Domain partitioning;

1
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
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
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
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
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
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
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
The cabinet enlarged
9
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
The computer room enlarged
11
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
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
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
How to learn abouttransfer 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 -------------------------