Flow field and forces on a highly curved plate

Abstract

While both slender wings and bluff bodies are the usual focus of classical fluid dynamics, the behavior of a high-lift not-so-slender body remains somehow original. This work presents an experimental investigation of a high-camber curved thin plate with a sharp leading edge, in a wide range of angle of attack (-10° to 28°), at a Reynolds number of 1:82:105. Forces are measured with a strain-gauge balance and the flow field is determined thanks to time-resolved 2D Particle Image Velocimetry (PIV) in a nominally 2D flow. Despite this very simple geometry, the section generates a high lift and shows a rather original behavior, with characteristics of both bluff and slender lifting bodies. The sectional lift coefficient is estimated by the velocity circulation around the section from the PIV fields. The time-averaged lift computed from the circulation compares reasonably well with the lift measured by the force balance, even in the presence of flow separation. Furthermore, the sectional lift coefficient time series enables a detailed spectral analysis of the flow behavior, highlighting the vortex shedding in the wake. The flow pattern is characterized with a vortex identification method, and the transition between a wing-like flow and bluff-body-like flow is evidenced. It is shown that when the angle of attack exceeds 10°, the lift is sharply increased with a reduction of trailing edge separation, as a consequence of an earlier transition of the boundary layer on the suction side, triggered by separation at the sharp leading edge.