Numerical investigation of the effect of wedge-type cavitating-bubble generator on attached unsteady cavitating flows using proper orthogonal decomposition method

The objective of this work is to reveal the effect of a passive control method called wedge-type cavitating-bubble generator (WCG) on the cloud cavitation dynamics of National Advisory Committee for Aeronautics (NACA) 66 hydrofoil. The simulations are performed using the Partially-averaged Navier-Stokes (PANS) method coupled with the Zwart cavitation model. The proper orthogonal decomposition (POD) method is applied to extract the dominant flow structures. The results show that the WCG can induce the attached cavity to occur just behind the WCG instead of the hydrofoil leading edge. During the periodical time-evolution process of the unsteady cavity, it is found that the attached cavity with a larger scale around the hydrofoil with WCG has a rougher surface, accompanied with more shedding behaviors of small cavities. This is further illustrated by the POD modes, that is, the mode 1 and modes 2–4 present the large and small cavity vortex structures respectively. Meanwhile, the dominant frequencies of 50 Hz, 47.5 Hz are given by the POD method respectively for the hydrofoils without and with WCG, which is in good agreement with that of FFT analysis. In addition, the correlation distribution of POD modal coefficients shows that the WCG can strengthen the vortex energy as well as the turbulence intensity.