Improved solution approach for aerodynamics loads of helicopter rotor blade in forward flight

Abstract

This paper presents the numerical model developed for rotor blade aerodynamics loads calculation. The model is unsteady and fully three-dimensional. Helicopter blade is assumed to be rigid, and its motion during rotation is modeled in the manner that rotor presents a model of rotor of helicopter Aerospatiale SA 341 "Gazelle" (the blade is attached to the hub by flap, pitch and pseudo lead-lag hinges). Flow field around the blade is observed in succession of several azimuth locations. Flow field around helicopter rotor is modeled as fully three-dimensional, unsteady and potential. Blade aerodynamics is modeled using a lifting surface model. Rotor wake is generated from the straight elements of constant vorticity, released from the trailing edge, at fixed azimuth angles. These vortices represent both trailed and shed wake components, and are allowed to freely convect along local velocity vectors. Wake is modeled as free one, and its shape at certain moment can be calculated from simple kinematics laws applied on collocation points of the wake. Wake distortion is calculated only in the rotor near-field, i.e. in finite number of rotor revolutions. Vortex elements are modeled with vortex core. The radius of the vortex core is assumed independent of time, and it depends on circulation gradient at the point of vortex element released from the blade.