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首页> 外文期刊>Boundary-layer Meteorology >Large-eddy simulation of turbulent flow across a forest edge. Part II: momentum and turbulent kinetic energy budgets
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Large-eddy simulation of turbulent flow across a forest edge. Part II: momentum and turbulent kinetic energy budgets

机译：穿过森林边缘的湍流的大涡模拟。第二部分：动量和湍动能预算

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Momentum and turbulent kinetic energy (TKE) budgets across a forest edge have been investigated using large-eddy simulation (LES). Edge effects are observed in the rapid variation of a number of budget terms across this vegetation transition. The enhanced drag force at the forest edge is largely balanced by the pressure gradient force and by streamwise advection of upstream momentum, while vertical turbulent diffusion is relatively insignificant. For variance and TKE budgets, the most important processes at the forest edge are production due to the convergence (or divergence) of the mean flow, streamwise advection, pressure diffusion and enhanced dissipation by canopy drag. Turbulent diffusion, pressure redistribution and vertical shear production,which are characteristic processes in homogeneous canopy flow, are less important at the forest transition. We demonstrate that, in the equilibrated canopy flow, a substantial amount of TKE produced in the streamwise direction by the vertical shear of the mean flow is redistributed in the vertical direction by pressure fluctuations. This redistribution process occurs in the upper canopy layers. Part of the TKE in the vertical velocity component is transferred by turbulent and pressure diffusion to the lower canopy levels, where pressure redistribution takes place again and feeds TKE back to the streamwise direction. In this TKE cycle, the primary source terms are vertical shear production for streamwise velocity variance and pressure redistribution forvertical velocity variance. The evolution of these primary source terms downwind of the forest edge largely controls the adjustment rates of velocity variances.
机译：使用大涡模拟（LES）研究了森林边缘的动量和湍动能（TKE）预算。在整个植被过渡期间，许多预算条款的快速变化都观察到了边缘效应。在森林边缘的增强阻力在很大程度上由压力梯度力和上游动量的顺流平流平衡，而垂直湍流的扩散相对较小。对于方差和TKE预算，由于平均流量的收敛（或发散），沿河的对流，压力扩散和冠层阻力的增强消散，森林边缘最重要的过程是生产。湍流扩散，压力再分布和垂直切变产生是均匀冠层流中的典型过程，在森林过渡期的重要性不高。我们证明，在平衡的冠层流中，由平均流的垂直剪切作用在流向产生的大量TKE在垂直方向上由于压力波动而重新分布。这种重新分布过程发生在上部冠层中。垂直速度分量中的一部分TKE通过湍流和压力扩散传递到较低的树冠层，在那里再次发生压力重新分配，并将TKE送回流向。在这个TKE循环中，主要的源项是沿流速度变化的垂直切变生产和沿垂直速度变化的压力再分布。这些主要来源项的演变在森林边缘顺风处很大程度上控制着速度变化的调整率。

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