Xfoil

XFOIL is a widely used interactive program for the design and analysis of subsonic isolated airfoils. Developed by Mark Drela and Harold Youngren at MIT, it is primarily used by aerodynamicists and engineers to predict airfoil performance. The program can calculate the lift and drag coefficients for a given airfoil shape at a specified Reynolds number and Mach number.

XFOIL's core functionality lies in its iterative inverse design method and direct analysis capabilities. The inverse design method allows users to specify a desired pressure distribution, and XFOIL will then generate an airfoil shape that produces that distribution. This is particularly useful for creating airfoils with optimized characteristics. The direct analysis method, on the other hand, takes an existing airfoil shape and calculates its aerodynamic performance.

The program is known for its ability to handle laminar and turbulent boundary layer calculations, including transition prediction. It is also capable of modeling viscous effects and separation. XFOIL has been instrumental in the development of numerous airfoil families used in aircraft, wind turbines, and other aerodynamic applications. While originally developed for research purposes, its accessibility and robust capabilities have made it a de facto standard in the field of airfoil design. Despite its age, XFOIL remains a valuable tool, though modern computational fluid dynamics (CFD) solvers are often employed for more complex or high-fidelity analyses.