Gateways to PHOENICS
- Gateways in preparation
- Relationship to 'special-purpose programs'
- Differences from conventional PHOENICS
Gateways to PHOENICS have been designed so as to make it easy for
persons who wish to simulate fluid flow in situations of
narrowly-defined types to do so without:
- having their attention drawn to matters which do not concern them;
- needing to know anything about PHOENICS in general.
Individual gateways are accessed by clicking one of the icons presented on
the left of the main-gateway panel, whereupon further icons will
appear which offer simulations of particular kinds.
Clicking on these will load the selected generic input file into an interactive
software module called PRELUDE, which enables its user to:
- inspect both the items on offer, and the geometrical and other specified
relations between them
[The REL in pRELude refers to 'RELations' which are PRELUDE's reason for existence];
- modify the items provided, including both their attributes and their relations;
- delete items or introduce new ones:
- when satisfied with the resulting scenario, launch one or more flow-simulating
- thereafter inspect the results.
3. What gateways are currently in preparation?
In various stages of completeness are:
- The 'Virtual Wind Tunnel', whether for:
- vehicles such as automobiles, motor-cycles or airplanes; or
- structures such as apartment blocks, bridges, telegraph poles or cooling towers.
- HVAC, i.e. Heating, Ventilating and Air-Conditioning, whereby users are enabled to furnish their rooms, concert halls or supermarkets with such items as:
- chairs, tables, filing cabinets and computers:
- doors, windows, exhaust ducts and under-floor air supplies:
- fans, heaters,air-inflow and outflow apertures.
- Fires and smoke-movement in buildings, for which, in addition to the objects which the HVAC specialist needs, the scenario is populated with:
- conflagrations of various kinds, almost all of which produce heat and smoke at rates which are limited by the flow of oxygen into them.
- flame-extinction devices such as carbon-dioxide cylinders or water-sprinklers, and even firemen's hoses.
- heat exchangers of various kinds, all based upon the use of volume-averaged parameters.
4. The relationship of 'gateways' to 'special-purpose programs'
4.1 A new form of an old idea
That special-purpose versions of PHOENICS should be provided for narrow-sector uses was a central feature of CHAM's thinking from the very beginning. Indeed, the word SATELLITE springs from the notion that the solver-module EARTH would be supplied with data from special-purpose satellites.
An early graphical representation of the concept can be seen below:
Things did not work out quite as expected: there is now a single satellite; but CHAM sought to express the distinctions between applications areas by:
- attempting to create distinct packages of software, library examples and documentation for each application sector:
- inventing names for each package, e.g. FLAIR, HOTBOX, COFFUS.
The task of creating, documenting, exemplifying and selling these distinct packages proved to be too great; and finally it was recognised as being unnecessary. In fact, there is ONE PHOENICS; and attempts to sub-divide it in accordance with application areas are pointless.
It is among the users that the differences lie which need to be respected; and each group, it is now recognised, requires a 'gateway to PHOENICS', designed to suit that group's special needs.
In designing a gateway therefore, CHAM seeks to:
- identify a group of potential users having similar needs;
- define those needs as precisely as possible;
- prepare for them:
- a starting scene which already contains the items which a typical user will need;
- a 'store-cupboard' stocked with such other items as the user may wish to add; and
- a 'wizard' which will assist the user to:
- add and remove items,
- adjust their positions and other attributes,
- conduct the flow-simulating calculation, and
- inspect the results.
Some examples will now be discussed.
4.2 The Virtual Wind Tunnel
The starting scene of the virtual wind tunnel consists of:
- A duct of rectangular cross-section along which air flows steadily;
- an inlet at one end, at which the prescribed air velocity, temperature and pressure are prescribed,
- an outlet at the other end, at which the air pressure is prescribed,
- a solid object placed near the middle of the duct, the forces on which it is desired to calculate.
- The store-cupboard of the virtual wind tunnel contains:
- A collection of objects which might be used to replace the one in the starting scene, including an idealised automobile, consisting of four wheels, two axles and a body;
- a few car bodies of varied shape;
- a moving floor, for use when it is desired to simulate the aerodynamics of a vehicle moving along a road; and
- some alternative inlet-velocity profiles.
