approach: why LES/RANS hybrid methodology

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Due to the importance of understanding the base flows, various experimental and numerical approaches have been performed to understand base flows in the past. As for an experimental approach, traditional wind-tunnel tests usually use a support sting from the rear of a test model, and presence of the support sting largely influences the flow structure behind the test model near its wake axis. Furthermore, there are difficulties in measuring various types of detailed flow data. As a result, experimental approaches are not completely adequate for the estimation of the base flowfield and force acting on the base.

As for a numerical approach, traditional RANS simulations with any RANS-level turbulence models do not give quantitative or even qualitative predictions of massively separated high Reynolds number base flows.

Mach number distributions behind base: experiment vs. RANS.

Because of the restriction in the present computer capability, LES and MILES which are potentially more accurate than RANS are not be an easy approach for the analysis of base flows at realistic Reynolds number. Therefore, to overcome these disadvantages of the numerical approaches and to develop the CFD into a more useful design tool, the needs of the computational method in recent is an accurate prediction of such unsteady flows at high-Reynolds number within practical computational cost. Considering the situation, our choice is LES/RANS hybrid methodology which requires much less computational cost than that of LES and MILES and is considered to have an accuracy of similar level as LES and MILES.

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