Experimental investigation of the flow pattern for ventilated partial cavitating flows with effect of Froude number and gas entrainment

The objective of this paper is to investigate the ventilated partial cavitation flow pattern with experimental methods. The experiments are conducted in a closed-loop cavitation tunnel, and the flow pattern is recorded with a high speed camera. In the experiments, the flow conditions are varied systematically to cover a broad range of water velocity, ventilation flow rate, which correspond to different Froude numbers Fr, gas entrainment coefficients C_Q, respectively. Firstly, a flow pattern map is constructed to depict the flow pattern and structures, i.e. the range of Fr and C_Q. As shown in the flow pattern map, four relatively stable states of a ventilated cavity could be observed, which include three partial cavity, namely continuous transparent and asymmetric cavity (CTAC), bubbly cavity (BC), continuous transparent and bubbly cavity (CTBC), and super cavity (SC). In addition, three unstable flow patterns are also observed, i.e., foamy cavity (FC), continuous transparent and foamy cavity (CTFC), and hybrid continuous transparent and foamy cavity (CFC). It has been observed the Fr number and C_Q play a significant role on the globe ventilated multiphase structures. Moreover, we observed that the differences of the flow patterns lead to discrepancy of the unsteady cavity shedding characteristics.