Effect of the gradient of the velocity of the flow on the effectiveness of a gas curtain in axisymmetric nozzles

Cooling curtains set up in axisymmetric nozzles to protect surfaces from the thermal action of gas flows were studied to determine the effect of a strong acceleration in the axisymmetric main flow on the insulation capacity of the curtains. The experimental apparatus included two nozzles of similar geometry, capable of producing different flow accelerations corresponding to maximum velocity gradient values of 22,000 and 42,000 per sec. The data indicated that the effectiveness of the gas curtain is decreased by an increase in the velocity gradient of the main flow.