Secondary Flow in a Two-Dimensional Cascade of High Turning Angle Turbine Blades

Abstract

<p>Modern trends in gas turbine design have been geared to producing a compact high work output engine as a power unit. To achieve this, the turbine rotor must be comprised of high turning angle blades. Secondary flow has always accounted for a major portion of the losses within a blade row and high turning angle blades tend to reinforce these losses. A review of the current literature on secondary flows shows that there is a void of data for two-dimensional high turning angle turbine blade cascades.</p> <p>The object of this study was to construct and experiment upon a large scale two-dimensional high turning angle turbine blade cascade. Each of the four blades within the cascade had a chord and span of 214 mm and 188.5 mm respectively. The overall test rig was an open circuit wind tunnel which was operated at a Reynolds number of 3.68 X 10⁵ (based on the blade chord) which corresponded to a mean blade inlet velocity VI of 26.5 m/s (87 ft/s). The rig was designed with the facility to adjust the inlet flow in the pitchwise direction to ensure periodicity. Suction chambers were installed on the inlet channel endwalls to control the boundary layers and hence observe their effect on the measured secondary losses. The flow parameters were measured and recorded at the inlet bellmouth throat, at the inlet and the exit from the cascade and at a distance of 1.5C in the streamwise direction from the cascade exit.</p> <p>A blade passage surface static pressure distribution is presented and the exit flow parameters are given in the form of contour of total pressure loss coefficients and static pressure coefficients. The spanwise distribution of pitchwise averaged flow parameters is given and the measured losses are reported and compared with existing correlations. The measured losses were found to be significantly lower than those predicted by these correlations.</p>