Experimental Analysis of Geometric, Pressure Gradient and Surface Temperature Effects on Boundary-Layer Transition in Compressible High Reynolds Number Flows
Experimental Analysis of Geometric, Pressure Gradient and Surface Temperature Effects on Boundary-Layer Transition in Compressible High Reynolds Number Flows
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几何、压力梯度和表面温度对可压缩高雷诺数流动边界层转变影响的实验分析
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发表时间：
2016
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通讯作者：
M. Costantini
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作者：
M. Costantini
本实验结合流向压力梯度、雷诺数、马赫数和非绝热表面等参数变化的影响，系统地研究了急剧的前向台阶对边界层转变的影响。研究是在哥廷根低温路德维格管中以高雷诺数以及低和高亚音速马赫数进行的准二维流中进行的。采用的实验设置允许上述参数的独立变化，并能够解耦它们各自对边界层转变的影响。通过对温度敏感的涂料进行非侵入式测量，发现随着台阶雷诺数和相对台阶高度的增加，过渡逐渐向上游移向台阶位置。即使存在前向台阶，更强的流动加速度和更低的壁温比也会导致过渡雷诺数增加；然而，当无量纲步骤参数值较大时，这种有利的影响变得不那么明显。使用过渡位置相对于台阶位置的相对变化来表示结果，针对无量纲台阶参数绘制，给出了良好的相关性，并且允许将台阶对边界层过渡的影响与其他参数变化的影响隔离开来。目前的结果被证明适用并可转移到自然层流翼型的实际情况。现在可以从本工作中确定的函数关系中得出未扫掠和适度扫掠的自然层流表面上可接受的前向台阶高度的标准。
The effect of sharp forward-facing steps on boundary-layer transition was systematically investigated in this experimental work in combination with the influence of changes in the following parameters: streamwise pressure gradient, Reynolds number, Mach number, and a non-adiabatic surface. The investigations were carried out in a quasi-two-dimensional flow at high Reynolds numbers and at both low and high subsonic Mach numbers in the Cryogenic Ludwieg-Tube Gottingen. The adopted experimental setup allowed an independent variation of the aforementioned parameters and enabled a decoupling of their respective effects on the boundary-layer transition. Transition, measured non-intrusively by means of temperature-sensitive paint, was found to move gradually upstream towards the step location with increasing step Reynolds number and relative step height. Stronger flow acceleration and lower wall temperature ratios led to an increase in the transition Reynolds number even in the presence of forward-facing steps; this favorable influence became, however, less pronounced at larger values of the non-dimensional step parameters. The representation of the results using the relative change in transition location with respect to the step location, plotted against the non-dimensional step parameters, gave good correlation and allowed the effect of the steps on boundary-layer transition to be isolated from the influence of variations in the other parameters. The present results were demonstrated to be applicable and transferable to the practical case of a natural laminar flow airfoil. Criteria for acceptable heights of forward-facing steps on unswept and moderately swept natural laminar flow surfaces can now be derived from the functional relations determined in this work.