Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade

Abstract

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. 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 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.

Effect of film-hole configuration on film-cooling effectiveness of squealer tips

“…For type-A, a strip zone with high film-cooling effectiveness appears close to the pressure-side squealer, as seen in Figure 9(a). This feature is well validated by the experimental result (Kwak and Han (2003a)). Also, because the coolant jet is mainly directed toward the pressure-side squealer and exhausts out of the tip from the rear suction-side squealer, the top surface of squealer in the rear section of blade is effectively protected by the coolant flow.…”

“…Figure 5 shows the comparison between the current numerical result and the experimental result of Kwak and Han (2003a) for the film-cooling effectiveness on the squealer tip. It is seen that the distribution features of film-cooling effectiveness illustrated by the experiment of Kwak and Han (2003a) are also observed in the current numerical simulation. The high film-cooling effectiveness appears on the local zone between the middle camber line and the pressure-side squealer (marked as 'A').…”

“…In order to validate the numerical method, a computational model is built according to the experimental model of Kwak and Han (2003a). Figure 5 shows the comparison between the current numerical result and the experimental result of Kwak and Han (2003a) for the film-cooling effectiveness on the squealer tip.…”

“…Their results indicated that the cooling air ejected Cheng, Chang, Zhang and Tian, Journal of Thermal Science and Technology, Vol.12, No.1 (2017) from discrete slots provides better film protection than the traditional round film holes under a given mass flow ratio. Kwak et al (2003a) experimentally studied the effect of film-cooling on the thermal performance of squealer and flat tips. Their results showed that the film-cooled squealer tip achieves better thermal performance than the film-cooled flat tip.…”

Effects of casing motion on tip leakage flow and film-cooling effectiveness of squealer tips

“…The accuracy of the numerical method is validated by applying it to a simulation of an experimental case (kwak and Han, 2003). The computational model and boundary conditions are the same as the experiment.…”