Unsteady numerical study of film cooling and heat transfer on turbine blade squealer tip with coolant jet

Abstract

Cooling performance of blade squealer tip with film holes in its cavity was investigated numerically under unsteady condition, and the effects of blowing ratio (BR), cavity depth, and tip clearance were comprehensively discussed. Results show that flow inside tip gap periodically fluctuates and affects the outlet pressure, BR, and jet characteristics of film hole, resulting in unsteady tip cooling effectiveness which could not be observed in steady condition. Average cooling effectiveness on 40-70% axial chord of tip changes the most over time. In comparison to steady result, unsteady time-average cooling effectiveness of tip and its region before 40% axial chord is lower while it is relatively higher in the region after 40% axial chord. Coolant from tip hole located in the flow area of rolling vortex is strongly mixed with rolling vortex, leading to high heat transfer coefficient downstream of that hole. Unsteady leakage flow and boundary layer flow cause stronger heat transfer on squealer rim than steady result. Small BR under unsteady condition could result in insufficient coolant supply and high temperature gas intrusion in tip holes located in 40-70% axial chord of tip. Increasing cavity depth brings longer normal jet distance and higher momentum of coolant, leading to coverage deterioration on floor with a drop in tip average cooling effectiveness of 11.6-34.7%. Large tip clearance causes the distribution of BR to become more uneven, and then more coolant flows out from trailing region, resulting in decrease tendency of average cooling efficiency with change in the range of −23.4%∼6.1% over time compared to base design.