ESDU 98031:1998

ESDU 98031 presents an extended VGK program (termed VGKE) and describes the method of using it to provide values of the various parameters needed for the estimation of the excrescence drag appropriate to isolated two-dimensional excrescences. The method may be used for small excrescences, such as those produced by skin joints and joints between flaps or slats and the main wing, provided the excrescences are in a region where the boundary layer is locally turbulent. The method is appropriate to aerofoils operating at subsonic freestream speeds, for values of lift coefficient for which the upper- and lower-surface flows are attached or have only very limited regions of separation. The excrescences must be small enough for the available methods for estimating local excrescence drag coefficient increments (such as those in ESDU 75028, ESDU 75031 and ESDU 76008) to be applicable. The parameters provided by the method, for a given flow case, are local values of: Mach number, Reynolds number, skin friction coefficient, non-dimensional boundary layer thickness, and excrescence drag magnification factor. The use of VGKE to obtain consistent results for subcritical and supercritical flow cases is described. Runs of the program VGKE are facilitated by two control programs EXCCON and DRAGCON. Detailed descriptions are given for using those programs, suited both for MS-DOS and UNIX operating systems. Comparisons of results from VGKE with those from an extended version of another aerofoil program (BVGK) suggest a prediction accuracy for the parameters that is likely to be adequate for aircraft drag estimation studies.

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