Experimental and numerical investigations of a low aspect ratio transonic linear turbine cascade

Abstract

Turbine blades with ultra-low aspect ratio are not covered by loss correlations and the physics of merging secondary flows is only rarely investigated. Experimental investigations in a transonic cascade test-rig with 10 and 6 mm channel height, corresponding an aspect ratio of 0.23 and 0.13 will be presented. The measurement results are compared to numerical cascade simulations representing the same geometry. The influence of the gap flow is evaluated by using test-blades with and without tip clear-ance. The blade turning angle is varied between 70° (zero incidence) and 85° (15° inci-dence). Total and static pressure and total temperature have been measured at the inlet and far outlet. For this reason, a combined pressure/temperature probe was designed and used in the measurement campaign. Moreover, the density field has been determined by using conventional schlieren and background oriented schlieren techniques. Oil film painting was applied on the blades suction sides and end-walls to visualize the near wall shear stress and point out the penetration depth of the secondary flow. The present paper will describe the experimental and numerical setup, compare signif-icant results on both sides to show the CFD validity and finally point out the secondary flow behaviour and its interaction with the gap flow in the transonic ultra-low aspect ratio turbine cascade.