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  • vwt4.htm
    will see the following Pay attention to the calculation time which is 6 seconds Switch on to the graphics window by clicking on the Graphics tab Click on the object tree icon to reveal it then select the CELLGRID object It is now time to mention that the accuracy of the results obtained depend on the calculation grid fineness the smaller are the grid cell sizes the more accurate will be the results we shall get Click on the red tick icon in the tool bar to show its attributes It will result in the picture like this The number of cells in X direction is 37 there are 8 cells both in Y and Z direction As we have found out after the simulation the flow pattern is the same on each constant Z plane what makes us possible to change the cell numbers in each box Let us have only one cell in Z direction and double the number of cells both in X and Y direction See the picture below Now run the Solver by clicking on Options then on Run Solver after that repeat all the other steps of your first run In the VR Viewer window we advice you to display the same image viz pressure contours on a constant Z plane with velocity vectors to admit of comparison of the results obtained As you can see although quantitatively pressure values did not change very much qualitatively pressure contours became more intricate Let us also display forces and moments acting on the test item for easier comparison of the results Click on the test item to select it then right click to display the contextual menu and select the Show results command At the very bottom you will read the following Let us now close the VR Viewer window and return to the Prelude Editor At the very bottom of the opened tab with the result file you will see the following The calculation time has been even reduced to 2 seconds at the expense of diminution of the number of cells in Z direction It is convenient to to test the accuracy of the results obtained by making a series of runs We already explained how to do this in the VWT1 Tutorial 3 Making a series of runs In this series of runs we are going to increase the number of cells in X and Y direction proportionally leaving each time only one cell in Z direction In the Prelude Editor window click on the Functions tab We are going to introduce a new function a coefficient that will be changed during each run and during each run a new number of cells will be obtained by multiplication of the base number by a specific value of this coefficient In the Add box type the word factor and click OK Set the type of this parameter to int meaning integer and its initial value to 3 Return to the Graphics window clicking on

    Original URL path: http://www.cham.co.uk/phoenics/d_prelud/gateways/vwt/d_tuts/vwt4.htm (2016-02-15)
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  • Gateways to PHOENICS
    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 and 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

    Original URL path: http://www.cham.co.uk/phoenics/d_pc/htms/english/guidance/gateways.htm (2016-02-15)
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  • ADVICE on the use of PHOENICS
    they do so that either because of the round off limits of the computer or because the iteration process is prematurely terminated the solution yielded by a computer program will differ somewhat from the true solution of the equations governing the discontinua that to compute solutions to the discontinua equations which are very close to the solutions of the continuum equations therefore entails greater costs than providing approximate solutions because both accuracy and cost increase with the number of volumes with the number of time intervals and with the number of iterations that providing computed solutions which are close to those for the continuum equations is still not the same as simulating physical reality the success of which depends additionally on the validity i e truth to Nature of the continuum equations them selves the appropriateness of the information concerning material properties and the correctness of the formulation of the initial and boundary conditions that as a consequence the use of computer codes for the simul ation of flow processes is an art as well as a science for it concerns the creation of significant abstracts from reality which have most merit when they can economically and rationally persuade experienced persons to base their decisions and actions upon them and finally that credibility economy and relevance to important practical concerns are all qualities that the simulation spec ialist values highly 2 Why caution is needed The ideal user of PHOENICS has been identified in this way in order that should less experienced persons use it they should have received due warning that computer simulations of fluid flow differ appreciably from calculations of the kind which are customary in say structural engineering or in rigid body dynamics In the those fields non linearities are often of secondary importance if indeed they

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/advice.htm (2016-02-15)
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    source subroutine gxknvst htm in phoenics d earth d core to the following values CMU 0 5478 CD 0 1643 C1E 1 44 C2E 1 92 CMUCD CMU CD AK 0 41 EWM 8 6 Users may change any of

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/turmod/turbmc.htm (2016-02-15)
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  • ANGLED-PLATE objects
    the geometry of the obliquely cut cells It sets to zero or otherwise shrinks the cut cell areas and volumes thus in effect treating the cell cutting surface as impervious to flow Having done so it notes that the PRPS value is 299 and resets it to 1 which indicates domain material If the open cells of the object are to be filled with some material other than the current domain material then the material index should be set to 300 imat Note that the PROPS file must then contain this material number Earth will then reset PRPS by subtracting 300 to recover the desired material number Cells in both side of the cut surface are then treated as containing domain fluid but the cut surface acts as an obstacle 2 An Example Input File Library Case v206 provides an example some results of which are shown here Case 1 The flow is aligned with the plate therefore the pressure drop which it causes is very small the effect on the flow direction likewise pressures velocities Case 2 The upstream flow is horizontal and the plate inclined The pressure increases on the upstream side of the plate and falls on the downstream side The fluid is strongly deflected and a recirculation region appears on its downstream side pressures velocities Case 3 The upstream flow is horizontal and the plate inclined at a smaller angle The pressure increases and decreases are smaller as is the size of the recirculation region pressures velocities Case 4 The upstream flow is horizontal and the plate inclined so that the stream impinges on its lower side The pressure and velocity fields mirror those of case 3 pressures velocities Case 5 The upstream flow is horizontal and there are now two plates positioned so as to

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/anglplat.htm (2016-02-15)
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    be saved from Transients Streamlines General screen capture Details are given in TR 326 Animations in PHOTON PHOTON displays relating to successive time steps or to successive downstream distances in a parabolic are best seen by saving the individual pictures as gif files and then linking them together with a suitable animation package Clicking on the titles below will enable some examples to be seen viscous flow in a distorting

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/animate.htm (2016-02-15)
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  • TR326: VR Program Arguments
    when a Q1 file does exist in the working directory and a phi or phida file likewise Often a viewer macro is also present commonly with the filename u Optional additional arguments The arguments vre and vrv can be followed by one or more optional arguments as follows Valid for both vre and vrv fullscreen Starts with the main graphics window filling the whole of the screen pq1 Causes the Satellite whether in VR editor VR viewer or text mode to start with VREDIT F This is required when a Parameterised Q1 is being used case casename Load specified user case User is prompted on whether to overwrite the current case unless silent argument is also used dir directoryname Start VR in specified directory find true false If set true also the default when just find specified VR will open in an existing VR window if available last Starts in same folder as on last exit silent Indicates not to prompt user before overwriting any existing files When used in combination with quit doesn t prompt for confirmation before quitting quit May be used in combination with find will close an existing VR window open on the desktop In VR viewer when used in combination with macro will quit the VR viewer after completing the macro If silent used in combination with quit then VR will terminate without further prompts If quit is not used in combination with find then the argument has no effect display Starts in read only display mode The menu bar control panel and movement panel are not available in this mode Valid for vre only lib libname Load specified libname from the PHOENICS library The user is prompted on whether to overwrite the current case unless silent argument is also used watch filename VR Editor

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_docs/tr326/vr-args.htm (2016-02-15)
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  • Automatic Meshing
    meshing feature For most cases it generates a default grid without user input based upon a maximum cell size as a fraction of the domain size and a maximum change in cell size across region boundaries This default grid can

    Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/automesh.htm (2016-02-15)
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web-archive-uk.com, 2017-12-12