Confinement effects in wind-turbine and propeller measurements

Abstract

AbstractA new model to account for the presence of the test-section wall in wind-turbine or propeller measurements is proposed. The test section, here assumed to be cylindrical, is modelled by means of axisymmetric source panels, while the wind turbine (or the propeller) is modelled with a simplified vortex model (Segalini & Alfredsson, J. Fluid Mech., vol. 725, 2013, pp. 91–116). Combining both models in an iterative scheme allows the simulation of the effect of the test-section wall on the flow field around the rotor. Based on this novel approach, an analysis of the flow modification due to blockage is conducted together with a comparison of actuator-disk theory results. Glauert’s concept of equivalent unconfined turbine is reviewed and extended to account for the angular velocity of the rotor. It is shown that Glauert’s equivalent free-stream velocity concept is beneficial and can correct most of the systematic error introduced by the presence of the test-section wall, although some discrepancies remain, especially in the power coefficient. The effect of the confinement on the wake structure is also discussed in terms of wake expansion/contraction, pitch of the tip vortices and forces at the rotor.