CFD Based Airfoil Shape Optimization for Aerodynamic Drag Reduction

Abstract

Commercial airplanes generally follow specific flight profiles consisting of take-off, climb, cruise, descend and landing. These flight profiles essentially change the freestream conditions in which the aircrafts operate. Furthermore, over the course of the flight, the required lift force changes as the fuel gets consumed. The conventional fixed wing designs account for these requirements by catering to multiple but fixed design points which, however, compromise the overall flight performance. Employing adaptive wing technology allows to fully exploring the aerodynamic flow potential at each point of the flight envelope. The objective of this research is to develop an aerodynamic optimization framework for optimizing a baseline airfoil shape at specific off-design operating points within a typical transonic flight envelope. The objective function is the lift-moment constrained drag minimization problem. B-spline curve fitting is used to parameterize the airfoil geometry and the control points along with the angle of attack are used as the design variables for the optimization process. An iterative response surface optimization methodology is employed for carrying out the shape optimization process. Design of Experiments (DoE) using the Latin Hypercube Sampling algorithm is used to construct the response surface model. This model is then optimized using the SQP technique. The various parameters that gauge the aerodynamic performance (lift, drag and moment coefficients) are obtained using CFD simulations. GridPro is used as the meshing tool to generate the flow mesh, and the CFD simulation is performed using ANSYS-FLUENT. The parameterization, design of experiments, and the response surface model optimization are performed using MATLAB. RAE 2822 design study is carried out to validate the optimization algorithm developed. The adaptive airfoil concept is demonstrated using a Boeing-737 classic airfoil at three steady flight operating points that lie within a typical aircraft flight envelope. The aerodynamic performance of the adaptive airfoil is then compared to that of the baseline airfoil.