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- TR211: GENTRA User Guide Chapter 5

has been updated the particle properties at the beginning of the current time step are assigned the values prevailing at the end of the previous one the continuous phase properties at the particle position have been found see Section C 1 for a list of these variables and Section 6 8 3 for further information and the stagnation check has been passed see Section 6 8 1 and before the time step is calculated see Section 6 7 1 and the particle is moved see Section 6 8 Users can in this group specify the maximum time step by resetting the variable GDTMAX initially set in the Q1 file menu or inspect and with caution change the continuous phase properties experienced by the particle see Section 6 8 3 GENIUS Group 4 Particle reaches cell boundary GENIUS Group 4 is visited when a particle reaches a cell boundary The value of IGENSC is used to distinguish between several events as follows IGENSC 1 means that the particle has reached an exit i e the appropriate face of a patch whose name starts with GX IGENSC 2 means that the particle has reached a wall or obstacle Note that the visit to GENIUS takes place after the velocity components have been changed after bouncing if the particle is to be bounced IGENSC 3 means that the particle has been reflected at an axis surface of symmetry IGENSC 4 means that the particle is in a new cell note that the particle might in this case be inside the new cell and not just on the boundary GENIUS Group 5 End of current Lagrangian time step Group 5 of GENIUS is called at the end of the current Lagrangian time step after the cell residence time CTIME and the absolute time TIME have been increased by GDT the current time step size the several end of tracking criteria such as timeouts have been checked the cell residence time CTIME has been reset if the particle is in a new cell and transferred to the full field store in EARTH if the current particle IPARTI is GRESTI Users can in group 5 of GENIUS kill the tracking of the particle by setting the logical variable KILPAR to TRUE The tracking of the particle will be then abandoned and GENTRA will start tracking the next one GENIUS Group 6 End of current track Group 6 of GENIUS is visited before finishing the track for the current particle and moving on to the next one It is visited after the plot trajectory and history files have been written if appropriate and closed GENIUS Group 7 GENTRA returns control to EARTH GENIUS Group 7 is visited immediately before RETURN ing the control to EARTH after the CALL to GENTRA for the current sweep GENIUS Group 8 Special calls Group 8 of GENIUS is designed to allow the user to modify the built in Lagrangian equations There are 5 sections in this group Section 1 Particle momentum

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Open archived version from archive - TR211: GENTRA User Guide Chapter 6

