PBiCG: Suggest changing to the more robust PBiCGStab solver

if convergence is not achieved within the maximum number of iterations.

Sometimes, particularly running in parallel, PBiCG fails to converge or diverges
without warning or obvious cause leaving a solution field containing significant
errors which can cause divergence of the application.  PBiCGStab is more robust
and does not suffer from the problems encountered with PBiCG.

src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrix.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -122,6 +122,9 @@ public:
             //- Dictionary of controls
             dictionary controlDict_;
 
+            //- Default maximum number of iterations in the solver
+            static const label defaultMaxIter_ = 1000;
+
             //- Maximum number of iterations in the solver
             label maxIter_;
 

src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixSolver.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -131,7 +131,7 @@ Foam::LduMatrix<Type, DType, LUType>::solver::solver
 
     controlDict_(solverDict),
 
-    maxIter_(1000),
+    maxIter_(defaultMaxIter_),
     minIter_(0),
     tolerance_(1e-6*pTraits<Type>::one),
     relTol_(Zero)

src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrix.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -35,6 +35,9 @@ namespace Foam
 }
 
 
+const Foam::label Foam::lduMatrix::solver::defaultMaxIter_ = 1000;
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 Foam::lduMatrix::lduMatrix(const lduMesh& mesh)

src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrix.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -106,6 +106,9 @@ public:
             //- Dictionary of controls
             dictionary controlDict_;
 
+            //- Default maximum number of iterations in the solver
+            static const label defaultMaxIter_;
+
             //- Maximum number of iterations in the solver
             label maxIter_;
 

src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixSolver.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -157,10 +157,10 @@ Foam::lduMatrix::solver::solver
 
 void Foam::lduMatrix::solver::readControls()
 {
-    maxIter_   = controlDict_.lookupOrDefault<label>("maxIter", 1000);
-    minIter_   = controlDict_.lookupOrDefault<label>("minIter", 0);
+    maxIter_ = controlDict_.lookupOrDefault<label>("maxIter", defaultMaxIter_);
+    minIter_ = controlDict_.lookupOrDefault<label>("minIter", 0);
     tolerance_ = controlDict_.lookupOrDefault<scalar>("tolerance", 1e-6);
-    relTol_    = controlDict_.lookupOrDefault<scalar>("relTol", 0);
+    relTol_ = controlDict_.lookupOrDefault<scalar>("relTol", 0);
 }
 
 

src/OpenFOAM/matrices/lduMatrix/solvers/PBiCG/PBiCG.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -208,6 +208,16 @@ Foam::solverPerformance Foam::PBiCG::solve
         );
     }
 
+    // Recommend PBiCGStab if PBiCG fails to converge
+    if (solverPerf.nIterations() > max(defaultMaxIter_, maxIter_))
+    {
+        FatalErrorInFunction
+            << "PBiCG has failed to converge within the maximum number"
+               " of iterations " << max(defaultMaxIter_, maxIter_) << nl
+            << "    Please try the more robust PBiCGStab solver."
+            << exit(FatalError);
+    }
+
     return solverPerf;
 }