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Transcript of 1 Computational Investigation of Two- Dimensional Ejector Performance validation and extension of an...
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Computational Investigation of Two-Dimensional Ejector Performance
validation and extension of an experimental investigation
Rich Margason
Paul Bevilaqua
May 21, 2011
Create and Deliver Superior Products Through Innovative Minds
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• Validate 2010 experimental investigation* of a 2-D ejector using computational fluid dynamic solutions of the Navier-Stokes 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 Thrust-Augmenting Ejector, M.S. Thesis, California State Polytechnic University, Pomona, 2010
Objective
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Thrust Augmenting Ejector• An ejector is a jet pump that uses
entrainment by an engine exhaust to increase mass flow
• 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
Suction forces primary jet thrust
Color scale is proportional to velocity
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XFV-12A Ejector Wing Aircraft
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Momentum Theory Calculation of Ejector Performance
Parabolic Flow Assumption Gives Incorrect Results for Large Inlets
1.0
1.5
2.0
2.5
3.0
0 10 20 30 40 50
Inlet Area Ratio
Thrust Augmentation
Ratio
1.0
1.2
1.4
1.6
1.8
Diffuser Area Ratio
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Predictions of Lifting Surface Theory
• Momentum Theory Gives Correct Results for Small Inlets• Lifting Surface Theory Gives Correct Results for Large Inlets• Combined, These Theories Suggest a Performance Envelope
1.0
1.5
2.0
2.5
3.0
0 10 20 30 40 50
Inlet Area Ratio
Thrust Augmentation
Ratio
Momentum Theory
Lifting Surface Theory
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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
C
W
A0
A30
0
vm
FT shroud
A2
d
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Bonner 2-D Ejector Tests Conducted in 2010
ShroudFlap
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 :
– 5 & 11.25 shroud inch exp/CFD cases agree
– 2D CFD 17.5 inch shroud case was much greater than experiment which may have had flow separation
0 20 40 60 80 100 1200.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
5 exp.
11.25 exp.
17.5 exp.
5 CFD
11.25 CFD
17.5 CFD
A3/A0
f C, in Source
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Blowing Centerbody and Shroud
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Centerbody & Shroud BlowingCFD solution
• Centerbody & shroud blowing CFD results are compared with experimental data with centerbody blowing only cases
• 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
0 20 40 60 80 100 1200.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4 Centerbody and Shroud Blowing CFD Solution
5 exp.
11.25 exp.
17.5 exp.
11.25 CFD
5 CFD
17" CFD
fC, in Source
experimental data uses only centerbody blowing
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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
• 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
0 4 8 12 16 200.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6Centerbody & Shroud Blowing CFD Solution
45 27 19
chord/width, C/W
f
A2/A0
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Deflected Shroud Trailing Edge with Centerbody & Shroud BlowingCFD Solution
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Deflected Shroud Trailing Edge with Centerbody & Shroud BlowingCFD Solution
• A3/A2 = 1 with zero degrees of shroud trailing edge deflection
• 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
• Further deflection reduces f
• Maximum f increases with increasing shroud chord length 0 2 4 6 8
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8Centerbody & Shroud Blowing A2/A0 = 15
5 11.25
A3/A2
f
Shroud Chord Length, in.
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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