Effect of Endwall Contouring on a Transonic Turbine Blade Passage: Part 2—Heat Transfer Performance

Abstract

Contouring of turbine endwalls has been widely studied for aerodynamic performance improvement of turbine passages. However, it is equally important to investigate the effect of contouring on endwall heat transfer, because a substantial increase in endwall heat transfer due to contouring will render the design impractical. In this paper, the effect of contouring on endwall heat transfer performance of a high-turning HP-turbine blade passage, operating under transonic exit Mach number conditions, is reported. Three endwall geometries were experimentally investigated at three different passage exit Mach numbers, 0.71, 0.88(design) and 0.95, for their heat transfer performance. One endwall is a non-contoured baseline endwall and the other two are contoured endwall geometries. One of the contoured endwall geometry was generated with the goal of reduction in stagnation pressure losses and the other was generated with the goal of reduced overall heat transfer through the endwall. The experiments were carried out in Virginia Tech’s transient, blow down, transonic linear cascade facility. Endwall surface temperatures were measured using infrared thermography technique. Local heat transfer coefficient values were calculated using the measured temperatures. The heat transfer coefficient values were then related to the endwall geometries using a camera matrix model. The measurement technique and the methodology for the post-processing of the heat transfer coefficient data have been presented in detail. Details of the flow behavior for these endwalls were obtained using CFD simulations and have been used to assist the interpretation of the experimental results. In this study, the heat transfer performance of the contoured endwalls in comparison to the non-contoured baseline case is presented. Both the contoured endwalls demonstrated a significant reduction in the overall average heat transfer coefficient values. The surface heat transfer coefficient distributions also indicated a reduction in the level of hot spots for most of the endwall surface. However, increase in the heat transfer coefficient values was observed especially in the area near the leading edge. The results indicate that, in addition to a probable improvement in aerodynamic performance, endwall contouring may also be used to improve the heat transfer performance of turbine passages. Additionally, aerodynamic behavior of these endwalls is discussed in detail in the companion paper GT2012-68425, “Effect of endwall contouring on a transonic turbine endwall: Part 1 – Aerodynamic performance.”

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

“…Saha and Acharya [16] computationally evaluated nine endwall shapes and found that the best design reduced overall heat transfer by 8%, with significant reductions of over 300% near the suction side (SS) leading edge and approximately 20% in the throat compared to a flat endwall. Panchal et al [17] also found reductions in local and endwall-average heat transfer at high subsonic conditions for contoured endwalls, attributed to redirection of the passage vortex with contouring. A contour studied by Lynch et al [18] (same as in this study) significantly decreased endwall heat transfer near the PS of the passage relative to a flat endwall, which was attributed to reduced strength of the passage vortex.…”

“…The linear cascade ( Fig. 1(b)) contained seven blades based on a low-pressure turbine airfoil geometry that has been studied extensively in the literature, particularly with regards to nonaxisymmetric endwall contouring [14][15][16][17][18][19]. Table 1 lists the geometrical parameters and operating conditions for the cascade.…”

Computational and Experimental Studies of Midpassage Gap Leakage and Misalignment for a Non-Axisymmetric Contoured Turbine Blade Endwall

“…Many studies have focused on aerodynamic optimization (reduced exit flow angle deviation [3,4], or reduced total pressure loss [5,6]). Endwall heat transfer performance has also been considered as a driving metric [7,8]. In most cases, experiments indicate that an aerodynamically optimized endwall also has improved heat transfer performance ( [7,9]).…”

“…Endwall heat transfer performance has also been considered as a driving metric [7,8]. In most cases, experiments indicate that an aerodynamically optimized endwall also has improved heat transfer performance ( [7,9]). Many other studies have demonstrated the effectiveness of contouring in rig and engine environments (e.g., [10,11]).…”