Do you know that CFD refers to Colorful Fluid Dynamics ? OK, it is not exactly that but … it can be !

Moreover, do you know also that the best moments you spend after running a simulation are those where you visualize your results. With TRUST, this is surely possible. However, keep in mind that you should explicitly define what you want to visualize, which fields, probes, statistics, which format and at what frequency.

All this is done via the TRUST C++ classes: Post_processing or Post_processings (aliases Postraitement or Postraitements). The difference between both classes is that the first one creates a single post-processing object, while the other can creates N objects if you ask for N post-processing blocks. These keywords should be placed at the end of the Problem block. Click here to see the Doxygen documentation of the Postraitement class.

In both cases (whatever which class you use, Post_processing or Post_processings) you can define the following.

Probes

This is done by the C++ class Sonde or Sondes (list of probes). You can request spatial/temporal variation/evolution of any field (should be known by TRUST). The values can be extracted at a single point in space, at a segment of points or in a plane.

Attention: The probe coordinates should be given in Cartesian coordinates (X, Y, Z) even in axisymmetric cases.

Define New Fields (Advanced Fields)

This is done by the C++ class Definition_champs. In this block, you can create new complex fields for advanced post-processings. For example, post-process custom quantities not directly available from the datafile (average of a field, error between TRUST and analytical solution, …).

Write Fields

This is done by the C++ class Fields or Champs. Here you can specify the frequency by the keyword dt_post. For example, the following syntax is used to post-process (and therefore visualize) the pressure (at center of the elements) each 1000 physical seconds of the simulation.

Post_processing
{
    Fields dt_post 1000
    {
        pression elem
    }
}

It is also possible to specify the output format of files. This is done by the keywoed Format, where three formats are available: Lml, Lata and Med. The default format is Lml, used for the non-regression verification only. We recommend Lata format for post-processing. Results can be visualized by VisIt, Salome (Paravis module), Paraview. It is possible to use TecPlot too !

Note: It is possible to convert files written in the Lata format into Lml and Med format. This is done by the Class Lata_to_other. The syntax is the following

lata_to_other med NOM_DU_CAS NOM_DU_CAS or 

lata_to_other lml NOM_DU_CAS NOM_DU_CAS

Remark 1: By default, fields are post-processed on the whole domain. You can choose to post-process fields on a boundary or on a specific domain region.

Remark 2: Remember fields location for each discretization! If you specify in post-processing block for a field a different location than where it is computed, values will be interpolated.

List of Existing and Pre-defined Fields

Here is a list of post-processable fields, but it is not the only ones !


Physical values	Keyword for field_name	Unit
Velocity	Vitesse or Velocity	m.s−1
Velocity residual	Vitesse_residu	m.s−2
Kinetic energy per elements	Energie_cinetique_elem	kg.m−1.s−2
Total kinetic energy	Energie_cinetique_totale	kg.m−1.s−2
Vorticity	Vorticite	s−1
Pressure in incompressible flow (P/ρ + gz)	Pression	Pa.m3.kg−1
Pressure in incompressible flow (P+ρgz)	Pression_pa or Pressure	Pa
Pressure in compressible flow	Pression	Pa
Hydrostatic pressure (ρgz)	Pression_hydrostatique	Pa
Totale pressure	Pression_tot	Pa
Pressure gradient	Gradient_pression	m.s−2
Velocity gradient	gradient_vitesse	s−1
Temperature	Temperature	C or K
Temperature residual	Temperature_residu	C.s−1 or K.s−1
Temperature variance	Variance_Temperature	K2
Temperature dissipation rate	Taux_Dissipation_Temperature	K2.s−1
Temperature gradient	Gradient_temperature	K.m−1
Heat exchange coefficient	H_echange_Tref	W.m−2.K−1
Turbulent viscosity	Viscosite_turbulente	m2.s−1
Turbulent dynamic viscosity	Viscosite_dynamique_turbulente	kg.m.s−1
Turbulent kinetic	Energy	K m2.s−2
Turbulent dissipation rate	Eps	m3.s−1
Constituent concentration	Concentration	-
Constituent concentration residual	Concentration_residu	-
Component velocity along X	VitesseX	m.s−1
Component velocity along Y	VitesseY	m.s−1
Component velocity along Z	VitesseZ	m.s−1
Mass balance on each cell	Divergence_U	m3.s−1
Irradiancy	Irradiance	W.m−2
Q-criteria	Critere_Q	s−1
Distance to the wall Y +	Y_plus	-
Friction velocity	U_star	m.s−1
Void fraction	Alpha	-
Cell volumes	Volume_maille	m3
Source term in non Galinean referential	Acceleration_terme_source	m.s−2
Stability time steps	Pas_de_temps	s
Volumetric porosity	Porosite_volumique	-
Distance to the wall	Distance_Paroi	m
Volumic thermal power	Puissance_volumique	W.m−3
Local shear strain rate	Taux_cisaillement	s−1
Cell Courant number (VDF only)	Courant_maille	-
Cell Reynolds number (VDF only)	Reynolds_maille	-
Viscous force	Viscous_force	kg.m2.s−1
Pressure force	Pressure_force	kg.m2.s−1
Total force	Total_force	kg.m2.s−1
Viscous force along X	Viscous_force_x	kg.m2.s−1
Viscous force along Y	Viscous_force_y	kg.m2.s−1
Viscous force along Z	Viscous_force_z	kg.m2.s−1
Pressure force along X	Pressure_force_x	kg.m2.s−1
Pressure force along Y	Pressure_force_y	kg.m2.s−1
Pressure force along Z	Pressure_force_z	kg.m2.s−1
Total force along X	Total_force_x	kg.m2.s−1
Total force along Y	Total_force_y	kg.m2.s−1
Total force along Z	Total_force_z	kg.m2.s−1

