Aero-Vibro Acoustics For Wind Noise Application - … Acoustics For Wind Noise Application ... Full...

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


A-Pillar Vortex

Flow separation/Vortex shading

Cavity Resonance Flow separation/ vortex shading

Flow separation/ Vortex shading

Cavity Resonance

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]

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

Simulation Methodology [1]


A-pillar Mirror Turbulence

Mic.

Glass Interior Walls

Outer Walls (Rigid)

Connection between Vibrating walls and Rigid walls

External CFD Model – Transient Flow

Vibrating Surfaces (Side Glass, Windshield)

Acoustics Model (Car Interior)

Vibroacoustics Modeling

Inflow

CFD modeling

Simulation Methodology [2]


………

Solve Transient

CFD

Time Freq. domain

transform

Mapping Freq. Domain

Pressure Loading

Solve “Vibro-Acoustics”

Model

Workflow Studied


ANSYS Fluent Harmonic Strongly

Coupled Vibro-acoustic

ANSYS Fluent Harmonic Structural

Harmonic Acoustic

Pressure Mapping after

FFT

Pressure Mapping after

FFT

Velocity Mapping

Strong Vibroacoustic Coupling

One Way Vibroacoustic Coupling

Test Measurement Points


650mm

1000mm

200mm

90mm

Interior Microphone Locations

Accelerometers mounted on LH Side

Glass

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

Boundary Conditions Inlet Vel. Profile

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

Solver Settings : Transient CFD Simulation

1. Solver : ANSYS Fluent, Pressure Based, Double Precision, Transient , Gradient – Green Gauss Node Based

2. Transient Formulation : 2nd 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


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


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

Source Data : Transformation Time Frequency Domain


1

2 3

4

5

Acoustic Source FFT is a Beta Feature in R 16.0

1. Set Modes (Real /Img.)

2. Octave (SPL)

3. 1/3rd Octave (SPL)

4. Constant Band (SPL)

Surface dB Map


1/3rd Octave 100 Hz 1/3rd Octave 1000 Hz

1/3rd Octave 500 Hz 1/3rd Octave 1600 Hz

Acoustics Pressure Loading in Freq. Domain


Freq. 455 Hz Freq. 455 Hz

Freq. 1575 Hz Freq. 1575 Hz

Acoustics Source Mapping

Thursday, October 02, 2014 18

Mapping for 100 Hz ANSYS Fluent ANSYS Mechanical

Mapping for 1000 Hz

Vibroacoustics Modeling Structural Material Properties


PROPERTIES GLASS AL 6061 HEAVY LAYER

Thickness (mm) 4 12 1

Density (kg/m3) 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/m3) 1.2 1.2

Sound Speed (m/s) 343 343

Fluid Resistivity (N s /m4) 6.83E+16

Porosity 0.879

Tortuosity 3.31

Viscous Length (m) 9.483e-10

Thermal Length (m) 1.2174e-10

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)


Results : Acceleration vs Frequency


Results : SPL(dB) vs 1/3rd Octave Freq. @ Interior Microphone


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


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