which the term representing evaporation is not present Vaporising droplets 6 19 in which the solidification term is absent Submodels Stochastic turbulence model GENTRA features an optional stochastic turbulence model Gosman and Ioannides 1981 which accounts for the effects on particle dispersion of the turbulent fluctuations of the continuous phase velocity The model uses as the continuous phase velocity in the drag force term of the momentum equation equation 6 3 a sum of the average velocity U c and a fluctuating component U c U U c U c 6 20 where U c the average velocity is obtained from the Eulerian equations for the continuous phase and U c the fluctuating component is calculated assuming that each component follows a normal distribution with a mean value of 0 0 and a standard deviation of 6 21 where K is the turbulence kinetic energy The fluctuating component U c is assumed to act over a time interval D ts which is the minimum of a D t e the lifetime of the local eddy which the particle is assumed to be traversing and b D t r the transit time taken for the particle to cross the eddy The eddy lifetime D t e is computed as 6 22 where le is the eddy size 6 23 where e is the rate of dissipation of turbulence kinetic energy and Cµ is a constant in the turbulence model The particle transit time D t r is given by 6 24 Rotating coordinate systems In rotating coordinate systems the particle U p and continuous phase U c velocities solved for by GENTRA and PHOENICS are the ones relative to the rotating system Coriolis and centrifugal sources must therefore be included in the momentum equations For the particle the extra term in the momentum equation equation 6 3 is 6 25 where is the angular speed of rotation expressed here as a vector along the axis of rotation x p is the particle position vector and indicates cross product The rotating co ordinate feature of GENTRA is activated automatically when its PHOENICS counterpart is activated See the entry ROTA in the SATELLITE help dictionary for details on how to activate it and how to specify the axis of rotation and the angular speed Note that the FORTRAN logical variable ROTCOO can be used to deactivate the automatic introduction of this feature See Appendix C for details Integration of the equations The numerical integration of the particle equations takes place according to the following sequence a The Lagrangian time step is calculated b The particle is moved c The particle properties at the new position are calculated d The interphase sources are calculated These four steps are dealt with in subsequent subsections Calculation of the Lagrangian time step tl The Lagrangian time step is computed by GENTRA as D tl max t 0 min t 1 t 2 t 3 6 26 where t 0 to t 3 are as follows a t 0 is a minimum time step size given by the FORTRAN variable GDTMIN Its default value is 10 0 7 users can re set it in Group 1 of GENIUS b t 1 is the minimum cell crossing time divided by the Q1 set variable GLAGTS the minimum number of Lagrangian time steps per cell specified by the user The minimum cell crossing time is estimated by GENTRA for each cell using the minimum cell dimension and the maximum velocity component c t2 is the momentum relaxation time If the particle momentum equation is re written as 6 27 t2 is calculated as where a is a multiplication factor a is available through GENIUS as the FORTRAN variable GRTFRL Its default value of 10 10 effectively excludes t2 as a criterion in equation 6 26 since it is larger than the others Users wanting to relate the time step D tl to the momentum relaxation time t2 can reset GRTFRC in Group 1 of GENIUS However this might result in very small time steps for small particles d t 3 is the user supplied maximum time step size PIL variable GDTMAX Note that the time step thus computed may be further reduced by GENTRA after the integration of the position equations as follows a The particle is not allowed to jump in the current time step beyond the neighbouring cells b for boundary cells i e cells at the boundaries of the computational domain or cells next to internal blockages a particle crossing the cell boundary is placed on the cell boundary by reducing the time step Moving the particle After computing the time step tl the particle is moved by integrating the particle position equations The particle position equation equation 6 2 d x p dt U p is integrated as x n p x o p U o p D t 6 28 where n denotes the value at the end of the time step and o denotes the value at the beginning of the time step GENTRA integrates the position equations in the GENTRA Cartesian System in cylindrical polar grids equation 6 28 can optionally be integrated in polar co ordinates i e using the radius the angle and the circumferential and radial velocities as variables The FORTRAN logical variable POLTRC see Appendix C accessible from GENIUS controls this option Note however that in order to avoid the singularity at the polar axis y 0 GENTRA will always track in Cartesian co ordinates in the centre of the grid IY 1 Integration of momentum mass and enthalpy equation The equations representing the momentum mass and enthalpy of the particles can be represented in the following generalized form d x dt A B x 6 29 where x represents the variable to be solved i e momentum mass or enthalpy and A and B are constants The equation is integrated over the Lagrangian time step tl such that the value at the end of the time step x

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Open archived version from archive - TR211: GENTRA User Guide Appendix A

in physical space may be used FIXVAL OBSTACLES GENTRA will not recognise obstacles that are represented by FIXVALing the velocity components to zero as is the case at the surface of solids in conjugate heat transfer problems However in such problems a property index field PRPS is stored the value of which denotes the material or fluid in each cell PRPS values greater than a certain number 99 by default represent solid materials and GENTRA tests the PRPS field if it is stored to determine the presence of solid obstructions This method cannot be applied to locate cell faces which have been blocked by fixing the velocities to zero and which would therefore represent thin plates However users can represent these obstacles by in addition to FIXVALling the velocities to 0 using a porosity of 0 999 and alter accordingly the porosity threshold of GENTRA in the BOUNDARY CONDITIONS section A porosity of 0 999 will then be recognised by GENTRA as an obstacle while leaving the domain virtually unblocked for the diffusion of the continuous phase Fine Grid Embedding GENTRA is not compatible with the use Fine Grid Volume objects GCV and CCM GENTRA is not compatible with the GCV or CCM forms of BFC in single or multi block form OUT OF CORE MODE The out of core device of PHOENICS cannot be used with GENTRA PARABOLIC MODE GENTRA does not work with the parabolic solution procedure of PHOENICS PARAB T PARTICLE TO PARTICLE INTERACTIONS Particle to particle effects such as particle collision and droplet coalescence are not considered RINNER In cylindrical polar grids the PHOENICS variable RINNER which specifies the inner radius of the computational domain must be 0 if GENTRA is used Annular geometries may be represented by specifying RINNER 0 0 and setting the dimension

