Experimental study on the unsteady characteristics of flow evolution for two vehicles with ventilated partial cavitation

The object of this article is two parallel underwater vehicles with ventilated partial cavitation, which results in partial deformation of the ventilated cavity and is accompanied by nonlinear changes in the internal flow structure. In our experiments, a high-speed camera system was used to observe transient cavity evolution, and dynamic pressure measurement systems were employed to measure pressure fluctuations under different ventilation flow rates and parallel distances. The results indicated that cavity evolution goes through three stages after ventilation begins: the growth stage, the shortening stage, and the periodic shedding stage, with their periods being influenced by different variables. The dominant frequencies of grayscale variation in the three stages are significantly different, as are the pressure variations. Moreover, the dominant frequency of periodic shedding in the two cavities decreases as ventilation flow rates increase. A critical distance of d^* = 1.6 was identified under the experimental conditions, which differentiates the pressure fluctuation characteristics at different parallel distances. Furthermore, the two main mechanisms of pressure fluctuation during the periodic shedding stage were clarified.