Improvement of film cooling effectiveness on a flat surface subjected to streamwise pressure gradient by using ramp

Abstract

In this study, a numerical study was performed to elucidate the influence of triangular with concave edge shaped (TCES) ramp on film cooling effectiveness (FCE) and flow characteristics. Since the turbine airfoil subjects to the streamwise pressure gradient (SPG) in real operating conditions, the influence of various SPG in which acceleration parameters (K) are −1.20 × 10−6, 0, 0.45 × 10−6, 0.8 × 10−6, 1.50 × 10−6 and 2.13 × 10−6 on FCE were investigated comprehensively. Numerical computations were carried out with various blowing ratio (M) including 0.40, 0.85, 1.00 and 1.25 to explore the performance of TCES on FCE under different blowing ratio. On the other hand, three different ramp locations on the surface were investigated to evince the optimum design parameter of the TCES ramp. Results were compared with the baseline case. Air was used as the hot gas flow for the turbine airfoil and CO2 was assumed to be the coolant flow to simulate the real operation condition of the turbine. Therefore, corresponding density ratio of the fluids is DR = 1.50. Numerical simulations were performed using SST k-ω with low-Re correction turbulence model. Flow characteristics and area-averaged, laterally-averaged, longitudinally-averaged FCE were investigated quantitatively. Results showed that mounting TCES ramp on the surface has a great potential for the enhancement of FCE by forming a pair of anti-CRV on the flow that counteracts the detrimental effect of CRV on FCE. Hereby, area-averaged FCE enhanced 435.15% using upstream TCES ramp (Case2) at K = 0.45 × 10−6 and M = 1.25 compared to the baseline case. On the other hand, the favorable pressure gradient (FPG) contributed to the enhancement of FCE by tilting jet stream towards the wall. Consequently, upstream TCES ramp was the best design for laterally spreading the coolant and showed the best performance for thermal protection of turbine airfoil from the hot working fluid compared to other cases.