automotive Simulation World Congress 15
Surface db Map 1/3 rd Octave 100 Hz 1/3 rd Octave 1000 Hz 1/3 rd Octave 500 Hz 1/3 rd Octave 1600 Hz Thursday, October 02, 2014 2014 Automotive Simulation World Congress 16
Acoustics Pressure Loading in Freq. Domain Freq. 455 Hz Freq. 455 Hz Freq. 1575 Hz Freq. 1575 Hz Thursday, October 02, 2014 2014 Automotive Simulation World Congress 17
Acoustics Source Mapping ANSYS Fluent Mapping for 100 Hz ANSYS Mechanical Mapping for 1000 Hz Thursday, October 02, 2014 18
Vibroacoustics Modeling Structural Material Properties PROPERTIES GLASS AL 6061 HEAVY LAYER Thickness (mm) 4 12 1 Density (kg/m 3 ) 2500 2700 2000 Young s Modulus (GPa) 70 69 0.04 Poisson's ratio 0.22 0.33 0.45 PROPERTIES Air Foam Mass Density (kg/m 3 ) 1.2 1.2 Sound Speed (m/s) 343 343 Fluid Resistivity (N s /m 4 ) 6.83E+16 Porosity 0.879 Tortuosity 3.31 Viscous Length (m) 9.483e-10 Thermal Length (m) 1.2174e-10 Thursday, October 02, 2014 2014 Automotive Simulation World Congress 19
Vibroacoustics Modeling Strong Coupling: Full Vibroacoustics harmonic analysis from 50 to 1000 Hz (117 frequencies) Weak Coupling: Full structural harmonic analysis from 50 to 1000 Hz (117 frequencies) Full acoustic harmonic analysis from 50 to 1000 Hz (117 frequencies) Thursday, October 02, 2014 2014 Automotive Simulation World Congress 20
Results : Acceleration vs Frequency Thursday, October 02, 2014 2014 Automotive Simulation World Congress 21
Results : SPL(dB) vs 1/3 rd Octave Freq. @ Interior Microphone Thursday, October 02, 2014 2014 Automotive Simulation World Congress 22
Summary 1. Aero and Vibroacoustics coupling is demonstrated using transient CFD and Vibroacoustics modeling 2. ANSYS Fluent solver is used for transient aeroacoustics simulation 3. A Vibroacoustics simulation is done using ANSYS Mechanical using two approaches Strong Vibroacoustics coupling approach Weak Vibroacoustics coupling approach 4. Simulation Results are fairly in good agreement with Test Data 5. Differences between strong and weak Vibroacoustics coupling are observed It doesn t seem possible to neglected the effects of the acoustics cavity on the deformation of the structure Thursday, October 02, 2014 2014 Automotive Simulation World Congress 23