Encyclopaedia Index

What's New in PHOENICS

Document last revised: 13.03.13

Changes made between November 2011 and January 2013

Details about new changes to the VR Editor and solver are reported here.

1. The general trends

The "New Trends" of 2011 have continued with increased concentration, momentum and practical effect.

In respect of concentration, attention is now focussed on three classes of PHOENICS user, namely:

1. End users, who wish to have 'simulation engines' designed for their specific closely-defined applications. These are the diners in the 'PHOENICS Restaurant', who choose from the menu what suits their appetite; and who pay the bill at the end,
2. Creative users, who provide the specialised packages which the end users employ. They are the cooks who prepare the familiar dishes; and some of them are chefs who create never--before-tasted ones.
3. Do-it-yourself users, who are content to use the long-established VR-Editor so as to set up problems on their own.

Of the End-User class the following may be said:

• They are conceived to be specialists in their application area, and so able to recognise and reject simulations which are obviously incorrect; but they are in no way required to be CFD specialists. They rely on the package providers to supply all the guidance and protection which they need; and to ensure that using the package is easy.
• Students and teachers of fluid mechanics and heat transfer fall into this category, Their focus is on what is to be learned and taught about the various chapters of their subjects; not on how PHOENICS happens to express their implications.
• End Users should however know enough about computational fluid dynamics to understand that it deals in probabilities rather than certainties; and that its predictions become less and less reliable the more are the phenomena in question complicated by turbulence, multi-phase flow and chemical reaction.

For the do-it-yourself users, PHOENICS has been improved in various manners, an overview of these changes are listed in the 2012 What's New report. For example a 'sun object' has been introduced.

However, no fundamental reduction has been made in the VR-Editor's limitations. It remains as a single-instance-run launcher; and it is still unable to assist its users to exploit the full powers of the PHOENICS Input Language, PIL.

It is for the Creative-User class that the greatest new benefits have been provided, Specifically:

• Special-application packages have now been given the formal status of Simulation Scenarios, or SimScenes for short. These are both easier to create and simpler to use than the PRELUDE-based Gateways which were emphasised in 2011.
• These can be supplied to customers either as specielly-ordered add-ons to standard PHOENICS or as stand-alone single-purpose packages.
• Each has an easy-to-use menu, which is designed to assist a specific End-User group.
• Each SimScene is defined by a PQ1, i.e. Parameterised Q1, written in PIL, which contains the new VREDIT=F entry, so enabling all the "protected-mode" saveXbegin and saveXend statements to be dispensed with.
• Writing of PQ1s is aided by a new PQ1 editor which is copiously supplied with 'macros' and 'line-completion' items which reduce the writer's labour and reduce his chance of making mistakes. Moreover this editor is customisable, in the sense that users can add the macros and line-completions which most suit them.
• Of great convenience is the 'multirun' facility which enables many runs to be performed, with systematically varied input parameters, and their results to be easily compared.
• Also created, but not yet greatly used, is the multi-language SimScene capability. When Japanese, Russian, Chinese and Arabic users recognise its existence, they will surely exploit it with enthusiasm.
• Two new PIL commands have been added, namely WRITE( , ) and EXEC( , ). The former enables PIL entries to instruct Satellite to write files with whatever content the PQ1-writer needs. For example it can write PHOTON_USE files; and what it writes can be parameterised, so that, for example, the 'use' file to which PHOTON responds already knows what are the values of NX, NY, etcetera.
• The ShapeMaker program has been modified to enable it to accept instructions from files as well as interactively. As a consequence, the creative-user PQ1 writer can now:
  • use WRITE to define the instruction to Shapemaker which cause it to create some never-existing-before object;
  • use EXEC to instruct ShapeMaker to read the file and create the object;
  • place in the PQ1 the lines which cause Satellite to display the object and to tell Earth how to react to it.
• In this manner a severe limitation of the past has been removed. Formerly, users were restricted (as DIY ones still are) to using such objects as they could find in the sub-folders beneath \phoenics\d_satell\d_object. Therefore, if they needed a hollow solid cyinder, they had to create one for themselves by introducing a not-hollow solid cylinder and a smaller-diameter concentric fluid-containing cylinder to represent its hollow inside. Such contortions are no longer necessary.

In summary, it would be no exaggeration to state that PHOENICS underwent a radical change in 2012; and prospective not-yet-users may find that that these changes have increased its attractiveness.

Other developments during 2012

• PARSOL improvements, especially in relation to cylindrical-polar grids.
• Wind-farm related improvements, especially in relation of use of un-structured grids, and of GCV rather than MIGAL for body-fitted-coordinate grids

Work in progress, 2012-2013

• Replacement of PARSOL with SPARSOL (i.e. Structured PARSOL) which allows thin-plate objects to be simulated.
• Unificaton and speed-up of linear-equation solvers.
• Unification of treatment of VR (facet-described) and In-Form (parameterised) objects.
• Creation of heat-exchanger-related SimScenes.

