The Effect of Reynolds and Mach Number on End-Wall Profiling Performance

Abstract

This paper shows an experimental back-to-back comparison carried out between two annular cascades of identical turbine airfoils operating at the same flow conditions; one of them had axysimmetric endwalls and, the other, non-axysimmetric. The annular cascades consisted of 100 high lift, high aspect ratio and high turning blades that are characteristic of modern low pressure (LP) turbines. Upstream and downstream data were obtained with miniature pneumatic probes. The static pressure fields on the airfoil surface and the end-walls were measured with more than 200 sensors. The motivation of this work is to improve the understanding of profiled end-wall performance in the following three aspects: A. Explore the performance of profiled non-axysimmetric end-walls at off design conditions, namely its sensitivity to Reynolds and Mach numbers, analyzing how the turbine characteristics are modified. For that purpose, the experiment was carried out for a wide range of Reynolds numbers, extending from 120k to 315k, and exit Mach numbers, extending from 0.5 to 0.9. B. Determine experimentally the stagnation pressure loss improvement due to profiled non-axysimmetric end-walls in a relevant environment. C. Investigate further the physical mechanisms that govern the variation of stagnation pressure losses of profiled end-walls. CFD results are presented and are compared with experimental results in terms of total pressure loss, helicity and SKEH.

Aerodynamic Loss for a Turbine Blade With Endwall Leakage Features and Contouring

“…Efficiency was slightly improved with endwall contouring for low and design-level loading, but was decreased for high loading. In a study by Vazquez and Fidalgo [17], the performance benefit of a non-axisymmetric contoured endwall did not vary with Reynolds number, but for increasing Mach number, the contoured endwall exhibited higher losses than the baseline as the airfoil became more aft-loaded. Schuepbach, et al [18] considered the combination of rim seal purge flow and endwall contouring and found that the contour resulted in a larger rate of performance degradation with increasing purge flow, relative to a baseline flat endwall.…”