Experimental and numerical investigation on the cavity regime and drag reduction of ventilated partial cavity

Abstract

This study presents the experimental and numerical investigation on the ventilated partial cavity (VPC) under the influence of the 3-D flow effect (i.e. the flow non-uniformity induced by the lateral space). The VPC is generated from the backward-facing step of a flat plate in water tunnel. The computational fluid dynamics together with the VOF method is applied to simulate the cavity flow. Four cavity regimes are clarified, referred to as two-branch cavity (TBC), single-tail cavity (STC), intermittent fully covered cavity (IFCC), and fully covered cavity (FCC). The cavity length of TBC in current experiments is much smaller than that observed in experiments of 2D wall-mounted cavitators. This contradictory observation is attributed to the stream-wise vortexes induced by the 3-D flow effects. The stream-wise vortexes induce local low-pressure cores and make cavity branches easier to extend downstream. The cavity length and drag reduction of VPC are both found to first increase linearly and then plateaus with ventilation rate. For TBC and STC, the drag reduction is only determined by the cavity coverage. For FCC and IFCC, no clear relevance of cavity length and drag reduction is observed, which means the stability of IFCC and FCC should be taken into consideration.