Instantaneous and time-averaged flow structures around a blunt double-cone with or without supersonic film cooling visualized via nano-tracer planar laser scattering

In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scattering （NPLS）, which has a high spatiotemporal resolution. Three experimental cases with different injection mass flux rates were carried out. Many typical flow structures were clearly shown, such as shock waves, expansion fans, shear layers, mixing layers, and turbulent boundary layers. The analysis of two NPLS images with an interval of 5 us revealed the temporal evolution characteristics of flow structures. With matched pressures, the laminar length of the mixing layer was longer than that in the case with a larger mass flux rate, but the full covered region was shorter. Structures like K-H （Kelvin-Helmholtz） vortices were clearly seen in both flows. Without injection, the flow was similar to the supersonic flow over a backward- facing step, and the structures were relatively simpler, and there was a longer laminar region. Large scale structures such as hairpin vortices were visualized. In addition, the results were compared in part with the schlieren images captured by others under similar conditions.

Large eddy simulation of boundary layer combustion of hydrogen and hydrocarbon fuel films in a modeled scramjet combustor

Supersonic fuel film cooling is a promising way to simultaneously reduce the severe wall heat and friction load of the internal passage in a scramjet engine when operating at hypersonic conditions.Large eddy simulations were performed to investigate the cooling and wall friction characteristics of hydrogen and hydrocarbon films under inert and reactive circumstances.The results show that the essential difference of the turbulent state in the mixing layer contributes to the totally different behaviors of the cooling and wall friction reduction performances of the two fuel films.The turbulent transport processes between the hydrogen film and the mainstream are much weaker as compared to the case of hydrocarbon film,making inert hydrogen rather superior in cooling and friction reduction applications.Besides,the increase of wall temperature for hydrogen film under the inert case is mainly driven by the loss of hydrogen with high heat capacity instead of by direct heat addition.However,the film cooling performance severely deteriorates when the hydrogen film burns due to presence of severe heat release sources near the wall.On the other hand,combustion of hydrocarbon film in the boundary layer can remarkably improve its originally barely-satisfactory cooling and friction reduction performance to the level comparable to that of hydrogen film,due to the suppression of turbulent transport processes in the mixing layer and presence of heat absorption sources near the wall.Overall,the hydrogen film is more advantageous in friction reduction,while the hydrocarbon film is more suitable for cooling.

Experiments on film cooling with sonic injection into a supersonic flow

Film cooling experiments with sonic injection were conducted to investigate the effects of the number of the injection holes,the mass flow ratio,and the hole spacing on the film cooling effectiveness.The mainstream was obtained by the hydrogen-oxygen combustion,entering the experimental section at a Mach number of 2.0.The nitrogen with ambient temperature was injected into the experimental section at a sonic speed.The measured mainstream recovery temperature was approximately 910K.The mass flow ratio was regulated by varying the nitrogen injection pressure.The experimental results show that for the investigated cooling surface,the cooling effectiveness increases with the increase in the number of the injection holes with other parameters held constant.For a fixed cooling configuration,the cooling effectiveness increases with the increase in the mass flow ratio.Different from the subsonic film cooling,the optimal mass flow ratio is not observed.When the hole spacing is less than 4,no obvious difference is observed on the cooling effectiveness and lateral uniformity.With the mass flow ratio increasing further,this difference becomes much smaller.The shock wave also has an effect on the cooling effectiveness.Downstream the incident point of the shock wave,the cooling effectiveness is lower than that in the case without the shock wave.