Drag reduction of a transport helicopter by application of an adjoint-based fuselage optimization chain and modification of the rotor head

Abstract

In this paper two approaches are investigated to reduce the parasite drag of a helicopter. The first approach is to optimize the surface of the fuselage back door. This is done by applying an automatic, adjoint-based optimization chain; developed by DLR for these purposes. This optimization chain combines the RANS-solver TAU with a solver for the discrete adjoint equation and a conjugate-gradient based optimization algorithm. The parameterization is done by Free Form Deformation. A description of the functionality of the chain is given, before the results of the optimization run are presented. The resulting surfaces were able to bring benefits, up to 3.75% drag reduction compared to the baseline geometry. The second approach is to reduce the main rotor head drag, by installing a hub fairing. During this investigation, two different hub geometries were tested. By using a fully closed fairing, a drag reduction of about 19% could be achieved.