1

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

2

• 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

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

Figure 1 Thrust Augmenting Ejector

Suction forces primary jet thrust

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

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

7

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

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

C

W

A0

A30

0

vm

FT shroud

A2

d

9

Bonner 2-D Ejector Tests Conducted in 2010

ShroudFlap

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 & 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

13

Blowing Centerbody and Shroud

14

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

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

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

16

Deflected Shroud Trailing Edge with Centerbody & Shroud BlowingCFD Solution

17

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.

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 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