Free Wake Analyses of a Hovering Rotor Using Panel Method

Using a higher order vortex panel method, three dimensional free wake analyses for a rotor in hover are carried out. The purpose of this paper is to propose new methods being able to incorporate wake deformations due to wake-ground interactions into performance predictions. Both rotors at isolated and at close proximity to arbitrary shaped ground surfaces are investigated. The blade is modeled as a lifting surface with one row of cells (equivalent to Weissinger's L model). The wake is divided into the adjoining, near and far regions. The ground is approximated by the quadrilateral panels. The first two regions of the wake are modeled by triangular shaped panels with linear vorticity distribution which are adopted by their flexibility for roll up deformations of the wake. A semi-infinite vortex cylinder with the constant radius is substituted for the far wake to avoid instabilities of the wake geometry.

Numerical results of wake geometries for rotors both at isolated and close proximity to inclined ground surface are presented and advantages of the proposed method are discussed.