Simulation And Experiment Of Two-Phase Mixing And Combustion In The Scramjet Combustor

As hypersonic aircrafts developed rapidly, the present research studied the mechanisms and applications of the fuel mixing enhancement and the flame stabilizing to scramjet combustor, using numerical simulation and experimental observations.The models for the two-phase supersonic flow and combustion were established and predigested. The parallel calculation program for Large Eddy Simulation (LES) of two-phase flow was developed by the MPI transfer function database. The method of grid partition, the course of grid sub-zone interface communication, and the data transfer between Euler and Lagrange coordinate system in the process of parallel calculating were studied.To reveal the mechanisms of the mixing enhancement in supersonic flow, the work studied the basal free shear mixing layer at first. The two-phase supersonic mixing layer was simulated with LES and disparting-phase model. The characteristics of eddies structure in the mixing layer was analyzed. The movement characters of non-evaporation droplets at different Stocks numbers were obtained. The development of micro- disturbances which were enforced to mixing layer inlet indicated that the course of droplets evaporation would increase the thickness of mixing layer and accelerate the development of mixing layer, which obviously enhanced the process of mixing. Then the phase space for the time series of mixing layer pressure was reconstructed, and the results manifested that the different developing stages of mixing layer had close relationship with its nonlinear eigenvalue.Based on the analysis of the above mixing layer and aiming at the developing trend of the cavity shear layer, this treatise studied the mechanisms of cavity mixing enhancement and the flame stabilizing in supersonic flow, by experiments and simulations. The nonlinear theory of fractal was used to analyze the relationship among flame fractal dimension, combustion degree and flame stabilization, and the results were consistent with the flow fractal dimensions of numerical simulations. Then the shear layer evolvement, the shock effects and the self-sustained oscillations of cavities were studied in single phase and two-phase supersonic flows. The results revealed that the disturbances of the heat wave could accelerate the mixing enhancement of cavities shearing layers; the resonating shocks could break up the shearing layer and conduce to mixing enhancement; the self-sustained oscillations of the specified cavities could be explained coincide with the acoustic-vortex resonance model both in single phase and two-phase flow.To increase the low expandable ratio of the supersonic shear layer, the physical ramp injectors were designed by combining functions of mixing enhancement and fuel injection, via the scheme of streamwise vorticity mixing enhancement. Experiments and numerical simulations were conducted to study four types of physical ramps. The results indicated that the swept structures could facilitate the formation of streamwise vorticities and accelerate the lift of fuel jet flow, which would not only promote the mixing but also stabilize the flame. On the other hand, streamwise vorticities developed modes of expansion ramp was different from that of compression ramp, this is due to the similar structures between the cavity and expansion ramp, which were favorable for mixing obviously.To overcome the shortcoming of the physical ramps intrusion into the flow, this thesis studied the interaction of the supersonic fuel injection by numerical simulation, and designed the aerodynamic ramp injectors. The results of experiments indicated that the designed injector arrays could accelerate the roll up procedure of streamwise vortices downstream of the injection, which benefit for mixing. Because of the small angle between the injection and the main stream, the total pressure loss of the aerodynamic ramps was less than that of the physical ramps and transverse injection. For the aerodynamic ramp injectors had poor capability of the flame stabilizing, various combined structures of aerodynamic ramp and cavity were designed to contrastively study the structures capability of mixing and combustion in supersonic flows.