As noted in Chapter 1, GENTRA is equipped with three user-interfaces:
A data-input menu;
The use of PIL commands in the Q1 file;
The use of FORTRAN in subroutine GENIUS.
This chapter explains how to use the input menu for problem specification. The use of the GENTRA Input Library of simulations is also discussed at the end of the chapter.
(a) The GENTRA menu allows the user to specify the input data for the disperse phase as choices from a set of hierarchically-organised menu panels. On-line help is available to assist the user in the selection process.
(b) The GENTRA menu makes, automatically, all the other provisions needed for the EARTH run. Chapter 3 of this Guide details the nature of these provisions for the benefit of the expert user.
(c) The GENTRA menu writes, at the end of the current Q1 file, and as PIL commands, the results of (1) and (2) above.
The GENTRA menu is accessed from the Models page of the VR Main Menu, which in turn is accessed by clicking on the Menu button of the hand-set. Full details of the VR Environment are given in TR326: PHOENICS-VR Reference Guide.
Figure 2.1 Main Menu Models
Turn GENTRA on by clicking on OFF next to Lagrangian Particle Tracker (GENTRA). A new button labelled Settings will appear. To enter the GENTRA Menu, click on Settings
As pointed out in Section 2.2.1, the GENTRA menu is used to specify data for the disperse phase; the user must, additionally, specify the data for the continuous phase. This can be done in any of the ways that are available in PHOENICS, for instance:
(a) By using another menu system, such as the Main Menu;
(b) By entering the PIL commands directly in the Q1 file; or
(c) By loading a case from the PHOENICS Input Library.
The provisions made by the GENTRA menu will depend on the continuous-phase set-up (for instance, the auxiliary storage allocated by the GENTRA menu for the GENTRA-EARTH run will depend on the dimensionality of the problem). For this reason, you are advised to enter the GENTRA menu after the continuous-phase settings have been effected.
All the menu options have associated help entries. To obtain help on an option, click the question mark "?" at the top right corner of the dialog box, then click on the item in question.
If you are following the worked example provided in this chapter, enter the PHOENICS-VR environment. Click on the PHOENICS icon on the desktop, or click on Start, Programs, PHOENICS, PHOENICS. Load the PHOENICS Library Case B534 by clicking on File, Load from Libraries, entering B534 and clicking 'OK'. This case simulates the flow of a liquid (water) through a ball valve, and will be used as the basis of the worked example. Particles (e.g., solids in suspension) will be included in the flow simulation by means of the GENTRA Input Menu.
After loading the case, you can inspect the settings by double-clicking on the various objects to bring up their Attribute dialog boxes, and check the domain settings by clicking on Menu on the hand-set.
Once you are ready to move on to GENTRA, click on Menu on the hand-set, then on Models, turn GENTRA ON and click on Settings.
After loading the GENTRA menu as detailed in Section 2.2, the first menu panel to appear on the screen is the GENTRA Main Menu Panel, shown in figure 2.2. The options in this panel can be divided into two groups:
The options in these groups will now be explained in this manual. Section 2.4 below will explain what help and information are available on-line. Sections 2.5 to 2.9 will deal with the first group (i.e., data entry); and Section 2.10 will explain how to finish the menu session.
Figure 2.2: The main menu panel
The option Help and information of the Main Menu (figure 2.2), brings up the menu panel shown in figure 2.3.
Figure 2.3: Help and information
The options in this panel are explained below.
1 Help on each menu option can be obtained as explained in Section 2.2.4 above.
2 Help items on special topics are available as choices from the menu. For instance, all the options in the current menu panel are informative ones.
The GENTRA Glossary has been included in this Guide as Appendix H.
The information contained in this entry is listed in this Guide as Appendix E
GENTRA errors are classified into:-
Warnings (with numbers between 001 and 299), which do not abort the program but reset some of the user-supplied parameters, that are detected to be inconsistent;
Fatal errors (with numbers between 300 and 599), which abort the program;
Internal errors (with numbers between 600 and 899), which should be referred to CHAM.
By default, all the error messages are written to the screen, but you can change this in the GENIUS subroutine. Section 5.3 below provides details.
The information provided is summarised in Appendix B of this Guide.
* If you are following the worked example, you can now explore all these sources of information if you so wish, and return to the GENTRA main menu.
The option Particle type of the Main Menu (figure 2.2), allows you to specify the type of particle (e.g., vaporising droplet, melting particle, etc); and the physics of the particle type (e.g., drag law, specific heat, buoyancy effects, turbulent dispersion).
