A numerical investigation of blade tip loadings on thick-bladed helicopter rotors

AbstractA procedure is developed for computing the pressure and velocity distributions on the surface of thick helicopter-rotor blades in hovering flight with particular attention directed at the distributions near the blade tips. The fluid medium is incompressible and inviscid. The lifting rotor and its wake are represented by vortex systems which, for the most part, satisfy the Helmholtz theorems. The vortex systems include thin, superimposed, vortex sheets whose filaments are oriented in the blade spanwise and chordwise directions and are constrained to move along the blade surfaces, force-free, inner-wake vortex sheets which are shed from the blade-trailing edges and concentrated tip vortices of prescribed geometry which are shed from the vicinity of the blade tips. A lifting-line, two-dimensional, blade-element approach is used to determine initial values of the vortex-strength distributions and inner-sheet geometries. A transfer is then made to the thick-bladed system and an iterative vortex-panel procedure is used to reach essentially converged results. The computed pressure distributions in the blade-tip region show good agreement with model data, but improvement is needed in the region of the upper surface where the pressure field is dominated by the formation of the tip vortex. Since the objective was to establish the viability and limits of perfect fluid modeling, the results indicate that viscous-flow modeling may be necessary only in this region of limited extent