Transonic Airfoil Shape Optimization in Preliminary Design Environment

A modified profile optimization method using a smoothest shape modification strategy (POSSEM) is developed for airfoil shape optimization in a preliminary design environment. POSSEM is formulated to overcome two technical difficulties frequently encountered when conducting multipoint airfoil optimization within a high-resolution design space: the generation of undesirable optimal airfoil shapes due to high frequency components in the parametric geometry model and significant degradation in the off-design performance. To demonstrate the usefulness of POSSEM in a preliminary design environment, a design competition was conducted with the objective of improving a fairly well-designed baseline airfoil at four transonic flight conditions without incurring any off-design performance degradation. Independently, two designs were generated from the inverse design tool CDISC, while a third design was generated from POSSEM using over 200 control points of a cubic B-spline curve representation of the airfoil as design variables for the shape optimization. Pros and cons of all the airfoil designs are documented along with in-depth analyses of simulation results. The POSSEM design exhibits a fairly smooth curvature and no degradation in the off-design performance. Moreover, it has the lowest average drag among the three designs at the design conditions, as evaluated from three different flow solvers. This study demonstrates the potential of POSSEM as a practical airfoil optimization tool for use in a preliminary design environment. The novel ideas used in POSSEM, such as the smoothest shape modification and modified profile optimization strategies, are applicable to minimizing aircraft drag at multiple flight conditions.