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  • type subroutines of special FORTRAN coding sequences This entry is intended to assist users of the second kind by explaining how they can create such coding sequences and also by introducing some of the features which PHOENICS provides to make their task easier These explanations make reference to how PHOENICS stores its data in memory in the so called F array and since different classes of variable are stored in

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/enc_for1.htm (2016-02-15)
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    does not call GROUND when it is concerned with the activities associated with GROUPs 7 12 15 16 17 18 21 or 22 By contrast several of the other groups are entered for so many different purposes that they have been divided into sections for example GROUPs 8 9 10 13 and 19 How EARTH calls GROUND EARTH calls the empty GROUND subroutine via GREX3 see PHENC entry which is structured similarly to GROUND but with many CALLs and other executable statements in the blank spaces These calls to GREX3 are made at pre set occasions in the equation solving process sometimes on the prompting of information supplied by SATELLITE If the variable USEGRX has been set as T by SATELLITE the statements in GREX will be executed first otherwise control is passed to label 25 near the end of the subroutine where conditio nal CALLs are provided to other GROUND style subroutines of which the last is the empty GROUND The statement IF USEGRD CALL GROUND at the end of GREX is the one in question Functions of the active GROUPs and sections These are indicated briefly by comments in the listing qv and much more extensively by the examples in GREX3 Both may be inspected via POLIS PHOENICS 2 Fortran How to make use of GROUND Common uses of GROUND are for the introduction of coding sequences which add to those supplied by CHAM in respect of boundary conditions sources fluid properties and print out of variables and derived quantities calling in other program modules and reading data files Users contemplating the creation of their own GROUND subroutine are advised first to inspect GREX3 and indeed the GX subroutines which it calls for two reasons First they may find that what they need is already in fact provided

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/ground.htm (2016-02-15)
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  • which permits users to augment the flow simulating power of PHOENICS by supplying formulae for material properties sources and sinks of heat mass and momentum initial values novel boundary conditions fixed and moving grids case specific output numerical control features and much more PLANT then interprets the formulae creates and compiles the corresponding Fortran coding automatically re builds the executable and executes the flow simulating calculation PLANT can be regarded

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_lecs/plant/plan0.htm (2016-02-15)
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    the third corner POINT p4 Name of the fourth corner POINT m1 List of intermediate points between the first and second corner points listed in the direction from the first corner point to the second one m2 List of intermediate points between the second and third corner points listed in the direction from the second corner point to the third one m3 List of intermediate points between the third and fourth corner points listed in the direction from the third corner point to the fourth one m4 List of intermediate points between the fourth and first corner points listed in the direction from the fourth corner point to the first one If there are two or more intermediate points they must be separated by a dot in the list ie P5 P6 if P5 and P6 are the names of intermediate points When there is no intermediate point use a hyphen instead This command defines a FRAME which will be used for holding a grid mesh Up to 20 frames can be defined A frame must have four corners each marked by a named POINT The corner points must be linked by existing lines or by a number of contiguous lines passing through intermediate named points The total number of subdivisions on opposing edges of the frame must be equal In graphics mode eg using the VIEW command the frame name and extent in terms of number of cells is displayed to assist the user in determining the overall grid dimensions and the grid plane limits when matching frames to grid planes 5 GSET M Match a Grid Mesh Format GSET M fnam direc i1 j1 k1 style fnam Name of the frame to which a grid mesh will be matched direc A string of four characters which shows the directions of grid lines to be matched to the frame edges The first two characters can be one of I I J J K K which sets the direction for the frame edge from corner point 1 to corner point 2 The last two characters can also be one of the above six options and set the direction for the frame edge from corner point 2 to corner point 3 i1 j1 k1 The index for the grid corner which is to be matched to the first corner POINT of the named frame style The interpolation method for matching the grid with the following options for example TRANS trans finite interpolation LAP5 Laplace solver with 5 iterations LAP14 FFTFTF Laplace solver with 14 iterations FFTFTF is the string to control the sliding boundary conditions The order is SLIDW SLIDE SLIDS SLIDN SLIDL SLIDH So the string above sets the SOUTH and LOW boundaries as sliding ones This command matches a section of grid mesh to a frame This section of the grid must be the same size as the frame in terms of grid cell numbers The origin of the mesh is defined by i1 j1 k1 and its orientation

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/gset.htm (2016-02-15)
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    colour capabilities of the display device For example COL GR 4 5 will change the colour of grid element 5 to colour 4 The command COL VEC 8 2 5 will change the colour of the vector elements 2 through to 5 to colour 8 COLOUR Photon Help Colour Mono toggles the colour By default all colours are displayed as specified in the SAVE file Mono forces REPLAY only to plot in the default colour black white This can be useful if a colour plot is to be replayed to a monochrome plotter Colour Photon Help Colour prompts you to select the text colour from the colour bar near the bottom of the window Once the right colour has been chosen PHOTON asks you to pick the text to be coloured Pick the text by positioning the cursor on the text and clicking the mouse button If no text is being picked up only the text written afterward uses the new colour Colour Photon Help Colour shows the colour index of the current TEXT element It can be given values between 1 and 15 Colour Photon Help The colour of the current CONTOUR element Colour Photon Help The colour of the current STREAMLINE element Colour Photon Help The colour of the current SURFACE element Colour Photon Help The colour of the current GEOMETRY segment COLOUR command in AUTOPLOT The command COLOUR for plotting coloured data elements can be used to affect the colour of all the other parts of the plot thus COLOUR LEVEL n all subsequent levels will be drawn in colour n COLOUR GRID the ruled grid will be drawn in colour n COLOUR AXES n the axes will be drawn in colour n COLOUR BOX n the box around the plot will be drawn in colour n