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Open archived version from archive - TR211: GENTRA User Guide Appendix B

liquid for solid melt particle GCPSOL REAL Cp of solid GCPVAP REAL Cp of Vapour GDRAG REAL Drag coefficient GGRAX REAL X component of gravity vector GGRAY REAL Y component of gravity vector GGRAZ REAL Z component of gravity vector GHLIQD REAL Particle liquid saturation enthalpy GKONC REAL Thermal conduct of the cont phase without vapour GKONV REAL Thermal conductivity of vapour GLAGTS INT Time steps cell GLATVP REAL Latent heat of evaporation GLHEAS REAL Latent heat of solidification GLIQST REAL Liquidus temperature GMWCON REAL Mol Weight of continuous phase GMWVAP REAL Mol Weight of particle GNUSS REAL Nusselt number GPTYPE INT Particle type GSOLIN REAL Index for solid fraction formula GSOLST REAL Solidus temperature GSTOCH BOOL Switch of stochastic turbulence model GSTPRE REAL Saturation pressure of vapour GSURPR BOOL Switch for pressure gradient effects GVAPST REAL Saturation temperature of vapour B 2 2 GENTRA Group 2 Boundary conditions Variable Type Meaning GINFIL CHAR Name of the file for particle inlet condition GINSYS INT Co ordinate system for particle inlet condition GPOROS REAL Threshold for obstacle porosity GWALLC NT Wall type GWREST REAL Restitution coefficient of wall B 2 3 GENTRA Group 3 Numerical controls Variable Type Meaning GDTMAX REAL

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Open archived version from archive - TR211: GENTRA User Guide Appendix C

of particle containing cell KILPAR BOOL Current particle is killed LABPAR INT Particle ID internal use only LASTF INT Last F array address used LSTLAB INT ID of last particle MASS INT Index of mass source MOMX INT Index of X momentum source MOMY INT Index of Y momentum source MOMZ INT Index of Z momentum source NPORTS INT Number of parcels introduced in the current Eulerian time step NTRACK INT Total number of parcels in the domain PARNUM REAL Number of particles in the current parcel PMASSN REAL New parcel mass PMASSO REAL Old parcel mass PRVLIN REAL Internal variable for particle init condition RELVEC REAL Magnitude of relative velocity slip velocity REYNOL REAL Particle Reynolds number ROLIQD REAL Liquid density of particle ROPARN REAL New particle density ROPARO REAL Old particle density ROSOLD REAL Solid density of particle ROTCOO BOOL Simulation is in rotating co ordinate system SATPRS REAL Vapour saturation pressure SOLFR0 REAL Initial particle solid fraction SOLFRN REAL New particle solid fraction SOLFRO REAL Old particle solid fraction SOLIDF BOOL Switch for solid melt SOLLAT REAL Latent heat of solidification SPALD REAL Spalding number STARAT REAL Velocity criterion for particle stagnation THRMKV REAL Thermal conduct of vapour TPARTN REAL New particle temperature TPARTO REAL Old particle temperature TUROFF BOOL Turning off turb stochastic model Internal use UCNDRG REAL Internal variable for particle momentum calculation UCPARN REAL New particle velocity in Cartesian system UCPARO REAL Old particle velocity in Cartesian system UPPARN REAL New particle velocity in polar system UPPARO REAL Old particle velocity in polar system VAPSOL BOOL Flag for solving vapour concentration VCNDRG REAL Internal variable for particle momentum calculation VCPARN REAL New particle velocity in Cartesian system VCPARO REAL Old particle velocity in Cartesian system VPPARN REAL New particle velocity in polar system VPPARO REAL Old particle velocity in polar system WCNDRG REAL Internal variable for particle momentum calculation WCPARN REAL New particle velocity in Cartesian system WCPARO REAL Old particle velocity in Cartesian system WPGASN REAL Velocity of the continuous phase in polar system WPPARN REAL New particle velocity in polar system WPPARO REAL Old particle velocity in polar system XCPARN REAL New particle position in Cartesian system XCPARO REAL Old particle position in Cartesian system XPPARN REAL New particle position in polar system XPPARO REAL Old particle position in polar system YCPARN REAL New particle position in Cartesian system YCPARO REAL Old particle position in Cartesian system YPPARN REAL New particle position in polar system YPPARO REAL Old particle position in polar system ZCPARN REAL New particle position in Cartesian system ZCPARO REAL Old particle position in Cartesian system ZPPARN REAL New particle position in polar system ZPPARO REAL Old particle position in polar system C 3 Printout variables Name Type Meaning LUFAT INT Logical unit for GENTRA fatal error LUHIS INT Logical unit for GENTRA global history file LUPRO INT Logical unit for screen output LUTRA INT Logical unit for PHOTON use file LUWAR INT Logical unit for GENTRA warning message

