19 October 20062006 AME Graduate Student

Conference

Flow Induced Oscillations of a Helmholtz Resonator

Paul E. Slaboch

Advisor: Scott C. Morris

20 November 20052006 AME Graduate Student

Conference

Motivation

Interior pressure oscillations are a problem for both the automotive and aerospace communities.

In automotive vehicles, the very low frequency (~14-17 Hz) high amplitude pressure oscillations can exceed 120 dB, which can be painful to both drivers and passengers.

The goal of this study is to determine the underlying flow physics of the problem and to generate design guidelines for future vehicles to minimize buffeting.

20 November 20052006 AME Graduate Student

Conference

Introduction

Helmholtz resonators occur when flow passes over an orifice, through a neck and into a volume.

The resonator can be modeled as a spring-mass system.

Uonset occurs when fn=fR

0 0

0

0

4

( 0.25 2 )

0.375 ( 1)

0.875 ( 2)

2 ( )

(when 0)2 2

n

n

n

R

R

f L cn

U U

f Ln const

U

f Ln const

U

a Sf

V l C S

a S a Sf l

VC V

20 November 20052006 AME Graduate Student

Conference

Previous Work

20 November 20052006 AME Graduate Student

Conference

Previous Work

20 November 20052006 AME Graduate Student

Conference

Experimental Setup

PIV Cameras

Cavity

Open Orifice

20 November 20052006 AME Graduate Student

Conference

Pressure Measurements

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 520

40

60

80

100

120

140

f/fHR

Cav

ity p

' (dB

)

Volume=0.1m3, Window 12.5cmx12.5cm, U=UOnset

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 220

40

60

80

100

120

140

f*L/U

Cav

ity p

' (dB

)

Volume=0.1m3, Window 12.5cmx12.5cm, U=UOnset

20 November 20052006 AME Graduate Student

Conference

Pressure Measurements

f*L/U

U/U

Ons

et

log10

(sqrt(Gpp

)/q), Volume=0.1m3, Window 12.5cmx12.5cm

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

f/fHR

U/U

Ons

et

log10

(sqrt(Gpp

)/q), Volume=0.1m3, Window 12.5cmx12.5cm

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

f*L/U

U/U

Ons

et

Cavity p' (dB), Volume=0.1m3, Window 12.5cmx12.5cm

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

20

40

60

80

100

120

140

f/fHR

U/U

Ons

et

Cavity p' (dB), Volume=0.1m3, Window 12.5cmx12.5cm

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

20

40

60

80

100

120

140

20 November 20052006 AME Graduate Student

Conference

Pressure Measurements

f*L/U

U/U

Ons

et

log10

(sqrt(Gpp

)/q), Volume=0.1m3, Window 12.5cmx12.5cm

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

20 November 20052006 AME Graduate Student

Conference

PIV Flow Visualization

20 November 20052006 AME Graduate Student

Conference

PIV Measurements

20 November 20052006 AME Graduate Student

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Effect of Free Stream Velocity

20 November 20052006 AME Graduate Student

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Effect of BL Thickness

20 November 20052006 AME Graduate Student

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Future Work

20 November 20052006 AME Graduate Student

Conference

Future Work

20 November 20052006 AME Graduate Student

Conference

Conclusions A series of experiments has been performed to

determine the underlying flow physics of a flow induced Helmholtz resonator.

The actual mechanism of the oscillations is neither the roll up of discrete vortices nor a flag flapping shear layer instability. Rather, it appears to be a combination of the two.

The effect of free stream velocity is to spread the vorticity into a more continuous stream while the effect of the boundary layer thickness is to alter the location of the formation of a vortex.

This study, combined with future work, will provide design guidelines for automotive designers.

20 November 20052006 AME Graduate Student

Conference

Thank you for your attention.

Questions?