AIAA Orlando Porous Surface

Noise and Flowfield Characteristics of a Supersonic

Jet Impinging on a Porous Surface

Alex Wiley*, Rajan Kumar*, Farrukh Alvi*,

Isaac Choutapalli#

*Advanced Aero Propulsions Laboratory (AAPL)

Florida Center for Advanced Aero Propulsion (FCAAP)

Florida A&M University and Florida State University

# University of Texas – Pan American, Edinburg, TX

Outline

4/11/2012 1

• Impinging Jet Flowfield

• Previous Control Techniques

• Current Control Strategy

• STOVL Facility and Experimental Setup

• Results

• Conclusions

Flowfield of a Supersonic Impinging Jet

4/11/2012 2

• Resonance-Dominated Flow

• High Amplitude Unsteadiness

• Feedback Loop

• Sonic Fatigue of Aircraft

• Lift Loss

Previous Control Strategies

4/11/2012 3

• Elavarsan et al., 2001 – Placed

a baffle near the nozzle exit to

suppress feedback.

• Sheplak and Spina, 1994 –

Used annular co-flow.

• Alvi et al., 2003 – Placed

inclined microjets axisymmetric

around the nozzle exit.

Current Control Strategy

4/11/2012 4

• Most of the previous control strategies involved either a modification to the

aircraft and/or nozzle or manipulation of the shear layer near the nozzle exit

making them impractical and difficult to implement.

• The current control strategy involves disrupting the feedback loop by placing a

porous surface (essentially a screen) near the impingement point instead.

Porous Surface

STOVL Facility

4/11/2012 5

• Primarily used to study

the flowfield of a

supersonic impinging jet

with applications in

STOVL aircraft.

• Blowdown facility

• Ma=1.5 C-D Nozzle

• Inline Heater

• Nozzle-to-ground

distance (h) may be varied

between 2-40d (d=Nozzle

Throat Diameter).

Experimental Setup

4/11/2012 6

• Ground-to-Porous

Surface spacing (L) was

varied.

• Measurements were

taken with and without

microjet control.

Measurement Setup (Acoustic and

Unsteady Pressure)

4/11/2012 7

• Sideline Microphone at r/d=15

• Noise Transmission Mic at

y/d=5 below point of

impingement (shielded using

acoustic foam).

Two Kulites® flush-mounted with the lift-plate at r/d=2,3.

Measurement Setup (PIV)

4/11/2012 8

• ND-YAG Laser

• Dt = 1.25ms

• Main jet seeded using modified nebulizer

• Ambient air seeded using a Rosco® Smoke Machine

• Rosco® fog fluid used.

• Extra care to gain adequate illumination and seeding in

the space between the ground and porous surface.

Sheet-forming Optics.

Laser Sheet

Jet

• 1000 image pairs

recorded to resolve the

turbulent statistics of the

flow. ScreenGround

4/11/2012 9

Results

Experimental Results

Acoustics and Unsteady Pressure

4/11/2012 10

100

101

90

100

110

120

130

140

150

Freq (kHz)

SP

L (

dB

; re

: 20

Pa)

Baseline

Passive Control

Sideline Mic @ 15d

100

101

100

110

120

130

140

150

160

170

180

Freq (kHz)

SP

L (

dB

; re

: 20

Pa)

Baseline

Passive Control

Lift Plate Kulite @ 2d

• Strong impinging tone at ~7kHz along with the corresponding harmonics.

• Passive Control (screen) shifts the impinging tone to ~5.5kHz.

• Slight reduction in the magnitude of the tone and harmonics.

• Significant reduction in the broadband levels (~5dB) across the spectra.

~5dB

Experimental Results

Acoustics

4/11/2012 11

100

101

90

100

110

120

130

140

150

Freq (kHz)

SP

L (

dB

; re

: 20

Pa)

Baseline

Microjet Control

Sideline Mic @ 15d

100

101

90

100

110

120

130

140

150

Freq (kHz)S

PL

(dB

; re

: 20

Pa)

Baseline

Passive Control

Sideline Mic @ 15d

Comparison of Microjet Control and Passive Control using Porous Surface

• Microjet Control has been shown to reduce impinging jet noise mostly in the

attenuation or elimination of the impinging tone and corresponding harmonics.