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Open archived version from archive - TR211: GENTRA User Guide Appendix D

not be read correctly The likely causes of this warning are 1 A character was used instead of a number e g letter O instead of number zero 2 A comment line was included in the table but without an asterisk Warning number 008 Inlet data from Q1 but no END GENTRA INLET mark Mark assumed Explanation When reading inlet data from the Q1 file the END GENTRA INLET mark which flags the end of the inlet data table was not found The mark was assumed and the calculation continues Warning number 009 Variable out of range Variable var Value value Valid range range Explanation Variable var was supplied a value which is not within the permissible range Warning number 010 FALSDT relaxation not available for source name The source is left unrelaxed Explanation False time step FALSDT relaxation was specified for the inter phase source indicated in the warning message Since only linear relaxation LINRLX is allowed for the sources the source in question was left unrelaxed by GENTRA D 3 Error messages Error number 301 Mass transfer active but MASS not STOREd Explanation Mass transfer between particles and gas was activated in the GENTRA menu but the user has not STOREd the variable MASS in the Q1 file Remedy STORE MASS in the Q1 file This is done automatically by the GENTRA menu when the particle type chosen by the user entails mass transfer Error number 302 Invalid particle type GPTYPE Explanation An invalid particle type was specified through the variable PIL variable GPTYPE Remedy See the information on GPTYPE in the GENTRA User Guide or through the menu for a list of available particle types Error number 303 NCRT must be 1 Explanation In BFC cases the PIL variable NCRT the sweep frequency for the calculation of the Cartesian components must be 1 Remedy Set NCRT 1 in the Q1 file then re run the SATELLITE and EARTH Error number 305 GENIUS called but property not set Property prop Explanation A GRNDn flag was used for the particle property prop indicating that its value was to be computed in the FORTRAN subroutine GENIUS However no value for the property was supplied there Remedy Insert the appropriate coding in GENIUS and then re compile and re link Error number 306 Inlet data from Q1 but no GENTRA INLET DATA mark Explanation The user has specified that the Q1 file is the file where the inlet data table is to be found but GENTRA could not find the GENTRA INLET DATA mark Remedy If there is no GENTRA INLET DATA mark at the beginning of your data insert it If there is check that the line starts from the third column of the Q1 file the mark is separated from other text in the line by blank spaces there is not an asterisk in the same line Error number 307 F Array too small for particle data Current size size Increase Explanation GENTRA stores the particle inlet data in

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Open archived version from archive - TR211: GENTRA User Guide Appendix E

