Direct Numerical Simulation Of Medium Reynolds Flow Past Square Cylinder

Turbulence is a complex flow phenomenon that widely existing in both the nature and the engineering and it’s also one of the seldom difficult problems whose mechanism problems haven’t been solved yet. There are mainly three methods to study the turbulence: Reynoldsaverage N-S(RANS); Large eddy simulation(LES); Direct numerical simulation(DNS).DNS is the most accurate numerical method of turbulence, which solve the intact threedimensional governing equations of the unsteady flow directly without using turbulent models and can simulate the time evolution process of all the turbulent instantaneous flow parameter including the fluctuation motion. Flow past square cylinder has the property of simple geometric shape but very complex flow field structure, which makes itself typical object of the research of the flow past bluff body. DNS of flow past square cylinder can simulate more meticulous flow filed structure and has very important value in both theoretical research and engineering practice.In this dissertation, parallel code of DNS of flow past cylinder is designed and programmed with FORTRAN 95 language, the mainly research contents are focused on the simulation and analysis of the vortices in the flow field. main works are as follow:First, the governing equations(Navier-Stokes equations) are discreted by finite volume method based on the staggered grid arrangement, the discrete process and the final discretized algebraic equations are presented in this dissertation.Second, comparison and analysis of the results of the incompressible lid-driven flow are completed, which is solved by three different decoupled solvers(SIMPLE, PISO and pseudocompressible method). SIMPLE method is chosen as the solver of the flow past square cylinder.Then, parallel FORTRAN 95 code of the lid-driven flow is completed. The detailed design process of the paralleled SIMPLE solver based on the MPI(Message Passing Interface) and the final obtained accelerate performance curve are presented in this dissertation.After that, DNS of different Reynolds flows past two-dimensional square cylinder are completed. Detailed flow field structure is obtained and analysed. Comparison and analysis of the results of medium Reynold(Re=10000) flow simulated by the RANS, LES and DNS are carried out.Finally, the parallel code of both the three-dimensional lid-driven flow and the Re=10 flow past the three-dimensional square cylinder are designed, results are compared to the related reference to justify this code. DNS of the unsteady(Re=250) flow past the three-dimensional square cylinder is carried out, some specific phenomenon can be simulated.