Experimental Investigation of Waterhammer in Simplified Feed Lines of Satellite Propulsion Systems

Abstract

Operation of spacecraft propulsion systems is regularly adversely faced with waterhammer. The presence of very low pressures or vacuum complicate the classically known waterhammer due to various multiphase phenomena such as cavitation, absorption and desorption of a pressurizing gas, boiling, etc. This complex behavior is hard to model due to a lack of understanding of the physical processes taking place. To build up an experimental database on waterhammers in multiphase confined environments for validation of physical models, a literature survey was first undertaken on detailed waterhammer experiments. Only a few papers with well-documented experiments were found. None of the experiments found matched all the specifications needed for proper simulation and validation in satellite and spacecraft hardware and physical configurations. To complement the literature database, a detailed experimental investigation of the waterhammer phenomenon in a confined environment was required. This investigation was carried out using a simplified setup with two inert fluids, ethanol and acetaldehyde, and an actual propellant, monomethylhydrazine. Numerous tests were performed that confirmed excellent reproducibility of the results. The experiments showed that ethanol can be used instead of toxic monomethylhydrazine for estimating the waterhammer amplitude. The initial pipe pressure has a great influence on the waterhammer amplitude, but it would appear that the fluid vapor pressure is not a physical boundary with respect to waterhammer characteristics. The waterhammer phenomenon produced in a pipe with a low initial pressure exhibited a complex evolution over time and slight differences in amplitude and features according to the pipe geometry.