Effects of cooling hole blockage on heat transfer and film cooling effectiveness of gas turbine squealer tip

Abstract

The complex flow fields in the squealer tip region are conducive to the particle deposition and cooling hole blockage of gas turbine blades. The blockage of film cooling hole causes the elevation of heat load and reduction of film cooling effect in the squealer tip gap. In this paper, influences of cooling hole blockage on the film cooling effectiveness and heat transfer on the squealer tip are investigated by means of numerical methods. To describe the degree of hole blockage, the blockage ratio B and the blockage angle β are introduced for the film cooled squealer tip with cooling hole blockage. The film cooling effectiveness and heat transfer coefficient on the squealer tip are obtained at the three blowing ratios (M = 0.5, 1.0, and 2.0), three blockage ratios (B = 0.2, 0.4, and 0.8), and three blockage angles (β = 20°, 30°, and 40°). The results show that the film cooling effectiveness and heat transfer on the squealer tip is highly dependent on the blockage ratio, but not sensitive to the variation of blockage angle. The cooling hole blockage has a profound effect on the coolant ejection velocity and angle. At M = 0.5 and 1.0, the film cooling effectiveness is reduced by 32.11 % and 39.40 % respectively for the blocked case with B = 0.6 and β = 40° compared to the design case (i.e. no blockage), whereas the averaged heat transfer coefficient on the cavity floor for the blocked case with B = 0.6 and β = 20° is increased by 9.77 % and 12.57 % respectively compared to the design case. The effect of cooling hole blockage on the heat transfer coefficient of the squealer tip exhibits irregular characteristic at M = 2.0. The highest heat load is observed on the squealer tip at B = 0.4 and β = 40°, and the lowest film cooling effectiveness is observed at B = 0.4, β = 30°. In these cases, the averaged film cooling effectiveness is decreased by 25.49 % compared to the design cases, and the averaged heat transfer coefficient on the cavity floor is increased by 14.6 %.