Application Of An Inverse Design Methodology To Rotor Tip Design

Abstract

An inverse design technique is described for improving the aerodynamic characteristics of 2-D rotor sections and helicopter rotor blade tip regions. This methodology requires the specification of a target pressure distribution that achieves the design lift coefficient, while reducing the profile drag by delaying transition to turbulent flow and mitigating boundary layer growth by reducing the adverse pressure gradients wherever possible. The peak local Mach numbers are also kept low enough to delay the formation of shock waves and the attendant wave drag and shock noise. This methodology is independent of the flow solver used to predict the surface pressure data over the intermediate geometries during the design iterations, allowing a variety of flow solvers to be used. Sample 2-D applications are shown for 2-D airfoil design where the present methodology is used with an in-house panel method which is used to generate the surface pressures. This methodology is subsequently applied to the redesign of the S76 rotor tip region for improved performance at high thrust settings.