Influence of periodic wakes on the unsteady flow near endwalls in full annular axial turbine cascades

目前叶轮机械在提高压比、减少叶片数、减小展弦比、高强度部分负荷运行等方面所做的努力，导致侧壁附近的流动对发动机整体性能的影响越来越大。尤其是这些流动对工作范围、损失和换热都有影响。虽然几十年来一直在研究，但对其发生机制仍未完全了解。因此，当前的技术进步强烈要求有足够的基础研究活动。德累斯顿理工大学、明尼苏达州立大学和波鸿州立大学的四个研究小组将通过仔细协调的模拟和实验来解决这一不足，以产生相关的结果。除了研究传热学和开发有方法的工具外，这个联合项目的一个主要目标是详细分析系统旋转的影响。在波鸿大学热力透平机械教席的项目部分，应通过对轴流全环形轴流透平叶栅进行详细的实验研究，来评估近端壁流与选定的非定常现象之间的相互作用。特别是不能在简化的线性叶栅中再现的效应，因此仅限于全环形叶栅，是关注的焦点。跨跨、曲线和旋转端壁的不均匀间距以及倾斜的入口边界层就是其中之一。借助时间分辨和光学测量技术，需要澄清所检测的机制对端壁区域转变和分离行为的影响，以支持对所涉及的数值模型的紧急验证。在连续的两个装置中，应分析附加诱导的叶尖间隙涡对已识别的相互作用的影响。为了分离压力梯度驱动的尖端流动和通道端壁相对运动的相反影响，将进行固定和旋转通道轮毂轮廓的测量。随后，将与研究伙伴一起评估关于压气机叶栅中叶片尖端流动的结果与涡轮叶栅中的结果的可转换性。为了模拟上游开口叶片尾迹的影响，配备了圆柱杆的转子创造了周期性的非定常静子流入条件。实验数据得到了额外的(U)RANS模拟的补充。

Current efforts in turbomachinery to increase pressure ratio, reduce blade count, decrease the aspect ratio, intense part load operation, etc. lead to increasing influence of flows near the side walls on the overall engine performance. Especially the operating range, losses and heat transfer are influenced by these flows. The occurring mechanisms are not fully understood although being investigated since decades. Thus the current technological progress strongly requests adequate basic research activity. This deficit will be addressed by a joint research program of four research groups at TU Dresden, UniBw München und RU Bochum, by carefully coordinated simulations and experiments to produce relevant results. Beside the investigation of heat transfer and the development of methodical tools a major goal of this joint program is the detailed analysis of the effect of system rotation. Therefor a number of specially planed and adjusted configurations will be investigated and compared with each other.Within the project part at the Chair for Thermal Turbomachinery at Ruhr-Universität Bochum the interaction between near end-wall flow and selected unsteady phenomena should be evaluated by means of detailed experimental investigations in axial full annular axial turbine cascades. Particularly effects, which cannot be reproduced in simplified linear cascades and which are thus limited to full annular cascades are in the focus of attention. Non-uniform pitch across span, curvilinear and rotating end-walls as well as skewed inlet boundary layers are among these. With the aid of time-resolved and optical measurement techniques the impact of the detected mechanisms on transition and separation behavior in the end-wall region is to be clarified to support the urgent validation of involved numerical models. In two consecutive setups the effect of an additionally induced tip clearance vortex on the identified interactions should be analyzed. To separate the opposing effects of pressure-gradient driven tip flow and of the relative-motion of the passage end-wall, measurements will be conducted with fixed as well as rotating passage hub contour. Subsequently the transferability of the results regarding blade tip flow conducted in compressor cascades with the ones from turbine cascades is to be evaluated with the research partners. To simulate the impact of upstream shed blade wakes, a rotor equipped with cylindrical bars creates periodically unsteady stator inflow conditions. The experimental data is complemented by additional (U)RANS simulations.