Comparisons between forward- and backward-inclined film injection over an effusion wall with internal jet-array impingement: Cooling effectiveness, heat transfer, and analytical model

In a backward injection configuration, the film jets are injected into mainstream flows in a reverse direction, which could effectively weaken the development of kidney vortexes and improve the film coverage and uniformity. This experimental study provides comprehensive and integrated comparisons of forward and backward injection of an effusion wall with internal jet array impingement, concerning heat transfer coefficient, and adiabatic and overall cooling effectiveness. The shapes of the film holes involve cylindrical and fan-shaped holes. Pressure Sensitive Paint technique is applied to measure detailed adiabatic film cooling effectiveness distribution. Heat transfer coefficient is obtained by a steady heat flux method with a film foil heater. Furthermore, a conjugate heat transfer method evaluates combined cooling effect, and resulting overall cooling effectiveness is measured by the infrared technology. Results demonstrate that within the blowing ratios of 0.3-2.0, adiabatic effectiveness peaks at blowing ratios of 0.6 and 1.5 for the cylindrical and fan-shaped film holes with forward injection, and then decreases with further increasing the coolant flow rate. Compared with forward injection, backward injection enhances lateral diffusion of the coolant and reduces sensitivity to blowing ratio, maintaining high external cooling performance under a variety of blowing ratios. However, due to a more vigorous interaction, backward injection produces higher external heat transfer, suppressing superior external cooling at high blowing ratios, thereby resulting in a poorer overall cooling performance. Finally, an analytical model for conjugate heat transfer of impingement-effusion cooling structures is developed and verified.