Gas expansion into low pressure volume update Barbara Kedzierska BGC regular meeting, 2nd November 2018 Outline Next time: Nozzle shape design Nozzle theory Supersonic gas jet into no-vacuum conditions Slightly underexpanded jet Highly
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Presentation Transcript
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Gas expansion into low pressure volume – update Barbara Kedzierska
BGC regular meeting, 2nd November 2018<br>
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Outline Next time:
Nozzle shape design Nozzle theory
Supersonic gas jet into no-vacuum conditions
Slightly underexpanded jet
Highly underexpanded jet
Overexpanded jet
Supersonic gas jet expansion into the vacuum<br>
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Three cases of supersonic gas jet<br>
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Basic concepts underexpanded gas jet – the gas leaves the nozzle at pressure higher than ambient (backpressure)
Slightly underexpanded
Highly underexpanded
overexpanded gas jet – the gas leaves the nozzle at pressure lower than ambient<br>
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Slightly underexpanded jet Gas leaves the nozzle
Gas expands and a rarefaction fan emanates from the orfice
Rarefaction fan – a set of infinite number of Mach waves, each of them accelerating and turning slightly the gas flow M.L. Norman, K.H.A.Winkler, Supersonic Jets, Los Alamos Science, 1985<br>
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Slightly underexpanded jet (2) Gas overexpands
At the boundary pa (backpressure) is present which pushes the jet back
Converging conical shock is formed
Incident shock – oblique shock wave before reflection M.L. Norman, K.H.A.Winkler, Supersonic Jets, Los Alamos Science, 1985<br>
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Slightly underexpanded jet (3) When the incident shock reaches the centerline, it reflects and forms diverging shock M.L. Norman, K.H.A.Winkler, Supersonic Jets, Los Alamos Science, 1985<br>
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Highly underexpanded jet Mach disk formation
Condition: highly underexpanded supersonic jet or overexpanded jet
Gas leaves the nozzle
Gas expands and a rarefaction fan emanates from the orfice
Gas overexpands
At the boundary pa is present which pushes the jet back
Converging conical shock is formed
The incident shock does not converge to a point on the axis
Shock reflects at the perimeter of the Mach disk
When gas goes through a shock, its parameters change
Sometimes when the angle is large, Mach reflections are present M.L. Norman, K.H.A.Winkler, Supersonic Jets, Los Alamos Science, 1985<br>
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Overexpanded jet Mach disk formation
Condition: highly underexpanded supersonic jet or overexpanded jet
Gas leaves the nozzle
Instead of rarefactions, shocks emanate from the nozzle orfice
Oblique shocks are reflected from the disk
Flow expansion starts with expansion fans creation
The pattern follows the same points as for highly underexpanded jet S.M.V. Rao, J. Gopalan, Acetone planar laser-induced fluorescence for supersonic flow visualization in air and nitrogen gas,
https://www.researchgate.net/publication/270762073<br>
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Supersonic jet expansion into the vacuum<br>
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No Mach disk in the flow A. Naβ, E. Steffens, Direct Simulation of Low-Pressure Supersonic Gas Expansions and its Experimental Verification, Preprint submitted to Elsevier Preprint, 28 May 2018 M. Grabe, Numerical simulation of nitrogen nozzle expansion using kinetic and continuum approaches, conference paper, September 2008, https://www.researchgate.net/publication/224999345<br>
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No Mach disk in the flow Ion thruster https://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html How is it related to space propulsion? University of Michigan, Plasma Science and Technology Laboratory
https://pstlab.engin.umich.edu/electric-propulsion-activities/<br>