• Passive control reduces noise mostly in consistent reductions in the broadband across

the spectra while leaving still a strong impinging tone and corresponding harmonics.

• For this case, both reduce the OASPL levels by ~4dB

4/11/2012 12

100

101

90

100

110

120

130

140

150

Freq (kHz)

SP

L (

dB

; re

: 20

Pa)

Baseline

Hybrid ControlSideline Mic @ 15d

Experimental Results (Acoustics)

• Combining both

control strategies results

in reductions in both the

impinging tone and the

broadband levels across

the spectra.

• The noise reduction as

a result of combining the

two control strategies is

more than additive in the

OASPL.

(DOASPL~11dB)

Experimental Results (Acoustics)

4/11/2012 13

• Passive control via a porous

surface in general reduces noise in

magnitudes comparable to microjet

control.

• It is sensitive to both screen-to-

ground spacing (L) and nozzle-to-

ground distance (h) when

compared to microjet control.

• Passive and microjet control

combined leads to the greatest

noise reductions for all cases

tested.

Experimental Results (PIV)

Mean Velocity Field Measurements

4/11/2012 14

• For this condition (h/d=5.0, L/d=1.5) it is seen that above the screen there is little change in the

mean velocity field.

• Below the mean velocity field we see a significant drop in the mean velocity as is to be

expected.

x/d

y/d

-2 -1 0 1 20

1

2

3

4

5 u/Uj:

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Baseline

x/d

y/d

-2 -1 0 1 20

1

2

3

4

5 u/Uj:

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Passive ControlL/d=1.5

Experimental Results (PIV)

Mean Velocity Field Measurements

4/11/2012 15

x/d

y/d

-2 -1 0 1 20

1

2

3

4

5 u/Uj:

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Passive ControlL/d=1.5

x/d

y/d

-2 -1 0 1 20

1

2

3

4

5 u/Ujet:

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Microjet Control

• When using microjet control there seems to be a stand-off shock near the impingement

point.

• Mean velocity field measurements only give so much information. A better indication of

the turbulent nature of the flow is the unsteadiness measurement, Urms

Experimental Results (PIV)

Turbulence Measurements, Urms

4/11/2012 16

• The two cases show little difference in unsteadiness near the nozzle exit.

• There is some unsteadiness near the screen (expected).

• When compared to the baseline flow, the presence of the passive control reduces

both the extent and magnitude of the Urms levels beneath the porous surface.

Experimental Results (PIV)

Turbulence Measurements, Urms

4/11/2012 17

• In the case of microjet control we see a pocket of high unsteadiness near the

impingement point where the velocity field shows the possible presence of a stand-off

shock.

• The extent of the unsteadiness (judged by the growth of the jet) is lower using

microjet control when compared to the passive control.

Experimental Results (PIV)

Turbulence Measurements, Urms

4/11/2012 18

• Both passive control and active microjet control have shown to reduce noise levels better

than their individual reductions combined. Will the turbulent statistics reflect these results.

• The Urms field shows a significant reduction in both extent and magnitude across the entire

field.

• Appears to be a very weak stand-off shock in front of the porous surface.

Conclusions

4/11/2012 19

• Passive control using a porous surface near the

impingement point generally reduces impinging jet noise.

• When compared to microjet control, it is seen that two

reduce different components of noise.

• Combined, the noise reduction is better than additive.

• PIV reflects the acoustic and unsteady pressure results

in the unsteadiness of the flow.

100

101

90

100

110

120

130

140

150

Freq (kHz)

SP

L (

dB

; re

: 20

Pa)

Baseline

Hybrid ControlSideline Mic @ 15d

Thank You

4/11/2012 20

Questions

Spectra Integration

4/11/2012 21

100

101

90

100

110

120

130

140

150

Baseline

Baseline

Microjet

Microjet

Screen

Screen

Hybrid

Hybrid