When you choose this option, the menu panel in figure 2.4 is produced. The options in the panel are now dealt with in successive subsections.
* Click on Particle type now.
Figure 2.4: Particle type
The particle type to be simulated is selected by clicking on the name of the particle type, which by default is Isothermal Particles. This displays a list of available particle types, shown in Figure 2.5. The settings button allows the specification of the physics and data of the chosen particle type. Finally, there is an option to return to the previous menu.
Figure 2.5: Particle type selection
* For the worked example, the isothermal particle type should be selected. The number of inputs for this particle type is small, but permits the typical features of all panels to be examined.
Lazy particles do not have a size or a temperature, and cannot undergo any physical process (such as solidification, or vaporisation) though turbulent dispersion is permitted. Lazy particles have no effect on the continuous-phase solution.
On hitting a wall or obstacle, the lazy particle will be removed from the domain.
Stubborn particles do not have a size or a temperature, and cannot undergo any physical process (such as dispersion by turbulence, or solidification, or vaporisation). They do not exchange momentum with the continuous phase.
On hitting a wall or obstacle, the stubborn particle will be removed from the domain.
On hitting an obstacle, an isothermal particle can either be removed from the domain or bounced with a user-supplied restitution-coefficient.
The choice of a particle type should normally be your first action when using the GENTRA Menu, as some of the menu options (e.g., those concerning physical data or particle-obstacle interaction) will depend on the type of particle.
The settings button on the Particle type panel enables the user to specify values for the particle physics (such as drag law, Nusselt numbers, specific heat, buoyancy effects, turbulent dispersion).
The data items to be supplied are dependent on the particle type selected in the previous menu panel. The user is therefore advised to select the correct particle type before visiting this data section.
The following subsections describe the data panels for each of the available particle types.
Figure 2.6: Data for lazy particles
The only data required for lazy particles concerns the use of the stochastic turbulence model for particle dispersion.
GENTRA has a built-in model that simulates the effect of the turbulent fluctuations of the continuous-phase velocity on the dispersion of particles.
The selection of the option Stochastic turbulence model in the Particle physics menu (figure 2.6) will alternately activate/deactivate this feature.
* Try this now by clicking not_active; the stochastic turbulence model will be activated. Click active, and it will be deactivated again. Then return to the GENTRA main menu panel by choosing Previous panel.
Note that, for the stochastic model to be available, the k-e model of turbulence must be used. GENTRA-EARTH will automatically deactivate it if KE and/or EP are not SOLVEd for or, at least, STOREd.
When the stochastic turbulence model is selected, the particle trajectories will be calculated from the sum of the mean continuous-phase velocity and an instantaneous turbulent velocity fluctuation determined from the local turbulence conditions.
No additional data is required for this particle type.
Figure 2.7: Data for isothermal particles
The drag coefficient (which is responsible for the exchange of momentum between the disperse and the continuous phase) can be specified in one of three ways:-
GRND1 (or -10120.)
GRND2 (or -10130.)
Drag coefficient read from table
(See Chapter 6 of this Guide for mathematical expressions)
You can introduce your own law in Section 1 of GPROPS (see Chapter 5 for details). Recompilation and re-linking of EARTH is needed after the modification of GPROPS.
The various forms of Drag Law are selected from a menu:
Figure 2.7a: Selecting the Drag Law
When the 'Drag Law from table file' option is selected, the dialog offers buttons to:
Figure 2.7b: Drag Law from table file
The file should contain two columns of numbers. The first is the Reynolds Number, the second the Drag Coefficient at that Reynolds Number. There is no limit to the number of lines. Blank lines, lines starting with # and anything after ! is ignored. The first active line can optionally contain headers for the columns. The columns can be separated by blanks, comma (,), semicolon (;) or tab. An extract from the example file, which gives the same Cd-Re relationship as the 'spheres' expression, is given below:
# Drag curve for spheres, taken from Clift, Grace & Weber # as implemented in GENTRA # https://www.cham.co.uk/phoenics/d_polis/d_docs/tr211/chap6.htm#6.3 # Valid for rigid spherical particles up to Re<3E5 Re , Cd 1.8 , 16.38612019 9.61 , 4.346219022 23.4 , 2.44605341 43.2 , 1.742424078 68.7 , 1.386829359 98.9 , 1.177059906 134.0, 1.036072042
* The built-in law will suffice for the worked example. However, you can enter other values, then enter GRND1 again for the sake of practice. Then return to the previous panel by clicking Previous panel.
