Numerical Simulation of Unsteady Rotor Wakes

A non linear unsteady vortex lattice scheme is presented. It is capable to predict the instantaneous configuration of the wake and the distribution of the aerodynamic load on rotor blades, during impulsive starts or arbitrarily unsteady flight conditions. Any number of independent blades, with general planform and twist distribution, moving with assigned pitch and flap angles can be treated. Rankine vortices are used to discretize vorticity. Turbulent diffusion of their cores is modeled in order to cope with the rapid roll-up process of unsteady and closely interfering wakes, without any form of tuning of the numerical parameters. The capabilities of the code are verified by comparing numerical predictions with available steady state experimental data. Also reported are some results related to realistic unsteady flight conditions.