Aerodynamic investigation of an airfoil under two hovering modes considering ground effect

摘要

In this work, we study the effects of the ground on an airfoil undergoing two hovering modes, "water treading" and "normal". We vary the ground clearance in order to have a better insight into the effects of the ground on the lift production as well as the energy consumption. Moreover, the effects of the ground on the vorticity contours and the pressure distribution on the airfoil are also analyzed. A finite volume method is used to simulate the flow field using a commercial software Fluent. It is found that the rapid pitching up and the delayed stall associated with the leading-edge vortex mechanisms are the responsible for the most of the lift production for both hovering modes. However, for the "normal" mode, two peaks were identified in the lift coefficient at each stroke. This is an indication of the presence of the wake capturing mechanism. As for the influence of the ground clearance, we found that it affects the two hovering modes differently, both in terms of energy consumption and lift force variations. Three force regimes are identified in the "normal" hovering mode, i.e., force reduction, force enhancement and force recovery. However, for the "water treading" mode only the enhancement regime is identified. (C) 2019 Elsevier Ltd. All rights reserved.