Investigations On The Mechanism Of Supersonic Flow And Combustion In Axisymmetric Scramjet Engines Based On GPU Acceleration Simulations

Circular cross-section engines in the supersonic field are becoming widely accepted by scholars both at home and abroad.The characteristics of the supersonic flow and supersonic combustion in pipes are more complex compared with the traditional twodimensional cross-section engines.In this thesis,we developed a GPU-accelerated highprecision massively parallel method and simulation platform based on the demand for large-scale high-precision and efficient simulation of supersonic flow,mixing,and combustion problems in the pipe flow.Based on the simulation platform,simulation studies of the pipe flow were carried out to verify the accuracy of the simulation platform developed in this paper,meanwhile,the characteristics of the supersonic flow,mixing,and combustion characteristics in the circular engine were numerically studied.In this paper,to build a GPU-based large-scale high-precision simulation platform for complex configurations,a high-precision low-dissipation spatial method,a time integrating method without spatial dependence,an efficient parallel partitioning method,and an improved turbulence inlet generation method are developed.For spatial discretization,a GPU-parallel high-precision low-dissipation WENO-CU4/energyconservative central difference hybrid method is developed to build a fourth-order precision hybrid method,and numerical tests on the boundary layer of supersonic turbulence show that the resolution accuracy of the flow field of this method can meet the requirements of LES and DNS.Based on the hardware characteristics of GPU architecture,an efficient partitioning algorithm is proposed,and an efficient and robust implicit DPLUR time integrating method based on GPU is developed.For the boundary conditions,this paper improves the distribution of radii,the moving velocity,and the regeneration positions of the eddies in the synthetic eddy method.Compared with the original synthetic eddy method,the improved method can generate fully developed turbulence more efficiently in complex inlets such as circular and toroidal.The differences in the jet mixing between the pipe and the channel are compared and analyzed based on the GPU simulation platform.It is found that due to the confining effect of the circumferential wall in the pipe,the shock in the pipe is stronger compared with that in the channel,and this brings about differences in separation,jet penetration,mixing efficiency,etc.The main reasons for the higher mixing efficiency in the pipe than that in the channel are: 1)the major vortex pair in the pipe is larger and higher due to the stronger separation and the lifting effect of the curved wall;2)the higher local momentum ratio and the jet penetration height in the pipe are higher,which accelerates mixing in the pipe;3)the stronger shock string in the pipe also enhances the mixing.The results of the pipe with step reveal that the conical-shaped shock waves interact with the bowed shock of the jet in the pipe to form a complex system of shock waves.The presence of the step in the pipe makes the recirculation region upstream of the jet more complex.Four vortices are obtained in the recirculation region,where the main vortex,which plays a controlling role,is generated due to the expansion of the step.The step provides more low-velocity space for the expansion of the jet gas and thus increases the penetration depth of the jet,while the conical shock increases the penetration height and mixing efficiency downstream of the jet.The theoretical analysis of the mixing layer growth rate shows that the compressible mixing layer at high total temperature and high Mach number is significantly influenced by the compression effect.Due to the compression effect,the compressible mixed layer growth rate forms a growth rate peak line in the transonic region.The results of the largeeddy simulations show that the empirical formula significantly overestimates the mixed layer growth rate,and the error increases rapidly after the static temperature exceeds 2000 K.The increasing effect of increasing the mainstream total temperature and Mach number on the mixed layer growth rate is mainly reflected in the amplitude of Reynolds stress,which will accelerate the mixing inside the mixing layer and make the components inside the mixing layer more uniform;due to the compression effect,the Reynolds stress does not increase in the vertical range,and the mixed layer growth rate does not change significantly due to the increase in the amplitude of Reynolds stress.Simulation studies were carried out for single-hole and double-hole transverse jets in the supersonic cross flow.Relative to the single-hole jet,the adjacent main rotating vortex in the double-hole jet,which is squeezed and positioned lower,simultaneously brings the fuel to the near-wall area in the middle section between the double jets,forming a fuel enrichment zone.The interaction of the large-scale vortex structure between the two jets accelerates the mixing of the fuel with the surrounding air,and there are more mixed flame regions in the combustion flow field of the double-hole jet relative to the single-hole jet.The evolution of contact burning in a rotating detonation engine is analyzed in detail.the fuel inside the OH zone is continuously mixed and burned with the oxygen outside the OH zone,maintaining the OH zone,and eventually,the OH is gradually depleted in the region between the oblique shock and the slip line.A more accurate flow field structure diagram of a non-premixed rotary detonation engine is given.By quantification,contact combustion releases about one-third of the total heat release,with the main heat release coming from CB2,and the configuration hardly affects the percentage of heat release from contact burning.