xFoil Analysis Interface Module (AIM)
xFoil Analysis Interface Module (AIM)
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A module in the Computational Aircraft Prototype Syntheses (CAPS) has been developed to interact (through input files) with the subsonic airfoil analysis tool xFoil [1]. xFoil is an open-source tool and may be freely downloaded from http://web.mit.edu/drela/Public/web/xfoil/ . At this time only a subsection of xFoil's capabilities are exposed through the AIM. Furthermore, only versions 6.97 and 6.99 of xFoil have been tested against (for Windows only 6.99).
An outline of the AIM's inputs and outputs are provided in AIM Inputs and AIM Outputs, respectively.
The accepted and expected geometric representation and analysis intentions are detailed in Geometry Representation and Analysis Intent.
Upon running preAnalysis the AIM generates two files: 1. "xfoilInput.txt" which contains instructions for xFoil to execute and 2. "caps.xfoil" which contains the geometry to be analyzed.
xFoil inherently assumes the airfoil cross-section is in the x-y plane, if it isn't an attempt is made to automatically rotate the provided body.
Within OpenCSM, there are a number of airfoil generation UDPs (User Defined Primitives). These include NACA 4 series, a more general NACA 4/5/6 series generator, Sobieczky's PARSEC parameterization and Kulfan's CST parameterization. All of these UDPs generate EGADS FaceBodies where the Face's underlying Surface is planar and the bounds of the Face is a closed set of Edges whose underlying Curves contain the airfoil shape. In all cases there is a Node that represents the Leading Edge point and one or two Nodes at the Trailing Edge – one if the representation is for a sharp TE and the other if the definition is open or blunt. If there are 2 Nodes at the back, then there are 3 Edges all together and closed, even though the airfoil definition was left open at the TE. All of this information will be used to automatically fill in the xFoil geometry description.
It should be noted that general construction in either OpenCSM or even EGADS will be supported as long as the topology described above is used. But care should be taken when constructing the airfoil shape so that a discontinuity (i.e., simply C0) is not generated at the Node representing the Leading Edge. This can be done by splining the entire shape as one and then intersecting the single Edge to place the LE Node.
An example problem using the xFoil AIM may be found at xFoil AIM Example .