Direct Numerical Simulation The Collision Rate Of Finite Inertia Particles Suspended In Homogeneous Isotropic Turbulence

Inhaled particulate matter originating from combustion does serious harm to human health and environment. Mechanism of formation and growth of inhaled particulate matter in combustion is the precondition of its control during combustion process, where the controlling process is inter-particle collision and coagulation. Because turbulence imposes complex transport and accumulation effects on fine particle, the collision rate of fine particles there may different from those predicted by the custom model. Research on collision rate of finite inertial particle with preferential concentration is one of hotspots in gas-particle flow mechanism and aerosol dynamics.After a brief summary of the research developments in particle average collision rate model, correlated mathematic models and numerical simulation algorithms, a retroactive algorithm-based program was built for direct numerical simulation (DNS) the collisions between particles in 3-dimenional space, with particle number up to 105~106. The second-order forecast-correction method was applied in solution of particle's momentum equation, where the fluid velocity at the particle location is determined using a fourth-order Lagrangian interpolation. The particle position was advanced by a second-order Adams integral method. The fluid velocity field was generated by a pseudo spectral method. By optimizing algorithms such as cell index, exclusive search and particle sequence et al., the program can fit the requirements of simulating collisions between huge numbers of particles on personal computer, whose computation load is two orders of magnitude less than that of custom algorithm. Verifications of the code were done by two cases: St<<1 particle in uniform shear flow and St>1 particle whose velocity distribution was Gaussian. The results were consistent with analytical solutions in literatures,which proved reliability of retroactive algorithm and the program. The principle of computational parameter selection was also discussed. Moreover, DNS study of finite inertial particle with preferential concentration in isotropic turbulence and its influence on collision rate were performed. The accumulation level of various St number particle was quantified by parameters such as radial distribution function, and conditional expectation of normalized particle number density et al.; It showed that collision rate of St =1 particle was 20~30 times larger than that of zero-inertial particle because of local preferential concentration.