Design of Laminar-Flow Airfoils Based On Boundary-Layer Integral Parameters

Abstract

An airfoil design framework is introduced in which boundary-layer integral parameters serve as the driving design mechanism. The method consists of generating a parametrized pressure distribution capable of producing desired boundary-layer characteristics for inverse design use. Additionally, by deduction from the Squire-Young theory, the method allows to determine the pressure distribution that results in the minimum theoretical drag. To assess this design framework, several airfoils were developed based on the mission requirements of the RQ-4B Global Hawk aircraft. Numerical results obtained using a viscous-inviscid solver of the integral boundary layer and Euler equations showed that the optimized airfoils achieved profile drag reductions of 9.06% and 6.00%, respectively, for α = 0° and L/Dmax design points. Additional airfoils were developed for high Reynolds and incompressible flow applications to display the applicability of the design method across a broad range of operating conditions, which also resulted in significant drag reductions. A validation experimental campaign was performed using the optimized CA5427-72 airfoil. The acquired data produced the expected pressure distribution characteristics and aerodynamic performance improvements, indicating that the airfoil successfully achieved the design objectives.