The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Pin fins are commonly used to augment heat transfer by increasing surface area and increasing turbulence. The present research is focused on but not limited to internal cooling of turbine airfoils using pin fins. Although the pin fins are not limited to a single shape, circular cross-sections are most common.The present study examines heat transfer from a single row of circular pin fins with the row oriented perpendicular to the flow. The configurations studied have spanwise spacing to pin diameter ratios of two, four, and eight. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. The experiments are

The hypothesis, posed in Part I [1], that excessive endwall loss of high lift low pressure turbine (LPT) airfoils is due to the influence of high stagger angles on the endwall pressure distribution and not front-loading is evaluated in a linear cascade at Re = 100,000 using both experimental and computational studies. A nominally high lift and high stagger angle front-loaded profile (L2F) with aspect ratio 3.5 is contoured at the endwall to reduce the stagger angle while maintaining the front loading. The contouring process effectively generates a fillet at the endwall, so the resulting airfoil is referred to as L2F-EF (Endwall Fillet). Although referred to as a fillet, this profile contouring process is novel in that it is designed to isolate the effect of stagger angle on endwall loss. Total pressure loss measurements downstream of the blade row indicate that the use of the lower stagger angle at the endwall reduces mixed out mass averaged endwall and passage losses approximately 23% and 10% respectively. This is in good agreement with computational results used to design the contour which predict 18% and 7% loss reductions. The endwall flow field of the L2F and L2F-EF models is measured using stereoscopic particle image velocimetry (PIV) in the passage. These data are used to quantify changes in the endwall flow field due to the contouring. PIV results show that this loss reduction is characterized by reduced inlet boundary layer separation as well as a change in strength and location of the suction side horseshoe vortex (SHV) and passage vortex (PV). The endwall profile contouring also produces a reduction in all terms of the Reynolds stress tensor consistent with a decrease in deformation work and overall flow unsteadiness. These results confirm that the stagger angle has a significant effect on high-lift front-loaded LPT endwall loss. Low stagger profiling is successful in reducing endwall loss by limiting the development and migration of the low momentum fluid associated with the SHV and PV interaction.

This paper presents the reasoning for and the design process of contouring a high lift front-loaded low pressure turbine (LPT) airfoil near the endwall to reduce the endwall loss. The test airfoil, L2F, was designed to the approximate gas angles with 38% larger pitchwise spacing than the widely studied Pack B airfoil. Being more front-loaded with a higher stagger angle, L2F is shown to produce more endwall losses than Pack B. It is suggested that the high endwall loss of L2F is due to the high stagger angle, not front-loading as usually suggested in the literature. A procedure is presented to approximate the front-loading and stall resistance of L2F and obtain a low stagger version of that airfoil, designated L2F-LS. A contoured airfoil is then designed by transitioning L2F into L2F-LS at the endwall to obtain a benefit from the reduced stagger angle at the endwall. The contouring process generates a fillet, so the contoured airfoil is referred to as L2F-EF (“Endwall Fillet”). Predictions in this paper suggest endwall loss reductions between 17% and 24% at Re = 100,000. Linear cascade experiments in Part II [1] of this paper indicate that L2F-EF reduces endwall losses more than 20% compared to L2F. The overall conclusion is that the stagger angle has a significant effect on endwall loss and should be considered for designing high lift LPT airfoils at the endwall.

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Pin fins are commonly used to augment heat transfer by increasing surface area and increasing turbulence. The present research is focused on but not limited to internal cooling of turbine airfoils using pin fins. Although the pin fins are not limited to a single shape, circular cross-sections are most common.The present study examines heat transfer from a single row of circular pin fins with the row oriented perpendicular to the flow. The configurations studied have spanwise spacing to pin diameter ratios of two, four, and eight. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. The experiments are

The hypothesis, posed in Part I, that excessive end wall loss of high lift low pressure turbine (LPT) airfoils is due to the influence of high stagger angles on the end wall pressure distribution and not front loading is evaluated in a linear cascade at Re = 100,000 using both experimental and computational studies. A nominally high lift and high stagger angle front-loaded profile (L2F) with aspect ratio 3.5 is contoured at the end wall to reduce the stagger angle while maintaining the front loading. The contouring process effectively generates a fillet at the end wall, so the resulting airfoil is referred to as L2F-EF (end wall fillet). Although referred to as a fillet, this profile contouring process is novel in that it is designed to isolate the effect of stagger angle on end wall loss. Total pressure loss measurements downstream of the blade row indicate that the use of the lower stagger angle at the end wall reduces mixed out mass averaged end wall and passage losses approximately 23% and 10%, respectively. This is in good agreement with computational results used to design the contour which predict 18% and 7% loss reductions. The end wall flow field of the L2F and L2F-EF models is measured using stereoscopic particle image velocimetry (PIV) in the passage. These data are used to quantify changes in the end wall flow field due to the contouring. PIV results show that this loss reduction is characterized by reduced inlet boundary layer separation as well as a change in strength and location of the suction side horseshoe vortex (SHV) and passage vortex (PV). The end wall profile contouring also produces a reduction in all terms of the Reynolds stress tensor consistent with a decrease in deformation work and overall flow unsteadiness. These results confirm that the stagger angle has a significant effect on high-lift front-loaded LPT end wall loss. Low stagger profiling is successful in reducing end wall loss by limiting the development and migration of the low momentum fluid associated with the SHV and PV interaction.