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A model problem for a supersonic gas jet from a moon

Hornung, H. G. (2016) A model problem for a supersonic gas jet from a moon. Journal of Fluid Mechanics, 795 . pp. 950-971. ISSN 0022-1120.

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Some celestial bodies such as planets, moons and comets (here referred to as moons for simplicity) emit jets of material at speeds that in some instances are large enough to escape gravity. Previous investigations have shown this problem to be highly complex, e.g. involving multi-phase flows, phase changes, radiation and gas rarefaction effects. In order to learn from exploring a manageable parameter space, and to provide a limiting case, the present study considers a much simpler model situation in which the material of the jet is an inviscid, non-heat-conducting, perfect gas that issues radially at the surface of the moon with sonic velocity. Theoretical considerations show that the escape velocity of a gas is much smaller than that of a solid body. An analytical solution is obtained for the maximum height reached by a jet in steady flow. A computational parameter study of unsteady, inviscid, axisymmetric flow, including the effect of an atmosphere, provides a rich picture of the features and behaviour of the model jet. The deficit of the computed maximum steady-state penetration height below the isentropic theoretical value may be explained by the effect of the atmosphere and of dissipation in shock waves that occur in the computed flows. Many of the features of the gas jet are qualitatively mirrored in an experiment using a water flow analogy in which the gravitational field is simulated by a surface of suitable shape.

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Hornung, H. G.0000-0002-4903-8419
Additional Information:© 2016 Cambridge University Press. Received 9 January 2016; accepted 3 March 2016; first published online 22 April 2016. My interest in this problem was sparked by discussions with D. Goldstein during his visit to Caltech in the fall of 2014. B. Valiferdowsi designed and built the experimental apparatus and also helped me with the performance of the experiments. I thank them both.
Subject Keywords:compressible flows, gas dynamics, jets
Record Number:CaltechAUTHORS:20160601-070542940
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Official Citation: H. G. Hornung (2016). A model problem for a supersonic gas jet from a moon. Journal of Fluid Mechanics, 795, pp 950-971 doi:10.1017/jfm.2016.184
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67510
Deposited By: Ruth Sustaita
Deposited On:01 Jun 2016 21:00
Last Modified:22 Nov 2019 09:58

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