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  • The PHOENICS-to-TECPLOT Interface
    capabilities multi frame workspace and high quality output gives you total control to get all the types of plots you want for effective analysis presentation and publication TECPLOT is written by Tecplot Inc Bellevue WA and runs under Windows on PCs and on most UNIX workstations 2 TECPLOT and PHOENICS An output file TECDATA DAT containing two TECPLOT zones for each PHOENICS domain is written One zone is contains data

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/tecplot.htm (2016-02-15)
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    values of LSWEEP RESREF etc will be appropriate It is therefore convenient that the restart facility of PHOENICS permits you to make a few sweeps to pause in order to inspect the results and then to continue the calculation with different settings of relaxation parameters if this seems desirable It is important to understand the differing roles of RESREF P1 RESREF R1 and RESREF R2 all of which are concerned with continuity balances RESREF P1 is the reference value of the volumetric flow imbalance and when two phase flows are in question it is compared with the sums of the volumetric imbalances for the two phases for each cell RESREF R1 and RESREF R2 by contrast represent mass imbalances and they relate to the individual phases When they are all set to values other than zero all contribute to the determination of whether sweeps should terminate prior to the performance of LSWEEP of them Since version 1 6 a self selection mechanism has been provided It is activated by setting SELREF T in the Q1 file Then the user has only to select a single value namely RESFAC which causes EARTH to set RESREF for each variable to RESFAC times a representative flow rate for that variable in that flow See PHENC entries SELREF RESFAC TSTSWP RESREF UWATCH USTEER b Slabwise iterations Group 16 For parabolic problems only one sweep is made through the integration domain because storage is provided only for variables belonging to two slabs at a time namely the slab for which variables are being calculated and its low neighbour LSWEEP is therefore set equal to 1 by EARTH whatever value happens to have been set by the SATELLITE The interconnectedness of the equations makes it necessary that in parabolic problems the whole cycle of variable adjustments should be repeated many times This is achieved by setting the variable LITHYD to a sufficiently large number See the Encyclopaedia entry LITHYD c Iterations in the linear equation solver Group 16 The linear equation solver of PHOENICS acts in an iterative manner except when all but one of NX NY and NZ are unity or when NX or NY is unity and whole field solution has been switched off In other circumstances the question arises how many iterations should be performed In terms of data settings the questions become what values should be ascribed to LITER to RESREF and to ENDIT for each of the solved for variables These questions are of importance for they often affect the speed with which the overall solution is arrived at and when the variable in question is P1 which is strongly connected with the satisfaction of mass continuity they may affect whether it is attained at all Especially because simulations with fine grids are often too expensive for comfort means of reducing cost without loss of accuracy are worthy of consideration The expense itself will of course be smallest if LITER is small or if both RESREF and ENDIT are large for

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/term.htm (2016-02-15)
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  • Time-dependent Boundary Conditions
    TEM1 FIXFLU 5 0 If LSTEP were 25 the resulting heat source would be Steps 1 5 5W m 3 Steps 6 10 10W m 3 Steps 11 15 15W m 3 Steps 16 20 10W m 3 Steps 21 25 5W m 3 More complicated functions can be set in this way by using PIL DO loops to generate the PATCH commands Note that the actual time the sources are active for is controlled by the size of the individual time steps the PATCH limits refer to time step numbers not times If the time steps are non uniform the resulting time variation may not be quite as expected 2 Using Built in Time Variations Although simple in concept the above method can be tedious in practice as it involves hand editing the Q1 file Several common forms of time variation are provided as built in options In PHOENICS VR these are available as heat sources From PIL they can be applied to any SOLVEd variable The available source forms are Linear variation with time Sine function of time Cosine function of time Step battlement function of time Increasing Saw tooth function of time Decreasing Saw tooth function of time Note that the variation is with time not time step number The shorter the time steps the better the representation will be The PIL settings for these sources are PATCH TIMabcde type ixf ixl iyf iyl izf izl itf itl COVAL TIMabcde phi CO VAL where The patch name must start with TIM The remaining abcde characters are at the user s discretion type can be VOLUME for a volumetric source or NORTH SOUTH EAST WEST HIGH or LOW for a source per unit area phi is the variable CO can be FIXVAL if the value is to change with time or FIXFLU if the source is to change with time For FIXVAL the time t used in the built in options is taken as the current time level i e t t TIM in PHOENICS For FIXFLU t is taken as the average of the current and previous time levels i e t 0 5 t t where t t D t and D t id the current time step VAL can be GRND4 Linear source GRND10 Sine GRND6 Cosine GRND7 Step battlement GRND8 Increasing Saw tooth GRND9 Decreasing Saw tooth The figure shows the general form of the source applied and defines the nomenclature used Several additional variables must be passed to EARTH This is done using the SPEDAT command For a Linear source GRND4 the formula used is VAL F s F e F s t t s t e t s and the additional settings are SPEDAT TIMabcde STARTphi R Phi value at start of cycle F s SPEDAT TIMabcde ENDphi R Phi value at end of cycle F e SPEDAT TIMabcde TSTARTphi R Start time t s SPEDAT TIMabcde TENDphi R End time t e For sine and cosine sources GRND10 GRND6 the formula

