multiphaseEulerFoam/.../aerosolDrag: Improvements

Expanded the documentation and updated the mean free path calculation

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

applications/solvers/multiphase/multiphaseEulerFoam/interfacialModels/dragModels/aerosolDrag/aerosolDrag.C

@@ -29,8 +29,6 @@ License
 #include "addToRunTimeSelectionTable.H"
 #include "constants.H"
 
-using namespace Foam::constant;
-
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
 namespace Foam
@@ -42,6 +40,9 @@ namespace dragModels
 }
 }
 
+using Foam::constant::physicoChemical::k;
+using Foam::constant::mathematical::pi;
+
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -56,7 +57,7 @@ Foam::dragModels::aerosolDrag::aerosolDrag
     A1_(dict.lookupOrDefault<scalar>("A1", 2.514)),
     A2_(dict.lookupOrDefault<scalar>("A2", 0.8)),
     A3_(dict.lookupOrDefault<scalar>("A3", 0.55)),
-    dm_(dimensionedScalar::lookupOrDefault("dm", dict, dimLength, 364e-12))
+    sigma_("sigma", dimLength, dict)
 {}
 
 
@@ -70,24 +71,14 @@ Foam::dragModels::aerosolDrag::~aerosolDrag()
 
 Foam::tmp<Foam::volScalarField> Foam::dragModels::aerosolDrag::CdRe() const
 {
-    const volScalarField lambda
-    (
-        physicoChemical::k
-       *pair_.continuous().thermo().T()
-       /sqrt(2.0)
-       /mathematical::pi
-       /pair_.continuous().thermo().p()
-       /sqr(dm_)
-    );
+    const volScalarField& T = pair_.continuous().thermo().T();
+    const volScalarField& p = pair_.continuous().thermo().p();
+    tmp<volScalarField> td(pair_.dispersed().d());
+    const volScalarField& d = td();
 
-    const volScalarField dp(pair_.dispersed().d());
+    const volScalarField lambda(k*T/(sqrt(2.0)*pi*p*sqr(sigma_)));
 
-    const volScalarField Cc
-    (
-        1 + lambda/dp*(A1_ + A2_*exp(-A3_*dp/lambda))
-    );
-
-    return 24/Cc;
+    return 24/(1 + lambda/d*(A1_ + A2_*exp(-A3_*d/lambda)));
 }
 
 

applications/solvers/multiphase/multiphaseEulerFoam/interfacialModels/dragModels/aerosolDrag/aerosolDrag.H

@@ -25,9 +25,42 @@ Class
     Foam::dragModels::aerosolDrag
 
 Description
-    This drag model is intended for simulations involving dispersed phase
-    with a very small diameter. It combines the Stokes drag with a
-    Cunningham correction factor.
+    Stokes drag with Cunningham slip correction. The slip correction coefficient
+    is implemented in the following form:
+
+    \f[
+        C_c = 1 + \lambda [A_1 + A_2 \exp(-A_3 d/\lambda)]/d\,.
+    \f]
+
+    The coefficients default to the values proposed by Davis (1945). The mean
+    free path is computed by
+
+    \f[
+        \lambda = \frac{kT}{\sqrt{2} \pi p \sigma^{2}}\,.
+    \f]
+
+    \vartable
+        A_1       | Coefficient [-]
+        A_2       | Coefficient [-]
+        A_3       | Coefficient [-]
+        \sigma    | Lennard-Jones parameter [m]
+    \endvartable
+
+    Reference:
+    \verbatim
+        Davies, C. N. (1945).
+        Definitive equations for the fluid resistance of spheres.
+        Proceedings of the Physical Society, 57(4), 259.
+    \endverbatim
+
+Usage
+    \table
+        Property    | Description                | Required    | Default value
+        A1          | Coefficient A1             | no          | 2.514
+        A2          | Coefficient A2             | no          | 0.8
+        A3          | Coefficient A2             | no          | 0.55
+        sigma       | Lennard-Jones parameter    | yes         | none
+    \endtable
 
 SourceFiles
     aerosolDrag.C
@@ -47,7 +80,7 @@ namespace dragModels
 {
 
 /*---------------------------------------------------------------------------*\
-                           Class aerosolDrag Declaration
+                         Class aerosolDrag Declaration
 \*---------------------------------------------------------------------------*/
 
 class aerosolDrag
@@ -56,17 +89,17 @@ class aerosolDrag
 {
     // Private Data
 
-        //- Model coefficient A1
-        const scalar A1_;
+        //- Cunningham slip correction coefficient A1
+        const dimensionedScalar A1_;
 
-        //- Model coefficient A2
-        const scalar A2_;
+        //- Cunningham slip correction coefficient A2
+        const dimensionedScalar A2_;
 
-        //- Model coefficient A3
-        const scalar A3_;
+        //- Cunningham slip correction coefficient A3
+        const dimensionedScalar A3_;
 
-        //- Diameter of the continuous phase molecules, defaults to value for N2
-        const dimensionedScalar dm_;
+        //- Lennard-Jones sigma parameter
+        const dimensionedScalar sigma_;
 
 
 public:

tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/phaseProperties

@@ -159,6 +159,8 @@ drag
         {
             type            aerosolDrag;
 
+            sigma           340e-12;
+
             swarmCorrection
             {
                 type    none;

tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/phaseProperties

@@ -173,6 +173,8 @@ drag
         {
             type            aerosolDrag;
 
+            sigma           340e-12;
+
             swarmCorrection
             {
                 type    none;