Computational-Fluid-Dynamics-Based Twist Optimization of Hovering Rotors

Abstract

Twist optimization of a helicopter rotor in hover is presented using compressible computational fluid dynamics as the aerodynamic model. A domain-element shape parameterization method has been developed, which solves both the geometry control and the volumemesh deformation problems simultaneously, using radial basis function global interpolation. This provides direct transfer of domain-element movements into deformations of the design surface and the computational fluid dynamics volume mesh, which is deformed in a high-quality fashion. The method is independent ofmesh type (structured or unstructured), and it has been linked to an advancedparallel gradient-based algorithm, for which independence from the flow solver is achieved by obtaining sensitivity information by finite differences. This has resulted in aflexible andversatilemodularmethod ofwraparound optimization. Previousfixedwing results have shown that a large proportion of the design space is accessible with the parameterization method, and heavily constrained drag optimization demonstrated significant performance improvements. In the present work, themethod is extended to a rotor blade, and this is optimized forminimum torque in hovering flight with strict constraints. Twist optimization results are presented for three tip Mach numbers, and the effects of different parameterization levels are analyzedusing various combinations of two levels: global and local. Torque reductions of over 12% are shown for a fully subsonic case, and for over 24% for a transonic case, using only three global and 15 local twist parameters.