twoPhaseEulerFoam: Add a residualSlip velocity magnitude for the drag

applications/solvers/multiphase/twoPhaseEulerFoam/createFields.H

@@ -112,7 +112,9 @@
         (
             "phi",
             runTime.timeName(),
-            mesh
+            mesh,
+            IOobject::NO_READ,
+            IOobject::AUTO_WRITE
         ),
         fvc::interpolate(alpha)*phia + fvc::interpolate(beta)*phib
     );
@@ -194,6 +196,13 @@
         }
     }
 
+    dimensionedScalar residualSlip
+    (
+        "residualSlip",
+        dimVelocity,
+        interfacialProperties.lookup("residualSlip")
+    );
+
     Info << "dragPhase is " << dragPhase << endl;
     kineticTheoryModel kineticTheory
     (

applications/solvers/multiphase/twoPhaseEulerFoam/liftDragCoeffs.H

@@ -1,5 +1,5 @@
     volVectorField Ur(Ua - Ub);
-    volScalarField magUr(mag(Ur));
+    volScalarField magUr(mag(Ur) + residualSlip);
 
     volScalarField Ka(draga->K(magUr));
     volScalarField K(Ka);