Dynamic effects on airfoil performance under unsteady inflow conditions at high Reynolds numbers*

Dynamic stall is a flow phenomenon where an instantaneous change in flow conditions leads to a momentary increase in the lift force on an airfoil due to the formation of a low-pressure vortex at the leading edge. It occurs on the airfoils of helicopters, wind turbines, and on aircraft wings during maneuvers or fluctuating wind conditions. Most existing experimental data on airfoil performance at high Reynolds numbers was taken under steady conditions, due to the practical challenges of conducting experiments at high Reynolds numbers and the appropriate time scales. As such, data from previous experiments gives limited insight into dynamic stall, or an airfoil’s performance in unsteady conditions at Reynolds numbers relevant for many applications.

Here, we use a pressurized facility to achieve very high Reynolds numbers at low velocities, which enables unsteady investigations at realistic time scales. Lift forces on a two-dimensional symmetrical airfoil, exposed to unsteady inflow conditions, are investigated in attached and separated conditions at high Reynolds numbers. The unique experimental set-up enables tests in real-world flow conditions which can inform both our understanding of this phenomenon and predictive models.