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03/02-03/2006 Robert Bosch GmbH reserves all rights even in the event of industrial property rights.

We reserve all rights of disposal such as copying and passing on to third parties.

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Fluent CFD Summit 2005

Computational Aero-Acoustics

3D Computational Aero-Acoustics

Simulation of Air Intake-Induced Whistles

Venkatesh Kannan4 Core Development, Robert Bosch Corporation, Farmington Hills, MI

Sandeep D. Sovani, Ph.D4 Fluent Inc, Ann Arbor, MI

Dave S. Greeley, Ph.D4

Air Flow Research, Robert Bosch Corporation, Waltham, MA

Ashok Khondge4 Fluent Pvt. Ltd., Pune, India

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Abstract

4 Introduction

4 Background

4 3D Computational Simulations

4 Correlation

4 Lessons Learnt

4 Conclusions

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A distinct whistle at

4 2900 - 3400 Engine RPM

4 72 - 78% Engine Load

4 35-45 Throttle Angle

Hemi-anechoic - Chassis Dyno

Test Data

Introduction

2200Hz

88.4dB

SPL,

dB

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Modified Geometry

Ramp (16) & Radius (2 mm)

Baseline Geometry

Cavity

Design Solution

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Baseline

110

100

90

80

70

60

50

SPL,

dB

Modified

Airflow

=43

Baseline

=43

Airflow

Modified

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4 Detailed sensitivity studies

conducted experimentally4 Presented at Fluent UGM

2004

4 Presented at SAE 2004

WorldCongress, Detroit, MIPaper # 2004-01-0395

4 Do provide a design solution but

do not provide insight into the

whistle physics

4 Experiments are expensive

Need for Simulation

__Disturb Flowat A & B

B

__Disturb Flow at A

A

Airflow

__Eliminate Cavity C

C

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4 CFD-CAA simulations conducted for physical insight

4 2D simulations conducted first

4 Can replicate whistle

4 But frequency under-predicted

4 Difference in whistle magnitude between baselineand modified designs not predicted well

4 Presented results at Fluent UGM2004

4 Also presented at SAE NVH Conference, TraverseCity, MI, Paper # 2005-01-2364

Background

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434 18000 2D Quad Cells,4 k- RNG Turbulent Model

4 Unsteady Simulation

4 Coupled Solver

4 2nd Order Upwind

4 Time Step = 2.5e-05s

4 Run Time = 0.04s

4 Ideal Gas Law

4 Double Precision Solver

High Mesh

Density

Inlet

(101325 Pa)Throttle

PlateSump

Zip TubeOutlet

92325Pa

P = 9kPa

2D Computational Simulation

Monitor

Point A

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80

100

120

140

160

180

0 1000 2000 3000 4000 5000Frequency (Hz)

SPL

(dB) Design A

152 dB @ 1710 Hz

Experimental - 3D Computational - 2D

159dB @

2125Hz

152dB @

1710Hz

Correlation - Sound Pressure Level at Point A

4 Baseline Geometry

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80

100

120

140

160

180

0 1000 2000 3000 4000 5000

Frequency (Hz)

SPL

(dB)

137dB @

2125Hz


149dB @

1800Hz


4 Modified Geometry

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4 4221265 cells ( Hex+tet, Hex dominant),

4 LES with Smagorinsky-Lilly subgrid

model (Dynamic Model)

4 Unsteady Simulation

4 Segregated Solver

4 Discretizations

4 2nd order upwind for pressure,density and energy

4 Bounded Central Differencing

for momentum

4 Time Step = 2.5e-05 sec

4 Total Run Time = 0.03775 sec

4 Ideal Gas Law

4 Double Precision Solver

3D Computational Simulation

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Simulated Flow Structure4 Contours of velocity magnitude on central vertical plane

2D 3D

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Simulated Flow Structure4 Contours of static pressure on central vertical plane

2D 3D

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80

100

120

140

160

180

0 1000 2000 3000 4000 5000

Frequency (Hz)

SPL(d

B)

Design A

152 dB @ 1710 Hz


159dB @

2125Hz

152dB @

1710Hz


4 Baseline Geometry

Computational - 3D

157.8dB @

2098Hz

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16



80

100

120

140

160

180

0 1000 2000 3000 4000 5000

Frequency (Hz)

SPL(dB)

137dB @

2125Hz


149dB @

1800Hz


4 Modified Geometry

Computational - 3D

152.6dB

@ 2098Hz

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Conclusions

4 Baseline geometry 3D simulations

4 Very accurate compared to experiments

4 Whistle frequency as well as magnitude predicted properly

4 Modified geometry 3D simulations

4 Whistle frequency predicted very accurately, but amplitude is off

4 Causes are under investigation

4 It is possible that CFD model differs slightly from actual geometry

4 3D computational simulation (although computation intensive) provide

additional insights better accuracy as compared with experiments than

2D simulations

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Long Term Goals

Benefits

4 Understanding of the influence of small geometric details on

the mechanism of whistle production and suppression

4 Novel ideas for the flow path geometry features that can

effectively suppress or produce the aero-acoustic sources

Conclusions

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Acknowledgements

4 Dave Hanner

4John RydzewskiGeneral Motors Corporation

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Questions & Answers

fluent ug m 2005

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