Application of Nonaxisymmetric Endwall Contouring to Conventional and High-Lift Turbine Airfoils

Abstract

Here, we report on the application of nonaxisymmetric endwall contouring to mitigate the endwall losses of one conventional and two high-lift low-pressure turbine airfoil designs. The design methodology presented combines a gradient-based optimization algorithm with a three-dimensional computational fluid dynamics (CFD) flow solver to systematically vary a free-form parameterization of the endwall. The ability of the CFD solver employed in this work to predict endwall loss modifications resulting from nonaxisymmetric contouring is demonstrated with previously published data. Based on the validated trend accuracy of the solver for predicting the effects of endwall contouring, the magnitude of predicted viscous losses forms the objective function for the endwall design methodology. This system has subsequently been employed to optimize contours for the conventional-lift Pack B and high-lift Pack D-F and Pack D-A low-pressure turbine airfoil designs. Comparisons between the predicted and measured loss benefits associated with the contouring for Pack D-F design are shown to be in reasonable agreement. Additionally, the predictions and data demonstrate that the Pack D-F endwall contour is effective at reducing losses primarily associated with the passage vortex. However, some deficiencies in predictive capabilities demonstrated here highlight the need for a better understanding of the physics of endwall loss-generation and improved predictive capabilities.

Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage

“…3). Note that the endwall contour in this study differs from typical designs in that there is a hill near the leading edge suction side, as opposed to the depression found in most other contour designs [24,25]. Simulations performed by MacIsaac, et al [26] for a flat endwall with the same rim seal geometry indicate a large recirculation vortex in the rim cavity that changes the trajectory of the suction side horseshoe vortex around the airfoil leading edge, relative to a smooth endwall.…”

“…A nonaxisymmetric contoured endwall, designed using the methodology described by Praisner et al [24], was employed in the passage of the cascade (see Fig. 3).…”

Measurements and Predictions of the Three-Dimensional Boundary Layer in a Turbine Blade Passage

“…The turbine blade cascade contained seven LPT airfoils based on the Pack-B design, which has been used in several studies of flow control (Bons et al [30] and McAuliffe and Sjolander [31]), end wall secondary flow (Knezevici et al [23] and Praisner et al [32]), and end wall heat transfer (Lynch et al [29] and Mensch and Thole [33]). The scale of the cascade was 8.6 times the engine scale to allow for high measurement resolution.…”

Investigation of improving the hydraulic turbine cascade performance using non-axisymmetric endwall contouring

“…This method has a limited influence on the geometric diversity of endwall profiles, and the modeling results do not represent an optimal contour. 9 Praisner proposed the matrix distribution method of the endwall control points to realize the non-axisymmetric contouring. It was a free parametric modeling method which gave floating upper and lower limits of the control points in radial direction, and then an optimization algorithm was used to choose a better shape.…”