Effect of rounded trailing edges on unsteady airfoil loading at low reynolds numbers

Abstract

The steady potential flow past a traditional airfoil with a round leading edge and a sharp trailing edge can usually be simulated using the assumption of Kutta condition at the trailing edge. However, for the airfoil undergoing unsteady motion, especially at high reduced frequencies, numerical and experimental studies have shown that the flow can curve around the trailing edge, resulting in the stagnation point moving away from the trailing edge. This phenomenon becomes increasingly apparent when the airfoil has a round trailing edge instead of the usual sharp one. Inspired by the success of using leading-edge suction force to represent the flow turn-around at the leading edge and the associated vortex shedding, this work introduces the trailing-edge suction force and connects it to the trailing-edge unsteady flow physics. In this work, the effect of trailing edge roundness on the unsteady airfoil flow is studied by generating airfoil shapes with various amounts of roundness. Computational fluid dynamics (CFD) studies of unsteady flow past airfoils with different round trailing edges are performed to study the effects of the trailing-edge suction force on the flowfield. A composite pressure-difference model, universally valid on the entire airfoil, is derived in this work to take into account the edge radii and the corresponding edge-suction effects. We show that, in scenarios where the stagnation point moves away from the trailing edge, a trailing-edge suction force, associated with the flow curving around the trailing edge, is necessary to better estimate the airfoil unsteady load distribution.