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Presented at the AIAA Aerospace Science Meeting, 2010, Orlando
Citation preview
Density Field Measurements of a Supersonic
Impinging Jet with Microjet Control
L. Venkatakrishnan#, Alex Wiley*, Rajan Kumar*,
Farrukh Alvi*
*Advanced Aero Propulsions Laboratory (AAPL)
Florida Center for Advanced Aero Propulsion (FCAAP)
Florida A&M University and Florida State University
# National Aerospace Laboratories (NAL)
Bangalore, India
Presentation Outline
• Impinging Jet Flowfield
• Current Study
• STOVL Facility
• BOS Technique
• Experimental Results
• Conclusions
• Future Work
4/11/2012 1
Impinging Jet Flowfield
4/11/2012 2
• Resonance-Dominated Flow
• High Amplitude Unsteadiness
• Feedback Loop
• Sonic Fatigue of Aircraft
• Lift Loss
Impinging Jet Flowfield
4/11/2012 3
Shadowgraph of a supersonic impinging jet.
Nozzle Exit with Thin Shear
Layer
Reflected Acoustic Wave
Strong Acoustic Wave
Large-Scale Vortical Structure
Wall Jet
Impinging Jet Flowfield
4/11/2012 4
100
101
90
100
110
120
130
140
150
Freq (kHz)
SP
L (
dB
; re
: 20
Pa)
Representative Unsteady Spectra
Nearfield Mic• High Broadband Levels
• Strong Impinging Tone
and Harmonics
• Characteristic of an
Impinging Jet
Microjet Control
4/11/2012 5
NO
CONTROL
Microjet
Streaks
MICROJET
CONTROL
Shadowgraph of Impinging Jet with and
without Microjet Control
16 Microjets
Angled 60°
Objectives of the Current Study
4/11/2012 6
1. Unanswered questions remain.
1. Why do microjets work?
2. Their effects on the mean density field of an impinging jet.
3. Free jet effects?
Can we answer some of these questions by
learning more about the density field?
Density field to be measured using
Background Oriented Schlieren
STOVL Facility
4/11/2012 7
• 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).
BOS (Experimental Setup)
4/11/2012 8
Light
Source
Randomly Oriented Illuminated
Dot-Pattern Background
Optical Disturbance, i.e.
the Flow
Camera
• Experimental Setup for BOS requires
minimal hardware.
• Quantitative
• Low Cost
• Simple to Setup
BOS (Experimental Setup)
4/11/2012 9
Lift Plate and Nozzle
Dot Pattern Background
LED Cluster Light
Source (IDT)
Camera
BOS – Raw Images
4/11/2012 10
Raw Image – NO FLOW Raw Image – WITH FLOW
Cold, Mildly Underexpanded (NPR=3.8 for a M=1.5 Nozzle)
Free Jet
BOS Requires two images. One reference image recorded
without the flow and one measurement image recorded with
the flow.
BOS - Processing
4/11/2012 11x/d
y/d
-2 -1 0 1 2-4
-3
-2
-1
BOS - Processing
4/11/2012 12
Interpreting BOS Data
U
V
)(1
Gn
Dale-Gladstone Relation
x y
ZZ
ZZi
x
x
n
ni
1
Venkatakrishnan & Meier, 2004
BOS – Finding Density
4/11/2012 13
x y
),(2
2
2
2
yxSyx
• Integrate in either the x or y-
directions
• Leads to noise in the
direction of integration
• Transform to the Poisson
Equation and Solve for r, the Line-
of-Sight Integrated Projected
Density Field
),(2 yxS
orProjected Density Field
Back-Projection Tomography
4/11/2012 14
Central Plane of the Mildly
Underexpanded Cold Jet
Procedure for BOS
1. Calculate the density gradient field
using PIV style cross-correlations
between a no flow image and an image
with the flow.
2. Find the projected density field by
solution of the Poisson Equation.
3. Use Filtered Back-Projection
tomography to reconstruct the 3D
density field of the flow based on the
assumption of symmetry about the
axis.
See Venkatakrishnan and Meier, EIF 2004 for more details
x/d
y/d
-2 -1 0 1 2-4
-3
-2
-1
Free jet Results
Effects of Microjet Injection
4/11/2012 15
Significant Reductions in the magnitude of the shock cells when microjet control is applied.
No ControlMicrojet
Control
Impinging Jet Results – Baseline Flow
4/11/2012 16
Simulated Bidirectional Schlieren
• Generated using the raw density
gradient data.
• The effects of unsteadiness are
manifested as a blurring of the shear layer
near the impingement region for time-
averaged data set (250 image pairs).
x/D-2 -1 0 1 2
h/D
0
1
2
3
4
amb:0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Central Slice Density Field
•Large extent of high density in the impingement region.
X
Y
-400 -200 0 200 400
-600
-400
-200
0
Density Gradient Field
h/D=4.0
Impinging Jet Results – Microjet Control
4/11/2012 17
x/D
h/D
-2 -1 0 1 2-4
-3
-2
-1
0
Simulated Bidirectional Schlieren
with Microjet ControlDensity Gradient Field with
Microjet Control
Impinging Jet Results – Microjet Control
4/11/2012 18
x/D
h/D
-1 -0.5 0 0.5 1-2
-1.5
-1
-0.5
0
x/Dh
/D
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-2
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
• Microjet Injection significantly alters the density field at the nozzle exit.
• The mild shock structure is disrupted beyond recognition when microjet control is
applied.
Density Gradient Field Near the Nozzle Exit with and without Microjet Control
No Control With Control
x/D-2 -1 0 1 2
h/D
0
1
2
3
4
amb:0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
x/D-2 -1 0 1 2
h/D
0
1
2
3
4
amb:0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Baseline
Impinging Jet Results – Microjet Control
4/11/2012 19
• The extent and magnitude of high density in the impingement region is greatly reduced.
• There is a low density region behind the stand-off shock when microjet control is
applied.
Central Slice Density Near the Nozzle Exit with and without Microjet Control
Microjet
Control
MICROJET
CONTROL
Conclusions
Impinging Jet
4/11/2012 20
Magnitude of the density field is
much lower in the presence of
microjet control for the impinging jet.
x/D-2 -1 0 1 2
h/D
0
1
2
3
4
amb:0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
x/D-2 -1 0 1 2
h/D
0
1
2
3
4
amb:0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Reflected in the Unsteady Pressure
Measurements
Conclusions
4/11/2012 21
Significant changes in the free jet as
well.
The differences are NOT seen in the
acoustics.
Future Work
4/11/2012 22
• Reconstruction of the instantaneous
density field, requires multiple
simultaneous views.
• Examining the density field variation
for other impinging jet conditions: TR,
h/D, NPR, etc…
• Simultaneous density and velocity
field measurements using BOS.
Thank You
4/11/2012 23
Questions
Line-Integrations
4/11/2012 24
X-Direction Integration Y-Direction Integration