A Rapid Method for Predicting Global and Local Performance of Cascades With Special Emphasis on the Calculation of the Transition Region

The principle of a rapid method of cascade performance prediction is presented. It is based on a strong coupling between a potential flow approach and an integral boundary layer method, and takes into account laminar, transitional and turbulent regimes as well as the separated regions. Special emphasis is given to the transitional region. In addition to a pre-existing bubble separation model and following an extensive literature survey, two transition onset and three transition length criteria have been incorporated in the method as well as a Görtler type approach. Comparison of the criteria on typical cascades show that they are relatively coherent between themselves and lead to a satisfactory prediction of the global performance for a large number of different compressor and turbine cascades among which the NACA and DCA cascades discussed in this paper. Local boundary layer performance is compared with Deutsch and Zierke’s data, where, unhappily, transition is chiefly through separation bubbles. The comparison shows the validity of Roberts ‘bubble transition model. Applying the Görtler curvature approach gives similar results to the other criteria. The global performance prediction for this case is also satisfactory. Additionally, parametric studies are carried out on the effect of external turbulence level.