DIRECT SIMULATION AND LARGE EDDY SIMULATION OF UNSTEADY FLOW INCLUDING SEPERATION,VORTEX MOTION AND TURBULENCE

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A purpose of this co-labolation research was to establish an accurate and effective method for the numerical simultion of unsteady flows with seperation and vortexes, esppecially using a direct numerical simulation (DNS) and a large eddy simulation (LES) of turbulence. For this purpose high-order accuracy schemes and boundary conditions were developed in the mathematical view and LES turbulence models were also examined from an physical analysis of turbulence structures.The above reseach had been performed in numerical methods of the compressible flow, high order accurate schemes and their application to the direct turbulence simulation by Chinese researchers, and also in numerical methods of the incompressible flows, boundary condition and their application to the large eddy simulation by Japanese researchers. This co-laboration promoted a development of more accurate and effective research in turbulence phenomena by an interaction between the both sides.The unsteady flows with the se … More perations and votexes are popular in the engineering, but have not been predicted correctly enough by a widely used Reynolds averaging model. The LES is expected to be applied generally and accurately to verious types of flows because it simulates a large scale part of turbulence motion directily. However, several problems should be researched before it is applied to the engineering : in mathematical view, 1) effective algorithms for the time marching analysis, 2) reducing numerical errors caused from the boundary conditions, 3) avoiding instability in the high order accuracy schemes, 4) boundary fitting method to the comlicated geometry, and also in the physical analysis, 5) development and validation of the LES turbulence models, 6) analysis of turbulence structures by the visualized data. Finally a large scale computation for the LES and DNS can be performed accurately and effectively enough.In 1995 budget year these researches were proceeded as fillows :Chinese researches investigated ina) development of stable and high order schemes with compact formulation,b) direct numarical simulation of the compressible turbulent shear flow. Japanese researchers investigated inc) instability and accuracy of the unsteady boundary conditions,d) development of dynamic models for the LES,e) large eddy simulations using the boundary fitted and unstructured grids, and also joint researches are performed inf) analysis of the visualization of the compressible shear flows by the DNS.g) applying the high order schemes to the incompressible flow simulations.This co-laboration has been proceeded by exchanging information constantly through an internet and also by visiting each other for discussing more detail. A part of this co-laboration results has been presented in an international symposium and will be published in an international journal coauthorized by the researchers from both Chinese and japanese side. This research program will be continued and extended to wider application of the DNS and LES to both the compressible and the incompressible turbulent flows. Less