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

摘要

Twist optimization of a helicopter rotor in hover is presented using compressible computational fluid dynamics asnthe aerodynamic model. A domain-element shape parameterization method has been developed, which solves bothnthe geometry control and the volumemesh deformation problems simultaneously, using radial basis function globalninterpolation. This provides direct transfer of domain-element movements into deformations of the design surfacenand the computational fluid dynamics volume mesh, which is deformed in a high-quality fashion. The method isnindependent ofmesh type (structured or unstructured), and it has been linked to an advanced parallel gradient-basednalgorithm, for which independence from the flow solver is achieved by obtaining sensitivity information by finitendifferences.This has resulted in a flexible and versatilemodularmethod ofwraparound optimization. Previous fixed-nwing results have shown that a large proportion of the design space is accessible with the parameterization method,nand heavily constrained drag optimization demonstrated significant performance improvements. In the presentnwork, themethod is extended to a rotor blade, and this is optimized forminimumtorque in hovering flight with strictnconstraints. Twist optimization results are presented for three tip Mach numbers, and the effects of differentnparameterization levels are analyzed using various combinations of two levels: global and local.Torque reductions ofnover 12%are shown for a fully subsonic case, and for over 24%for a transonic case, using only three global and 15nlocal twist parameters.