Flow Separation and Side-Loads in Rocket Nozzles

During the transient start-up of a rocket engine operating against an ambient pressure, the exhaust flow separates from the nozzle wall at a certain pressure ratio of wall pressure to ambient pressure. Furthermore, if the chamber pressure at nominal operation condition is not high enough to reach full flowing in overexpanded flow condition, flow separation will occur even for steady state operation Flow separation is a strongly three-dimensional instationary process, and lateral forces may be generated, the so called side-loads. The physical origins of flow separation and side-loads and its theoretical prediction have been the key objectives for several experimental and theoretical studies in the past decades. This paper addresses the physical background of flow separation and side-loads, and gives an overview on the state-of-the-art prediction for both phenomena