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首页> 外文期刊>International Journal of Heat and Fluid Flow >Direct and large eddy simulations of a bottom Ekman layer under an external stratification
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Direct and large eddy simulations of a bottom Ekman layer under an external stratification

机译：外部分层下底部埃克曼层的直接和大涡模拟

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摘要

A steady Ekman layer with a thermally stratified outer flow and an adiabatic boundary condition at the lower wall is studied using direct numerical simulation (DNS) and large eddy simulation (LES). An initially linear temperature profile is mixed by turbulence near the wall, and a stable thermocline forms above the mixed layer. The thickness of the mixed layer is reduced by the outer layer stratification. Observations from the DNS are used to evaluate the performance of the LES model and to examine the resolution requirements. A resolved LES and a near-wall model LES (NWM-LES) both compare reasonably well with the DNS when the thermal field is treated as a passive scalar. When buoyancy effects are included, the LES mean velocity and temperature profiles also agree well with the DNS. However, the NWM-LES does not sufficiently account for the overturning scales responsible for entrainment at the top of the mixed layer. As a result, the turbulent heat flux and the rate of change of the mixed layer temperature are significantly underestimated in the NWM-LES. In order to accurately simulate the boundary layer growth, the motions responsible for entrainment must either be resolved or more accurately represented in improved subgrid-scale models.
机译：使用直接数值模拟（DNS）和大涡模拟（LES）研究了具有热分层外流和下壁绝热边界条件的稳定Ekman层。最初的线性温度曲线通过壁附近的湍流混合，并且在混合层上方形成稳定的温跃层。通过外层分层减小了混合层的厚度。来自DNS的观察结果用于评估LES模型的性能并检查分辨率要求。当将热场视为被动标量时，解析的LES和近壁模型LES（NWM-LES）都可以与DNS很好地比较。如果包括浮力效应，则LES平均速度和温度曲线也与DNS一致。但是，NWM-LES不足以解决导致混合层顶部夹带的倾覆尺度。结果，在NWM-LES中，湍流通量和混合层温度的变化率被大大低估了。为了准确地模拟边界层的增长，必须解决导致夹带的运动，或者在改进的子网格规模模型中更准确地表示运动。

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