Experimental Study on Developed Air Cavities Under a Horizontal Flat Plate

Developed air cavities can be used on the bottom of a ship for frictional drag reduction. An experimental study on the air cavity was carried out in a water tunnel. The cavity was created under a flat plate in the turbulent botmdaiy layer (BL) behind a vertical cavitator.
A parameter study was performed in order to characterize the cavity under the flow conditions. Aspect ratio, pressure in the cavity, air losses and relevant scaling parameters were considered.
It was found that thin cavities become unstable due to relatively strong distortions of the free surface of the cavity. As a
result, the maximum cavity length based on a Froude number criterion could not be reached.