1 Group 7 Variables STOREd SOLVEd NAMEd ONEPHS T Non default variable names NAME 143 REST NAME 144 MOMZ NAME 145 MOMY NAME 146 NPOR NAME 147 VPOR NAME 148 WCRT NAME 149 VCRT NAME 150 UCRT Solved variables list SOLVE P1 V1 W1 Stored variables list STORE UCRT VCRT WCRT VPOR NPOR MOMY MOMZ REST Additional solver options SOLUTN P1 Y Y Y N N N Group 8 Terms Devices DIFCUT 0 000000E 00 Group 9 Properties RHO1 1 000000E 03 ENUL 1 000000E 06 CP1 1 000000E 00 ENUT 1 000000E 04 Group 10 Inter Phase Transfer Processes Group 11 Initialise Var Porosity Fields FIINIT W1 2 000000E 00 FIINIT NPOR 1 000000E 00 FIINIT VPOR 1 000000E 00 FIINIT WCRT 1 001000E 10 FIINIT VCRT 1 001000E 10 FIINIT UCRT 1 001000E 10 No PATCHes used for this Group INIADD F Group 12 Convection and diffusion adjustments No PATCHes used for this Group Group 13 Boundary Special Sources INLET INLET LOW 2 0 0 0 0 0 1 1 VALUE INLET P1 2 000000E 03 VALUE INLET W1 2 000000E 00 PATCH GENPAT CELL 0 0 0 0 0 0 1 1 COVAL GENPAT V1 FIXFLU GRND COVAL GENPAT W1 FIXFLU GRND Group 14 Downstream Pressure For PARAB Group 15 Terminate Sweeps LSWEEP 200 RESFAC 1 000000E 03 Group 16 Terminate Iterations Group 17 Relaxation RELAX P1 LINRLX 2 000000E 01 RELAX V1 FALSDT 3 333333E 03 RELAX W1 FALSDT 3 333333E 03 RELAX MOMZ LINRLX 7 000000E 01 RELAX MOMY LINRLX 7 000000E 01 Group 18 Limits VARMAX V1 1 000000E 06 VARMIN V1 1 000000E 06 VARMAX W1 1 000000E 06 VARMIN W1 1 000000E 06 Group 19 EARTH Calls To GROUND Station USEGRD T USEGRX T L G001 GENTR T GENTRA GROUP 1 Particle physics Particle type 30 GPTYPE 30 Gravity components in GENTRA Cartesian system GGRAX 0 000000E 00 GGRAY 0 000000E 00 GGRAZ 9 800000E 00 Buoyancy forces GBUOYA F GSURPR F Stochastic model of turbulence GSTOCH F Data for isothermal particles GDRAG GRND1 GENTRA GROUP 2 Boundary conditions for particles Inlet data file name GINFIL Q1 GENTRA INLET DATA YP ZP VP WP DI LDEN MDOT NUM 0 01 0 0 0 1 0 001 500 0 1 0E 5 0 04 0 0 0 2 0 0001 1000 0 1 0E 5 0 07 0 0 0 3 0 0015 1000 0 1 0E 5 0 10 0 0 0 0 5 0 002 1000 0 1 0E 5 0 13 0 0 0 1 0 001 1500 0 1 0E 5 END GENTRA INLET Wall treatment and rest coefficient if appropriate GWALLC 3 GWREST 7 500000E 01 Porosity threshold GPOROS 0 000000E 00 GENTRA GROUP 3 Numerical controls 1st GENTRA sweep frequency of calls GSWEP1 190 GSWEPF 1 Maximum Lagrangian time step time step size multplier GDTMAX 1 000000E 00 GRTFRC 7 000000E 01 Min of t steps per cell max of t steps timeout GLAGTS 5 GSTEMX 100

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Open archived version from archive - TR211: GENTRA User Guide Appendix F

dryer BFC T G204 Particles in radial impeller BFC rotating LIBREF 424 G205 Particles through ball valve BFC T LIBREF 534 G207 Rain in sample cup CARTES F LIBREF 237 G209 Particles in 2D curved duct BFC T CONJUGATE HEAT TRANSFER Group 3 Particles with heat transfer G301 Particle heating in pipe with constant gas temperature and particle velocity transient G302 Heat exchanging 1 d steady cp a bt G303

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