Exterior Flows in STAR-CCM+ Phil Shorter, CD-adapco Overview - - PowerPoint PPT Presentation

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Exterior Flows in STAR-CCM+ Phil Shorter, CD-adapco Overview - - PowerPoint PPT Presentation

Apr 23, 2023 281 likes •541 views

Diagnosing Interior Noise due to Exterior Flows in STAR-CCM+ Phil Shorter, CD-adapco Overview Problem of interest Analysis process Modeling direct field acoustic radiation from a panel Direct fields for individual modes Direct

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SLIDE 1

Diagnosing Interior Noise due to Exterior Flows in STAR-CCM+ Phil Shorter, CD-adapco

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SLIDE 2

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 3

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 4

Typical sources for interior noise

Many sources of interior noise are caused by exterior flow

Airborne : 300 Hz to 10 kHz Structure-borne : 0 to 800 Hz Wind-noise : 50 to 10 kHz

Front End Wipers Antennas/Racks Mirror/Greenhouse Rear turbulence Underbody HVAC

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SLIDE 5

Simplified example

Panel Exterior flow

40 m/s

Interior acoustic cavity Sound package

foam/fiber

A A Cross-Section AA Experimental setup

  • M. Smith et al “Validation tests for flow induced excitation

and noise radiation from a car window”, Proc. 33rd AIAA Aeroacoustics Conference.

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SLIDE 6

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 7

Analysis process

Unsteady transient analysis performed in STAR-CCM+ Pressure time history data exported across surface of panel

  • 1. Model flow
  • 2. Model direct field

Sff Vibro-Acoustic model used to predict direct field radiation into acoustic space when random fluctuating pressure applied across exterior surface of panel

  • 3. Model reverberant field

Vibro-Acoustic model used to predict reverberant response in cavity for a given input power in the direct field

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SLIDE 8

Step # 1 : modeling the flow

Unsteady transient analysis performed in STAR-CCM+ For details see:

  • M. Smith et al “Validation tests for flow induced

excitation and noise radiation from a car window”,

  • Proc. 33rd AIAA Aeroacoustics Conference 2012.
  • P. Bremner, “Vibroacoustic Source Mechanisms

under Aeroacoustic Loads” Proc. 33rd AIAA Aeroacoustics Conference 2012.

  • 1. Model flow
  • 2. Model direct field

Sff Vibro-Acoustic model used to predict direct field radiation into acoustic space when random fluctuating pressure applied across exterior surface of panel

  • 3. Model reverberant field

Vibro-Acoustic model used to predict reverberant response in cavity for a given input power in the direct field

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SLIDE 9

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 10

Step # 2 : modeling panel direct field

Unsteady transient analysis performed in STAR-CCM+ Pressure time history data exported across surface of panel

  • 1. Model flow
  • 2. Model direct field

Sff Vibro-Acoustic model used to predict direct field radiation into acoustic space when random fluctuating pressure applied across exterior surface of panel

  • 3. Model reverberant field

Vibro-Acoustic model used to predict reverberant response in cavity for a given input power in the direct field

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SLIDE 11

Modeling a glass panel

Mode 1 : ~380 Hz

Frequency (Hz)

  • Choice of Vibro-Acoustic method (FE, BEM, SEA etc.) depends on wavelengths
  • f interest and size of system
  • Small glass panel (0.4 x 0.2 x 5e-3 m) has approx. 45 modes below 10 kHz
  • This example therefore uses a deterministic (analytical) representation of the

panel and its modes

Mode 27 : ~3.9 kHz Mode 40: ~8.9 kHz

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SLIDE 12

“Modal” direct fields at 1 kHz

Mode 1 : ~380 Hz Mode 27 : ~3.9 kHz Mode 40: ~8.9 kHz Normalize mode shape to have maximum velocity of 0.1 mm/s, look at radiated sound at 1kHz when mode shape radiates in a baffle (in this example, acoustic radiation calculated using boundary integral)

