reactingEulerFoam: Fail if surface tension model does not exist

The access of the surface tension coefficient has been changed in some
places so that an error is generated rather than returning a default
value of zero. The reciprocal of the surface tension coefficient is
frequently used in sub-models, so returning zero can generate a floating
point exception. A "surface tension model does not exist" warning is
preferable in these cases.

Patch to populationBalanceModel.C contributed by Institute of Fluid
Dynamics, Helmholtz-Zentrum Dresden - Rossendorf (HZDR)

applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePair/phasePair.C

@@ -25,6 +25,7 @@ License
 
 #include "phasePair.H"
 #include "phaseSystem.H"
+#include "surfaceTensionModel.H"
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
@@ -165,7 +166,11 @@ Foam::tmp<Foam::volScalarField> Foam::phasePair::EoH2() const
 
 Foam::tmp<Foam::volScalarField> Foam::phasePair::sigma() const
 {
-    return phase1().fluid().sigma(phasePair(phase1(), phase2()));
+    return
+        phase1().fluid().lookupSubModel<surfaceTensionModel>
+        (
+            phasePair(phase1(), phase2())
+        ).sigma();
 }
 
 

applications/solvers/multiphase/reactingEulerFoam/phaseSystems/populationBalanceModel/populationBalanceModel/populationBalanceModel.C

@@ -30,6 +30,7 @@ License
 #include "driftModel.H"
 #include "nucleationModel.H"
 #include "phaseSystem.H"
+#include "surfaceTensionModel.H"
 #include "fvmDdt.H"
 #include "fvcDdt.H"
 #include "fvmSup.H"
@@ -1152,13 +1153,11 @@ Foam::diameterModels::populationBalanceModel::sigmaWithContinuousPhase
     const phaseModel& dispersedPhase
 ) const
 {
-    const phasePairKey key
-    (
-        dispersedPhase.name(),
-        continuousPhase_.name()
-    );
-
-    return fluid_.sigma(key);
+    return
+        fluid_.lookupSubModel<surfaceTensionModel>
+        (
+            phasePair(dispersedPhase, continuousPhase_)
+        ).sigma();
 }