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Computational Investigation of Two-
Dimensional Ejector Performance validation and extension of an experimental investigation
May 21, 2011
Rich Margason
Paul Bevilaqua
1

• 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
2

• 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
3

NASA Ejector Flap STOL Aircraft (QSRA)
4

XFV-12A Ejector Wing Aircraft
5

Momentum Theory Calculation of Ejector
Performance
3.0
2.5
1.0
1.2
1.4
1.6
1.8
Thrust
Augmentation 2.0
Ratio
Diffuser
Area
Ratio
1.5
1.0
0 10 20 30
Inlet Area Ratio
40 50
Parabolic Flow Assumption Gives Incorrect Results for Large Inlets
6

Predictions of Lifting Surface Theory
3.0
2.5
Thrust
Augmentation
Ratio
2.0
1.5
Lifting Surface Theory
1.0
0
Momentum Theory
10 20 30
Inlet Area Ratio
40 50
• Momentum Theory Gives Correct Results for Small Inlets
• Lifting Surface Theory Gives Correct Results for Large Inlets
• Combined, These Theories Suggest a Performance Envelope
7

• Primary jet exit area is A
0
• Ejector throat area A
2 between the flaps
(centerbody blowing case is shown below) is varied by changing the distance W
• Ejector exit area A
3 is varied by the flap angle d and flap length C
• Geometric non-dimensional parameters: C/W, A
3
/A
0
, A
3
/A
2
• Thrust augmentation ratio f is the performance parameter f 
T
0

F shroud m v
0
A
0
A
2
W A
3 d
C
8

Bonner 2-D Ejector Tests Conducted in 2010
Shroud
Flap
Nozzle
9

Length, C Width, W Area Ratio, A
3
/A
2
10

CFD Centerbody Blowing Axial Velocities
11

• 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
1,4
1,2
1,0 f
0,8
0,6
0,4
0,2
0,0
0 20 40 60
A
3
/A
0
80
C, in Source
5 exp.
11.25 exp.
17.5 exp.
5 CFD
11.25 CFD
17.5 CFD
100 120
12

Blowing Centerbody and Shroud
13

Centerbody & Shroud Blowing
CFD 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
f
1,0
0,8
0,6
1,4
Centerbody and Shroud Blowing CFD Solution
1,2 experimental data uses only centerbody blowing
0,4
0,2
0,0
0 20 40 60 80
C, in Source
5 exp.
11.25 exp.
17.5 exp.
11.25 CFD
5 CFD
17" CFD
100 120
14

Effect of Chord Length and A
2
/A
0
CFD solution on f
• Augmentation ratio f increases at low C/W values with A
2
/A
0
(or W) increases
1,6
1,5
• After f reaches a maximum value, there are scrubbing losses on the longer flaps that reduce f
1,4
•
The A
2
/A
0
= 4 case has a small W distance which appears to inhibit entrainment which reduces f
1,3 f
1,2
1,1
1,0
Centerbody & Shroud Blowing CFD Solution
0,9
0 4 8 12 chord/width, C/W
16
A
2
/A
0
45
27
19
10
4
20
15

Deflected Shroud Trailing Edge with Centerbody & Shroud Blowing
CFD Solution
16

Deflected Shroud Trailing Edge with Centerbody & Shroud Blowing
CFD Solution
• A
3
/A
2
= 1 with zero degrees of shroud trailing edge deflection 1,8
1,6
• A
3
/A
2
> 1 is achieved with increasing width at the ejector exit plane
1,4
1,2
•
Shroud trailing edge deflection initially increases f until a maximum value is achieved f 1,0
0,8
0,6
•
Further deflection reduces f
0,4
•
Maximum f increases with increasing shroud chord length
0,2
0,0
0
Centerbody & Shroud Blowing A
2
/A
0
= 15
2
Shroud Chord Length, in.
5
11.25
17.5
4
A
3
/A
2
6 8
17

• 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
18