Direct Numerical Simulation Of Compressible Gas-Solid Two-Phase Turbulent Boundary Layer And Transverse Jet

The supersonic combustion ramjet(scramjet)is the core part of hypersonic aircrafts,which is widely applied in the domains of national defense and aerospace technology.The solid fuel scramjet(SFSCRJ)has been extensively investigated in the past decades due to the advantages of high safety,ease of operation and quick response.There exist complex multi-scale and multi-physics processes of interactions among compressible turbulence,wall,transverse jet,shock waves and particle clusters in a SFSCRJ.Having a thorough investigation into these problems can improve the understandings of SFSCRJ and enhance the stability and efficiency of a scram-jet.Therefore,we establish a high-performance computing platform for direct numerical sim-ulation to solve the compressible multiphase turbulence problems.Based on this platform,we have separately investigated the compressible multiphase turbulent boundary layer,compress-ible mulitphase transverse jet and interaction between a planar shockwave and fully-resolved particle clutsers,aiming at revealing the mechanism of interactions among compressible turbu-lence,wall,transverse jet,shock waves and particle clutsers.We hope these efforts can provide some instructions and references for the research of SFSCRJ.Firstly,this thesis studies the characteristcs of particle dispersion,motion and preferencial accumulation of particles in a multiphase compressible turbulent boundary layer laden with Lagrangian point particles.The results show that particles tend to accumulate in the regions with low streamwise velocity and form particle streaks due to the dominance of ejection events.There exists a minimum particle mean concentration in the near-wall regions,normalized by which the particle mean concentration will show a self-similar distribution.Compared with small particles,large particles are more significantly affected by turbophoresis and demonstrate a stronger preferential accumulation.Thus,more large particles are clustered in the near-wall regions and the deviation between the mean velocities of particle and those of fluid increases.Due to the presence of wall,particles are clustered in high-vorticity regions in the buffer layer,which is in contrast to the phenomenon in turbulence without walls.A new mechanism for particle preferential accumulation based on local fluid density is discovered.Large particles are located in low-density regions in the inner zones and high-density regions in the outer zones.Nevertheless,small particles remain located in regions with low fluid density,as illustrated by the mechanism analysis of particle dilatation.Secondly,this thesis investigates the particle dispersion and turbulence modulation in the multiphase compressible transverse jet.The simulation results indicate that large particles mainly reside around the large-scale shear layer structures in the windward side of the central jet trajectory,whereas the small particles can be transported to the front and back recirculation regions through radial direction.What is more,small particles are widely spread in the bound-ary layer and large-scale shear layer,and are dominated by the streamwise vortex.Around the central plane in transverse direction,the back-reaction of partilces delay the recover of boundary layer thickness,intensity the oscillation of wall friction coefficient and enhance the boundary layer thickness and maximum wall friction coefficient.The jet trajectories are lowered by large particles,and lift up by small particles.At the central plane in transverse direction,the particles enhance the mean wall-normal velocity in the near-wall regions at the wake region of transverse jet,whereas decrease the mean streamwise and wall-normal velocities in outer regions.Parti-cles severely modify the fluid fluctuations around the shock fronts,i.e.decreasing the turbulent fluctuation around the windward barrel shock and bow shock,increasing the turbulent fluctu-ation around the leeward barrel shock,and lift up the bow shock in wall-normal direction.In other regions without shocks,small particles tend to enhance the Reynolds stress,whereas large particles decrease the turbulent kinetic energy.At last,this thesis investigates the interaction between a planar shockwave and particle clusters containing 300 fully-resolved particles with a high volume fraction through a ghost-cell immersed boundary method.Four cases of different incident shock Mach numbers up to6.0 are investigated to study the shockwave structures,instantaneous and peak drag and lift force coefficients,and fluctuations of the flow field.Results show that the reflected shocks form a planar shockwave propagating upstream,with its velocity decreasing with the increase in Mach number.The propagating speed of transmitted shocks shows the same trend,whereas its front is highly curved in high-Mach number cases.The peak drag coefficients of single par-ticles exhibit a linear decreasing correlation with the streamwise location,and the difference between them and the correlations can be well captured by the Gaussian distribution.The lift force coefficients come to the same order as the drag force coefficients in the high-Mach num-ber cases,indicating that the transverse force could not be ignored in a particle cluster with a high volume fraction,especially when the incident shock Mach number is high.Fluctuating flow quantities indicate that the increase in Mach number enhances the fluctuating turbulent kinetic energy compared with the mean flows.By comparing the differences in the main results obtained from an NS solver and an Euler solver,we identify that excluding viscous effects in an Euler solver would strengthen the fluctuations of particle drag and enhance the fluctuating turbulent kinetic energy in a long-time simulation of shockwave-cluster interaction,confirming the necessity of employing an NS solver in this problem.