Instantaneous aerodynamic load calculations in rotating airfoils from time resolved PIV measurements at low reynolds number

The time-resolved evolution of the instantaneous pressure fields and aerodynamic loads are obtained for rotating airfoils. This method allows evaluating the fluctuations in the instantaneous aerodynamic loads which cannot be evaluated with averaging methods. It also has the ability of capturing high temporal variations such as vortex shedding in the wake of the rotating blade. Briefly, this method obtains the velocity field from time-resolved particle image velocimetry TR-PIV. This is used to calculate the pressure field around the turbine from the Poisson pressure equation. Then, the forces are obtained using the integral momentum equation in a stationary reference frame. These experimental aerodynamic loads are compared to theoretical predictions from the Blade Element Momentum theory (BEM). Accurately determining instantaneous forces in turbines is needed for safety and understanding of their full range of operation. The standard deviation of the instantaneous forces establishes the limits of the forces expected on the turbine. The uncertainty in the measurements is calculated. The method presented may be used to measure unsteady forces in rotating airfoils, providing useful information not just for computational studies, but also for aerodynamics, material and structural optimization and safety purposes.