Extending the simulation capabilities of CFD codes The PHOENICS In-Form Facility by Brian Spalding

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Extending the simulation capabilities of CFD
codesThe PHOENICS In-Form Facilityby Brian
Spalding Nikolai Davits
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Summary

• In-Form is a recently-introduced feature which
  enables users of PHOENICS greatly to extend its
  capabilities, without the introduction of new
  coding.
• Users are enabled to express their requirements
  by way of easy-to-write formulae. These are read
  by the Input Module (Satellite), which transmits
  them to the Solver Module (EARTH) this then
  interprets them and performs the implied
  computations.
• Unlike PLANT, its predecessor in functionality,
  In-Form does not require use of a re-compilable
  version of PHOENICS.

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User programming Ground

• No CFD code can contain enough built-in modeling
  capability to satisfy all its users' needs. CHAM
  recognised this in 1981, and therefore provided
  its 'GROUND-programming' feature, with many
  examples for users to copy.
• To users benefit from user-programming facility
  they necessitate a strong knowledge about the
  program structure and Fortran language.
• The 'GROUND-programming' free the user to set
  up what he needs but the burden is to get
  reasonable trained on GROUND coding which may
  take a quite a time (over a year).

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Automated Fortran writing

• Recognizing the specialized training required to
  GROUND programming CHAM (and specifically its
  Moscow branch) developed PLANT.
• The feature writes perfect Fortran
  automatically, and automatically handles the
  compilation and re-building, without user
  intervention.
• Users are required only to express their
  requirements in terms of formulae, in accordance
  with prescribed rules the rest is automatic.
• Of course, the time and expense involved in
  compilation and re-building have to be afforded.

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INFORM Doing without the Fortran (or C)

• In-Form carries the PLANT idea one stage further,
  by
• eliminating the Fortran/C writing,
• eliminating the compilation,
• eliminating the executable-building,
• simplifying the syntax, and
• enlarging the functionality.
• In-Form provides the possibility of writing in
  the Q1 (data-input) file, formulae, or other
  statements, which dictate
• material properties,
• initial values,
• sources and boundary conditions,
• output requirements,
• many other specifications.
• At present therefore, In-Form represents the
  ultimate in user-friendly CFD-code extensibility

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The general idea the use of character strings

• PHOENICS has long been able to transmit
  character strings from its input module
  (SATELLITE) to its equation-solver module (EARTH)
  by way of the SPEDAT(....,C,....) command.
• In-Form uses this facility for communicating the
  user's wishes to EARTH. The character strings
  comprise statements composed by the user in
  easy-to-understand form and placed in the Q1
  file.
• SATELLITE turns these into SPEDAT statements,
  and writes their content to the EARDAT file for
  reading by EARTH.
• EARTH interprets the SPEDAT statements in terms
  of mathematical operations which it then
  executes.
• The creation of In-Form has therefore been
  achieved by enabling
• 1) SATELLITE to turn user-written statements
  into SPEDATs and
• 2) EARTH to undertake the operations which the
  SPEDAT statements imply.

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Typical Q1 statements

• Here are some examples of statements which a user
  might include in his Q1 file, in order so set the
  first-phase density RHO1
• (PROPERTY RHO1 is 1000.)
• (PROPERTY RHO1 is 1000. - 0.01TEM1)
• (PROPERTY RHO1 is P1/(287.0 (TEM1273.0) )
• (PROPERTY RHO1 is 1.1386E03 1.0388E00T1
  5.8115 E-04T1 2 - 6.7765E-07 T13)
• P1 stands for pressure,
• TEM1 (or T1) stands for temperature, and
• means 'continue on the next line'.

