aiaa orlando porous surface
DESCRIPTION
Presentation given at the AIAA Aerospace Sciences Meeting in Orlando, 2010TRANSCRIPT
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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
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Outline
4/11/2012 1
• Impinging Jet Flowfield
• Previous Control Techniques
• Current Control Strategy
• STOVL Facility and Experimental Setup
• Results
• Conclusions
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Flowfield of a Supersonic Impinging Jet
4/11/2012 2
• Resonance-Dominated Flow
• High Amplitude Unsteadiness
• Feedback Loop
• Sonic Fatigue of Aircraft
• Lift Loss
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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.
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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
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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).
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Experimental Setup
4/11/2012 6
• Ground-to-Porous
Surface spacing (L) was
varied.
• Measurements were
taken with and without
microjet control.
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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.
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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
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4/11/2012 9
Results
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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
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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
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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)
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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.
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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
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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
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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.
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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.
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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.
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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
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Thank You
4/11/2012 20
Questions
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Spectra Integration
4/11/2012 21
100
101
90
100
110
120
130
140
150
Baseline
Baseline
Microjet
Microjet
Screen
Screen
Hybrid
Hybrid