Experimental Investigation on the Effect of Film Exit Parameters on Film Cooling

Supersonic film cooling is an effective method for the thermal protection of key components such as optical windows on hypersonic vehicles. Optimizing film cooling performance under limited coolant mass constraints has become crucial for the development and application of these vehicles. Under Mach 6 wind tunnel conditions, the effects of film exit height (0.5, 1.0, and 2.0 mm) and exit Mach number (2.52, 3.16, and 4.06) on supersonic film cooling performance are systematically studied. The results indicate that at the same coolant mass flow rate, reducing the film exit height can significantly increase the film momentum per unit volume, which offsets the negative effects caused by the reduced exit height. The combined effect of these two factors leads to improved film cooling performance. For the same exit height and mass flow rate, increasing the film Mach number raises the film kinetic energy per unit volume. This enhances the film’s ability to resist mainstream aerodynamic heating, thereby extending the film effective cooling length. Furthermore, a similarity parameter applicable to different exit heights is proposed, based on which a predictive model for film cooling effectiveness is developed. This model accounts for the effect of changes in film geometry and state parameters on the development of the film boundary layer and mixing layer. As a result, its prediction accuracy for film cooling length surpasses that of two existing similarity parameters.