[flux][freeflow] doc flux functions

dumux/flux/staggered/freeflow/fickslaw.hh

@@ -84,6 +84,12 @@ public:
 
     using DiffusionCoefficientsContainer = FickianDiffusionCoefficients<Scalar, numPhases, numComponents>;
 
+    /*!
+     * \brief Returns the diffusive fluxes of all components within
+     *        a fluid phase across the given sub-control volume face.
+     *        The computed fluxes are given in mole/s or kg/s, depending
+     *        on the template parameter ReferenceSystemFormulation.
+     */
     template<class Problem, class ElementVolumeVariables>
     static NumEqVector flux(const Problem& problem,
                             const Element& element,

dumux/flux/staggered/freeflow/fourierslaw.hh

@@ -61,7 +61,13 @@ public:
     //! We don't cache anything for this law
     using Cache = FluxVariablesCaching::EmptyDiffusionCache;
 
-    //! calculate the diffusive energy fluxes
+    /*!
+     * \brief Returns the heat flux within the porous medium
+     *        (in J/s) across the given sub-control volume face.
+     * \note This law assumes thermal equilibrium between the fluid
+     *       and solid phases, and uses an effective thermal conductivity
+     *       for the overall aggregate.
+     */
     template<class Problem>
     static Scalar flux(const Problem& problem,
                        const Element& element,

dumux/flux/staggered/freeflow/maxwellstefanslaw.hh

@@ -88,6 +88,11 @@ public:
 
     using DiffusionCoefficientsContainer = MaxwellStefanDiffusionCoefficients<Scalar, numPhases, numComponents>;
 
+    /*!
+     * \brief Returns the diffusive fluxes of all components within
+     *        a fluid phase across the given sub-control volume face.
+     *        The computed fluxes are given in kg/s.
+     */
     template<class ElementVolumeVariables>
     static CellCenterPrimaryVariables flux(const Problem& problem,
                                            const Element& element,