The gravity/buoyancy forces option enables the user to activate gravity forces for the particles, and to include buoyancy and pressure gradient effects. The option brings up the menu panel displayed in figure 2.8.
Figure 2.8: Gravity/buoyancy
* Enter 9.8 for Z-component of gravity vector to specify an acceleration of 9.8 m/s2 acting along the z axis.
If P1 includes the hydrostatic pressure, then the user selects:
If P1 excludes the hydrostatic pressure (reduced pressure formulation), then the user should select:
Figure 2.9: Data for heat-exchanging particles
The selection of drag coefficient is identical to that for the case of isothermal particles; see subsection (c) above for a complete explanation.
1. Replace the constant value in the menu with a GRND number (i.e. GRND1).
2. Modify function routine GPROPS in the file GENTRA.FTN by adding coding in the relevant section. For this case, the coding should be added in the section commencing "GROUND1", and in the subsection commencing "3 Thermal Conductivity of the continuous phase". Coding relating the thermal conductivity (GPROPS) to the continuous-phase temperature (PARAMT) should then be inserted.
3. Before running EARTH, the GENTRA file will have to be recompiled and the EARTH executable relinked.
Gravity and buoyancy/pressure gradient effects and turbulent dispersion can be included; the reader is referred to the entries in sub-sections (c) and (a) above, for an explanation.
Figure 2.10: Data for melting/solidifying particles
The data required for melting/solidifying particles is as follows:
The constant values which appear in this menu can be replaced with functions set in function routine GPROPS, according to the method described in Subsection (c) above.
Figure 2.11: Data for vaporising droplets
The constant values, which appear in this menu, can be replaced with functions set in function routine GPROPS, according to the method described in Subsection (c) above.
The Boundary conditions button in the Main Menu panel (figure 2.2) is used to specify the boundary conditions for the particles. Boundary conditions fall into the following categories:-
* Click on Boundary conditions to bring up the Boundary conditions panel.
Figure 2.12: Boundary conditions for particles
The options in the Boundary conditions panel (shown in figure 2.12) are dealt with in subsequent subsections.
The Inlet conditions option of the Boundary conditions panel produces the panel in figure 2.13.
Figure 2.13 Particle inlet conditions
* The default file-name, Q1, will be used for the worked example.
This option allows the specification of inlet co-ordinates in the inlet file in either the GENTRA Cartesian system (see glossary entry for a definition) or in the grid system. The distinction is only relevant to cylindrical-polar grids, since in Cartesian and BFC the GENTRA Cartesian system and the grid system coincide.
At present, the particle positions must be specified in the grid co-ordinate system. Thus for cylindrical-polar grids, the co-ordinates are specified as ?, r, z. The alignment between the Cartesian and polar grid systems is explained in Appendix H.
This option allows the specification of inlet velocities in the inlet file in either the GENTRA Cartesian system (see glossary entry for a definition) or in the grid system. The distinction is only relevant to cylindrical-polar and BFC grids, since in Cartesian grids the velocity components in the GENTRA Cartesian system and in the grid system are the same.
At present, all inlet velocities must be specified in the Cartesian co-ordinate system, in the order Ucrt, Vcrt, Wcrt, where these represent the velocity components in the Cartesian X, y and Z directions respectively. For cylindrical-polar grids, the order of specification is Vcrt, Ucrt and Wcrt.
Inlet data In the inlet-data table, each parcel of particles has a data line; the data required is case-dependent. For the user's guidance, the GENTRA menu will generate, as a comment in the resulting Q1 file, a suitable heading for the inlet table.
The contents of the inlet table are also provided below for the different particle types.
POSTN VELOC DIAM DENSTY FRATE (NUMB)
POSTN VELOC DIAM DENSTY FRATE TEMP (NUMB)
POSTN VELOC DIAM LIQDEN FRATE TEMP SOLDEN (NUMB)
POSTN VELOC DIAM DENSTY FRATE TEMP (NUMB)
In the table above,
By setting the inlet-data file-name to Q1 (the default), GENTRA will expect the inlet-data table to be in the Q1 file. All of the format rules for the inlet-data table (listed above) apply to the Q1 file. In addition, when the inlet data-table is in the Q1 file, the following practices must be observed:-
The inlet-data table can be located anywhere in the Q1 file, and is normally written using a system file-editor after the menu session.
Note: GENTRA can generally cope with inlets lying exactly on the boundaries of the domain or on the grid pole; it is nevertheless a good practice to offset the inlet position by a small distance (e.g., 10-4 m).
* In this worked example, we will write the data table after finishing the menu session
In the VR-Environment, the file containing the inlet data table can be opened for editing by clicking on File, Open file for editing.
