PROPANE COMBUSTION (ADIABATIC PPDF)


I) Pre-processing:

    COMBUSTION MODEL:
     BOUNDARY CONDITIONS
    CONTROL PARAMETERS:

II)POST-PROCESSING:
    PANEL DEFINITION:
    RESULTS


    This ssection is a continuity of the modeling strategy. After preparing the model we set up use the Presumed Probability Density Function (PPDF) reaction model for non-premixed flames. The main aim is to use the PPDF database and its utilisation For adiabatic PPDF, the physical properties of fuel are not used as no additional transprot equations requiring these properties are solved. Temperature, density and species concentrations are evaluated using the "beta" function. The fuel is assumed to be pure propane.

    In this case we present only the main command or methodology to implemente and run the combustion with STAR-CD.

I) Pre-processing:

To set up the combustion model parameters , first activate the Chemical Module:
 
  1. Modules>Chemical
  2. Choose in the combustion option PPDF and Adiabatic,click Apply
  3. Click Define scheme
  4. Select option C3H8 PROPANE from PPDF Data Base,click apply
  5. Close the Chemical Module dialog
  6. Close PPDF Model Definition dialog
    The defined combustion model is not assigned to any material (steam) and is therefore currently inactive.The implication of this is that several chemical schemes can be defined within a single simulation and then activated as and when required After define sheme we are going to modify the model in function of the conditions for the combustion.
  1. Select Thermophysical Models and Properties
  2. Goto Liquids and Gases and then open the Chemical Scheme panel
  3. Click option button Chemical Scheme Number and then type 1
  4. click Apply
  5. Open the Molecular Properties panel .Note that as a result of the chemical scheme definition, the setting of the Density pop- up menu has changed automatically to PPDF.
  6. I n the Molecular Properties we check the differente scalars and put the leading reactants in passive action.The others components were active.
    We can note for an adiabatic PPDF model , correct specification of scalar properties is unimportant because the enthalpy and species transport equations are not solved(they are evalued instead by the model).Density is also calculated in the same way , so whether the species are definrd as'Active' or 'Passive'will not make any difference to the computation.

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    In this module ,we modify the fuel stream boundary values as follows:
 
  1. Select Define Boundary Conditions and then open panel Define Boundary Regions
  2. Select the region in the scroll list and modifiy the value
  3. Open the Scalar Boundaries panel
  4. Select Mixture Fraction in the scalar scroll list , type 1in the Concentration
  5. Select C3H8 in the scalar scroll list , type 1 in the Concentration
  6. We do the same command for the the O2(Concentration=0.21) and N2(Concentration=0.79)
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    In this module , we check the solution control parameters anmd then we change the under-relaxation factor and residual tolerance for mixture fraction and variance:
 

  1. Select Analysis Controls
  2. Select Solution Controls and then Equation Behaviour
  3. Open the Additionnal Scalars panel
  4. Select Mixture Fraction in the scalar scroll list
  5. Type 0.7 in the under-Relaxation Factor
  6. Type 0.001 in the Residual Tolerance
  7. Select Variance in the Scalar scroll list
  8. Type 0.7 in the under-Relaxation Factor
  9. Type 0.001 in the Residual Tolerance
    The pre-processing task is now complete.If we wish to terminate the session at this stage, save all model data, write the geometry and problem files and exit from PROSTAR, as shown below.

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II)POST-PROCESSING:

    The second  main hand in this study, is that we can create facilities for running STAR interactively.
We present two user- defined panels , Pgetc and Pgetv, that are specially designed to facilitate post-processing operations.It may already be available to us , ready-to-use, in a local or global panel .
 

