The Effects of Ribs and Tip Wall Distance on Heat Transfer for a Varying Aspect Ratio Two-Pass Ribbed Internal Cooling Channel

Abstract

Internal cooling channels with differing aspect ratios are typically found in gas turbine blades due to the varying thickness of the blade from the leading to trailing edge. These serpentine passages often contain several 180 deg bends, which are sharp edged in the region of the blade tip. The 180 deg bend has a pronounced effect on the heat transfer characteristics in the outlet channel and tip wall, where a strong influence is seen due to the divider wall-to-tip wall distance in the bend. The present study investigates the effect of the divider wall-to-tip wall distance for a ribbed two-pass cooling channel with a 2:1 inlet and 1:1 outlet channel. Spatially resolved heat transfer measurements were made using the transient thermochromic liquid crystal technique for a smooth and a ribbed configuration using parallel 45 deg ribs. Effects of the 180 deg bend on heat transfer and rib-induced enhancements were identified separately and bend effects were found to dominate the heat transfer increase in the outlet channel near the bend. Pressure losses due to the bend and ribs were also independently evaluated for a range of tip wall distances. Results show that the smaller tip wall distances increase heat transfer on the tip wall and outlet channel but at the cost of an increased pressure loss. An optimum tip wall position is suggested, forming a compromise between heat transfer improvement and increased pressure losses.

Numerical study of the influence of rib orientation on heat transfer enhancement in two-pass ribbed rectangular channel

“…It is shown that the overall heat convection strength reaches the highest when the width is 0.88 times the height. A similar conclusion is reached by Jenkins et al (2013) that the small width enhances the downstream heat convection strength in the second pass. Erelli, Saha, and Panigrahi (2015) research the influence of different bend shapes on the forced convection performance and flow energy loss in a two-pass passage.…”

Grid Generation and Fluid-Solid Coupling Methods for the Investigation of Gas Turbine Rotor Blade Internal Cooling

“…It is shown that, for the non-rotating cases, the sensitivity of the overall heat transfer performance to changes in the heating conditions is very low. Numerical simulations match well with our own experiments and the data obtained by Jenkins et al [154]. Tanda [136] reports a heat transfer rate around 8% lower than our own results, but it is within a reasonable range since the aspect ratios of both tests are different.…”

Heat transfer and pressure drop in a smooth and ribbed turn region of a two-pass channel

“…The 90 ribs have higher thermal performance than those of 60 and 45 angled ribs. [26] Smooth outer wall 30 1.8 Jenkins et al [13] Smooth outer wall 100 1.59 Bunker [29] Smooth outer wall 200 1.37 Xie et al [32] Smooth outer wall 200 1.20 Han et al [26] Smooth outer wall, but ribbed inlet and outlet 30 2.5e2.7 Jenkins et al [13] Smooth outer wall, but ribbed inlet and outlet 100 2.27 Present study…”

“…When the inlet/outlet channels were turbulated, larger heat transfer augmentation factors (2.5-2.7 and 2.27) in the turn region were found by Han et al [26] and Jenkins et al [13], respectively. The present study indicates that the ribs on the outer wall improve the average Nusselt number ratio from 1.97 to 2.69-2.92 at Re ¼ 20,000.…”

“…Reducing the turn clearance could augment the heat transfer but high pressure loss is accompanied. Jenkins et al [13] suggested an optimum divider wall-to-tip wall position to achieve the balance between heat transfer improvement and increased pressure losses. Heat transfer in a two-pass channel with varying aspect ratio was investigated by Siddique et al [14,15].…”