The Research On Gridless Method Of Compressible Multi-material Flows And Multi-component Reaction Flows

Gridless method discreted the flow fileds flexibly using points,and compared with the traditional numerical methods,it was more suitable to simulate the flows involving arbitrary configurations or moving boundaries.In the present dissertation,the adaptive gridless method for improving the efficiency and the gridless methods for solving compressible multi-material flows and multi-component reactive flows were studied.Firstly,the basic concepts of cloud of points and least square for computing the spatial derivatives were interpreted in detail.Several different automatic point filling strategies were listed and compared.Some technologies were applied to enhance the weighted-point filling strategy,such as optimizing the advancing fronts and satellitic points swapping.The quality coefficient of cloud of points were introduced into evaluating the points distribution.Based on the weighted-point filling strategy,the weighted-point adaptive gridless method was accomplished to improve the computation efficiency and point distribution robustness.The adaptive indicator was the function of the local pressure gradient and the weight of point.Therefore,this method could accurately regulate the distribution of weighted-points in the sensitive regions where the shock wave appeared,including clouds refinement and clouds coarseness.The weight of a new point was obtained by using the predictor-corrector iterative algorithm based on the adaptive standard.Steady and unsteady numerical examples showed that the proposed adaptive method was able to capture the static and moveable shock waves with initial scanty points and adjust the distribution of the points to improve the resolution of flow features constantly.Secondly,the dynamic gridless points were used to track the complex deformation of the free movable interfaces,and the gridless method for the compressible multi-material flows was developed.The material interface was treated as a series of dynamic gridless points with a dual definition corresponding to each material.The GFM(Ghost Fluid Method)was applied to deal with the interface points and create ghost fluid points,and the multi-material flow was divided into several independent single material flows.In order to restrain spurious numerical oscillations on material interface,the solver of the local Riemann problem on the interface was introduced into updating the flow parameters of the interface points and ghost points.For stiffened and general gas equation of state,the analytic and approximate solution of Riemann problem were deduced by employing Rankine-Hugoniot conditions.Spring analogy and local cloud rebuilding algorithm were utilized to deal with dynamic clouds of points.The slipping of interface points in tangent direction of the interface could result in bad clouds of points,and it was resolved by adaptively adding or deleting points with taking the interface as deformed boundary.AUFS(Artificially Upstream Flux Vector Splitting)and HLLC(Harten-Lax-van Leer-Contact)schemes were extended to calculate the numerical convective flux of the Euler equations in the ALE(Arbitrary Lagrangian-Eulerian)form.The equations were advanced in time by using four-stage Runge-Kutta method.For economizing computational time,the dynamical parallel arithmetic was built with allowing material interfaces passing through the zone boundary.The shocktubes problems under kinds of initial conditions were simulated,and the results showed the feasibility of the proposed gridless method.Further,supersonic aerofoil over water,shock-bubble and underwater explosion were simulated,which demonstrated that the proposed gridless method was able to keep track of the material interfaces and the shock waves accurately,and made a success of rebuilding the local deformated region.Finally,based on the multi-component N-S equations in the ALE form,the gridless method for reactive flows over moving boundaries was accomplished.Multi-component HLLC(Harten-Lax-van Leer-Contact)scheme was discussed to obtain the convective flux.The chemical source term was solved by employing the finit rate chemistry model.In order to overcome the stiff trouble caused by the chemical reactions,the time-splitting procedure was introduced into solving the three differential equations respectively.The isovolumic combustion process and the detonation wave induced by high-speed projectile were calculated to confirm the method in respect of the efficiency.And then,on the basis of the actual physical process of the projectile launch,coupled with the calculation of combustion productions in interior ballistics,the muzzle flow field was simulated using the gridless method.The change of gas components was studied throughout the entire process,and the influences of muzzle pressure and shooting environment were also given separately on the muzzle wave architecture and components.