In addition to using the GENTRA Input Menu, you can enter directly in the Q1 file the GENTRA commands that define your simulation. Since the GENTRA Menu will translate your menu choices into fully commented Q1 settings, you can also edit the Q1 file to effect small modifications once the menu has taken care of the bulk of the Q1-writing work.
This chapter explains how users can avail themselves of the GENTRA-PIL for problem specification. Section 3.2 below describes the group structure of the GENTRA settings in the Q1 file; and subsequent sections deal with each GENTRA input-data group.
The GENTRA menu will normally be called after some provisions have been made in the Q1 file for the specification of the continuous phase (e.g., through another menu or by loading a PHOENICS Library case).
The GENTRA menu will add to the existing Q1 file a "GENTRA section" with the following parts:
(a) GENTRA declarations
(b) Groups 1 to 4: GENTRA data
(c) Group 5: GENTRA provisions for the EARTH run
(d) Transmission of data to EARTH
All these groups are described in the next subsections; however, you will only need to use groups 1 to 4 and (occasionally) group 5.
The Q1 file for the example of the previous chapter has been attached as Appendix E. It can be referred to for exemplification.
The first section inserted by the GENTRA Menu into the Q1 file is used for declaration and initialisation of the GENTRA-PIL variables. Users do not need to modify in any way this section. The GENTRA PIL variables are initialised in the GENTRA Library case G0001. This is loaded by the command L($G0001, as can be seen in Group 19 of the Q1 listing in Appendix E, just before the line GENTR = T. It is this setting which tells EARTH that GENTRA is active.
This part of the Q1 file (see Appendix E for an example) carries the problem-definition settings. It comprises four groups, which are the same as those appearing in the main panel of the GENTRA menu (see figure 2.2), namely:
Group 1: Particle physics.
Group 2: Particle boundary-conditions.
Group 3: Numerical controls.
Group 4: Input/Output controls.
Settings in these groups are effected by assigning values to the GENTRA-PIL variables. A list of these variables (and, where appropriate, the acceptable range of values) can be found in Appendix B.
GENTRA Group 2 can also carry, optionally, the inlet-data table. See Section 2.7.1 for details.
In addition to performing the data specification for the disperse phase, the GENTRA Menu will also make a number of provisions for GENTRA EARTH, such as the allocation of auxiliary storage space or the set-up of interphase sources.
The provisions made by the GENTRA Menu depend on the dimensionality of the problem, the grid type, the continuous-phase variables that are being solved for and the particle type.
The settings will be found in Groups 7, 13 and 17 of the Q1 file.
A complete list of the actions undertaken by the GENTRA Menu can be found below for the user's reference:-
(a) If the grid is a BFC one, and the continuous-phase Cartesian velocity components UCRT, VCRT, WCRT have not been STOREd, a STORE command will be issued. (GENTRA uses the Cartesian velocity component for the integration of the particle momentum equations).
(b) For BFC grids, NCRT (ie, the sweep frequency for the calculation of the Cartesian components in (a)) is set to 1.
(c) 3D storage space is allocated through STORE commands for the following quantities:
MOMX, MOMY,MOMZ the interphase sources of momentum. (Not stored for "lazy" and "stubborn" particles.)
HEAT, the interphase source of heat, stored if the particle is exchanging heat with the continuous phase.
MASS, the interphase source of mass, stored if the particle is exchanging mass with the continuous phase.
(d) The variable VAPO (representing the vapour mass-fraction in the continuous phase for vaporising droplets) is SOLVEd for if appropriate; and its PRANDTL numbers PRNDTL(VAPO) (laminar) and PRT(VAP0) (turbulent) are assigned according to the menu settings.
(e) If the calculation of cell residence-time for a particle has been requested, 3D storage is allocated for the variable REST through a STORE command.
(f) PATCHes and COVALs are generated for the interphase sources, as follows:
PATCH (GENPAT, CELL, 0, 0, 0, 0, 0, 0, 1,
LSTEP)
COVAL (GENPAT, U1 , FIXFLU, GRND)
COVAL (GENPAT, V1 , FIXFLU, GRND)
COVAL (GENPAT, W1 , FIXFLU, GRND)
COVAL (GENPAT, H1 , FIXFLU, GRND)
COVAL (GENPAT, VAPO, FIXFLU, GRND)
(g) For vaporising droplets, PATCHes and COVALs are generated for the interphase source of mass, as follows:
PATCH (GENMAS, CELL, 0, 0, 0, 0, 0, 0, 1,
LSTEP)
COVAL (GENMAS, P1 , FIXFLU, GRND)
(h) Linear relaxation is introduced for the interphase sources through the command RELAX (<var>, LINRLX, <value>), where <value> is assigned in the menu (see Section 2.8).
(i) The call to the GENTRA Ground-station is activated by the command:
NAMGRD=GNTR
Note that, in the provisions (c), (f) and (h), the GENTRA Menu will take into account the dimensionality of the problem, and act accordingly.
The GENTRA-PIL variables are transmitted to EARTH through the PIL transfer arrays RG, LG, CG and IG for real, logical, character and integer variables respectively. The transmission takes via the command L(GENSET, which loads GENTRA Library case G002.
The contents of this group do not need to be modified in any way. However, the RG, LG, CG or IG variables are being used for the transmission of the user’s own data, please check this group for clashes with usage by GENTRA. The positions in the transfer arrays currently occupied by GENTRA are:
RG: RG(71) to RG(100)
IG: IG(9) to IG(20)
LG: LG(10) and LG(19) to LG(20)
CG: CG(6) to CG(10)
Exit and symmetry patches created through Inlet, Outlet and GENTRA_SYMMETRY objects (see Section 2.7) are written to the EARDAT file directly, and do not appear in the Q1 file.
Inlets and outlets which do not act as GENTRA outlets have the additional line:
> OBJ, GENTRA_EXIT, 1.000000E+00
as part of their definition. The absence of such a line is a signal that the inlet or outlet does act as a GENTRA exit.
GENTRA_SYMMETRY objects are written to the Q1 as:
> OBJ, NAME, name
> OBJ, POSITION, Xorigin, Yorigin, Zorigin
> OBJ, SIZE, Xsize, Ysize, Zsize
> OBJ, CLIPART, DEFAULT
> OBJ, TYPE, GENTRA_SYMMETRY