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이영모(Young Mo Lee),이정일(Jungil Lee),이재화(Jae Hwa Lee) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
Wall-modeled LES (WMLES) is promising to simulate a turbulent flow at high Reynolds number with a reasonable cost because the required computational cost of large-eddy simulation in the near-wall region is proportional to approximately square of the friction Reynolds number (Reτ). An equilibrium stress model is the most widely used method due to the high efficiency. However, this method is still required to enhance the accuracy and applicability because of the limitations of the equilibrium assumption. In the present study, an artificial neural network (ANN) is used to obtain the wall shear stress for WMLES. The proposed method shows good prediction on the profiles of mean velocity and Reynolds stresses compared to equilibrium model when direct numerical simulation dataset of turbulent channel flows is trained at Reτ=395, 540, 930 and 2000. In addition, the present method predicts well the turbulent statistics at Re<SUB>τ</SUB>=640 and 5200, which are untrained by the ANN.
평균 벽 전단 응력 경계 조건을 이용한 복잡한 난류유동의 벽모델 큰에디모사
조민정(Minjeong Cho),이정일(Jungil Lee),최해천(Haecheon Choi) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
The mean wall shear stress boundary condition was successfully applied to turbulent channel and boundary layer flows using large eddy simulation without resolving near-wall region. In the present study, we apply this boundary condition to more complex flows where flow separation and redeveloping flow exist. As a test problem, we consider flow over a backward-facing step at Reynolds number of 22860 based on the step height. Turbulent boundary layer flow at the inlet is obtained using inflow generation technique by Lund et al. (1998) but with wall shear stress boundary condition. First, we prescribe the mean wall shear stress distribution obtained from DNS (Kim, 2011, Ph.D. Thesis, Stanford U.) as the wall boundary condition of present simulation, and we give no-slip boundary condition at flow-reversal region. The results from present wall-modeled large eddy simulation are in good agreements with the flow statistics by DNS. Currently, a dynamic approach of obtaining mean wall shear stress based on the log-law is being applied.