Experimental studies of hysteresis behavior of partial cavitation around NACA0015 hydrofoil

Partial cavitation is one of the main cavitation regimes occurring in hydrofoil sections. In this study, the effect of gradually increasing and decreasing the angle of attack (alpha) on partial cavitation of hydrofoils, has been investigated. A new hysteresis phenomenon is observed in a difference of partial cavity length in increasing and decreasing of a. The angle of attack (alpha) changed from zero to twenty, then from twenty to zero by a step of two degrees at each level. In each alpha, twelve pictures are taken and optimized using image-processing techniques. Then the partial cavity length is defined as the average value of twelve obtained data. Comparing the results in zero to twenty range by twenty to zero range, hysteresis in partial cavity length is observed. To investigate the repeatability of the results, this procedure is repeated in nine different cavitation numbers varying between 2.35 and 1.72. The same phenomenon is observed in all experiments.