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Numerical Analysis of Under-Expanded Jet Plume and Shock Reflection Characteristics

This study investigates the characteristics of an under-expanded jet plume through experimental and numerical methods. The focus is on the repeated shock cell patterns and hysteresis phenomena observed during the jet's behavior. Utilizing advanced numerical techniques, including finite volume methods and pseudo-steady approaches, the study explores varied reservoir pressures, resulting shock cell structures, and temperature distributions within the plume. Findings highlight the significance of Computational Fluid Dynamics (CFD) in understanding jet behavior. Results indicate excellent agreement with experimental data, enhancing comprehension of jet plume dynamics.

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Numerical Analysis of Under-Expanded Jet Plume and Shock Reflection Characteristics

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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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