Investigation Of Supersonic Film Cooling Injected Through Slot Nozzles

Supersonic film cooling ejected through a slot has many applications,such as the cooling of the exterior and interior of supersonic and hypersonic vehicles,the nozzle extension of rocket engines.In this thesis,the supersonic film cooling injected through a backward facing slot,and inclined slot respectively were analyzed by the experiments and numerical simulation,and the typical flowfield structures and mechanism of heat transfer were investigated.The flowfield of supersonic film cooling with the unheated film coolant ejected through a backward facing slot was first studied.The typical flowfield structures of supersonic film cooling with the Laval nozzles of film coolant set in a backward facing step operated under the overexpanded,designed and underexpanded condition were investigated,respectively.The effect of the feeding pressures of the film coolant on the flowfield structures were also analyzed,which seemed to be closely related to the flowfield structures.Because the cooling effectiveness of supersonic film cooling couldn’t be got from the experiments that the film coolant and the mainstream are all in the ambient conditions,so the film coolant was heated in the subsequent tests.Test results showed that the film coolant under the unheated or heated conditions didn’t affect the flowfield structures of film cooling.The feeding pressures of film coolant seemed to be not only related to the flowfield structures of supersonic film cooling,the cooling effectiveness was better in a higher feeding pressure.The main parameters affecting the supersonic film cooling were analyzed respectively,such as the feeding Mach numbers of film coolant,the outlet of the slot nozzles,the step height of the slot and the state of the boundary layer of the mainstream.The feeding Mach numbers of the film coolant showed the same affect with the feeding pressure,while a slot nozzle with a much larger outlet was preferable when the feeding pressure kept the same.The lip thickness of the slot,and the boundary layer thicknesses at the streamwise position of the step seemed to be not sensitive to the cooling effectiveness of supersonic film cooling ejected through a backward facing slot.The shock wave was inevitable to the supersonic mainstream,so the effect of the shock wave on the supersonic film cooling ejected through the backward facing slot was analyzed.The effect of the incident positions at the different streamwise positions and the strength of the shock waves on the supersonic film cooling were investigated,respectively.The shock wave exerted a damage to the supersonic film cooling,and the effect is the most serious when the incident position was before the step.With a stronger shock wave,the cooling effectiveness was worse for the supersonic film cooling.When the Laval nozzle of film coolant was rotated to a certain angle,the step slot was changed to the inclined slot,and the typical flowfield structures and the heat transfer characteristics of the film coolant ejected through which were also analyzed in this thesis.The flowfield changes and cooling effectiveness of supersonic film cooling ejected though the inclined slot were also compared with the cases with the step height,and the former showed a worse cooling effectiveness.The main structure parameters affecting the supersonic film cooling ejected through an inclined slot were also studied,including the feeding pressures of the film coolant,the feeding Mach numbers of the film coolant,the tilt angles of the inclined slot.It turns out that a larger feeding pressure and Mach number of film coolant,a lower tilt angles of inclined slot showed a better cooling effectiveness of supersonic film cooling.The effect of the shock wave on the supersonic film cooling ejected through the inclined slot were also analyzed.