A conjugate study on the application of combined impingement and film cooling for a turbine blade tip

Abstract

The blade tip region is facing an extremely harsh environment, and it is critical to apply the cooling method here. Conventional film cooling (FC) has been commonly used for tip cooling till now, but it consumes a lot of coolant thereby reducing the gas turbine operating efficiency. It has been verified that the combined impingement and film cooling (CIFC) technique shows better cooling performance than the FC case, but its performance on the tip region is not yet known. Therefore, in this paper, the combined impingement and film cooling technique was implemented for the blade tip region, and was compared with the conventional film cooling using a conjugate method. Then, based on the CIFC technique, overall cooling effectiveness (φ) distributions of the tip were obtained via the Infrared thermography with different impingement hole layouts, blowing ratios (M = 1.0–2.5), and relative impingement distances (Xn = 1.5, 3.0, 6.0). The validated numerical simulations were adopted for additional analysis. The results show that, compared with the conventional FC, the application of the CIFC technique can increase the tip φ (increased by 70 %–80 %) and decrease the tip solid temperature. Moreover, the low φ values were detected near the leading edge (LE), and placing more impingement holes near the LE will help increase the φ values here. What’s more, increasing the relative impingement distance would weaken the cooling performance. At a coolant M = 1.0, the φ was decreased by 4.1 % and 12.9 % from Xn = 1.5 to Xn = 6.0, respectively. The application of the CIFC technique for the tip region can diminish the coolant supply and hence can be a reference in the tip cooling design.