    Panel Pgetc is designed as an aid to post-processing cell-centre based data.To set  up the panel , shown below,proceed as follows:
 
  1. Panel >Define Panel
  2. Click on the text box at the bottom of the dialog type Pgetc,the panel's name
  3. Click New. This adds a new panel with that name in the scroll list.Note that the full stop('.') in front of the name signifies that the panel definition is placed by default in the present working directory, in a file called Pgetc.PNL
  4. With the panel name still highlighted , click Open to display the new panel
    We specify the basic panel appearance via the panel menu , as follows:
  1. File>Layout
  2. In the Define Panel Layout dialog box, type 7 in the Number of Buttons Horizontally text box
  3. Type 4 in the Number of Buttons Vertically text box
  4. Type 260 inthe Panel Height text box
  5. Type 550 inthe Panel Width text box
  6. Click Apply
    Proceed with the definition of panel buttons.The latter are numbered in column order, so that buttons nos. 0-3 appear on the left hand side of the panel and nos 24-27 on the right-hand side.To create the the first column:
  1. Click on button no 0
  2. Type SU in the button Name
  3. Click on the Definition sub-window and type :
  4. getc u v w su$repl
  5. Click File>Save
    Repeat this operation for other no(1,2,3)

    The remaining columns are created in a similar manner, according to the definitions given.
After this long operation ,the panel also provides additionnal facilities for executing common data loading operations ,in the form of a local, user-defined menu.The definition of this special menu is as follows:

menu Load

MENU_ITEM 0 Load St
load tut.pst
MENU_ITEM 1 Load St
evfi conn
MENU_ITEM 2 Load St
trload tut.pstt

Complete the panel definition as follows:
 

  1. File>Layout
  2. Type 160 in the Panel Height
  3. Close the Define Panel
    Note that, in going through this process,you have the choice of leaving the panel in your present working directory , where it will be available only to the case you are working on at the moment , or copying/moving it to a local or global panel directory.You might to do the latterif you want the panel to be available for use by other members of your team (global ) or by youself in all your case directories(local).
    If the panel is moved or copied to a local or global directory, you need to make sure that PROSTAR knows the latter's name and location.This information may be available already in the form of environment variable definitions in your operatingh system set -upIn such a case ,next time you enter PROSTAR you will see the panel name displayed when you click Panels in the main menu bar.
    If the environment variables are not set ,it is still possible to supply the required information as part of the current session , as follows:
 
  1. Panels>Environment
  2. Type the full filename path in the PANEL_GLOBAL orPANEL_LOCAL text box, depending on the location of the panel definition file
  3. Click Apply
  4. Panels>DefinePanel >Re-Scan
  5. The above  operation causes the View panel name to be displayed in the list .preceded by the name appropriate
  6. Click Close
  7. Choose Panels from the main menu bar to confirm that Pgetc is included as a menu option
    Note that, if you are working with a local or global directory , any new panels you create cab be placed directly in that directory simply by prefixing the new panel name with a name ,as appropriate.

    Panel Pgetv is essentially identical to Pgetc apart from the fact that it performs vertex based post-processing operations.

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RESULTS
 

    In the first time we can note that velocities are in rotation due to the cyclic condition and the gradient of the velocity vectors is importante near combustion location (great perturbation) , and tend to zero farther away this state.
 






The  distribution of the temperature is only at the interior of the combustor(adiabatic condition) and we can note the temperature of the entry is not importante immediatly due to the fact that there is a little time during we have to  have a mixte of the two components before the combustion.
 

We active user-defined Pgetc and Pgettv  and use them to generate a 3-D display of the velocity magnitude distribution:
  1. Panels>Pgetc>Load
  2. Select option LoadSt.from the panel's Load menu
  3. In the main window, select plot option Contour Plot
  4. in the Pgetc panel, click VM
 We used the same idea to display the other





We have an importante magnitude for the velocity in the entry
 



Maximum temperature seems to be of a good value compared with given temperature of propane gases in bibliographe.
 

Gasous density is also found to corrolate to theoritical values found in bibliographic books. In fact, unburned gas density is greeter then burned gaz ones.
 

This figure shoes that fuel is burned in quasitotalite fare away combustor wall. This is due to air velocity
 
 



 
 
 



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