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 Science PicturesFlows in a Launcher Nozzle
To face substantial increase of the satellite mass, one way to obtain thrust increase is to use high area ratio nozzles. The performance of the propulsion engine of the first stage engine (see the circle showing the Vulcain engine) is high in vacuum owing to its design (see upper-part of the figure). However, at the very beginning of the flight, the wall pressure at the end of the extension required for full-flowing regime can be much lower than the ambient pressure. This leads to a flow separation in the nozzle (see lower-part of the figure). Flow separation is a highly three-dimensional and unsteady process which can result in lateral forces (side-loads) and might damage the nozzle. The knowledge of the origin of these loads as well as the capability to predict them play a key-role in the design of future aerospace engines. Hence, computational methods are becoming of growing interest in propulsion nozzle design. The figure above is issued from a Detached Eddy Simulation of the separated flow in a launcher nozzle in overexpansion regime. This figure illustrates the flow-field resulting from the boundary-layer interaction shock in the extension. Notice the complexity of this flowfield, occurring in a simple axisymmetrical nozzle.
By Sébastien Deck (DAAP/MHL) |
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Last Update: January 14, 2004 - © ONERA 2009 - Terms of use |