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/timsor.htm (2016-02-15)
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    44 C2E 1 92 EWAL 8 6 AK 0 41 CMUCD CMU CD The user of a re compilable version of PHOENICS may of course change the constants by editing re compiling and re linking However PHOENICS versions 3 5 and later allow them do be changed by means of the In Form REALREAD command The constants are used as follows in coding to be found in GXPROP F and

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turbmc.htm (2016-02-15)
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  • Ca Cb are constants S is the shear rate and Ca 0 03 Cb 0 01 Data from N Fueyo and DB Spalding 1995 5 2 7 Advantages of the two fluid model Like the Reynolds stress models two fluid models are free from the restrictions and lack of realism of the turbulent viscosity concept They can predict counter gradient diffusion Further and unlike any single fluid model they can portray adequately the interactions of pressure gradients and density fluctuations which are major sources of generation of turbulent motion Two fluid turbulence models allow proper account to be taken of the large differences and steep gradients of temperature and concentration which are present within turbulent reacting gases so they can in principle and practice simulate flames realistically 5 2 8 Disadvantages of the two fluid model The number of equations being twice as large as for single fluid models computer times are somewhat longer Moreover users of computer codes restricted to a single equation set are often reluctant to change to one such as PHOENICS which can handle two sets simultaneously This is probably the main reason that the two fluid model has not yet become popular The two fluid concept is found hard to grasp by some indeed there are real conceptual difficulties for example What is the best characteristic to use for distinguishing the two fluids Temperature Velocity Vorticity Density Knowledge of the fragment interaction rates and of what governs fragment size is far from adequate Much more research is needed 5 2 9 Implementation in PHOENICS The two phase option library contains the following list of cases ONE PHASE FLOWS computed by TWO PHASE METHODS Case no Two fluid turbulence model chemically inert Couette flow with buoyancy W975 Backward facing step using two fluid model W976 Mixing in a duct W974 Two fluid turbulence model Reacting flow Ducted flame using two fluid model W977 1D piston cylinder combustion W978 1D shock induced propagation detonation W979 Flame spread in plane channel W980 Although only one thermodynamic phase is involved in these cases they appear in the two phase option because they make use of the coding which was first introduced for two phase flow Extracts from the Q1 file of case W975 now follow GROUP 7 Variables including porosities named stored solved ONEPHS F SOLVE P1 V1 V2 W1 W2 R1 R2 H1 H2 SOLUTN C1 Y Y P P P P SOLUTN C2 Y Y P P P P SOLUTN C3 Y Y P P P P SOLUTN C4 Y Y P P P P SOLUTN C5 Y Y P P P P SOLUTN C6 Y Y P P P P INTMDT 22 LEN1 23 VIST 24 NAME INTMDT MDOT NAME LEN1 LEN NAME INTMDT MDOT NAME LEN1 LEN NAME VIST VIS SOLUTN MDOT Y N N N N N SOLUTN VIST Y N N N N N SOLUTN LEN1 Y N N N N N GROUP 10 Interphase transfer processes and properties CFIPS GRND4 CFIPA 0

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/enc_tu52.htm (2016-02-15)
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  • wall viscosity affected layer is resolved with a one equation model involving a length scale prescription PHOENICS has been equipped with the two layer model of Rodi 1991 which employs the one equation model of Norris and Reynolds 1975 in the near wall region 2 Description of the model In the near wall layer the two layer k e model fixes the dissipation rate EP which appears in the KE equation to EP CD KE 1 5 FTWO LM 2 1 with CD 0 1643 FTWO 1 5 3 REYN 2 2 REY KE 0 5 YN ENUL 2 3 and YN is the minimum distance to the nearest wall The turbulent kinematic viscosity in the near wall layer is calculated from ENUT CMU KE 0 5 FMU LM 2 4 where CMU 0 5478 FMU 1 EXP 0 0198 REYN 2 5 LM AK YN 2 6 and von Karman s constant AK 0 41 The one equation model is matched with the high Re k e model at those locations where REYN 350 3 Activation of the model The two layer KE EP model is selected by TURMOD KEMODL 2L which is equivalent to the following PIL commands TURMOD KEMODL IENUTA 8 DISWAL The DISWAL command activates the solution of a scalar variable LTLS from which is deduced the minimum distance to the nearest wall YN Subsequent WALL and CONPOR commands will set COVAL statements for the appropriate velocities LTLS and the turbulent kinetic energy No COVAL is required for EP as the near wall value is fixed according to eqn 2 1 via modification of the standard source terms for EP Where needed COVALs for wall PATCHes should take the form described below in Section 3 4 4 for the LAM Bremhorst KE EP turbulence model When

