Aerodynamic Shape Design of a Powered Helicopter Cell Using an Adjoint RANS Method with Actuator Disk Modelling

A shape optimization approach backed by adjoint RANS is suggested, which allows for helicopter cell-shape design in powered flight conditions and is realizable in context of industrial design. To this end the DLR TAU code was extended to support an actuator-disk rotor modelling for the discrete-adjoint gradient computation. The steady-state approach accounts for rotor effects in the shape optimization and reliefs from the burden associated with time-accurate adjoint computations for transient rotor analyses. The adjoint CFD method was included in a tool-chain for gradient-based helicopter cell-shape optimization in conjunction with a free-form parametrization of the cell shape and a radial-basis function approach that propagates surface deformations into the CFD volume mesh. The suggested approach was successfully demonstrated in a drag minimization study for the modified helicopter fuselage of the ROtor-Body-INteraction (ROBIN) configuration combined with a realistic load distribution for the 7AD main rotor. The shape optimization was conducted for forward flight conditions at full-scale using unstructured grids. The study confirmed the practical value of the suggested approach: accounting for the rotor downwash in the cell-shape design optimization turned out to be a critical factor for success; the cell shape obtained from an optimization in which rotor effects were neglected deteriorated the aerodynamic performance in powered flight conditions.