UCM model stability improvement. M. Nobrega etal

src/transportModels/viscoelastic/viscoelasticLaws/UCM/UCM.C

@@ -60,7 +60,8 @@ Foam::UCM::UCM
     ),
     rho_(dict.lookup("rho")),
     etaP_(dict.lookup("etaP")),
-    lambda_(dict.lookup("lambda"))
+    lambda_(dict.lookup("lambda")),
+    etaStab_(dimensionedScalar::lookupOrDefault("etaStab", dict, 0.0, dimMass/(dimLength*dimTime)))
 {}
 
 
@@ -68,6 +69,8 @@ Foam::UCM::UCM
 
 Foam::tmp<Foam::fvVectorMatrix> Foam::UCM::divTau(volVectorField& U) const
 {
+    if(etaStab_.value() < SMALL)
+    {
         dimensionedScalar etaPEff = etaP_;
 
     	return
@@ -76,6 +79,16 @@ Foam::tmp<Foam::fvVectorMatrix> Foam::UCM::divTau(volVectorField& U) const
     	  - fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)")
     	  + fvm::laplacian( (etaPEff)/rho_, U, "laplacian(etaPEff+etaS,U)")
     	);
+    }
+    else
+    {
+    	return
+    	(
+    	    fvc::div(tau_/rho_, "div(tau)")
+    	  - fvc::div((etaStab_/rho_)*fvc::grad(U), "div(tau)")
+    	  + fvm::laplacian( (etaStab_)/rho_, U, "laplacian(etaPEff+etaS,U)")
+    	);
+    }
 }
 
 

src/transportModels/viscoelastic/viscoelasticLaws/UCM/UCM.H

@@ -28,7 +28,8 @@ Description
     UCM non linear viscoelastic fluid model (BIRD et al., 1987).
 
 Author
-    Jovani L. Favero.  All rights reserved
+    Miguel Nóbrega, Silvino Araújo, Célio Fernandes, Luís Ferrás. 
+    All rights reserved
 
 SourceFiles
     UCM.C
@@ -70,6 +71,9 @@ class UCM
             //- Relaxation time
             dimensionedScalar lambda_;
 
+            //- Stabilization viscosity
+            dimensionedScalar etaStab_;
+
 
     // Private Member Functions