Large Eddy Simulation Of An Advancing Rotor For The Characterization Of Wake Signature And Wake Encounter Severity On Final Approach

Abstract

In this work, Large Eddy Simulations of the wake shed by a helicopter rotor in forward flight are performed using a hybrid Eulerian-Lagrangian Vortex Particle-Mesh (VPM) method. Fundamental wake properties are measured. The influence of the flight speed on the wake is investigated, from a high speed of 100 kt to a very low speed of 12.5 kt. At high airspeed, the wake rolls up in a typical compact two-vortex system. The vortex circulation is thus inversely proportional to the flight speed. At low airspeed, the wake departs from this simple behavior. The vortex spacing increases and the wake becomes overwhelmed by turbulence. The circulation is then no longer directly related to the flight speed. The VPM method is also used to measure the aerodynamic loads felt by a rotorcraft when crossing a wake. The main perturbation is found to be a pitching moment. The results show a proportionality relationship between the latter and the airspeed of the follower rotorcraft.