Model Studies of a Water Tunnel with an Air-Bubble Resorber Supplement I

The original closed-jet test section designed for use in a 36-in. water tunnel with an air-bubble resorber was cylindrical and 2.18 diameters long. It was followed by a parabolic transition, 0.5 diameter long, to the 7 degree diffuser cone. The effect of diverging test section with a longer diffuser transition in decreasing the pressure gradients and, as a result, lowering the cavitation indices attainable is discussed in this report. Tests on a one-sixth scale model and analyses indicate that a test section diverging at a total angle of about 0 degrees 9.6' would be expected to have an essentially constant core pressure throughout the length of the test section. This divergence angle followed by a nearly 1-diameter transition should result in a test section which can be operated at cavitation indices as low as 0.025 or 0.030 at velocities of 84.5 fps.