Theory (continued)

Potential-Flow Airfoil Analysis Method

The potential-flow airfoil analysis method employs panels with parabolic vorticity distributions. The geometry of the panels is determined by a spline fit of the airfoil coordinates, with the end points of the panels being the input airfoil coordinates themselves. The flow condition, which requires the inner tangential velocity to be zero, is satisfied at each airfoil coordinate (i.e., at the end points of the panels, not the midpoints). Two angles of attack, 0 and 90 degrees, are analyzed. The flow at an arbitrary angle of attack is derived from these two solutions by superposition. The entire procedure does not require any restrictions on the input point distribution, smoothing, or rearranging of the coordinates; only the original airfoil coordinates are used. An option is included by which additional points can be splined in between the original coordinates. This option allows more precise results to be obtained should a portion of the airfoil have a sparse distribution of points. An option is provided for smoothing airfoils. In addition, several options are available for the generation of coordinates for NACA 4-digit, 5-digit, and 6-series airfoils as well as FX (Wortmann) airfoils.

A flap deflection can be introduced by geometrically rotating part of the airfoil about a flap-hinge point. The connection between the forward portion of the airfoil and the flap is defined by an arc consisting of additional points that are generated automatically according to an input arc length. In addition, an option is included that allows the analysis of chord-increasing flaps. It should be noted that, while the airfoil shape that results from the exercise of this option does have an increased chord, it does not contain a slot and, therefore, is still a single-element as opposed to a multielement airfoil. An option is also provided for analyzing cascades.

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