Effects of Ribs on Internal Blade-Tip Cooling

Abstract

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct with relevance for tip cooling of gas turbine blades. The U-duct models the internal blade cooling flow passages. Both friction factors and convective heat transfer coefficients were measured along the bend (turn) part of the U-duct for three different rib configuration cases, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs with three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratios were 10 and 20. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configurations can be changed. The surface temperature was measured by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. Both the friction factor and heat transfer coefficient were affected by the position and configuration of the ribs along the bend wall. The highest friction factor was found for two ribs placed at the middle and outlet positions of the bend wall, respectively. The highest heat transfer coefficient was found for two ribs placed at the inlet and middle positions of the bend wall, respectively. The uncertainties in the experiments were estimated to be 3% and 6% for the Nusselt number and friction factor, respectively.

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

“…A parameter called thermal performance is calculated as shown in Eq. 6 which is used in the literature [38][39][40][41] to calculate the intensity of the drawback of possible pressure drop associated with the augmented heat transfer. This is used to compare the heat transfer enhancement performance at the bend region (total cumulative value for face 3 and 4).…”

Heat Transfer Augmentation Technologies for Internal Cooling of Turbine Components of Gas Turbine Engines

“…Recent investigations of rib turbulators address different rib configurations [143][144][145][146][147][148][149][150][151][152][153][154], as well as a variety of other geometric parameters, such as continuous and truncated ribs [155,156], semiattached rib configurations [157], and effects of a turning vane arrangement within a ribbed internal cooling channel [11,149,158]. A variety of internal flow arrangements are addressed, including extraction flow effects and bleed holes [159,160], different crossflow schemes [161], conjugate heat transfer with crossing jets [162], and impingement and effusion cooling with ribbed surfaces [163,164].…”

Numerical Study on Convective Heat Transfer of Liquid Metal Gallium in Turbine Guide Vane

“…The rib height to hydraulic diameter ratio e/D h = 0.235, and the rib spacing to the rib height ratio p/e = 7.5, have relatively high heat transfer coefficients and low pressure loss. Tareq et al [9] studied the influence of rib placement at the inlet, middle, and outlet of the U-shaped channel on the flow and heat transfer in the channel and found by comparison that the model pressure loss coefficient of the two ribs at the middle and outlet position was the largest, while the model heat transfer coefficient of the two ribs at the entrance and middle position was the largest. With respect to the air film cooling technology of the blades, Gao et al [10] examined the cooling characteristics of the blade surface covered by a full air film with a dustpan hole with a compound angle.…”