Changes made between September 2010 and December 2012

For more details about the following changes click here.

Pre-processing

• Inlet objects have a vector arrow showing the direction of flow.
• Main Menu allows setting of domain edge boundary conditions.
  Wall Yes - create a PLATE object at this domain face. The name (for X) will be DOM_XMIN_W or DOM_XMAX_W
  Open Yes - create an OUTLET object at this domain face. The name (for X) will be DOM_XMIN_O or DOM_XMAX_O
  Flow Yes - create an INLET object at this domain face. The name (for X) will be DOM_XMIN_I or DOM_XMAX_I
  Objects are created with default settings – the user must set any non-default values.
  Existing PLATE, OUTLET or INLET objects (with any name) that cover a whole domain face will be recognised and will set the flags on the dialog.
• Activation of transient restarts made easier.
  On the ‘Time step settings’ dialog, set ‘First step number’ > 1 and a dialog will offer to activate the restart.
  All necessary file names will be deduced.
• Object names can be up to 12 characters long.
• The Q1 can be saved to a different name without saving all the output files ‘File – Save Q1 As...’.
• The dialog for starting parallel has been updated to allow more flexibility.
• The facilities for repairing and manipulating CAD data during and after import have been improved with the introduction of the new DatMaker utility.

Post-processing

• Start-up dialog offers most recent set of results
• New function key F9 always loads most recent set of results.
• The domain can be mirrored in any direction.
• Vectors can be drawn as 3D arrows.
• Contours and vectors can be plotted on an arbitrary surface of any shape – the ‘Plotting Surface’ object.
  • Rotate to any position:
  • Select the new object, right-click and select 'Surface contours'
  • Or select 'Surface vectors'
 
• Contours have new options [1] Fill, [2] Lines and [3] Lines and fill. These can be applied to contour planes, contours on surfaces of objects and contours on Plotting Surface objects:-

Fill	Lines	Lines and Fill

   
• An extra selection mode has been added. Holding shift+cntrl when selecting an object on the screen selects all objects under the cursor, not just the nearest. Objects have a 'Selectability' flag. Objects that obstruct others can be made 'unselectable' (from the screen) so that those behind can be selected. The view centre can be set to the middle of a selected object and the working directory is displayed in the status bar at the bottom of the window.

Earth Solver

There have been many modifications to EARTH. A full double-precision version of the EARTH solver is now available. In some cases this converges much better than the standard single-precision version. This is especially true for transient cases where the domain is huge and not much is happening. The price is doubling the memory requirement.

The normalised residuals displayed on the monitor screen have been a cause of wonder and amazement for some time. The idea – to normalise the errors by the sums of sources and fluxes – was good, but the implementation was suspect. Residual values of a thousand % were common, and the normalised error increased as the number of cells increased. PHOENICS-FLAIR users have the CONV_TABLE.CSV file which contains the errors normalised by the inflow fluxes. The problem with the internal normalisation has been fixed, so that the normalised residuals are now a much-improved reflection of the level of convergence.

The actual residual is almost the same, but the normalised value is very small and more like that in CONV_TABLE.CSV.

There have been three modes of operation for the graphical convergence monitor:

• Spot value and residual;
• Maximum correction and sum of nett sources; or
• Maximum and minimum value in the field.

It has always been possible to switch mode during the run, but the graph only switched at the moment of changing, so the previous values were not displayed. All monitoring values for all three modes are now held, and when the mode is changed the entire graph is redrawn in the new mode. It is possible to set a flag (Options, Solver Monitor Options) to have images of all three modes saved at the end of a run.

Some further changes and bug fixes include:-

• There is a new ‘rolling’ mode for the convergence monitor where only the last, say, 100 sweeps values are shown. This can help show the detailed behaviour of long runs, where the normal display crushes everything together.
• The wall function coding has been updated so that the same code sequences are used for cut-cells and fully blocked cell faces. This should result in better heat transfer calculations when cut cells are present.
• There was a problem with fully-rough wall functions when the roughness height was set <= the near-wall cell half-height. Previously, the run would fail but this has now been fixed. As a by-product of this work, the boundary conditions required by the various low-Reynolds Number turbulence models have been made available for cut cells and the so-called EARTH-generated wall functions. Previously the low-Re models only worked properly with plates and with EGWF=F.
• There is a new InForm command: NETS(var,place) where var is the name of a variable and place is the name of an object or patch. It returns the net source of the variable. This is very useful for linking two or more objects.
• Calculation of the average outlet temperature for printing in RESULT has been made more accurate and robust.
• The net friction force on a BLOCKAGE object is now printed to RESULT.
• Diffusive/conductive heat fluxes can be stored by adding STORE(QDX,QDY,QDZ) to Q1.
• In parallel PHOENICS, the infrequent but long-standing ‘Neighbour has other number of pbc-bound cells’ error has been removed.
• The working directory, 32-bit or 64-bit and single or double precision status are echoed to the title bar of the Earth solver window, as shown,
  
  and to the RESULT file.
  

