Free-Wake Analysis on Massively Parallel Computers and Validation with HART Test Data

This paper presents the parallelization procedure of a free-wake code recently developed at DLR as a spin-off from the HART program, that exhibited the complex wake structures of a rotor under active control and the need of free-wake codes being able to correctly simulate them. The performance of parallel computation is shown, and the question of realtime free-wake computation is addressed. Topics like discretization of the wake and energy conservation of vortex elements within the wake are discussed in this paper. A new formulation of tip vortex core radius development is presented, incorporating a wake thickness, radial extension of trailed vorticity building up the tip vortex, vortex age, and the number of close encounters with a blade. For the vortex circulation strength, a time decay model is presented. Both models are based on experimental data from the joined German-American-French HART program. Free-wake results are validated with HART data.