Multiscale Lagrangian-Eulerian Algorithm for Determining the Vorticity Confinement Term for Rotorcraft Computational Fluid Dynamics (CFD) Computations

A multi-scale Lagrangian-Eulerian algorithm has been developed during Phase I to determine the vorticity confinement term for rotorcraft Computational Fluid Dynamics (CFD) computations. Similar to the Large Eddy Simulation approach, the present algorithm simulates the large scales in the flow field and models the unresolved small scales like the tip vortices in the computations. The large scales are simulated using the Eulerian approach while the unresolved small scales are modeled using the Lagrangian approach. The effects of the unresolved small scales are included into the governing equations as the Vorticity Confinement terms. As a result, one is able to perform a rotorcraft CFD computation on a regular CFD grid without excessive numerical diffusion of the tip vortices. The feasibility study of the four-bladed model of the UH-60A main rotor with the Black Hawk blades is successful, demonstrating the capability of the proposed algorithm for accurate prediction of both structure and location of the rotor tip vortices. During Phase II, we will further extend the methodology to viscous computations and apply it to simulate the seven-bladed model of the heavy helicopter CH-53E main rotor and the complete CH-53E configuration.