OpenFOAM-6/tutorials/multiphase/interPhaseChangeDyMFoam/propeller/system/surfaceFeatureExtractDictDefaults

// How to obtain raw features (extractFromFile || extractFromSurface)
extractionMethod    extractFromSurface;

extractFromSurfaceCoeffs
{
    // Mark edges whose adjacent surface normals are at an angle less
    // than includedAngle as features
    // - 0  : selects no edges
    // - 180: selects all edges
    includedAngle   150;
}

trimFeatures
{
    // Remove features with fewer than the specified number of edges
    minElem         10;
}