ENH: Enable flowRateInletVelocity BC to operate as VFR by setting 'rho' to 'none' when phi is kg/s

src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.C

@@ -129,11 +129,19 @@ void Foam::flowRateInletVelocityFvPatchVectorField::updateCoeffs()
     }
     else if (phi.dimensions() == dimDensity*dimVelocity*dimArea)
     {
-        const fvPatchField<scalar>& rhop =
-            patch().lookupPatchField<volScalarField, scalar>(rhoName_);
-
-        // mass flow-rate
-        operator==(n*avgU/rhop);
+        if (rhoName_ == "none")
+        {
+            // volumetric flow-rate if density not given
+            operator==(n*avgU);
+        }
+        else
+        {
+            // mass flow-rate
+            const fvPatchField<scalar>& rhop =
+                patch().lookupPatchField<volScalarField, scalar>(rhoName_);
+
+            operator==(n*avgU/rhop);
+        }
     }
     else
     {

src/finiteVolume/fields/fvPatchFields/derived/flowRateInletVelocity/flowRateInletVelocityFvPatchVectorField.H

@@ -30,8 +30,10 @@ Description
 
     The basis of the patch (volumetric or mass) is determined by the
     dimensions of the flux, phi.
-    The current density is used to correct the velocity when applying the
-    mass basis.
+
+    If the flux is mass-based
+    - the current density is used to correct the velocity
+    - volumetric flow rate can be applied by setting the 'rho' entry to 'none'
 
     Example of the boundary condition specification:
     \verbatim
@@ -39,6 +41,7 @@ Description
     {
         type        flowRateInletVelocity;
         flowRate    0.2;        // Volumetric/mass flow rate [m3/s or kg/s]
+        rho         rho;        // none | rho [m3/s or kg/s]
         value       uniform (0 0 0); // placeholder
     }
     \endverbatim