XFOIL — The Complete Guide: Free Airfoil Analysis and Design at Low Reynolds Numbers

XFOIL is a program for analysing and designing 2D airfoil sections, written by Mark Drela at MIT. It combines a panel method for the inviscid flow with an integral boundary-layer model, so it computes drag and separation as well — very quickly. It looks like software from the nineties, which is exactly what it is, yet it is still the reference point every other tool in the field is measured against.

XFOIL

MIT — Mark Drela

Airfoil analysis and design at low Reynolds numbers — the classic reference in the field.

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What you get

Polars — lift, drag and moment coefficients versus angle of attack and Reynolds number.
Pressure distribution — pressure coefficient along the airfoil and separation points.
Transition — e^N prediction, with a parameter for freestream turbulence level.
Inverse design — edit the target velocity distribution and get the shape.
Geometry editing — thickness, camber and flaps, plus built-in NACA airfoils.

What to know

You work with text commands in a terminal window, so keep a command sheet handy. Results are reliable for attached flow and moderate separation; near stall and in transonic flow accuracy drops. If you prefer a graphical interface, you get the same engine inside XFLR5.