Modeling the Unsteady Cavitating Flow in a Cross-Flow Water Turbine

The noncavitating and cavitating flows over a cross-flow water turbine are simulated by using an unsteady Navier-Stokes formulation. For the cavitating flow case, a homogeneous mixture with a varying density is considered and one additional transport equation is explicitly solved in time for the liquid volume fraction. The instantaneous rate of vapor production and absorption appearing as a source term is governed by a hydrodynamic model based on a simplified bubble dynamic equation. The spatial discretization is achieved by a 2D multiblock technique consisting of fixed and rotating blocks, which were especially adapted for Darrieus geometry. Several test cases corresponding to experiments performed on fixed and rotating blades are selected to compare the numerical results with experimental data. Finally, a calculation of a monobladed cavitating cross-flow turbine is presented. The effect of cavitation on the dynamic stall phenomenon and on the turbine performance is analyzed. In particular, it is shown that cavitation earlier reveals the stall phenomenon on the blades and magnifies the size of the shedding vortex structures in the turbine. [DOI: 10.1115/1.4001966]