Research On Mixing And Combustion Characteristics Of Supersonic Airflow Based On Support Plate/baffle Configuratio

Scramjet combustor is a core component of air-breathing propulsion system,which can determine the overall performance of hypersonic vehicles.In the Research on Scramjet technology,not noly the overall performance of the combustor is under the spotlight,but also the key point of overall performance,flow and combustion of the supersonic mixing layer,is the key point of the research interests.In this paper,the RANS program,which is suitable for the simulation of supercombustion ramjet engines,and the program for numerical simulation of supersonic flow and combustion,which is suitable for supersonic mixing layers,are both based on the finite volume method and developed by using computational fluid dynamics.The effect of double-strut configurations on the performance of scramjet and mechanism of the effect of the splitter palte configurations on the characteristics of the supersonic mixing layer are systematically studied to improve the understanding of the scramjet engines and flow and combustion mechanism of the supersonic mixing layer.The main work,in this paper,is as follows.(1)Based on the finite volume method,the turbulence model is based on the SST twoequation model,the eddy dissipation/finite rate model is adopted for the turbulent combustion model,the convective fluxes are calculated by the AUSMPW+,the mesh interface reconstruction adopts the second order NND scheme,the viscous fluxes and diffusion terms are calculated by the central difference scheme,and the time advance is based on the LU-SGS method for constant Reynolds-averaged calculations,so the multi-component Reynoldsaveraged Navier-Stokes equation is solved.And a program,for simulating the steady flow of scramjet combustor,is developed.Considering the complex flow structure of scramjet engine,classical experiments with different flows and combustion characteristics are selected to verify the accuracy and reliability of the RANS turbulent combustion code,developed in this paper.(2)For scramjet model combustor adopting double struts with backward-facing steps,the effects of single-strut and double-strut configurations on the flow field structure and performance of the scramjet combustor are compared,wchic are based on the the RANS turbulent combustion code.Also,the advantages of the proposed double-strut configuration are clarified.On this basis,present study investigates the effects of the structure parameters of backward-facing steps,vertical spacing of the double struts and horizontally staggered spacing of double struts on the performance of the combustor.Next,the variation patterns of the flow field structure and combustor performance along with different backward-facing steps,vertical spacings of double struts and horizontally staggered spacings of double struts are obtained.(3)Based on the finite volume method,AUSMPW+ scheme is used for circulation calculations,the third order MUSCL method is utilized for mesh interface reconstruction.Also,the central difference scheme is adopted for the calculation of viscous fluxes and diffusion terms.And the third-order Range-kutta method is used for the time advance of non-constant compressible simulations,therefore,the multi-component Navier-Stokes equation coupled multi-step finite rate model is solved.And a program,for simulating the unsteady flow of supersonic mixing layer,is developed.Next,numerical verifications are also carried out,in detail,for the flow and combustion in the supersonic mixing layer.Taking into account the presence of shock wave-vortex interaction,shear layer and shock wave-flame interaction in the supersonic mixing layer,and so on.The classical flow and combustion problems are selected to verify the accuracy and reliability of the code for numerical simulation of compressible flow developed in this paper,especially for supersonic mixing layer.(4)In order to further explore the development and evolution mechanism of the supersonic mixing layer,which usually exists in the sramjet combustor,the flow mechanism and growth characteristics of the supersonic mixing layer under a typical splitter plate are investigated based on the method for numerical simulation of supersonic flow.Next,typical structures,such as vortices and excitations,are obtained.In addition,it is found that a phenomenon of relarminarization appears in the mixing layer under a typical splitter plate.On this basis,three new configurations are proposed,and the growth characteristics of the supersonic mixing layer under these four splitter plates are compared and analysed in detail.The mechanism of the oblique shock wave on the mixing layer and the destination of different energy loss in the flow channel are clarified.The splitter plate with cavity,strut and step can avoid the relaminarization of the mixing layer,effectively.(5)For the characteristics of the supersonic reacting mixing layer,the combustion process and growth characteristics of the supersonic reacting mixing layer are investigated numerically,which are all based on the method numerical simulation of compressible flow,coupled with finite rate model.Firstly,the turbulent combustion characteristics of the supersonic reacting mixing layer are analysed under different splitter plates,and the contribution of different combustion modes to the flow field is clarified.Secondly,it is found that the flame propagates steadily in the typical splitter plate and splitter plate with cavity,while the flame fkashback appears in the splitter plate with strut and step.For the typical splitter plate and splitter plate with cavity,the differences in the growth characteristics of the supersonic reacting mixing layer and the dominant combustion mode are clarified through in-depth analysis.Also,the results reveal the combustion and heat release characteristics of the supersonic reacting mixing layer.Finally,a preliminary analysis of the causes of flame flashback is carried out,in the splitter plate with strut and step.