Effect of a Cutback Squealer and Cavity Depth on Film-Cooling Effectiveness on a Gas Turbine Blade Tip

Abstract

Film-cooling effectiveness from shaped holes on the near tip pressure side and cylindrical holes on the squealer cavity floor is investigated. The pressure side squealer rim wall is cut near the trailing edge to allow the accumulated coolant in the cavity to escape and cool the tip trailing edge. Effects of varying blowing ratios and squealer cavity depth are also examined on film-cooling effectiveness. The film-cooling effectiveness distributions are measured on the blade tip, near tip pressure side and the inner pressure side and suction side rim walls using pressure sensitive paint technique. The internal coolant-supply passages of the squealer tipped blade are modeled similar to those in the GE-E3 rotor blade with two separate serpentine loops supplying coolant to the film-cooling holes. Two rows of cylindrical film-cooling holes are arranged offset to the suction side profile and along the camber line on the tip. Another row of shaped film-cooling holes is arranged along the pressure side just below the tip. The average blowing ratio of the cooling gas is controlled to be 0.5, 1.0, 1.5, and 2.0. A five-bladed linear cascade in a blow down facility with a tip gap clearance of 1.5% is used to perform the experiments. The free-stream Reynolds number, based on the axial chord length and the exit velocity, was 1,480,000 and the inlet and exit Mach numbers were 0.23 and 0.65, respectively. A blowing ratio of 1.0 is found to give best results on the pressure side, whereas the tip surfaces forming the squealer cavity give best results for M=2. Results show high film-cooling effectiveness magnitudes near the trailing edge of the blade tip due to coolant accumulation from upstream holes in the tip cavity. A squealer depth with a recess of 2.1mm causes the average effectiveness magnitudes to decrease slightly as compared to a squealer depth of 4.2mm.

Turbine Blade Film Cooling Using PSP Technique

“…(e.g. Wright et al (2005); Ahn et al (2005); Mhetras et al (2008a)). More recently, it has been possible to simulate actual engine density ratios using the PSP mass transfer analogy.…”

“…In general, the literature agrees that a higher blowing ratio and a lower tip clearance result in better film cooling performance. Ahn et al (2005) and Mhetras et al (2008a) measured effectiveness using the PSP technique with holes on the pressure side (tip region) and the tip. Gao et al (2009b) characterized the effect of blade angle-of-attack on film cooling effectiveness using the PSP technique.…”

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

“…Based on the squealer tip, the cutback squealer tip is developed as a newly designed tip configuration for the cooling method. Mhetras et al 10 found that the gathered coolant flow in the squealer cavity flows outside through the cutback region, cooling the trailing edge at the same time.…”

“…He proved the general rule that a deeper cavity produces lower HTC is true. Mhetras et al 10 found that a larger cavity depth can strengthen the flow reattachment near the leading edge on the cavity floor, and the recirculation velocity is higher for a small cavity depth.…”

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

“…In addition, with the increase of blowing ratio the heat transfer coefficient decreases and the film-cooling effectiveness increases. Mhetras et al (2006Mhetras et al ( , 2008 investigated the film-cooling effectiveness on the blade tip and near tip regions. They found that the geometry and location of film-cooling holes affect the film-cooling performance significantly.…”