If the inlet data table is in Q1, select Q1, and then click Yes to save the current settings to Q1. After editing the inlet data table, save the file and exit the editor. Click Yes to reload the Q1 into VR-Editor, otherwise the new data will be lost.
To open any other file, select Any file, then open it from within the editor.
The editor used can be selected from Options, Text file editor.
Particle exits in GENTRA are represented through PATCH commands. Particle exit-PATCHes must have names beginning with GX, and be of an area type (ie, EAST, WEST, NORTH, SOUTH, HIGH, LOW).
In the VR Environment, all Inlet and Outlet objects act as GENTRA exits by default the PATCHes they create all have names starting with GX. This behaviour can be altered by the Acts as GENTRA exit buttons at the foot of the Inlet and Outlet object attribute dialogs. Note that these buttons only appear once GENTRA is active. The buttons can be seen in Figure 2.14.
Figure 2.14: Inlet and Outlet attribute dialogs
To create an exit where only particles can leave the domain, set the coefficient for the pressure to zero in the Outlet attributes dialog. This will prevent the continuous phase from passing through.
The treatment for particles at an axis/surface of symmetry is always reflection (i.e., bouncing with a restitution coefficient of 1), regardless of the wall treatment selected for the problem.
GENTRA will automatically detect symmetry axes in the following two circumstances:
In all other cases, axes/surfaces of symmetry must be declared by the user, so that GENTRA can act appropriately when a particle hits the axis/surface.
Symmetry surfaces in GENTRA are represented through PATCH commands whose PATCH name starts with GS. Each symmetry PATCH has also an associated PATCH type. This indicates on which face of the cells covered by the PATCH the symmetry surface is. The PATCH type can be EAST, WEST, NORTH, SOUTH, HIGH or LOW.
In the VR Environment, GENTRA symmetry surfaces are created by making a new object, with type GENTRA_SYMMETRY. This object type is only available when GENTRA is active. The PATCH created by such an object will have a name starting with GS, and will be of the correct type.
* The grid in the worked example is of the "wedge-like" kind; the axis will therefore be automatically detected by GENTRA.
The option Wall/obstacle treatment in the Boundary conditions panel (figure 2.12) specifies how the particle interacts with walls and obstacles (e.g., bouncing, sticking, removal).
See the GENTRA Glossary for a definition of wall/obstacle.
The options available depend on the type of particle; the user is therefore advised to set the particle type before visiting this menu. (The panel in figure 2.15 shows all of the possible treatments.)
Figure 2.15: Wall/obstacle treatment
The menu Wall/obstacle treatment has, in the general case, the following options (figure 2.15):
(Note that REMOVE PARTICLE and STICK PARTICLE have the same effect for isothermal particles.)
See Section 6.6.2 for more information on bouncing.
* Choose Bounce and set a restitution coefficient of 0.75 for the worked example. Then return to the previous panel.
This option is available only for VAPORISING DROPLETS.
This option of the Boundary conditions panel (figure 2.12) allows the user to set the level of porosity that will be considered by GENTRA to constitute an obstacle for the particles.
For instance, a value of 0.75 will indicate that cells and cell faces with porosities between 0.0 and 0.75 will be taken as obstacles for the particulate phase.
Only values between 0 and 0.999 are accepted.
The option Numerical controls of the main menu (figure 2.2) allows the user to control the solution procedure for the particulate phase. Users can, for instance:-
Figure 2.16: Numerical controls
It is often a good practice to start the particle tracking when the continuous-phase field is developed. The selection of values greater than 1 for this option will have that effect.
This option can also be used to switch off the particle tracking by setting a value greater than the number of PHOENICS sweep (LSWEEP). If GENTRA is deactivated in this fashion, all the GENTRA settings will be retained in the Q1. It will be possible to turn GENTRA on again later. If GENTRA is turned off from the Models panel, all GENTRA settings are cleared. To turn GENTRA back on would involve re-setting all the non-default values.
* The number of PHOENICS sweeps for the example is LSWEEP=200; choose 190 as the first GENTRA sweep.
Values greater than 1 are recommended, in conjunction with source relaxation, for high particle loadings; for the continuous phase is then able to "absorb" the interphase sources before the next call to GENTRA.
* Since the particle loading will not be a high one in the worked example, the default value will suffice.
This device can, for instance, avoid large computing times arising from very small time-steps.
The step number n can be positive, negative or zero:-
* Enter -100 for the worked example.
This device can avoid large computing times arising, for instance, from particles being trapped in recirculation regions.
