potentialFoam: Solve for velocity potential named Phi rather than using the pressure field for this purpose

The Phi field is read if available otherwise created automatically with
boundary conditions obtained automatically from the pressure field if
available (with optional name) otherwise inferred from the velocity
field.  Phi Laplacian scheme and solver specification are required.  See
tutorials for examples.

tutorials/lagrangian/reactingParcelFoam/verticalChannel/system/fvSchemes

@@ -58,6 +58,7 @@ fluxRequired
 {
     default         no;
     p;
+    Phi;
 }
 
 wallDist

tutorials/lagrangian/reactingParcelFoam/verticalChannel/system/fvSolution

@@ -68,6 +68,11 @@ solvers
         relTol          0;
     }
 
+    Phi
+    {
+        $p;
+    }
+
     "(Yi|O2|N2|H2O)"
     {
         solver          PBiCG;
@@ -88,7 +93,7 @@ solvers
 
 potentialFlow
 {
-    // used for potentialFoam initialisation
+    // Used for potentialFoam initialisation
     nNonOrthogonalCorrectors 5;
 }
 

tutorials/lagrangian/simpleReactingParcelFoam/verticalChannel/system/fvSchemes

@@ -59,6 +59,7 @@ fluxRequired
 {
     default         no;
     p;
+    Phi;
 }
 
 wallDist

tutorials/lagrangian/simpleReactingParcelFoam/verticalChannel/system/fvSolution

@@ -37,6 +37,11 @@ solvers
         maxIter          50;
     };
 
+    Phi
+    {
+        $p;
+    }
+
     "(U|Yi|h|k|omega)"
     {
         solver          smoothSolver;