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978-3-8439-0588-6, Reihe Strömungsmechanik

Olga Alhaj Optical Investigation of Profile Loss in a Linear Turbine Cascade

83 Seiten, Dissertation Universität Hannover (2011), Softcover, A5

Only few of the multi-dimensional flow visualization techniques have been developed into quantitative measurement techniques which are applicable to turbo machinery flow conditions. This study demonstrates the application of completely optical measurements for the estimation of the loss coefficient of turbine blades in a linear cascade wind tunnel, which represents conditions very near to the real turbomachinery conditions.

Two optical measurement techniques were combined for this purpose. To determine the velocity field of the wake, two-component Particle Image Velocimetry (PIV) was employed. Tomographical Background Oriented Schlieren method (BOS), using 8 cameras placed in 180° around the cascade, was used for measuring a 3-D density field in the wake. The flow and its density gradients were analysed and the image post processing was applied for the BOS measurements. Based on these analyses a simple mathematical model is proposed. This mathematical model can be used for the production of synthetic data which in turn leads to the reduction of the amount of the BOS cameras used. The losses estimated with the optical

techniques are compared with the measurements of 5-hole pressure probes.

The optical techniques are, much faster than any other conventional method, e.g. pneumatic probes. Moreover, optical techniques can be used for investigation of periodically transient flows.