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The SPEDAT equivalents

• What the SATELLITE writes to Q1EAR file is the
  corresponding set of SPEDATS, namely
• SPEDAT(SET,PROPERTY,RHO1,C,1000.) or
• SPEDAT(SET,PROPERTY,RHO1,C,1000.-0.01TEM1) or
• SPEDAT(SET,PROPERTY,RHO1,C,P1/(287.0(TEM1273.0)
  )) or
• SPEDAT(SET,PROPERTY,RHO1,C,1.1386E031.0388E00
  T15.8115E-04T1)
  SPEDAT(SET,PROPERTY,RHO1
  ,C,2-6.7765E-07T13)
• These also appear in EARTH's RESULT file, when
  the variable ECHO has been set to T in the Q1.
  Users do not have to read them.

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The EARDAT equivalents

• The corresponding lines in the EARDAT file are
• PROPERTY RHO1 C1000. or
• PROPERTY RHO1 C1000.-0.01TEM1 or
• PROPERTY RHO1 CP1/(8300.0(TEM1273.0)) or
• PROPERTY RHO1 C1.1386E031.0388E00T15.8115E
  PROPERTY RHO1 C-04T12-6.7765E-07T13
• These have evidently the same significance,
  although the locations of the differ somewhat,
  a detail which is immaterial to the user.
• There is no need for the user to read either the
  SPEDATS or the EARDAT equivalents but it may
  sometimes be useful for him/her to check that
  they actually exist, should he/she fear to have
  made an error.

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Available formulae

• The formulae which can be used in In-Form
  statements are extremely varied, as may be seen
  from the relevant entry in the PHOENICS
  Encyclopaedia, and in its appendices
• 1 Functions used in In-Form
• 2 The list of In-Form statements
• 3 In-Form options
• A cursory glance is all that is appropriate in
  the present lecture.

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The merits of In-Form

• The above presentation, although it has shown
  only a small fraction of the capabilities of
  In-Form, strongly suggests that In-Form provides
  PHOENICS users with an enormous increase in their
  ability to simulate never-before-investigated
  fluid-flow, heat-transfer and chemical-reaction
  phenomena.
• It can do everything which PLANT can do, and
  more and moreover,
• its syntax is closer to English and therefore
  easier to learn and
• it requires only the non-recompilable version of
  PHOENICS.
• It makes it unnecessary for users to learn about
  the (rather limited) property and other options
  signalled by the GRNDx pointers.
• Most of the long-familiar COVAL settings can
  also be replaced by the much-more-flexible
  (INITIAL and (SOURCE statements.

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The 'down' side computer time

• From the start, it was recognised that In-Form's
  necessity to parse character strings might impose
  a computer-time burden. Therefore a watch has
  been kept on computer-time differences between
  the In-Form and GROUND-coding methods of solving
  the same problem.
• Early results showed differences which varied
  between 'negligible' and 'a few percent'.
• Per-cent differences were smaller for large
  grids (especially 2D-XY ones) because then
  parsing time is much less than arithmetic-operatio
  n time.
• Recently some cases showing differences of some
  hundreds per cent have come to light. They are
  under investigation and may have nothing to do
  with parsing time.
• Attention is also being given to a
  parse-once-and-store procedure which should
  eliminate this cause of computer-time increase.

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Useful POLIS Entries Related to In-Form

• Introductory Lecture
• TR003 In-Form
• Tutorial Inlet Boundary Layer Profile
• Tutorial Time Dependent Heat Source
• Functions used in In-Form
• The list of In-Form statements
• In-Form options

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The Class Structure

• The following sections the In-Form features are
  introduced by way of a series of workshops.
• They will handle with some selected In-Form
  capabilities due to the limited time during this
  regular course.
• It is expected though that this training will
  enable the beginner to get acquainted with
  In-Form and develop its own cases.

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The Workshop Structures

• The In-Form features and command syntaxes will
  be introduced by a sequence of workshops.
• The workshop themes are structured on simple
  cases and the features are introduced in one to
  one basis to each case.
• The workshop sequence is
• 1. Setting Material Properties
• 2. Using Auxiliary Variables
• 3. Setting Boundary Conditions
• 4. Setting Initials Values
• 5. Residuals and Imbalance Patches
• 6. Moving Objects