Study On Mixing Enhancement Methods And Mechanisms In Supersonic Mixing Layers

The scramjet engine has a short residence time of fuel and oxidant due to high speed.The rapid and efficient mixing of fuel and oxidant can reduce the combustor length and improve the combustion efficiency.The mixing enhancement for the supersonic mixing layer is greatly important for the scramjet engine development.The growth rate of the supersonic mixing layer is smaller than that of the subsonic mixing layer.The mixing enhancement becomes more difficult as the compressibility increases.The growth rate of the supersonic mixing layers is slower than that of their subsonic counterparts.Compressibility considerably reduces the mixing layers growth rate in supersonic flows.Researching the mixing enhancement methods and mechanisms is important.The influence of the splitter plate thickness on the supersonic mixing layer was investigated by a two-dimensional numerical simulation.The dynamic mode decomposition was used to analyze the simulation results to investigate the influence of the splitter plate thickness.Consequently,the plate thickness can influence the main modes.The thickness of the supersonic mixing layer is decided by the main modes.The plate thickness increase decreases the frequency of the main modes.If the plate thickness is in a low level,the supersonic mixing layer is influenced by the frequency of vortex shedding of the splitter plate.If the plate thickness is in a high level,the supersonic mixing layer is influenced by the frequency of recirculation zone.The influence of the sawtooth splitter plate on the supersonic mixing layers was also studied herein through an experiment.The structures’ width of the supersonic mixing layers in the X-Z are influenced by the sawtooth width.The influence of the co-streamwise vortices on the mixing enhancement was studied by numerical simulation and experiment.The location of the two vortex generators and the distance between the two vortex generators can influence the mixing enhancement.The mixing enhancement of the separating arrangement is good compared to the overlapping arrangement.Furthermore,the loss of the total pressure of the separating arrangement is large compared to the overlapping arrangement.Increasing the distance of the two vortex generators can improve the mixing rate.The loss of the total pressure is also increased.The mixing enhancement characteristics achieved using a pulsed plasma synthetic jet(PSJ)were investigated via experiments.The results show that the PSJ is an effective method for the mixing enhancement.Nanoparticle-based planar laser scattering(NPLS)was used to obtain the flow structures.A system was made to control the PSJ electronic system and the NPLS system.The characteristics of the supersonic mixing layer for different delays and different locations were investigated.The actuators’ mixing enhancement effects and performances at three locations were investigated by numerical simulation.The three actuators are located on the upper,bottom,and end surfaces of the splitter plate.The influence of the actuator shape was then investigated.A new dynamic actuator was proposed,which is applicable to supersonic mixing layers.The effect of double actuators was also studied.The numerical simulation results show that the mixing layer thickness is increased by the plasma synthetic jet perturbation.Two mechanisms of perturbations are considered,the actuators are located at different positions.The actuators installed on the upper and lower surfaces of the splitter plate influence the mixing layer by perturbing the upper and lower streams,respectively.The actuator installed at the end of the splitter plate directly affects the mixing layer.The incline hole velocity is larger than the square hole.The separate shock wave before the incline hole weakens.The new dynamic actuator proves that the cavity gas can be renewed.The numerical results of the double actuators suggest that the velocity of the second actuators is larger than that of the first actuators.