A good possibility to improve the performance of a helicopter is to reduce the parasite drag force. During forward flight this drag is manly caused by the helicopter fuselage. Due to its back door shape for loading purposes, transport helicopters usually possess a blunt fuselage geometry. Such a shape is known to cause a flow separation that is responsible for increasing parasite drag.
By optimizing the surface geometry it is possible to reduce the flow separation effects and to improve the aerodynamic performance. For this purpose, DLR developed in the scope of the GRC2-project (Green Rotor Craft) a fully automatic optimization chain. This chain is based on the DLR TAU-code and uses different modules of this program. For the parameterization of the surface, the Free Form Deformation module is used. The adaptation of the deformed surface to the computational grid is done by the RBF-module (Radial Basis Function). To investigate the optimum modifications of the design variables (Control points of the FFD-box), a gradient based approach is applied. To reduce the computational time of this approach, the integrated adjoint solver of TAU is used which decouples the gradient calculation of the cost function (in general the drag coefficient) from the number of design variables.
This optimization chain had already been applied successfully on the back door of an EC-135 and a NH90 model. By further developments of this optimization tool, the required computational costs should be reduced. Additionally, this optimization tool will be extended for further investigations on different target surfaces (Nose, sponsons, cowling, …).