Coupled Boundary-Layer Suction and Airfoil Optimization for Hybrid Laminar Flow Control

Abstract

The present work incorporates the effects of boundary-layer suction in designing airfoils for hybrid laminar flow control application. The overall airfoil shape, the suction velocity distribution, and its location are optimized for minimum total drag while sustaining laminar flow over 80% of the airfoil top surface. Nondominated Sorting Genetic Algorithm II is used with the aerodynamic load computations from XFOILSUC and transition prediction from the improved Van Ingen method. The airfoil is designed for short-range subsonic conditions for three design lift-coefficient scenarios: 1) 0.4, 2) in the range of 0.3–0.7, and 3) in the range of 0.3–0.7 with suction onset at midchord. The optimized airfoil for scenario 3, with suction onset at midchord, results in a thicker airfoil with natural laminar flow (NLF) on the upper surface comparable to NLF airfoils. The total drag reduces by one-third due to the effects of suction. On the other hand, without limiting the suction onset (scenario 2), a thinner airfoil with longer NLF on the bottom surface and lower total drag is obtained. Optimum suction onset location is predicted to be at 30% of the chord. Suction is also observed to improve the drag bucket at off-design conditions.