1. Computational Investigation of Two-Dimensional Ejector Performance
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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

2. Objective
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

3. 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
Suction forces primary jet thrust
Figure 1 Thrust Augmenting Ejector
Color scale is proportional to velocity

4. NASA Ejector Flap STOL Aircraft (QSRA)

5. XFV-12A Ejector Wing Aircraft

6. Momentum Theory Calculation of Ejector Performance
Diffuser Area Ratio
Parabolic Flow Assumption Gives Incorrect Results for Large Inlets

7. Predictions of Lifting Surface Theory
Momentum 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

8. 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 A2 W A3 A0 C

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

10. Ejector Test Variables
Length, C Width, W Area Ratio, A3/A2

11. CFD Centerbody Blowing Axial Velocities

12. Centerbody Blowing Case
Recent experiment/CFD data for three shroud chord lengths C showed the following augmentation ratio f correlation :
5 & shroud inch exp/CFD cases agree
2D CFD 17.5 inch shroud case was much greater than experiment which may have had flow separation

13. Blowing Centerbody and Shroud

14. 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

15. 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

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

17. Deflected Shroud Trailing Edge with Centerbody & Shroud Blowing CFD 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

18. 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 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