An Efficient Shape Parameterisation Method Applied to Aerodynamic Optimisation of Helicopter Rotors

A novel, generic and efficient shape parameterisation method is applied to CFD-based shape optimisation of helicopter rotors in hovering flight. Radial basis functions are used to provide an interpolation that transfers domain element movements into deformations of the design surface. The interpolation also extends to the CFD volume mesh, which is correspondingly deformed in a high-quality fashion. The shape parameterisation method requires very few design variables to allow free-form design, and the method of shape and CFD mesh parameterisation is independent of mesh type (structured or unstructured), and optimisation independence from the flow solver (inviscid, viscous, aeroelastic) is achieved by obtaining sensitivity information for an advanced gradient-based algorithm by finite-difference. This has resulted in a flexible and versatile method of ’wrap-around ’ optimisa-tion framework, which has also been parallelised. The shape parameterisation and optimisation method has been applied previously to two-dimensional highly constrained aerofoil optimisations, which showed that significant drag reductions can be achieved. Recent three-dimensional fixed-wing optimisations have led to novel planform designs also with substantial performance benefits. In the present work, the method is extended to rotor blades, which will be subsequently optimised for improved performance (reduced torque) in hovering flight with rigid constraints in thrust, internal volume and root moments. The blades can be parameterised at various levels, focusing on gross planform deformations, local detailed surface changes, or combinations of both. Initial results are presented for the Caradonna and Tung two-bladed case. I