1. PHOENICS User Meeting 2006 PHOENICS Today Domain partitioning; exporting and importing. Domain-partitioning reduces a large calculation to a succession of smaller ones It is useful for computer simulation of flow phenomena. characterised by a predominant direction of flow, as for example when several chemical-plant vessels are connected in series. A similar situation arises when it is necessary to simulate the flow over an extensive tract of terrain, for example a complete city or a wide forest. Partitioning is then possible because usually the direction of wind varies little from place to place. Upstream partitions are simulated first; their results are dumped as export objects which are treated as import objects by the next-downstream partitions. The computations are carried out successively. How this can be done with PHOENICS will now be explained.

2. PHOENICS User Meeting 2006 PHOENICS Today Using transfer objects for import and export The idea is simple to understand; but implementation has to be made easy for users. Therefore Transfer Objects have been introduced into PHOENICS by providing two new keywords for In-Form, namely: (EXPORT and (IMPORT The first causes the PHOENICS solver module, EARTH, to write a transfer- object file at the end of its run; and the second causes EARTH to read such a file at the start of its run. Transfer objects can be created by placing in the Q1 file an In-Form statement such as: (EXPORT in NAME_OF_TRANSFER_OBJECT at PATCH_NAME), or (EXPORT in NAME_OF_TRANSFER_OBJECT at OBJECT_NAME). Some tests now follow.

3. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 1 This 2D test of steady laminar convective flow shows how one gets the same answer whether one partitions the domain (B) or not (A) when the flow is uni-directional, and the Reynolds number is much larger than 1. This is Library case 856. The variable is H1.

4. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 2 This 3D example shows partitioning in two directions. It represents a steady atmospheric boundary layer with a point source of pollutant. The results with (i.e. B) and without (i.e. A) partitioning are in close agreement. Library case 858.

5. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 3 This example concerns unsteady spread of a finite release of pollutant into the atmosphere. With (bottom) and without (top) partitioning, the concentration distribution at a fixed time is much the same, Library case 859.

6. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 4 The partitions may be connected in more complex ways. For example, the first might be used to compute the flow and heat transfer within, and the output from, a computer cabinet; then the second might comprise a computer room with several identical computers within it, Or the first might be a room with a smoke- producing fire in it, the second the space around the building, and the third another room into which smoke enters through open windows. Both of these will be illustrated in what follows.

7. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 5 Here is the result of computing the temperature distribution within, and the heat output from, a (highly idealised) computer cabinet. Its output is exported to its environment via transfer objects at its fan inlets and outlets. The library case is 863.

8. PHOENICS User Meeting 2006 PHOENICS Today The cabinet enlarged

9. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 6 This is the result of the subsequent simulation of the temperature distribution in a room containing several identical computers. Their effects are imported via the export objects of the previous calculation, This is library case 864.

10. PHOENICS User Meeting 2006 PHOENICS Today The computer room enlarged

11. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 7 Now for the smoke- producing fire in a room. It exports its smoke through open windows. This is library case 860. It is treated as steady, which is not realistic; but it suffices to show how transfer objects can be used.

12. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 8 The second computation shows how the smoke is imported into the surroundings which export some of it to other rooms in the building. This is library case 861.

13. PHOENICS User Meeting 2006 PHOENICS Today Transfer-object tests, 9 Simulation number 3 shows how the adjoining room imports smoke through its open windows. This is library case 862. Of course, the simulation could have been carried out in a time-dependent manner; And all the rooms in the building could have been treated in the same way. Finally, if two-way interactions between rooms are suspected, it is necessary to iterate.

14. PHOENICS User Meeting 2006 PHOENICS Today How to learn about transfer objects Look in the PHOENICS Encyclopaedia. Try the tutorial (Its quite good). Look in the library (you wont find any, because the search engine has not yet been told what to look for!) Create some examples for yourself. Send them to CHAM for use by all. ------------ The End -------------------------