# Deutsches Zentrum f. Luft- und Raumfahrt e.V. (DLR)

## A model problem for supersonic gas jets from a moon

REFERENT: Prof Hans Hornung, California Institute of Technology

(Eingeladen von Prof. Klaus Hannemann, AS-RFZ)

TITEL: A model problem for supersonic gas jets from a moon

ZEIT: 21.06.2016

16.00 Uhr Vortragsbeginn

ORT: DLR Göttingen, Adolf-Busemann-Raum (Hörsaal Haus 7, EG)

When a gas jet issues from a celestial body, such as is the case on Saturn's moon Enceladus, the problem may be reduced to its simplest form by considering the gas to be ideal and the flow to be inviscid.

In that case the steady-flow energy equation may be integrated. It turns out that the escape velocity of a gas is much smaller than that of a solid body, because the thermal energy of the gas gets converted to ordered kinetic energy in the expansion.

A closed-form solution can be obtained for the altitude above the moon's surface to which a jet will penetrate when the surface speed is smaller than the escape velocity. This altitude is typically an order of magnitude greater than that reached by a solid body with the same surface speed.

Extensive computations show that the ideal isentropic penetration altitude (of a gas) is not quite reached in the real case, because of the presence of shock waves and the impediment of the atmosphere.

An experimental method of modelling this flow mirrors the qualitative features of the gasdynamic jet.