Euler solutions for self‐generated rotor blade‐vortex interactions

Abstract

AbstractA finite‐difference procedure has been developed for the prediction of three‐dimensional rotor blade‐vortex interactions. The interaction velocity field was obtained through a non‐linear superposition of the rotor flow field, computed using the unsteady three‐dimensional Euler equations, and the embedded vortex wake flow field, computed using the law of Biot‐Savart. In the Euler model, near wake rotational effects were simulated using the surface velocity ‘transpiration’ approach. As a result, a modified surface boundary condition was prescribed and enforced at each time step of the computations to satisfy the tangency boundary condition. For supercritical interactions using an upstream‐generated vortex, accuracy of the numerical results were found to rely on the user‐specified vortex core radius and vortex strength. For the more general self‐generated subcritical interactions, vortex wake trajectories were computed using the lifting‐line helicopter/rotor trim code CAMRAD. For these interactions, accuracy of the results were found to rely heavily on the CAMRAD‐predicted vortex strength, vortex orientation with respect to the blade, and to a large extent on the user‐specified vortex core radius. Results for the one‐seventh scale model OLS rotor and for a non‐lifting rectangular blade having a NACA0012 section are presented. Comparisons with the experimental windtunnel data are also made.