ENH: Surface films - using alternatove form for momentum sink contribution

src/regionModels/surfaceFilmModels/kinematicSingleLayer/kinematicSingleLayer.C

@@ -308,7 +308,8 @@ tmp<Foam::fvVectorMatrix> kinematicSingleLayer::solveMomentum
       + fvm::div(phi_, U_)
      ==
       - USp_
-      - fvm::SuSp(rhoSp_, U_)
+//      - fvm::SuSp(rhoSp_, U_)
+      - rhoSp_*U_
       + forces_.correct(U_)
     );