Caching deltaT in the DsmcCloud as it is expensive to repeated lookup in the

parcel and in submodels.  Approx 20% speed in solution.

src/lagrangian/dsmc/clouds/Templates/DsmcCloud/DsmcCloud.C

@@ -299,7 +299,7 @@ void Foam::DsmcCloud<ParcelType>::collisions()
     // Temporary storage for subCells
     List<DynamicList<label> > subCells(8);
 
-    scalar deltaT = mesh_.time().deltaT().value();
+    scalar deltaT = cachedDeltaT();
 
     label collisionCandidates = 0;
 
@@ -778,6 +778,9 @@ Foam::DsmcCloud<ParcelType>::~DsmcCloud()
 template<class ParcelType>
 void Foam::DsmcCloud<ParcelType>::evolve()
 {
+    // cache the value of deltaT for this timestep
+    storeDeltaT();
+
     typename ParcelType::trackData td(*this);
 
     // Reset the surface data collection fields

src/lagrangian/dsmc/clouds/Templates/DsmcCloud/DsmcCloud.H

@@ -116,6 +116,10 @@ class DsmcCloud
         //- Random number generator
         Random rndGen_;
 
+        //- In-cloud cache of deltaT, lookup in submodels and parcel is
+        //  expensive
+        scalar cachedDeltaT_;
+
 
         // References to the macroscopic fields
 
@@ -243,6 +247,12 @@ public:
                 //- Return refernce to the random object
                 inline Random& rndGen();
 
+                //- Store (cache) the current value of deltaT
+                inline void storeDeltaT();
+
+                //- Return the cached value of deltaT
+                inline scalar cachedDeltaT() const;
+
 
             // References to the surface data collection fields
 

src/lagrangian/dsmc/clouds/Templates/DsmcCloud/DsmcCloudI.H

@@ -120,6 +120,20 @@ inline Foam::Random& Foam::DsmcCloud<ParcelType>::rndGen()
 }
 
 
+template<class ParcelType>
+inline void Foam::DsmcCloud<ParcelType>::storeDeltaT()
+{
+    cachedDeltaT_ = mesh().time().deltaT().value();
+}
+
+
+template<class ParcelType>
+inline Foam::scalar Foam::DsmcCloud<ParcelType>::cachedDeltaT() const
+{
+    return cachedDeltaT_;
+}
+
+
 template<class ParcelType>
 inline const Foam::volScalarField& Foam::DsmcCloud<ParcelType>::q() const
 {

src/lagrangian/dsmc/parcels/Templates/DsmcParcel/DsmcParcel.C

@@ -44,7 +44,7 @@ bool Foam::DsmcParcel<ParcelType>::move
     const polyMesh& mesh = td.cloud().pMesh();
     const polyBoundaryMesh& pbMesh = mesh.boundaryMesh();
 
-    const scalar deltaT = mesh.time().deltaT().value();
+    const scalar deltaT = td.cloud().cachedDeltaT();
     scalar tEnd = (1.0 - p.stepFraction())*deltaT;
     const scalar dtMax = tEnd;
 
@@ -145,7 +145,7 @@ void Foam::DsmcParcel<ParcelType>::hitWallPatch
 
     const scalar fA = mag(wpp.faceAreas()[wppLocalFace]);
 
-    const scalar deltaT = td.cloud().mesh().time().deltaT().value();
+    const scalar deltaT = td.cloud().cachedDeltaT();
 
     scalar deltaQ = td.cloud().nParticle()*(preIE - postIE)/(deltaT*fA);
 

src/lagrangian/dsmc/submodels/InflowBoundaryModel/FreeStream/FreeStream.C

@@ -126,7 +126,7 @@ void Foam::FreeStream<CloudType>::inflow()
 
     const polyMesh& mesh(cloud.mesh());
 
-    const scalar deltaT = mesh.time().deltaT().value();
+    const scalar deltaT = cloud.cachedDeltaT();
 
     Random& rndGen(cloud.rndGen());