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/enc_t331.htm (2016-02-15)
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  • to the dissipation range ET is the dissipation rate RHO is the fluid density ENUT is the turbulent viscosity PK is the volumetric production rate of turbulent kinetic energy and PRT KP and PRT KT are constant coeffcients The corresponding transport equations for the energy transfer rate and the dissipation rate are given by RHO EP t RHO U i EP RHO ENUT PRT EP EP i i RHO CP1 Pk Pk KP CP2 Pk EP KP CP3 EP EP KP 2 4 RHO ET t RHO U i ET RHO ENUT PRT ET ET i i RHO CT1 EP EP KT CT2 EP ET KT CT3 ET ET KT 2 5 where PRT EP PRT ET CP1 CP2 CP3 CT1 CT2 and CT3 are constant model coefficients The CP1 PK PK KP and CT1 EP EP KT terms can be interpreted as variable energy transfer functions The former term increases the energy transfer rate when production is high and the second term increases the dissipation rate when the energy transfer rate is high The model constants are given as PRT KP 0 75 PRT EP 1 15 PRT KT 0 75 PRT ET 1 15 CP1 0 21 CP2 1 24 CP3 1 84 CT1 0 29 CT2 1 28 and CT3 1 66 The eddy viscosity is computed from ENUT CMUCDF KE 2 EP CMUCD KE 2 ET 2 6 where CMUCD CMUCDF ET EP is the effective eddy viscosity coefficient and CMUCDF 0 09 For turbulent flows in equilibrium Pk ET and ET EP so that CMUCDF CMUCD In this case the location of the partition is in the high wave number region When Pk EP ET CMUCD CMUCDF and the partition is located in a higher wave number region than that of the equilibrium case When the production vanishes KP KT EP CMUCDF and the partition is located in the low wave number region For arbitrary ratios of Pk ET the partition is determined as part of the solution 3 Boundary Conditions Wall boundary conditions The model may be used in combination with equilibrium GRND2 or non equilibrium GRND3 wall functions see the Encyclopaedia entry WALL Functions For equilibrium wall functions the following boundary conditions are applied for the turbulence variables KP KE 1 BETA 3 1 KT BETA KE 1 BETA 3 2 EP CMUCD 0 75 KE 1 5 k Y 3 3 ET EP 3 4 Here KE UTAU 2 SQRT CMUCD UTAU is the resultant friction velocity SQRT TAUW RHO TAUW is the wall shear stress Y is the normal distance of the first grid point from the wall k is von Karman s constant and BETA is given by BETA K 2 PRT EP SQRT CMUCD CP3 CP1 CP2 1 3 5 which yields a value of BETA 0 25 For the non equilibrium wall functions the treatment is similar to that employed for the standard KE EP model with KP and KT determined from their respective balance equations and for

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/enc_t351.htm (2016-02-15)
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  • Multi-fluid Combustion Model
    rate of one fluid by the other proportional to velocity difference the chemical reaction rate the effective viscosity The simulation featured in the Imperial College research of Jeremy Wu 1987 It is now PHOENICS Input Library Case no W977 Agreement with experimental data eg Williams Hottel and Scurlock is good Contours of reactedness of the faster fluid The flow is from left to right Only the upper half of the duct is shown Contours of reactedness of the slower fluid These contours differ from the previous ones in that the cooler slower moving fluid is the less reacted f Examples of two fluid model simulations mixing and unmixing The two fluid turbulence model is of use for other phenomena than combustion and especially for those in which density differences interact with body forces Many examples arise in the atmosphere lakes rivers and oceans The two fluid model for example can satisfactorily simulate the mixing followed by unmixing behaviour when a salt water layer lying below fresh water is heated for a short time fresh salty start later later still Mixing appears to take place soon after heating equalises the densities But it is macro not micro mixing so unmixing follows Experiments by Spalding and Stafford at Imperial College during 1979 in which the heating was effected by passing an electric current through the fluids brought the mixing unmixing phenomenon to light It was consideration of these experiments which prompted the development of the two fluid model of turbulence which has here been used to simulate it In this and the following pictures which show contours computed by way of the two fluid turbulence model the vertical scale represents height from the bottom of the fluid layers while the horizontal scale represents time The first picture shows the volume fraction of lower saline fluid Note the initial delay then mixing then unmixing This picture shows how the temperature of the saline fluid first rises it falls later as heat is transferred to the fresh water fluid This picture shows how the fresh water temperature rises gaining its heat from the saline fluid Here is shown the density of the saline fluid It first diminishes because of the temperature rise eventually becoming lighter than the fresh water As it cools it becomes heavier again Here is shown the density of the fresh water fluid This also diminishes as heat is transferred from the saline solution but it also increases later because some salt diffuses into it This picture shows how the vertical velocity of the saline fluid becomes positive once its density falls below that of the fresh water Here are the corresponding vertical velocity contours of the fresh water Later cooling causes it to become negative again Reminder the horizontal dimension is time increasing to the right The salt content of the lower fluid does diminish somewhat in the course of time The salt content of the upper fluid correspondingly increases Click here for more about the two fluid model g

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_lecs/mfm/mfm2.htm (2016-02-15)
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web-archive-uk.com, 2016-10-25