Coupling EMMS-based Turbulence Model With Lattice Boltzmann Method

Turbulence is a typical nonlinear non-equilibrium system and it is widespread in nature and various engineering applications,and turbulence is widely considered as one of the most difficult problems to be solved.With rapid development of computer technology,numerical simulation has become an important means to investigate turbulence.At present,the Reynolds-averaged Navier-Stokes model is a feasible solution for engineering turbulence.However,the traditional turbulence models always assumes that the fluids in the computational grid are fully turbulent states and neglects the laminar portion of the fluid flow,which leads to a source of inaccuracies in modeling practical engineering flows.The Energy Minimization Multi-Scale(EMMS)based turbulence model is a mesoscale turbulence model originated from the principle of compromise-in-competition between viscosity and inertia.The model draws on the idea of phase separation in two-phase flows and regards single-phase turbulence as a mixture of turbulent fluid components and laminar fluid components.The inhomogeneous structure in the computational grid is characterized by adjusting the turbulent fluid volume fraction f.EMMS-based turbulence model can calculate the flow state of laminar and turbulent coexistence and effectively solve the quantitative simulation of non-uniform turbulence system.As an efficient fluid solver,explicit scheme,easy parallelism and capability of handling complex boundaries are some of the characteristics of lattice Boltzmann method and it is very suitable for large-scale computation on GPUs.Therefore,combining EMMS-based turbulence model with the lattice Boltzmann method and implementing the parallel algorithm on multi-GPUs will improve the speed and accuracy of engineering turbulence simulation.Based on the LBM and EMMS-based turbulence model,the following chapters are as follows:Chapter 1 is literature review.Firstly,the current main turbulence models are reviewed.Then,EMMS-based turbulence model with consideration of the interaction between laminar and turbulent phases is summarized.Finally,the LBM is used to solve the flow field is introduced.Chapter 2 implements the algorithm of multi-GPUs parallelism of the LBM coupled EMMS-based turbulence model.A method coupled EMMS-based turbulence model and LBM is presented.The multi-GPUs parallelization of the proposed algorithm is implemented using CUDA and MPI.The acceleration performance of the proposed algorithm on Tesla K80 and Tesla P100 is tested.Chapter 3 mainly numerically verified the proposed algorithm.The proposed algorithm coupled LBM and EMMS-based turbulence model is validated by the cases of the lid-driven cavity and backward-facing step flows.It is found that the proposed model can obtain a certain accuracy of flow field without using the wall functions and features weak dependence on the mesh spacing of the computational grid.Finally,the implication is found that the proposed model can predict flow transitions to some extent.Chapter 4,the large-scale parallel computing of LBM coupled EMMS-based turbulence model algorithm is preliminarily explored.A grid generation technique for three-dimensional complex configuration is proposed.Then large-scale simulations of flow through the multi-stage turbine and F22 are carried out,which demonstrates the powerful parallelism and good industrial application prospects of the multi-GPUs parallel algorithm of LBM coupled EMMS-based turbulence model.Chapter 5 summarizes the main achievements and conclusions of the work of this thesis,and looks forward to some efforts in the theoretical basis and large-scale algorithm implementation of the LBM coupled EMMS-based turbulence model.