ENH: More general approach to momentum source direction for

the actuation disk FO

src/fvOptions/sources/derived/actuationDiskSource/actuationDiskSourceTemplates.C

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -55,11 +55,11 @@ void Foam::fv::actuationDiskSource::addActuationDiskAxialInertialResistance
     reduce(upU, minOp<vector>());
     reduce(upRho, minOp<scalar>());
 
-    scalar T = 2.0*upRho*diskArea_*mag(upU)*a*(1 - a);
+    scalar T = 2.0*upRho*diskArea_*sqr(mag(upU & uniDiskDir))*a*(1 - a);
 
     for (const label celli : cells)
     {
-        Usource[celli] += ((Vcells[celli]/V())*T*E) & upU;
+        Usource[celli] += ((Vcells[celli]/V())*T)*uniDiskDir;
     }
 }