To investigate the three dimensional unsteady flow behind rotating blade rows of turbomachines, a high response pressure probe has been developed. Surface mounted miniature pressure transducers are used to measure the flow fluctuations, while the mean pressures are measured simultaneously with adjacent conventional pressure lead tubes. The steady state and the dynamic behaviour of the probe were investigated. The application of the probe to the rotor exit flow of an axial compressor is described and results are presented.
Up to now the determination of flow conditions across the entire circumference in LP steam turbines appears to be a difficult undertaking. The difficulties are mainly caused by the condensing medium steam and by the limited access to the stage from outside. The Last Stage Test Stand at the University of Stuttgart is a suitable facility for flow measurements in the LP part of steam turbines. Besides a short description of the test stand itself, the measuring equipment and the newly developed methods for data acquisition and evaluation are presented. Finally the flow field behind the last stage is shown and the results interpreted.
In exhaust diffusers of steam turbines pressure oscillations may occur at certain operating conditions, due to shock–boundary layer interactions. These self-excited flow oscillations are caused by the high-speed clearance flow between blade tip and outer contour, leading to an excitation of the running blades. The paper describes the behavior of this unsteady flow phenomenon in the diffuser, identified with steady state and unsteady measurements at the wall, along with probe measurements behind the runner blading. A deeper physical understanding was gained by simulation of this flow pattern on the base of the water analogy.
Improvements of large steam turbines require results from experimental investigations on real turbines. At the Institute fur Thermische Stromungsmaschinen a new Last-Stage test stand has been built providing extended facilities for investigations of flow, steam moisture and vibration phenomona. This contribution presents a description of the test stand with its various set-up configurations for the evaluation of the data to be obtained. The measurement, data acquisition and evaluation systems are explained.
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