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The flow about an airfoil in free air can be described approximately by a boundary-layer flow near the surface of the airfoil and by a potential flow everywhere else. Boundary-layer theory can be applied to the flow about an airfoil in two ways. First, the boundary-layer development can be determined for a given potential flow velocity distribution. This is the direct or analysis problem. Second, the potential-flow field, or at least some of its properties, can be determined for a given boundary-layer development. This is the inverse or design problem. This second application of boundary-layer theory requires the solution of the inverse potential-flow problem where the potential-flow velocity distribution is specified and the airfoil shape is computed. Thus, the viscous airfoil design (inverse) problem can be described as the computation of a shape from a potential flow velocity distribution which is consistent with a desired boundary-layer development. Because Tollmien, Schlichting,Ulrich, Pretsch, and others had shown that favorable pressure gradients delay the transition from laminar to turbulent flow, airfoils were designed with aft pressure recoveries. The experimental results for these airfoils confirmed the theoretical predictions. This breakthrough led to the laminar flow airfoil series. Since that time, boundary-layer and potential flow theories have been steadily improved.

Different computer programs have been developed for low-speed (incompressible)airfoils. The present paper describes one of these programs. The potential flow inverse problem still plays a major role in airfoil design. This problem has been solved exactly by means of conformal mapping. The method is similar to that of Lighthill, is direct, and solves most multipoint design problems in a very simple manner. A potential-flow analysis method is also required for comparison with wind tunnel tests of given airfoils and for analyses of airfoils generated by the design method and then modified by a flap deflection. The airfoil analysis problem is solved using a distributed surface singularity method. Some of the details of this method are new and previously unpublished. The boundary-layer method uses integral momentum and energy equations. The present method does not contain a boundary-layer displacement iteration. The program has been successfully applied at Reynolds numbers from 20 thousand to 100 million.

Italic text above is from TM 80210.

Although this program is of great historical importance and one still finds current papers that refer to calculations made with PROFILE, it is not the program of choice for someone learning about airfoil plus boundary layer calculations. I would recommend Xfoil for today's students. Xfoil is an interactive program for the design and analysis of subsonic isolated airfoils written by Mark Drela and Harold Youngren. Check the Virginia Tech site for valuable notes on running Xfoil.

PDAS home > Contents > Eppler
Public Domain Aeronautical Software (PDAS)