Direct Numerical Simulation Of Particle Drag Characteristics In The Complex Compressible System

Compressible two-phase reaction systems are often encountered in the fields of energy and astrophysics,especially in the detonation propulsion technology.One of the remarkable characteristics of this system is the strong coupling of multi-scale,multifield and multi-physical processes.In a typical detonation engine,the scale of the system varies from the shock wave thickness scale of a few nanometers to the equipment scale of a few meters or even tens of meters.The physical process involves fluid dynamics,flow field,electromagnetic field,energy field,density field and chemical reaction and so on.Similarly,three approaches(theoretical,experimental and numerical)have been combined to address these issues.With the rapid development of computer hardware and algorithm,numerical simulation,as an important supplement to theoretical analysis and experimental measurement,plays an increasingly important role.In this paper,based on direct numerical simulation technology,a weakly compressible and fully compressible large-scale parallel computing platform suitable for fully analyzable two-phase flows is developed,and a ghost-cell immersed boundary method is developed,which can be used to analyze the particle boundary layer and be coupled to track the particle boundary.Using the above method,this paper studied the weakly compressible particle effects of Mach number and the shape effect on drag force and particle heterogeneous chemical reaction on the particle stress and heat transfer coefficient.And besides,direct numerical simulation study of the influence of the full compressible basin with a constant average speed of compressible turbulent flow and the interaction of shock wave/detonation wave with the particles are carried out.In the first part,a weakly compressible direct numerical simulation platform based on the 5th order upwind scheme and ghost-cell immersed boundary algorithm is developed.On this platform,the Mach number effect and shape effect on particle drag force are first studied.The results show that,firstly,in the weakly compressible regime,with the increase of Mach number,the drag force on the particles increases,which is due to the increase of boundary layer thickness.Second,only in the vortex shedding regime,streamlining particles have a drag reduction effect.Then,this paper reveals the behind physical mechanism of the turn in the coke combustion rate at 1700 k and explores the effect of gas phase chemical reactions on drag force and the coefficient of heat transfer between particles and the gas phase.The results showed that when a chemical reaction occurs,the particle drag force increases and a significant increase also happens to the heat transfer coefficient.In the second part,the interaction between a strongly compressible turbulent flow with a constant average flow rate and a fixed particle is studied based on a fully compressible full-scale direct numerical simulation of a massively parallel computing platform.Three cases with different inflow turbulence intensities are studied.It is shown that with the turbulence intensity increasing the drag force coefficient presents a smaller relative increase compared to the incompressible situation.Analysis of the bow shock-turbulence interaction is also reported.Similar to the normal shockturbulence interaction,both the Kolmogorov and Taylor scales decrease after being compressed by the shock.Moreover,both the streamwise and transverse Reynolds stresses have a peak at the shock position.These results indicate the significance of taking the effects of shock into consideration when modeling the modulation of a solid particle to the compressible turbulence.In the third part,the direct numerical simulation of the interaction between shock waves and particles is carried out.First,through theoretical derivation,two important conclusions are drawn in this paper.One is that the contribution of viscous force to drag force can be neglected in a time scale of shock wave and particle interference.Second,for commonly used metal particles(particle to gas density ratio greater than 1000),particle motion can be ignored during the interaction between shock wave and particles.Direct numerical simulation results for the above theoretical derivation show that the large particles meet the first conclusion,but for small particles(diameter less than 100 ?m),the difference caused by introducing viscosity is about 10%.The contribution of viscous force can not be neglected when unsteady drag force model is constructed.This is because the theoretical relationship between the thickness of the particle boundary layer and the particle diameter is only true when the particle diameter is relatively large.In addition,in the process of interaction between shock waves and particles,although particle motion can be ignored,the velocity acquired by particles in this process cannot be ignored.Besides,based on the DNS of the interaction between shock wave and particle group,this paper analyzes the flow state within particle,measured the leading factor that induced flow instability,and puts forward to a mathematical model to predict the peak in the drag force,by adding the linear relationship of the average model to a standard gaussian distribution model.In the fourth part,the direct numerical simulation of reflection and diffraction of detonation wave on a single particle surface is preliminarily carried out.Firstly,the analysis of detonation wave characteristics shows that detonation combustion is a very unstable physical process,and its front is an envelope structure containing a complex three-wave structure.Due to the above complexity of detonation wave front,the collision process between detonation wave and particle is much more complicated than that between shock wave and particle.This leads to the nonlinear and fluctuating characteristics of the three-wave point trajectory and the uncertainty of the particle drag.The analysis of the direct numerical simulation results of detonation wave diffraction and reflection on the surface of a single particle shows that when the strong reflection wave meets the weak transverse wave in the same direction,instead of forming the Mach stem,the three-wave structure merges.The weak transverse wave or attenuated reflection wave collides with the transverse wave to form the Mach stem and three wave structure.Two strong diffraction Mach stems/shock waves collide(focus)to form a new Mach stem and three wave structure.Therefore,the collision of two waves propagating in the opposite direction is a sufficient condition for the formation of detonation wave Mach stem.