Vortex dynamic analysis of unsteady cavitating flows around a hydrofoil

Vortex dynamics methods were used to analyze the 3-dimensional unsteady cavitating flows around a hydrofoil based on both experimental and numerical results. The experiment was conducted in the cavitation tunnel in Beijing Institute of Technology. High speed video camera technique was used to capture the 3-dimensional cavity evolutions. Filter-based density correction turbulent model and classical interface mass transfer cavitation model were used in the simulations. Comparing with experimental results, the numerical method is able to capture the initiation of the cavity, growth toward the trailing edge, and subsequent shedding. Based on the computations, vorticity transport equations and complex vortex identify methods were conducted to analyze the influence of cavitation on vorticity transport process. Following conclusions can be drawn: re-entrant jet near trailing of attached cavity leads to distinct changes of velocity gradient, which has great influence on production and dissipation of vorticity. Intensive mass transfer between liquid and vapor phase may induce the dilation and baroclinic torque. Two factors mentioned above keep changing and result in unsteady distributions of vorticity. Cavitation may lead to unsteady mass and momentum transfers between liquid and vapor phase, which will change turbulence and vorticity distributions distinctly. With Q and R methods, following conclusions can be drawn: rotation effect is stronger in the area near the leading edge of attached cavity, while rotation and deformation effect work together in area of detached cloud cavity.