Experimental Investigation of Shear Driven Liquid Films for Film Cooling Applications in Liquid Rocket Engines.

摘要

Liquid film cooling is an important method for cooling the walls of a liquid rocket engine. Mass transfer via entrainment decreases the effectiveness of the film coolant and it is therefore important to estimate the amount of film coolant that establishes itself along the wall of a combustion chamber if the coolant flow rate is to be optimized. However, film entrainment research is limited in regards to film cooling applications in rockets. The correlations and theories that have been published are often limited in scope and have only been tested at momentum fluxes that are an order of magnitude less than those typically experienced in rockets. Experimental research has been conducted in a cold-flow test article at AFRL in order to investigate the effects of the gas stream momentum flux on the coolant flow rate that remains attached to the wall. Specifically, the objective of this study was to investigate the establishment of a shear driven liquid film introduced into a rectangular test section by a .38 mm X 25.4 mm slot, perpendicular to the stream-wise direction of the gas phase. A secondary objective of this thesis was to investigate the ability of several diagnostics to measure the interfacial shear stress, mean film thickness, and the film mass flow rate of a liquid water film shear-driven by nitrogen gas in cold flow conditions. Ultimately, a film removal slot was chosen to measure the film mass flow rate, differential pressure taps were chosen to indirectly deduce the interfacial shear stress by measuring a stream-wise pressure drop, and a laser focus displacement meter was chosen to measure the liquid film thickness. Lastly, a high-speed video camera was used to obtain qualitative visual data of the surface of the shear driven liquid film.