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Numerical Study of an Under-Expanded Jet

Numerical Study of an Under-Expanded Jet. Brian Gribben. Motivation. Experimental study of under-expanded jet plume (Welsh, Dera/Qinetiq Farnborough) : Repeated shock cell pattern Hysteresis in shock-reflection type. 2D Shock Relection Hysteresis. 2D Shock Relection Hysteresis.

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Numerical Study of an Under-Expanded Jet

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  1. Numerical Study of an Under-Expanded Jet Brian Gribben

  2. Motivation Experimental study of under-expanded jet plume (Welsh, Dera/Qinetiq Farnborough) : • Repeated shock cell pattern • Hysteresis in shock-reflection type

  3. 2D Shock Relection Hysteresis

  4. 2D Shock Relection Hysteresis

  5. Shock diamonds in plume

  6. Structure of Under-expanded Jet

  7. SRH in Under-expanded Jet • LDT DERA/Qinetiq Farnborough • Ambient pressure 35 mtorr • Reservoir pressure varied from 2 to 70 torr • Nozzle throat diameter 15mm • First shock cell length ~ 300mm • Exit Mach number between 2.4 and 2.8

  8. Numerical Method 1 • PMB (Glasgow University) • Block structured, finite volume • Osher’s scheme, MUSCL extrapolation • Implicit scheme

  9. Boundary Conditions: Adiabatic wall Symmetry Extrapolation (except when M<1, impose p) Impose pressure and density, extrapolate velocity As D Numerical Method 2 • Pseudo-steady approach • Step change in reservoir pressure of 0.1 torr

  10. Results 1 : Plume Structure Pr/Pb = 285.7, 15mm nozzle

  11. Results 2 : Hysteresis Loop

  12. Results 3 : RR Centre-line temperature

  13. Results 4 : MR Centre-line temperature

  14. Results 5 : Apparent RR

  15. Results 6 : Mach Disc

  16. Results 7 : Compression behind Mach Disc

  17. Conclusion • SRH in an underexpanded jey plume predicted using CFD • Confidence in results from good agreement • Detail of numerical results promoted understanding of plume structure

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