On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient
On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient
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有利压力梯度下湍流点的动量和热结构
DOI：
10.1115/1.2218520
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发表时间：
2006
影响因子：
1.7
通讯作者：
S. Zhong
中科院分区：
文献类型：
--
作者：
T. Chong;S. Zhong
本文介绍了在燃气涡轮机叶片吸力面上观察到的动量边界层和热边界层参数所指示的过渡区长度差异背后的流动物理的实验研究结果。实验是在零压力梯度和有利压力梯度下加热平板上发展的层流边界层中人工产生的湍流斑上进行的。采用一种特殊设计的微型三线探针，在光斑通过过程中同时测量流向速度分量U、横向速度分量V和温度T。本文讨论了整体平均速度和温度扰动、均方根脉动和二阶矩湍流量的一般特性，并考察了有利压力梯度对这些参数的影响。当存在有利的压力梯度时，与在对称平面和展向周边上都出现显著的速度波动和雷诺剪应力的速度边界层不同，高温波动（和湍流热通量）被限制在对称平面内。在这两个位置处的速度/温度波动水平的差异给出了跨斑点跨度的动量/热传递的有效性的指示。研究结果表明，在有利的压力梯度存在的情况下，斑点内的传热比动量传递受到的抑制更大。这种现象预计将减缓过渡热边界层的发展，导致由文献中报道的传热参数指示的更长的过渡区长度。
This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favorable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity component U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations, and the second moment turbulent quantities are discussed and the influence of favorable pressure gradient on these parameters is examined. When a favorable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations and Reynolds shear stress occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (and turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/ temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study indicate that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favorable pressure gradient. This phenomenon is expected to slow down the development of a transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.