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Investigation of tip clearance flow physics in axial flow turbine rotors.

机译：轴流式涡轮转子中叶尖间隙流动的物理研究。

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In axial turbines, the tip clearance between casing wall and rotating blades results in a tip leakage flow, which significantly affects loss production, heat protection, vibration and noise. It is important to minimize these effects for a better turbine engine performance and higher reliability. Most of previous efforts were concentrated on turbine cascades that however may not completely and correctly simulate the flow physics in practical turbine rotors. An investigation has to be performed in turbine rotors to reveal the real tip leakage flow physics in order to provide a scientific basis for minimizing its effects. This is the objective of this thesis research.; The three dimensional flow field near the end wall/tip clearance region in a turbine rotor has been investigated experimentally, complemented by a numerical simulation to study the influences of inlet turbulence intensities on the development of the tip leakage flow. The experimental investigation is carried out in a modern unshrouded high pressure turbine stage. The survey region covers 20% span near the end wall, and extends axially from 10% chord upstream of the leading edge, through the rotor passage, and to 20% chord downstream of the trailing edge. It has been found that the tip leakage effects extend only to the surveyed region.; The three dimensional LDV technique is used to measure the velocity and turbulence field upstream of the rotor, inside the rotor passage, and near the trailing edge. The static pressure on blade surfaces is surveyed from the rotating frame. The transient pressure on the casing wall is measured using a dynamic pressure sensor with a shaft encoder. A rotating Five Hole Probe is employed to measure the losses as well as the pressure and the three dimensional velocity field at 20% chord downstream of the rotor. The unsteady flow field is also investigated at this location by using a slanted single-element Hot Wire technique. The physics of the tip leakage flow and vortex in turbine rotors, including its inception location, development, interaction with the main stream and the passage vortex, and decay, are revealed. The rotation effects on the boundary layer flow and the turbulence structure are discussed. The effects of the relative motion between the blade and the casing wall on the flow field near the tip clearance region are also investigated. The structure of the rotor wake, the nozzle wake, and their interaction are interpreted based on the instantaneous Hot Wire data.; The numerical simulation on the influence of the inlet turbulence intensity on the development of the tip leakage flow is based on previous efforts. The results indicate that the tip leakage vortex diffuses very quickly under a high inlet turbulence intensity, resulting in a very weak tip leakage vortex and less losses.
机译：在轴流式涡轮机中，机壳壁和旋转叶片之间的叶尖间隙会导致叶尖泄漏流，这会严重影响损耗产生，热保护，振动和噪音。重要的是最小化这些影响，以获得更好的涡轮发动机性能和更高的可靠性。以前的大多数努力都集中在涡轮机叶栅上，但是这些涡轮机可能无法完全正确地模拟实际涡轮机转子中的流场。必须对涡轮转子进行研究，以揭示真正的叶尖泄漏流物理现象，从而为最小化其影响提供科学依据。这是本文研究的目的。对涡轮转子端壁/叶尖间隙区域附近的三维流场进行了实验研究，并辅以数值模拟研究了入口湍流强度对叶尖泄漏流发展的影响。实验研究是在现代无罩高压涡轮机阶段进行的。调查区域在端壁附近覆盖20％的跨度，并从前缘上游的弦长10％通过转子通道轴向延伸到后缘下游的弦长20％。已经发现，尖端泄漏效应仅扩展到所调查的区域。三维LDV技术用于测量转子上游，转子通道内部以及后缘附近的速度和湍流场。叶片表面上的静压力是从旋转框架中测量的。使用带有轴编码器的动态压力传感器测量套管壁上的瞬态压力。使用旋转的五孔探头测量转子下游20％弦时的损耗以及压力和三维速度场。还通过使用倾斜的单元素热线技术在此位置研究了非稳态流场。揭示了涡轮转子中的尖端泄漏流和涡流的物理原理，包括其起始位置，展开，与主流和通道涡流的相互作用以及衰减。讨论了旋转对边界层流动和湍流结构的影响。还研究了叶片和壳体壁之间的相对运动对叶尖间隙区域附近的流场的影响。转子尾流，喷嘴尾流及其相互作用的结构是根据瞬时热丝数据进行解释的。入口湍流强度对尖端泄漏流发展的影响的数值模拟是基于先前的努力。结果表明，在高入口湍流强度下，尖端泄漏涡旋非常迅速地扩散，从而导致尖端泄漏涡旋非常弱并且损失更少。

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