- The wizard of the virtual wind tunnel consists of the PRELUDE software module, with:
- its general capabilities of:
- displaying the scene from various view-points;
- moving, re-sizing, hiding, restoring to view, and changing attributes of, objects selected by the user;
- removing objects from the scene;
- bringing in objects from the store-cupboard or from any location specified by the user; and
- defining relationships between positions and other data items,
- augmented by VWT-specific relations which, namely:
- cause the wind-tunnel to change its size in proportion to that of the object;
- enable the air-inlet velocity to be determined by reference to Reynolds number and/or Mach Number;
- allow the 'angle of attack' of the object to be varied;
- allow computer time to be spared, when object has a plane of symmetry, by simulating just one-half of the scene;
- allow heat transfer to be included in the simulation; and
- when the temperature does vary, to take the effect of buoyancy into account.
4.3 The Gateway to Heating, Ventilating and Air-Conditioning
The starting scene of the HVAC Gateway consists of:
- Two rooms partly separated by a partition wall;
- doors and windows in the external walls of the rooms, which may allow inflow and outflow of air, and in the case of the windows, of sunlight;
- a table, two chairs and a computer cabinet;
- a fan which circulates air in one of the rooms;
- a 'diffuser', placed in the ceiling of one room, which blows in fresh air from an outside source;
- an air-extractor placed in the ceiling of the other room;
- several heat sources in the form of near-wall panels of fixed temperature; and
- further fixed-input heat-sources in the form of standing or seated human beings, the air temperature in the vicinity of whom it is desired to compute.
The store-cupboard of the HVAC Gateway contains:
- Various items of furniture;
- windows of circular shape;
- perforated tiles, through which air can be blown into the room;
- sources of cigarette smoke;
- a sunlight object.
The wizard of the HVAC Gateway consists of the PRELUDE software module, with:
- the same general capabilities as the Virtual Wind Tunnel wizard
- augmented by HVAC-specific relations which, namely:
- enable the simulation to conducted in either steady state or transient mode;
- enable the air-inlet rate from the diffuser to be varied in accordance with the temperature prevailing at a prescribed 'sensor' location;
- allow the direction of flow of the fan to be varied cyclically with time;
- enable groups of items (e.g. furniture, persons, heaters) to be re-positioned as a group;
- allow the calculation of the distribution of various 'comfort indices'.
5. Differences from conventional PHOENICS operation
Persons who are familiar with PHOENICS may be interested to know that:
CHAM's introduction of PRELUDE also expresses its new approach to the market-place.
- PRELUDE can be regarded as a pre-pre-processor, in that it delivers its output to the standard SATELLITE, which then converts it into EARTH-usable form.
- PRELUDE does both more and less than the SATELLITE, namely:
- more in that it works with an input file which is like a 'parameterized Q1', which can express user-definable relationships between input variables, such as:
* 'this' is twice as big as 'that';
* 'viscosity is inlet-velocity times duct width divided by Reynolds number'.
and that it can launch a series of runs with varied inputs.
- less in that it facilitates the user's access to only the limited set of PHOENICS features which the input-file writer has believed to be necessary.
- PRELUDE has its own graphics package, based on the OpenSceneGraph library.
- PRELUDE is written in TclTk, and is therefore platform-independent.
- The input file (at the present moment called a Q3 file), can be hand-edited.
- The Q3 contains (and retains) all generic features of the class of scenarios; but it can generate as many single-instance Q1 files as its user decides.
- Although PRELUDE, operating in 'gateway' mode draws the user's attention only to those features which the gateway-designer has selected, it in no way diminishes the user's freedom to activate any other feature of PHOENICS; for, it allows the user, once PRELUDE has done its work, to spend as long as he or she wishes in an extended Satellite session, before the final EARTH run is launched.
In the past, the developers of PHOENICS have furnished it with many valuable features, some of which are described in 'what's new' announcements or 'newsletters', and fewer of which have been illustrated in single-instance examples added to the input-file library. The developers may have then hoped that some salesman will convey the message to prospective custmers, who will thereby be persuaded to purchase the software.
PRELUDE has been designed so as to enable CHAM itself to create the 'gateways' which are described in this document and of which the essential feature is their users require no knowledge of PHOENICS, or even of computational fluid dynamics.
Were CHAM now to say to prospective customers: 'Here's PRELUDE. You can use it to make your own gateways', probably not one of them would be bold enough to accept.
Television-set manufacturers provide ready-to-operate handsets, not tool-kits from which customers have to construct their own. So it must be with CHAM and the PHOENICS Gateways.