    ----------------------------------------------------------  
     Running with 64-bit Single Precision executable             
     Working directory: 
     W:\phoenics\d_polis\d_docs\tr324\example
    

• If a table file is open (in Excel for example) when Earth wants to write to it, the Earth run would crash as the file was locked. This could lose many hours of computations. Now, the Earth run will pause and a dialog will open advising that the file should be closed before continuing. Similarly, if the hard drive becomes full when writing the solution file, the Earth run will pause allowing an opportunity to delete files and create more space.

SUNLIGHT OBJECT Update

The SUNLIGHT feature was created in 2010 in response to the demand from users for a HeatIsle module. The prototype for which is described here. This has now been updated to improve its flexibility.

The preliminary version was accessed through the WIND object dialog, and had several limitations:

• The latitude was a user-input
• The direct solar radiation was a user-input
• There was no allowance for diffuse solar radiation
• Transient operation was very limited, with multiple WINDs being required.

The WIND object can also use the weather data file

• The pre-attached data file is used, and the current data are shown
 
• The WIND object graphic shows the current North (blue) and wind (red) direction.
• In a transient case, the time-step setting dialog controls the time step size and number of steps to run. The time of day at the start of the run is the time chosen from the weather data file. The data values from the file are transmitted to EARTH, and at each time step the solver interpolates between the data-file values to get the current inlet values. The solar shading is updated at the start of each time step, and the current direct and diffuse solar radiation values are interpolated from the weather data file. Animation is available to show, for example, a 24-hour sequence.
• When a weather file is in use for a transient case, the external pressure and temperature are updated at each time step from the weather file. This was done by updating the external pressure at outflow boundaries. In practice, it turned out that changing the external pressure can have unexpected consequences, for example creating inflows when the external pressure rises. This has been addressed by keeping the external pressure at zero relative to the reference pressure, PRESS0, and updating PRESS0 each time step.
• In addition, the reference density for buoyancy, BUOYD, is also updated each time step to match the new external pressure and temperature. The transient behaviour is much improved by these two measures.
• When a SUN object is active, the 'Solar absorption' factor of the WIND ground plane can also be set. The 'Wind Amplification Factor' (local absolute velocity divided by reference velocity) can be STOREd by a button-click on the WIND object attributes dialog.

DATMAKER and CAD conversion

The facilities for repairing and manipulating CAD data during and after import have been improved . The new DatMaker utility can:

• Mend holes
• Ensure all facets point outwards
• Repair folded facets
• Split an object into separate bodies
• Merge objects
• Subtract objects

Often problems with geometry detection can be eased or removed by merging several touching or overlapping objects into one. The same applies to subtracting an air space from a surrounding blockage. DatMaker is now used by default when importing single or multiple CAD files, to translate the CAD to DAT format. The supported formats are, as before :-

DatMaker can also be used to perform operations on objects already created in VR. Existing objects can be merged, split or subtracted. (1) Here there are 5 air blockages making a channel through a hidden solid; (2) then merged into one object; and (3) now subtracted from the solid leaving a channel.

[1]	[2]	[3]

A further utility already built into PHOENICS is called AC3D from Inivis. As well as creating shapes from scratch, AC3D can import a variety of additional formats that can be exported in the native .DAT format used by PHOENICS. Alternatively, products such as Okino NuGraph can also import, repair, convert and export a variety of formats, including the 3DS format readily accepted by PHOENICS.

HIGHLIGHTS from the previous update

Here follow some improvements made in the previous release which are worth mentioning again, in case they have been missed. In the VR-Editor:-

• The ‘Object affects grid’ attribute has been split into the three coordinate directions.
• A long-standing error in the Auto-mesher has been corrected.
• The grid refinement stops when the ratio between the size of the last cell in one region and the first in the next region falls below a set criterion.
• On the auto-mesh dialog, this was set as a fraction of the domain size, but was then treated as an actual physical dimension when being compared to the cell sizes.
• This means that for large domains, the refinement process terminated earlier than expected.
• There is also a new option to set the minimum and initial cell sizes as physical dimensions rather than fractions of the domain size.

In the EARTH solver of PHOENICS/FLAIR, the ‘Calculate link temperature’ and ‘Activation temperature’ settings for a SPRAY_HEAD object activates automatically the spray when the activation temperature is reached. In previous versions, a message was written to RESULT when the criterion was met, but the spray was not activated automatically. A table file containing the calculated link temperatures at the end of each step is also produced.

For details of these previous updates Click here