Separation of upslope flow over a uniform slope
Separation of upslope flow over a uniform slope
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DOI：
10.1017/jfm.2015.298
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发表时间：
2015-06
影响因子：
3.7
通讯作者：
C. Hocut;D. Liberzon;H. Fernando
中科院分区：
文献类型：
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作者：
C. Hocut;D. Liberzon;H. Fernando
出于理解热对流期间山地天气的重要性，进行了一项实验室研究，以探究在无背景平均流的情况下二维加热山坡上的上坡（上升）气流的分离情况。确定了三种流态。第一种情况是，当坡度角β大于临界值βc≈20°时，分离流产生一个完全由前部上坡流供给的上升羽流。对于这种情况，提出了一个基于斜压涡度和切变涡度相互平衡的简单模型，以预测分离点相对于山底的位置。该模型还预测了分离时的速度和长度尺度以及分离后上升羽流的相关尺度。在第二种流态中，10°<β≤βc，分离羽流的体积流量并非完全由上坡流提供，需要在羽流源底部卷入额外的环境流体。第三种流态发生在β≤10°时，此时羽流几乎完全吞没山坡，类似于从有限尺寸源发出的浮力羽流，从而遮蔽了上坡流。在MATERHORN实地研究项目期间进行的分离点测量结果与实验室实验和建模结果一致。
Motivated by the importance of understanding mountain weather during periods of thermal convection, a laboratory study was conducted to investigate the separation of an upslope (anabatic) flow on a two-dimensional heated mountainous slope in the absence of a background mean flow. Three flow regimes were identified. In the first, at slope angles ${\it\beta}$ larger than a critical value ${\it\beta}_{c}\approx 20^{\circ }$ , the separated flow generated a rising plume completely fed by the anterior upslope flow. For this case, a simple model based on a balance between the opposing vorticities of baroclinicity and shear was proposed to predict the location of the separation point relative to the mountain base. The model also predicts the velocity and length scales at separation as well as those of the rising plume after separation. In the second regime, $10^{\circ }<{\it\beta}\leqslant {\it\beta}_{c}$ , the volume flow of the separated plume was not fully supplied by the upslope flow, requiring entrainment of additional ambient fluid at the base of the plume source. The third regime occurred when ${\it\beta}\leqslant 10^{\circ }$ , wherein the plume almost completely engulfed the slope, similar to a buoyant plume emanating from a source of finite dimensions, thus overshadowing the upslope flow. Measurements of the separation point conducted during the MATERHORN field research program were consistent with the results of the laboratory experiments and modelling.