Aerodynamic Performance of a Two-Dimensional Flapping Elliptic Airfoil in Ground Proximity

Abstract

In this numerical study, we have investigated the transient and time-averaged thrust performance of a two-dimensional elliptic airfoil sinusoidally flapping near a flat ground surface. To characterize the ground effects on the aerodynamic performance of the flapping airfoil, we have varied the mean ground clearances of the airfoil, flapping frequency, and pivot location on the airfoil. However, the Reynolds number of the incoming flow and effective angle of attack of the flapping airfoil is fixed as 5000 and 15 degrees, respectively. It is observed that regardless of the mean ground clearance and pivot location, the time-averaged thrust performance of the flapping airfoil increases monotonically with flapping frequency until it reaches a peak value at some critical flapping frequency; beyond which the thrust performance deteriorates considerably. Additionally, we observed when the mean ground clearance is reduced; the time-averaged thrust of the flapping airfoil is augmented at all pivot locations and flapping frequencies. Furthermore, we found that for the considered parameters, the pivot location near the leading-edge side of the airfoil provides a better time-average thrust performance than any other pivot location when the flapping airfoil experiences ground effects. Besides, we noticed that the transient thrust profile in a flapping cycle gets modified with a change in the flapping frequency, pivot location and mean ground clearances. We have thoroughly identified the specific types of transient thrust profiles associated with the increasing and reducing regions of the time-averaged thrust of the flapping airfoil at different pivot locations and mean ground clearances.