The timeout value r can be positive, negative or zero:-
* Enter 10 for the worked example. Since the fluid inlet-velocity is 2.0 m/s, and the domain length in that direction is 2 m, the particles can be expected to have left the domain in that time.
Values between 0 and 1 have the effect of setting the source to be a weighted average of the sources calculated at the current and previous sweeps i.e.:
Sf = aSfn + (a - 1) Sfn-1.
This may be beneficial for the convergence of the continuous-phase solution when the source is changing significantly from sweep to sweep;
* Set a relaxation factor of 0.7
This is the last option of the Main Menu Panel (figure 2.2), which controls the input and output data flow of GENTRA. When I/O controls is selected in the Main Menu Panel, the following panel will appear.
Figure 2.17: Input/Output controls
Selection of this option produces the panel of figure 2.18.
Figure 2.18: History and trajectory files
The global history file contains the results for all of the particles that are tracked. It can be post-processed using the UNPACK program to produce individual history and/or trajectory files. Details of the operation of the UNPACK program can be found in Appendix K.
* We will require individual trajectory files so choose this option.
Figure 2.19: Output for individual particle
Note that a maximum of 20 trajectory, and 20 history files can be created in this way. Trajectory and history information for all particles is held in the global history file (see figure 2.18 and Appendix K).
The name of the GENTRA restart file. This option is not relevant to steady-state cases. In a transient case, it is the name to which GENTRA writes the particle information at the end of the last time step. Files are also written each time an intermediate dump file is written. These can then be used to continue the run.
When a restart is activated from the Time step setting dialog and GENTRA is active, the name of the GENTRA restart file will also be set.
This option in the Output control panel selects a particle for which the cell residence-time will be calculated by GENTRA. The particle is identified by the user through the particle number. In addition to the particle number, two special numbers can be used as flags to perform special functions:-
0 will deactivate the calculation of residence time;
-1 will add the residence time of all the particles in each cell.
-2 will activate the calculation of a "particle volume-fraction" for each cell, representing the fraction of the cell volume occupied by particles. See Section 6.6.4 for additional details.
* Choose, as an example, to compute the residence time for particle number 2. (Remember that you will define the particle inlet data after the menu session.)
When choosing a value different from 0, the GENTRA menu will automatically allocate whole-field storage-space for the variable REST through the command STORE(REST). The variable REST will be used by GENTRA to store the cell residence-time; this can be inspected in the printout of that variable in the RESULT file.
The foregoing options are available for steady flows only (STEADY=T), and the particle volume fraction option is not available for lazy particles (GPTYPE=10) because the particle mass is zero.
For unsteady flow (STEADY=F), the particle volume fraction will be calculated for each cell (see section 6.6.4) provided that STORE(PVFR) appears in the Q1 input file.
This option in the Output control panel provides for the calculation of the particle mass concentration for each cell (see Section 6.6.5). It can also be activated by setting STORE(PMCO) in the Q1 input file.
This option in the Output control panel provides for the calculation of the mixture density for each cell (see Section 6.6.6). It can also be activated by setting STORE(RHMX) in the Q1 input file.
This option in the Output control panel provides for the calculation of the particle mass fraction for each cell (see Section 6.6.7). It can also be activated by setting STORE(PMFR) in the Q1 input file.
The GENTRA Menu session is ended from the GENTRA Main Menu Panel, shown in figure 2.2 by clicking on Previous panel. This returns control to the normal VR Main menu.
* Choose this option now to finish. Click on Top and OK to quit the VR Main Menu. Now edit the Q1 file and insert, as comments, the inlet data for the particles. The inlet data must be inserted between the marks <GENTRA-INLET-DATA> and <END-GENTRA-INLET> in the Q1 file. Refer to Section 22.214.171.124 above for instructions, and to the Q1 file in Appendix E for an example. Copy the settings from Appendix E.
GENTRA has a library of ready-to-run examples and tests. To see the contents of the GENTRA Input Library, click on File, Load from Libraries on the VR Environment top menu.
Figure 2.20: Accessing the Libraries
On the library dialog, click on Browse, then open the Option Libraries branch of the library tree. The GENTRA libraries are further subdivided as shown in Figure 2.21
Figure 2.21: The GENTRA Input Library
The contents of the Library are listed as Appendix F of this Guide.
Once the GENTRA Menu session is ended, or a library case has been loaded, you are ready to execute the calculating program EARTH. Chapter 4 explains how to do so. (You can skip Chapter 3, which gives additional details on data input using PIL, if you are a beginner.)
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