Comparison of pressure surge events in water and liquid nitrogen as a substitute fluid for rocket engine feed lines

Abstract

Testing transient phenomena in space propulsion systems is very complex due to propellants being reactive and often cryogenic. The use of non-reactive replacement fluids lowers the risk and therefore the effort of testing. A common replacement fluid is water, which is easy to handle and widely accessible. This paper aims for the comparison between water and liquid nitrogen (LN2) as a cryogenic replacement fluid. Several fluid hammer tests with both fluids were performed at the Fluid Transient Test Facility (FTTF) at DLR Lampoldshausen. Seven test cases with LN2 are presented in detail. At high pressure levels, there is good agreement with the predicted Joukowsky pressure rise and fluid hammer eigenfrequencies. Furthermore, a systematically interruption of the first pressure rise was observed. By comparing LN2 and water experiments, it was found that higher eigenmodes of the fluid hammer occurred after cavitation only in water experiments.