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首页> 外文期刊>Journal of the Atmospheric Sciences >Strongly nonlinear flow over and around a three-dimensional mountain as a function of the horizontal aspect ratio
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Strongly nonlinear flow over and around a three-dimensional mountain as a function of the horizontal aspect ratio

机译：三维山上和周围的强烈非线性流动与水平纵横比的关系

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The influence of the obstacle shape, expressed through the ratio of spanwise to streamwise extension beta, on flow over and around a mesoscale mountain is examined numerically. The initial wind U as well as the buoyancy frequency N are constant; the earth's rotation and surface friction are neglected. In these conditions the flow response depends primarily on the nondimensional mountain height H-m = h(m)N/U (where h(m) is the maximum mountain height) and the horizontal aspect ratio b. A regime diagram for the onset of wave breaking, lee vortex formation, and windward stagnation is compiled. When beta is increased, smaller H-m are required for the occurrence of all three features. It is demonstrated that lee vortices can form with neither wave breaking above the lee slope nor upstream stagnation. For beta less than or equal to 0.5 a vortex pair can appear although the isentropes above the lee slope do not overturn for any H-m. For beta> 1, on the other hand, lee vortex formation is triggered by wave breaking. On the windward side two distinct processes can lead to a complete blocking of the flow: the piling up of heavier air ahead of the barrier and the upstream propagation of columnar modes, which are generated by the wave breaking process for beta> 1. "High-drag'' states and "downslope windstorms'' exist above the threshold of wave breaking as long as no lee vortices appear (or, at least, as long as they are very small). Hence, the interval of H-m where a high-drag state occurs becomes progressively larger for larger beta. With the growth of lee vortices the maximum wind speed along the leeward slope is dampened. The normalized drag drops rapidly below its linear counterpart and asymptotically approaches zero. [References: 43]
机译：以数值方式研究了障碍物形状（通过跨度与流向扩展率β之比表示）对中尺度山脉上方和周围的水流的影响。初始风U和浮力频率N是恒定的。忽略了地球的自转和表面摩擦。在这些条件下，流动响应主要取决于无量纲的山高H-m = h（m）N / U（其中h（m）是最大山高）和水平纵横比b。绘制了波浪破裂，lee涡旋形成和迎风停滞开始的状态图。当beta增加时，所有三个特征的出现都需要较小的H-m。事实证明，不会在背风斜面以上破裂或上游停滞的情况下形成背风涡流。对于β小于或等于0.5的情况，尽管在lee斜率上方的等熵线对于任何H-m都不会翻转，但会出现涡旋对。另一方面，对于beta> 1，回波形成会引起回旋涡的形成。在迎风侧，两个截然不同的过程可能导致气流的完全阻塞：在屏障之前堆积大量空气，并通过β> 1的波浪破碎过程产生柱状模态的上游传播。只要没有出现涡旋（或者至少是很小的涡旋），就在波浪破裂的阈值以上存在“拖曳”状态和“下坡风暴”。因此，对于较大的β，发生高拖动状态的H-m的间隔逐渐变大。随着背风涡的增长，沿背风坡的最大风速被衰减。归一化阻力迅速下降至其线性对应值以下，并且渐近趋近于零。 [参考：43]

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