AERODYNAMIC CALCULATION METHOD OF THE MAIN ROTOR TAKING INTO ACCOUNT DIFFUSION OF FREE VORTICES FOR SMALL FLIGHT SPEEDS

摘要

The object of investigation is a five-blade model of a main helicopter rotor. The work purpose is to find an acceptable mathematical modeling of the nonlinear diffusion vortex wake of the main helicopter rotor and loadings on the main rotor's blades connected with the induction of the wake. The increase of vortices descending from the blade's cross dimension during the diffusion process, along with their circulation decrease, was taken into account. In the investigation in question, these two variables are interconnected. The distribution of vorticity in diffusing vortex lines with the axis moving in the velocity field given was considered. Formulas for the calculation of induced velocities caused by vortex lines were derived. The velocities from the finite cross section volumetric vortex tubes concerned were reduced to the linear integral about the tube axis of expression, representing a generalization of Biot-Savart law. The problems of vortex diffusion influence on aerodynamic loadings, blade-span instant induced velocities, and average induced velocities at points of free diffusion vortices wake in working conditions in a system of joint definition of loadings and induced velocities were numerically investigated. The calculation series for a blade of a five-blade model main rotor on determination of vortex wake shape and induced velocities on a disk, taking into account flight speed diffusion corresponding to μ = 0.15, was fulfilled. In this work, the attempt was made to determine the thickness of the vortices descending from the blade based on the thickness of the boundary layer 6, with a further increasing value of 6 depending on time. Calculations were compared using this method with experiments both in the location of the vortex plane and in determining the values of average induced velocities in the wake behind the rotor.