Heat Transfer Coefficient and Film-Cooling Effectiveness on a Gas Turbine Blade Tip

Abstract

The detailed distributions of heat transfer coefficient and film cooling effectiveness on a gas turbine blade tip were measured using a hue detection based transient liquid crystal technique. Tests were performed on a five-bladed linear cascade with blow down facility. The blade was a 2-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The Reynolds number based on cascade exit velocity and axial chord length was 1.1 × 106 and the total turning angle of the blade was 97.7°. The overall pressure ratio was 1.32 and the inlet and exit Mach number were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. The blade model was equipped with a single row of film cooling holes at both the tip portion along the camber line and near the tip region of the pressure-side. All measurements were made at the three different tip gap clearances of 1%, 1.5%, and 2.5% of blade span and the three blowing ratios of 0.5, 1.0, and 2.0. Results showed that, in general, heat transfer coefficient and film effectiveness increased with increasing tip gap clearance. As blowing ratio increased, heat transfer coefficient decreased, while film effectiveness increased. Results also showed that adding pressure-side coolant injection would further decrease blade tip heat transfer coefficient but increase film effectiveness.

Gas Turbine Film Cooling

“…In a review paper on tip heat transfer, Bunker 66 states that for a blade tip there has been very little film-cooling research reported in the literature even though film cooling is widely used. Blowing from the tip has been considered by Kim and Metzger, 67 Kim et al, 68 Kwak and Han, 69,70 Ahn et al, 71 Christophel et al, 72 Acharya et al, 73 and Hohlfeld et al 74 Kim et al 68 present a summary of the experimental work that Metzger performed on tip blowing, as shown in Fig. 22.…”

Turbine Blade Cooling Studies at Texas A&M University: 1980-2004

“…Ahn et al 139 presented film-cooling effectiveness results using the PSP technique on a plane and squealer blade tip with one row of holes on the camber line and another row of angled holes near the pressure-side tip. They used the same high flow cascade as the previous study by Kwak and Han 136,137 and investigated the effects of tip-gap clearance (1.0, 1.5, and 2.5 blade span) and blowing ratio (M = 0.5, 1, and 2). Air and nitrogen gas were used as the film-cooling gases, and the oxygen concentration distribution for each case was measured.…”

Modelling of heat transfer and fluid flow in the hot section of gas turbines used in power generation: A comprehensive survey

“…As mentioned by these authors, heat transfer coefficients increase with tip clearance and turbulence intensity. Furthermore, Kwak et al investigated heat transfer on several different squealer geometries. They found that the suction side squealer tips gave the lowest heat transfer coefficient among all the tip geometries tested.…”