The influence of ventilated cavitation on vortex shedding behind a bluff body

Abstract

The objective of this paper is to investigate the influence of ventilated cavitation on vortex shedding in the wake behind a bluff body at Re = 6.7 × 104 combining high-speed camera and TR-PIV measurement with POD analysis. The results show that three different vortex shedding behaviors exist in the wake. With the increase of gas entrainment coefficient Qv, the ventilated cavity area increases, while the corresponding frequency decreases. The proper orthogonal decomposition (POD) analysis, containing the variations of the POD mode energy, POD coefficients, and POD modes, is used to reveal the influence of ventilated cavitation on the vortex shedding behavior. The results demonstrate that ventilated cavitation affects vortex shedding in both time and spatial scales. In terms of time scales, the frequency of the first two modes reduces with the increase of Qv, which is consistent with the ventilated cavitation vortex shedding frequency obtained by high-speed image processing. In terms of spatial scales, the energy of large-scale structures decreases with the increase of Qv, while the energy of relative small-scale structures increases. Based on the reconstruction by linear combination of the first four POD modes and the mean flow field, we obtain the dominant flow features and the influence of ventilated cavitation on the vortex-shedding process.