What cooling method involves a cool jet of gas being ejected into the boundary layer of an airfoil?

The cooling method that involves a cool jet of gas being ejected into the boundary layer of an airfoil is known as surface film cooling. This technique is particularly effective in gas turbine engines, where it helps to manage the temperature of surfaces exposed to high levels of thermal stress.

In surface film cooling, the cool gas creates a protective layer along the surface of the airfoil, which helps to reduce the temperature of the material beneath. By injecting a stream of cooler gas, it alters the thermal profile in the vicinity of the airfoil and mitigates overheating, thus protecting the structural integrity of the engine components. This method is crucial for extending the life of the airfoil and enhancing the efficiency and performance of the engine.

Other cooling methods mentioned, such as direct cooling, conduction cooling, and radiant cooling, involve different principles and mechanisms that do not specifically utilize the technique of injecting gas into the boundary layer to achieve cooling effects on airfoils. Each of these methods has its unique applications, but they do not operate in the same manner as surface film cooling does.