Innovative Discrete-Vortex Model for Dynamic Stall Simulations

An innovative model based on the vortex theory is presented with the aim of simulating the two-dimensional airfoil dynamic behavior at pitching reduced frequencies related to vertical axis wind-turbine operative conditions. The model relies on the introduction of a second separated wake from the suction side to correctly account for the aerodynamic effects of stall conditions and is provided with correction models whose aim is to consider the dynamic evolution of the shed vortices and of the separation point. The model receives as input experimental data to estimate the nonoscillating steady-state separation point for different angles of attack. A validation procedure confirmed the model capabilities to provide reliable numerical estimations of the lift coefficient for a pitching airfoil compared to experimental tests and computational-fluid-dynamics approaches based on the unsteady Reynolds-averaged Navier-Stokes equations complemented with the k- shear-stress transport turbulence model. In particular, the dynamic stall phenomenon is correctly simulated, providing lift coefficients in a hysteresis cycle. In addition, the computational effort is strongly reduced compared to the other computational tools and therefore enables the model to be used in routines with several simulation calls (e.g., optimization).