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/colour.htm (2016-02-15)
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    participating solids d Now dispensed with features e Miscellaneous matters However it should be mentioned that the once popular setting CONPOR name 0 0 cell as a means of representing the presence of solid obstacles to flow is no longer necessary and is best avoided Indeed the Satellite of version 2 1 3 and later will replace settings of VPOR to zero by settings of PRPS to 198 0 which corresponds to an anonymous solid which is impervious to heat It is now best to use CONPOR only when some value other than 0 0 or 1 0 is to be set The presence of solids is better handled directly by way of PRPS What follows here is therefore mainly of historical interest a Omission of the name If the first ie NAME argument of CONPOR is omitted the PHOENICS SATELLITE will supply one naming the patches as CMP0 CMP1 CMP3 etc in the order of their appearance in the Q1 file b Activation of wall friction Although it has always been possible to introduce anywhere in the model the effect of wall friction early users of the CONPOR command desired that they could be spared the necessity for introducing six wall patches for each block fow which CONPOR had set the volume porosity to zero For this reason the CONPOR command was extended by the convention that if NEGATIVE values were introduced for the IXF argument say then a wall friction patch would be introduced for the WEST face of the block and such patches would be correspondingly introduced on the EAST SOUTH NORTH LOW and HIGH faces by making negative settings of IXL IYF IYL IZF and IZL Of course the location of the block was influenced only by the absolute values of IXF IXL etc This practice is still supported by PHOENICS version 2 1 for turbulent flow signalled by a negative value of ENUT but it has no influence for laminar flow for which wall friction is the default conditions Should any user wish to switch wall friction OFF for laminar flow he must now do so by introducing a GROUP 12 patch of diffusion type with a zero third argument in the relevant COVAL The advantages of the change of practice are a positive non zero third argument allows the friction to be set to a multiple whether greater or less than unity of its nominal value different values of the argument can be employed for each velocity component and whatever the value of the argument print out of the diffucion coefficients and the momnetum fluxes is elicited for the whole of the slab in question The current recommended practice is to avoid the use of negative IXF etc for turbulent flow also by the simple expedient of setting T the PIL variable EGWF which stands for Earth Generated Wall Functions see PHENC entry of that name for this causes EARTH to detect where a fluid adjoins a cell blocked by porosity or a true

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/conpor.htm (2016-02-15)
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  • 0 5 u 2 v 2 w 2 b The source of information about KE Prandtl postulated that the turbulence energy obeyed a transport equation of the form term representing D KE Dt time dependence convective transport div const2 EV grad KE turbulent diffusion EV vel grad 2 kinetic energy generation by shear const3 k 1 5 LM kinetic energy disipation Thus The turbulent viscosity concept was still used Comparison of the formula for EV in Prandtl s mixing length and energy models see section 3 1 3 above shows the connexion KE LM vel grad LM Whereas the PMLM requires only one empirical constant the Prandtl energy model PEM requires two more c Advantages and disadvantages The PEM does allow for convection and diffusion of turbulence into regions where there is zero local generation It is therefore inherently capable of simulating some phenomena more realistically than can the PML model On the other hand it is no more capable than is the PMLM of determining for itself what the value of LM should be and knowledge is almost totally absent for re circulating and 3D flows Consequently it has been little used and is considered useful only close to

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/enc_t321.htm (2016-02-15)
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  • from the wall BUT in the immediate vicinity of the wall where viscous effects predominate it diminishes more rapidly b Advantages Calculations based on the Prandtl mixing length model PMLM are easy to make because no additional differential equation must be solved In unbounded flows ie jets wakes plumes the variation of the PML across the layer width is not large so that velocity profiles can be fairly well predicted Although the PMLM is not useful very close to a wall unless modified in the manner of say Van Driest see below the processes occurring there can often be handled adequately by use of an empirically based wall function For most boundary layer flows at least the order of magnitude of the mixing length can be correctly guessed c Disadvantages For flows with recirculation or those with non planar walls it is impossible to estimate the distribution of mixing length magnitudes with acceptable accuracy There are many such flows The PMLM implies that the local level of turbulence depends only upon the local generation and dissipation rates but in reality turbulence may be carried or diffused to locations where no turbulence is actually being generated at all The PMLM cannot represent this The PMLM implies that the turbulent viscosity is always positive as do one and two equation models also in reality it can change sign d Activation in PHOENICS In order to activate the PMLM in PHOENICS the PIL command TURMOD needs to be inserted if the Q1 file with the argument MIXLEN Then the choice of mixing length formula is made by the setting of further parameters such as EL1A IENUT etc If no mixing length formula is specified then TURMOD MIXLEN selects the generalised turbulent length scale LTLS so that TURMOD MIXLEN is equivalent to ENUT GRND2

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/enc_t313.htm (2016-02-15)
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web-archive-uk.com, 2016-10-28