Water tunnel tests of NACA 4412 and Walchner profile 7 hydrofoils in noncavitating and cavitating flows

Abstract

The results of force and cavitation tests on two hydrofoils in two-dimensional flow are presented. The hydrofoils are the NACA 4412 profile and a modified circular arc, flat plate, hydrofoil designated as a Walchner profile 7. The results of experiments performed in wind tunnels and in other water tunnels are presented for comparison. The experiments described in this report are the first tests using the High Speed Water Tunnel two-dimensional working section and the new force balance; therefore, the experimental setup, procedure and methods of data reduction have been described in detail. 
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\nThe results of the tests on the NACA 4412 hydrofoil are in good agreement with those obtained for this profile in the Langley two-dimensional low-turbulence wind tunnel. The results of the tests on the circular arc, flat plate hydrofoil are not in good agreement with the results obtained by Walchner for cavitating flow. The differences in the forces on the hydrofoils can be accounted for with a difference in cavitation number of approximately 0.1. 
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\nThe tests indicate that accurate force measurements can be made with the new water tunnel force balance and that the methods developed during these tests provide a satisfactory means of obtaining the section characteristics of hydrofoils in cavitating and noncavitating flow.