ThermoSurfaceFilm: Corrected the splash kinetic energy

The splash kinetic energy has been changed to depend upon the velocity
of the parcel normal to the wall, rather than the absolute velocity, in
accordance with the original reference.

This patch was contributed by Stefan Hildenbrand at Pfinder
Resolves bug report https://bugs.openfoam.org/view.php?id=2682

src/lagrangian/intermediate/submodels/Thermodynamic/SurfaceFilmModel/ThermoSurfaceFilm/ThermoSurfaceFilm.C

@@ -400,7 +400,7 @@ void Foam::ThermoSurfaceFilm<CloudType>::splashInteraction
     }
 
     // Incident kinetic energy [J]
-    const scalar EKIn = 0.5*m*magSqr(Urel);
+    const scalar EKIn = 0.5*m*magSqr(Un);
 
     // Incident surface energy [J]
     const scalar ESigmaIn = np*sigma*p.areaS(d);