particle: Added trackToCell function

This is equivalent to track to face, but it additionally crosses
internal faces at the end of the track to move into the next cell. This
is a common procedure when performing post-processing tracking
operations.

src/lagrangian/basic/particle/particle.C

@@ -570,6 +570,23 @@ Foam::scalar Foam::particle::track
 }
 
 
+Foam::scalar Foam::particle::trackToCell
+(
+    const vector& displacement,
+    const scalar fraction
+)
+{
+    const scalar f = trackToFace(displacement, fraction);
+
+    if (onInternalFace())
+    {
+        changeCell();
+    }
+
+    return f;
+}
+
+
 Foam::scalar Foam::particle::trackToFace
 (
     const vector& displacement,

src/lagrangian/basic/particle/particle.H

@@ -513,16 +513,23 @@ public:
             const scalar fraction
         );
 
-        //- As particle::track, but also stops on internal faces.
+        //- As particle::track, but stops when a new cell is reached.
+        scalar trackToCell
+        (
+            const vector& displacement,
+            const scalar fraction
+        );
+
+        //- As particle::track, but stops when a face is hit.
         scalar trackToFace
         (
             const vector& displacement,
             const scalar fraction
         );
 
-        //- As particle::trackToFace, but also stops on tet triangles. On
+        //- As particle::trackToFace, but stops when a tet triangle is hit. On
-        //  exit, tetTriI is set to the index of the tet triangle that was
+        //  exit, tetTriI is set to the index of the tet triangle that was hit,
-        //  hit, or -1 if the end position was reached.
+        //  or -1 if the end position was reached.
         scalar trackToTri
         (
             const vector& displacement,