Abs(Re{P}) dB re:2e-5

Different modes have very different “radiation efficiencies” (below coincidence)

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SLIDE 13

“Modal” direct fields

Mode 1 : ~380 Hz Mode 27 : ~3.9 kHz Mode 40: ~8.9 kHz 500 Hz 1 kHz 5 kHz Directivity of radiated field from a given mode shape changes with frequency

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Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 15

Random modal forces due to flow (Sff)

Fluctuating surface pressure from STAR-CCM+ can be transformed to the frequency domain and averaged over overlapping segments to give modal cross-spectral force matrices : Sff(f)

F (t) <Sff(f)> FSP(x,y,t) (x,y)

Re{Sff(1kHz)}

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SLIDE 16

Random modal responses

In a random vibration analysis, the cross-spectral modal response (Sqq) is related to the cross-spectral modal forces (Sff) by

Modal dynamic stiffness matrix

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SLIDE 17

Direct field response (<Spp>)

Total direct field pressure response within the cavity can be found from Sqq and the modal direct fields calculated previously.

1 kHz 500 Hz 5 kHz

Spp (dB re:4e-10 Pa2/Hz) (80dB dynamic range) (60dB dynamic range) (40dB dynamic range)

Direct field radiation from flow induced random vibration

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SLIDE 18

Look at spatial variation along a line

1 kHz 500 Hz 5 kHz

(80dB dynamic range) (60dB dynamic range) (40dB dynamic range)

A2 A1

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SLIDE 19

Direct field pressure at 500 Hz

A2 A1 Typical drivers ear location Evanescent (‘sloshing’) in near-field, free-field propagation outside near field

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SLIDE 20

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 21

Step # 3 : modeling reverberant field

Unsteady transient analysis performed in STAR-CCM+ Pressure time history data exported across surface of panel

  • 1. Model flow
  • 2. Model direct field

Sff Vibro-Acoustic model used to predict direct field radiation into acoustic space when random fluctuating pressure applied across exterior surface of panel

  • 3. Model reverberant field

Vibro-Acoustic model used to predict reverberant response in cavity for a given input power in the direct field

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SLIDE 22

SEA model

Reverberant response within the cavity involves short wavelength system level response (function of sound package distribution within the cavity). FE/BEM typically frequency limited for many applications and so Statistical Energy Analysis (SEA) commonly used.

SEA is based on a set of power balance equations for the reverberant field (expressions developed for power input, power dissipation and power transmitted to adjacent subsystems)

Pin Pcoupling Pdissipated E

(reverberant energy)

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SLIDE 23

Direct and reverberant fields at 500 Hz

Decreasing absorption Total field Direct field Reverberant field Increasing absorption (Ensemble average) response in the reverberant field is spatially uniform. Levels depend on sound package within vehicle. For typical sound package configurations the direct and reverberant field contributions can often both be important at the drivers ear location.

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SLIDE 24

Overview

  • Problem of interest
  • Analysis process
  • Modeling direct field acoustic radiation from a panel
  • Direct fields for individual modes
  • Direct fields due to random vibration induced by flow
  • Modeling the random reverberant response in a

cavity

  • Summary
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SLIDE 25

Summary

  • Prediction of interior noise due to exterior flows of significant interest

in many applications (“Aero-Vibro-Acoustics”)

  • Aero-Vibro-Acoustic analysis requires STAR-CCM+ model of exterior

fluctuating surface pressures and vibro-acoustic models of interior noise

  • Simple numerical example presented in this paper (glass panel in wall
  • f wind tunnel radiating into an acoustic cavity)
  • Vibro-Acoustic analysis performed:
  • Hybrid (deterministic+SEA) modeling approach used
  • Direct fields calculated for individual modes
  • Direct fields calculated for flow induced random vibration
  • Reverberant field (and total cavity response) calculated using SEA
  • Example highlights that both direct and reverberant field contributions

may be important and may therefore need to be included in vibro- acoustic analysis of interior windnoise