Airfoil design for helicopter rotor blades - A three-dimensional approach

A finite difference procedure has been developed for the design of airfoil sections for helicopter rotor blades. The procedure is based on the coupled three-dimensional direct solutions to the full potential equation inherent in the rotor flow solver (RFS2) and the two-dimensional inverse solutions to an auxiliary equation, Here, the evolution of the airfoil geometries, at a number of a priori defined radial control stations is driven by the user-prescribed pressure distributions and the flowfield requirements imposed by the RFS2 flow solver. In this respect, the influence of the finite aspect ratio blade, sweep, taper and, more importantly, the tip vortex wake, are reflected in the final airfoil designs. The lifting-line CAMRAD/JA trim code was incorporated into the design procedure to allow for the simulation of the tip vortex wake effects. Results are presented for the redesign of a number of airfoil sections for a generic hovering rotor (with rectangular blades) with and without allowance for the tip vortex wake effects. Aerodynamic performance characteristics of the original blade and the redesigned blade in hover are assessed using the three-dimensional TURNS Navier-Stokes rotor flow solver.