Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls— Part I: Endwall Design and Performance

Abstract

This paper is the first part of a two part paper reporting the improvement of efficiency of a one-and-half stage high work axial flow turbine by nonaxisymmetric endwall contouring. In this first paper the design of the endwall contours is described, and the computational fluid dynamics (CFD) flow predictions are compared with five-hole-probe measurements. The endwalls have been designed using automatic numerical optimization by means of a sequential quadratic programming algorithm, the flow being computed with the 3D Reynolds averaged Navier-Stokes (RANS) solver TRACE. The aim of the design was to reduce the secondary kinetic energy and secondary losses. The experimental results confirm the improvement of turbine efficiency, showing a stage efficiency benefit of 1%±0.4%, revealing that the improvement is underestimated by CFD. The secondary flow and loss have been significantly reduced in the vane, but improvement of the midspan flow is also observed. Mainly this loss reduction in the first row and the more homogeneous flow is responsible for the overall improvement. Numerical investigations indicate that the transition modeling on the airfoil strongly influences the secondary loss predictions. The results confirm that nonaxisymmetric endwall profiling is an effective method to improve turbine efficiency but that further modeling work is needed to achieve a good predictability.

Secondary Flow Loss Reduction in a Turbine Cascade with a Linearly Varied Height Streamwise Endwall Fence

“…Pralsner et al [20] Endwall profiling Total pressure loss coefficient, SKE and TKE (turbulent kinetic energy) Ingram et al [9] Endwall profiling Exit flow angle deviation Germain et al [21] Endwall profiling Combination of total pressure loss coefficient and CSKE Schüpbach et al [22] Endwall profiling CSKE Moon and Koh [2] Streamwise endwall fence Stream wise vorticity no slip condition and are adiabatic. At inlet experimentally measured total pressure profile for 0…”

Effect of the nonaxisymmetric endwall on wet steam condensation flow in a stator cascade

“…12,13 Moreover, the concave streamline curvature can raise the local static pressure and reduce the flow velocity. 17 Ingram conducted similar studies and found that the nonaxisymmetric endwall can increase the efficiency of the high-pressure stage of an aircraft turbine by 0.4%. 14,15 Several achievements have been reported.…”

“…Germain et al found that the nonaxisymmetric endwall can increase the stage efficiency by 1%. 17 Ingram conducted similar studies and found that the nonaxisymmetric endwall can increase the efficiency of the high-pressure stage of an aircraft turbine by 0.4%. 20 Li et al reviewed the existing nonaxisymmetric endwall technology and proposed a new endwall modelling method.…”

“…Thus, the local velocity and pressure distribution are changed and the secondary flow loss is suppressed. 16 Various nonaxisymmetric endwall modelling methods have subsequently been proposed by Germain et al, 17 Harvey et al, 18 Hartland et al, 19 Ingram et al 20 and Axtmann et al 21 ; these methods were applied to turbine guide vanes. 12,13 Moreover, the concave streamline curvature can raise the local static pressure and reduce the flow velocity.…”

“…In 1981, Kopper et al studied the effect of the nonaxisymmetric endwall on secondary flow loss control. 16 Various nonaxisymmetric endwall modelling methods have subsequently been proposed by Germain et al, 17 Harvey et al, 18 Hartland et al, 19 Ingram et al 20 and Axtmann et al 21 ; these methods were applied to turbine guide vanes. Through numerical simulation and a straight cascade blower test, a nonaxisymmetric endwall was found to have an inhibitory effect on the secondary flow loss.…”