Transcript Centerbody & Shroud Blowing CFD solution Centerbody

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Computational Investigation of TwoDimensional Ejector Performance
validation and extension of an experimental investigation
May 21, 2011
Rich Margason
Paul Bevilaqua
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Objective
• Validate 2010 experimental investigation* of a 2-D ejector
using computational fluid dynamic solutions of the NavierStokes equations
• Extend range of selected variables to demonstrate their
effect on ejector performance; variables included primary jet
blowing configuration, shroud chord length, deflection of the
shroud trailing edge
* Bonner, Amie A; A Parametric Variation on a Two-Dimensional ThrustAugmenting Ejector, M.S. Thesis, California State Polytechnic University,
Pomona, 2010
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Thrust Augmenting Ejector
• An ejector is a jet pump that uses
entrainment by an engine exhaust
to increase mass flow
Suction forces
primary jet thrust
• An ejector consists of a primary jet
and a duct formed by two shroud
flaps
• The jet thrust is increased by the
suction force that the entrained
flow induces on the duct inlet
• The suction force is determined by
flap length C and separation
distance W as well as flap
deflection angle d
Figure 1 Thrust Augmenting Ejector
Color scale is proportional to velocity
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NASA Ejector Flap STOL Aircraft (QSRA)
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XFV-12A Ejector Wing Aircraft
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Momentum Theory Calculation of Ejector
Performance
3.0
1.0
Diffuser
Area
Ratio
1.2
2.5
1.4
1.6
1.8
Thrust
Augmentation 2.0
Ratio
1.5
1.0
0
10
20
30
40
50
Inlet Area Ratio
Parabolic Flow Assumption Gives Incorrect Results for Large Inlets
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Predictions of Lifting Surface Theory
3.0
2.5
Lifting Surface Theory
Thrust
Augmentation 2.0
Ratio
1.5
Momentum Theory
1.0
0
10
20
30
40
50
Inlet Area Ratio
• Momentum Theory Gives Correct Results for Small Inlets
• Lifting Surface Theory Gives Correct Results for Large Inlets
• Combined, These Theories Suggest a Performance Envelope
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Ejector Parameters
• Primary jet exit area is A0 (centerbody blowing case is shown below)
• Ejector throat area A2 is varied by changing the distance W
between the flaps
• Ejector exit area A3 is varied by the flap angle d and flap length C
• Geometric non-dimensional parameters: C/W, A3/A0 , A3/A2
• Thrust augmentation ratio f is the performance parameter
d
T0  Fshroud
f
 v0
m
A2
W
A3
A0
C
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Bonner 2-D Ejector Tests Conducted in 2010
Shroud
Flap
Nozzle
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Ejector Test Variables
Length, C
Width, W
Area Ratio, A3/A2
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CFD Centerbody Blowing Axial Velocities
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Centerbody Blowing Case
• Recent experiment/CFD data
for three shroud chord
lengths C showed the
following augmentation ratio
f correlation :
1.4
1.2
1.0
– 5 & 11.25 shroud inch
exp/CFD cases agree
0.8
C, in Source
f
5
0.6
– 2D CFD 17.5 inch shroud
case was much greater
than experiment which
may have had flow
separation
exp.
11.25 exp.
0.4
17.5
exp.
5
CFD
11.25 CFD
0.2
17.5
CFD
0.0
0
20
40
60
A3/A0
80
100
120
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Blowing Centerbody and Shroud
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Centerbody & Shroud Blowing
CFD solution
• Centerbody & shroud
blowing CFD results are
compared with
experimental data with
centerbody blowing only
cases
Centerbody and Shroud Blowing CFD Solution
1.4
1.2
1.0
f
• Total primary thrust was
equal for all of these cases
• Dividing the primary thrust
between the centerbody
and shroud increased f by
about 0.2
C, in Source
0.8
5
experimental data uses
only centerbody blowing
0.6
exp.
11.25 exp.
17.5
exp.
0.4
11.25 CFD
0.2
5
CFD
17"
CFD
0.0
0
20
40
60
80
100
120
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Effect of Chord Length and A2/A0 on f
CFD solution
• Augmentation ratio f
increases at low C/W values
with A2/A0 (or W) increases
Centerbody & Shroud Blowing CFD Solution
1.6
A2/A0
45
27
19
10
4
1.5
• After f reaches a maximum
value, there are scrubbing
losses on the longer flaps
that reduce f
• The A2/A0 = 4 case has a
small W distance which
appears to inhibit
entrainment which reduces f
1.4
1.3
f
1.2
1.1
1.0
0.9
0
4
8
12
chord/width, C/W
16
20
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Deflected Shroud Trailing Edge with Centerbody & Shroud Blowing
CFD Solution
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Deflected Shroud Trailing Edge with Centerbody & Shroud Blowing
CFD Solution
• A3/A2 = 1 with zero degrees of
shroud trailing edge deflection
Centerbody & Shroud Blowing
1.6
• A3/A2 > 1 is achieved with
increasing width at the ejector
exit plane
• Shroud trailing edge deflection
initially increases f until a
maximum value is achieved
A2/A0 = 15
1.8
1.4
1.2
f
1.0
0.8
0.6
• Further deflection reduces f
• Maximum f increases with
increasing shroud chord
length
Shroud Chord Length, in.
0.4
5
11.25
0.2
17.5
0.0
0
2
4
6
8
A3/A2
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Conclusions
• Recent experiment/CFD data comparisons for an ejector with centerbody blowing
and three shroud chord lengths C showed
– agreement for shroud chord lengths of 5 and 11.25 inches
– disagreement for a shroud chord length of 17.5 inches; further tests are
needed to determine if there is flow separation in the experiment
• CFD calculations for the centerbody blowing cases were done for a family of
chord lengths and showed how augmentation ratio f increases as ejector width
increases
• CFD calculations were done with the primary jet blowing split between the
centerbody and the shroud
– Results showed that f increased about 0.2 compared with blowing only from
the centerbody
– Further results with deflected shroud trailing edges showed f increases of 0.2
to 0.4 depending on the shroud chord length
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