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
