numerical study of an under-expanded jet
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Numerical Study of an Under-Expanded Jet
Brian Gribben
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Motivation
Experimental study of under-expanded jet plume (Welsh, Dera/Qinetiq Farnborough) :
• Repeated shock cell pattern
• Hysteresis in shock-reflection type
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2D Shock Relection Hysteresis
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2D Shock Relection Hysteresis
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Shock diamonds in plume
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Structure of Under-expanded Jet
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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
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Numerical Method 1
• PMB (Glasgow University)
• Block structured, finite volume
• Osher’s scheme, MUSCL extrapolation
• Implicit scheme
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Numerical Method 2
Boundary Conditions:A. Adiabatic wall
B. Symmetry
C. Extrapolation (except when M<1, impose p)
D. Impose pressure and density, extrapolate velocity
E. As D
Pseudo-steady approach
• Step change in reservoir pressure of 0.1 torr
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Results 1 : Plume Structure
Pr/Pb = 285.7, 15mm nozzle
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Results 2 : Hysteresis Loop
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Results 3 : RR Centre-line temperature
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Results 4 : MR Centre-line temperature
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Results 5 : Apparent RR
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Results 6 : Mach Disc
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Results 7 : Compression behind Mach Disc
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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