Measurements of Endwall Flows in Transonic Linear Turbine Cascades: Part I—Low Flow Turning

Abstract

The current two part paper presents the results of an experimental investigation of the endwall flows in four transonic linear turbine cascades with two levels of flow turning: 90° and 112° of total flow turning, respectively. For each case, two levels of aerodynamic loading were examined. Part I of the paper examines the low-turning case. A seven-hole pressure probe was used to document the flow fields downstream of the cascades. The experimental results include blade surface pressure distributions, total pressure losses, secondary kinetic energy and streamwise vorticity distributions. The turbine cascades considered in Part I are referred to as SL3F and SL4F (exit Mach number ≈ 0.8). The airfoils have the same inlet and outlet design flow angles, but different aerodynamic loading levels: SL4F has a Zweifel coefficient that is 30% higher than that for SL3F. The midspan flow measurements indicate that SL4F produces higher profile losses than SL3F. SL4F also exhibits stronger secondary flow with larger exit flow-angle variations. Consequently, SL4F produces higher secondary losses. Growth of secondary losses has been documented by collecting additional measurements downstream of the SL3F cascade. Vortex dissipation and endwall boundary layer growth result in additional secondary losses. The loss coefficients and the secondary flow parameters are integrated over the entire measurement plane to present their individual contributions to total entropy generation. In this context, the profile and secondary loss results from two different loss-breakdown schemes are presented and compared. The treatment of near-endwall losses in the absence of detailed pressure probe results is also discussed here.