Boundary Condition Treatments Of Unstructured Finite Volume Algorithms And Its Application In Detached Eddy Simulation

Turbulence is considered as”the last unsolved problem in classic physics”.With the continual development of high performance computing and numerical discretization methods,it becomes possible to conduct research on turbulence numerically.In spite of this,it is still not practical to simulate turbulence flow of high Reynolds number with direct numerical simulation or large eddy simulation.A compromise is to employ detached eddy simulation.To carry out the numerical simulation,the computational domain should be dis-cretized first.An efficient and flexible choice is to use unstructured grid.The present re-search is based on the second-order unstructured cell-centered algorithm.Currently,great attention is focused on developing more accurate gradient reconstruction algorithms and formulating suitable limiters.In this thesis,the purpose is to devise a general framework for boundary condition treatments.The new method for boundary condition treatments belongs to the weak-imposition approach,and for boundaries with characteristic waves propagating in and out of the computational domain,the non-reflecting requirement is ensured.Compared with the traditional characteristic method,the complexity and non-uniqueness with the usage of characteristic decomposition and Riemann invariants are avoided.With the newly developed algorithms,numerical simulation of wall-bounded flows is conducted with delayed detached eddy simulation.(?)-f model is chosen as the un-derlying RANS model for its capability of reflecting the anisotropy in the near-wall re-gion.However,one of the governing equations of (?)-f model is of elliptic type,which makes it more unstable in the numerical calculation.To cure this problem,a modification is proposed for original governing equations and the rationality of this modification is demonstrated through detailed analysis of the plane channel flow.In addition,a damping function is introduced to improve the turbulence resolving ability of the model when the grid scale is enough and the flow is filled with turbulence fluctuations.In addition,for the ribbed channel flow,to alleviate the discrepancy between the numerical solution and the experimental result,an anisotropic grid adapting technique is used to refine the grid based on local flow characteristics.Furthermore,the improved (?)-f detached eddy simulation is employed to simulate the flow around blunt bodies,including the circular cylinder in the sub-critical regime and the side by side square cylinders.For the circular cylinder,the bifurcation of veloc-ity profiles in the very near wake region is clarified through the comparison of the grid resolution,the spanwise length of the computational domain,and the spanwise grid res-olution.For the simulation of the near-wall region,the improved (?)-f detached eddy simulation behaves better.For the side by side square cylinders,the advantage of the improved (?)-f detached eddy simulation is demonstrated through the comparison with results of large eddy simulation.