The Determination of Turbulent Skin Friction by Means of Pitot Tubes
The Determination of Turbulent Skin Friction by Means of Pitot Tubes
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DOI：
10.1017/s0368393100097704
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发表时间：
1954-02
期刊：
影响因子：
--
通讯作者：
J. H. Preston
中科院分区：
文献类型：
--
作者：
J. H. Preston
本文提出了一种利用放置在光滑表面上的圆皮托管来确定光滑表面上局部湍流表面摩阻的简单方法。假定表面附近存在一个区域，在该区域内的条件只是表面摩擦、流体的有关物理常数和适当长度的函数，得到了管子记录的总压力与壁面静压之差与表面摩擦的普遍无量纲关系。在这个假设下，这个关系与压力梯度无关。这种关系的真实性和形式首先是在使用四个几何上相似的圆形皮托管的管道中建立的，其精度相当高--直径被认为是代表长度。然后利用这四根皮托管在不同的压力梯度条件下，测定了风洞壁上三个站点的局部摩擦系数。在每个测站，在实验精度范围内，对于每个皮托管，推导出的壁面摩擦系数是相同的，从而证实了基本假设，并对所得的壁面摩擦的正确性几乎没有疑问。然后在管子和风洞壁上的边界层中进行皮托管横移。结果在已经提出的基础上以两种无量纲形式绘制，它们在一个区域内紧密相连，该区域的外部极限代表了基本假设的崩溃，但由于皮托管的有效中心靠近壁面的未知位移，结果在壁面附近展开。这再次提供了进一步的证据，证明了局部动力相似区域的存在，以及用风洞壁上的圆形皮托管测量得出的壁面摩擦的正确性。对于远离分离和接近分离的条件，局部动力相似可能保持的区域的范围似乎分别从边界层厚度的约1/5到1/20变化。
Summary A simple method of determining local turbulent skin friction on a smooth surface has been developed which utilises a round pitot tube resting on the surface. Assuming the existence of a region near the surface in which conditions are functions only of the skin friction, the relevant physical constants of the fluid and a suitable length, a universal non-dimensional relation is obtained for the difference between the total pressure recorded by the tube and the static pressure at the wall, in terms of the skin friction. This relation, on this assumption, is independent of the pressure gradient. The truth and form of the relation were first established, to a considerable degree of accuracy, in a pipe using four geometrically similar round pitot tubes—the diameter being taken as representative length. These four pitot tubes were then used to determine the local skin friction coefficient at three stations on a wind tunnel wall, under varying conditions of pressure gradient. At each station, within the limits of experimental accuracy, the deduced skin friction coefficient was found to be the same for each pitot tube, thus confirming the basic assumption and leaving little doubt as to the correctness of the skin friction so found. Pitot traverses were then made in the pipe and in the boundary layer on the wind tunnel wall. The results were plotted in two non-dimensional forms on the basis already suggested and they fell close together in a region whose outer limit represented the breakdown of the basic assumption, but close to the wall the results spread out, due to the unknown displacement of the effective centre of a pitot tube near a wall. This again provides further evidence of the existence of a region of local dynamical similarity and of the correctness of the skin friction deduced from measurements with round pitot tubes on the wind tunnel wall. The extent of the region in which the local dynamical similarity may be expected to hold appears to vary from about 1/5 to 1/20 of the boundary-layer thickness for conditions remote from, and close to, separation respectively.