Complete Post-Processing Example

Here is a complete post-processing example taken from the TRUST’s upwind test case.

Post_processing
{
    Probes
    {
        sonde_pression pression periode 0.005 points 2 0.13 0.105 0.13 0.115
        sonde_vitesse vitesse periode 0.005 points 2 0.14 0.105 0.14 0.115
        sonde_vitesse_bis vitesse periode 0.005 position_like sonde_vitesse
        sonde_vitesse_ter vitesse periode 1e-5 position_like sonde_vitesse
    }

    Definition_champs
    {
        # Calcul du produit scalaire grad(Pression).Vitesse #
        pscal_gradP_vit Transformation {
            methode produit_scalaire
            sources {
                Interpolation { localisation elem source refChamp { Pb_champ pb gradient_pression } } ,
                Interpolation { localisation elem source refChamp { Pb_champ pb vitesse } }
            }
        }
        # Calcul du produit scalaire Vitesse.Vitesse #
        pscal_vit_vit_elem Transformation {
            methode produit_scalaire
            sources {
                refChamp { Pb_champ pb vitesse } ,
                refChamp { Pb_champ pb vitesse }
            }
            localisation elem
        }

        pscal_vit_vit_elem_interp Transformation {
            methode produit_scalaire
            sources {
                Interpolation { localisation elem source refChamp { Pb_champ pb vitesse } } ,
                Interpolation { localisation elem source refChamp { Pb_champ pb vitesse } }
            }
        }

        pscal_vit_vit_som Interpolation { localisation som sources_reference { pscal_vit_vit_elem_interp } }

        pscal_vit_vit_faces Interpolation { localisation faces sources_reference { pscal_vit_vit_elem_interp } }

        norme_transfo_vit Transformation {
            methode norme
            source Interpolation {
                localisation elem
                source refChamp { Pb_champ pb vitesse }
            }
        }

        vecteur_unitairex transformation { methode vecteur expression 2 1. 0. localisation faces }

        vecteur_transfo transformation { methode vecteur  expression 2 x t localisation faces }

        vecteur_source_elem Transformation {
            methode vecteur  expression 2 pression_natif_dom y
            source refChamp { Pb_champ pb pression }
            localisation elem
        }
        vecteur_source_faces Transformation {
            methode vecteur expression  2 pression_natif_dom y
            source refChamp { Pb_champ pb pression }
            localisation Faces
        }

        compo_vitessex Transformation {
            methode composante numero 0
            source refChamp { Pb_champ pb vitesse }
            localisation elem
        }

        compo_vitessex_elem Interpolation { localisation elem sources_reference { compo_vitessex } }

        # Calcul de la composante selon X du gradient de pression #
        compo_graPx Transformation {
            methode composante numero 0
            source refChamp { Pb_champ pb gradient_pression }
            localisation elem
        }
        # Interpolation de cette composante aux elements #
        compo_graPx_elem Interpolation { localisation elem sources_reference { compo_graPx } }
    }
    Format Lata
    fields dt_post 1.3 /* physical time */
    {
        pression elem
        vitesse elem
        masse_volumique elem
        gradient_pression elem
        pscal_gradP_vit elem
        pscal_vit_vit_elem
        pscal_vit_vit_elem_interp
        pscal_vit_vit_som
        norme_transfo_vit elem
        vecteur_unitairex elem
        vecteur_transfo elem
        vecteur_source_elem
        compo_vitessex_elem
        compo_graPx_elem
    }
}

liste_de_postraitements {
    test1 Post_processing {
        Definition_champs {
            test_nom reduction_0D {
                methode weighted_average
                sources { refchamp { pb_champ pb pression } }
            }
        }
        format lata
        fields dt_post 1.3
        {
            pression elem
            test_nom
        }
    }

    test2 Post_processing {
        format lata
        fields dt_post 1.3e9
        {
            pression elem
        }
    }
}

Post-Processing

Probes

Define New Fields (Advanced Fields)

Write Fields

List of Existing and Pre-defined Fields

Complete Post-Processing Example

TRUST Platform