Encyclopaedia Index

WORKSHOP - Introducing Contaminants

In this workshop contaminants will be introduced to the flow domain.

To start with, a contaminant of the same density as air at 20 C is introduced.

The workshop is then expanded to allow the introduction of a contaminant of a different density than that of air.

The method of introduction is through the Main Menu in the VR Editor

The two-dimensional flow domain used in this workshop is shown below.

Geometry

Within PHOENICS Environment:

Start with an 'empty' case - click on 'File' then on 'Start New Case', then on 'Core', then click on 'OK'; to confirm the resetting.

Within VR Editor:

Set the domain size, and activate solution of variables

Click on 'Main menu' and set 'Introducing contaminants' as the Title.

Click on 'Geometry'

Change x-direction Domain size to 0.6

Click on 'OK' to close the Grid mesh settings dialog.

Click on 'Models' and leave 'Solution for velocities and pressure' to ON

Change the Turbulence models to KEMODL. Click on 'OK';

Click on 'Solution controls / Extra variables'. You may have to click on 'page dn' if this button is not visible near the bottom of the panel. In the SOLVE entry box, type C1 and then click on 'Apply'.You will see a new variable called C1. This will represent the mass fraction of contaminant.

The default solution procedure is 'Slabwise' which in this case means on each Z line. To solve C1 more efficiently change the N in the third row (labelled SOLUTN 3 WHOF) for C1 to Y. This will activate a whole-field solution which will solve for C1 over the entire domain in one go. Click on 'Previous Panel'.

Click on 'Top Menu'; and 'OK';

Click on 'reset view parameters' then 'Fit to window' (on the hand-set) to re-scale the displayed geometry.

 

Create the CONTAMINANT INLET object.

Click on 'Settings', 'New' and 'New Object' on the top bar menu to bring up the Object specification dialog box.

Change name to INL1.

Click on 'Size' and Place' in order to change the following to:

XPos: 0.1 XSize: 0.15

YPos: 0.0 YSize: 1.0

ZPos: 1.0 ZSize: 0.0

Click on 'General'.

Click on 'Type' dialogue box and select INLET. Click on OK.

Click on 'Attributes' and change z-direction velocity to -1.0 m/s.

Enter 1.0 in the data entry box next to 'Inlet value' for C1. Click on OK.

Click on 'OK';.

 

Create the Air Inlet Object by duplication

Click on the above inlet object and make sure that it is selected.

Click on the 'Duplicate button' and 'OK' to confirm the action. The newly duplicated object will be at the the same place.

Use 'Position' movement button to change the following to:

XPos: 0.35

YPos: 0.0

ZPos: 1.0

Double click on the duplicated object to bring up the Object specification dialog box.

Change Name to INL2

Click on 'Attributes'.

Enter 0.0 in the data entry box next to 'Inlet value' for C1. Click on OK.

Click on OK

 

Create the OUTLET object.

Click on 'Settings', 'New' and 'New object'.

Change name to OUTLET.

Click on 'Size' and 'Place' respectively to change the following to:

XPos: 0.2 XSize: 0.2

YPos: 0.0 YSize: 1.0

ZPos: 0.0 ZSize: 0.0

Click on 'Type' dialogue box and select OUTLET. Click on OK

Click on OK

 

Create the first Blockage.

Click on 'Settings', 'New' and 'New Object'

Change name to BLOCK1.

Click on 'Size' and Place' respectively to change the following to:

XPos: 0.0 XSize: 0.3

YPos: 0.0 YSize: 1.0

ZPos: 0.71 ZSize: 0.02

Click on OK

 

Create the second Blockage.

Click on 'Settings', 'New' and 'New Object'

Change name to BLOCK2.

Click on 'Size' and Place' respectively to change the following to:

XPos: 0.3 XSize: 0.3

YPos: 0.0 YSize: 1.0

ZPos: 0.44 ZSize: 0.02

Click on OK

 

Create the third Blockage

Click on 'Settings', 'New' and 'New Object'

Change name to BLOCK3.

Click on 'Size' and Place' respectively to change the following to:

XPos: 0.0 XSize: 0.3

YPos: 0.0 YSize: 1.0

ZPos: 0.16 ZSize: 0.02

Click on OK

 

Set the grid

Click on the 'Mesh toggle' button. The default mesh will appear on the screen. The orange lines are region lines, and denote the edges of the bounding boxes of each object. The blue lines are ordinary grid lines introduced by the auto-mesher. This grid is adequate for the tutorial, and does not need to be changed.

 

Set the remaining solution control parameters

Click on 'Main menu'

Click on 'Numerics'

Change 'Total number of iterations' to 300

Click on Top Menu/OK

 

Set the monitoring point.

Move Monitoring Point using the Position buttons to:

x = 0.34 y = 0.5 z = 0.5

 

Running the Solver.

In the PHOENICS-VR environment, click on 'Run', 'Solver'(Earth), and click on 'OK'; to confirm running Earth.

 

Using the VR Viewer.

In the PHOENICS-VR environment, click on 'Run', 'Post processor',then GUI Post processor (VR Viewer) . Click 'OK' on the file names dialog to accept the default files.

To view:

To select the plotting variable:

To change the direction of the plotting plane, set the slice direction to X, Y or Z slice direction (927 bytes)

To change the position of the plotting plane, move the probe using the probe position buttons

probe position (927 bytes).

(Click on the 'C' button and select C1 to display the contaminant distribution)

A typical plot from this case is:

contam1.gif (8785 bytes)

 

Saving the results.

In the PHOENICS-VR environment, click on 'Save as a case', make a new folder called 'Contaminants' (e.g.) and save as 'CASE1' (e.g.).

 

In this section the density of the contaminant will be twice that of air

Theory

The density is to be calculated using the mass fraction in each cell, hence,

1/r = 1 / (C1/r1+C2/r2)

r = r1r2 / (r1+(r2-r1) C1)    (1)

where, r1 is the density of the contaminant (2 x 1.189 kg/m3), r2 is the density of air (1.189 kg/m3), C1 is the mass fraction of contaminant and C2  is the mass fraction of air (actually 1-C1).

One of the available density relationships is 'Inverse linear'. This uses the following expression for density:

r = 1/(A + B f)      (2)

where r is the resulting density in each cell and f is the variable.

Manipulating expression (1) to be in the same form as expression (2),

r = 1/((1/r2)+(r2-r1)/(r1r2)C1)

Hence, A = 1/r2 ; B = (r2-r1)/(r1r2) ; f = C1

 

Within VR Editor

Click on 'Run - Pre processor - GUI Pre processor (VR-Editor)' to return to the Editor.

Set the required density relationship

Click on 'Main Menu'

Click on 'Properties'

Click on 'Edit properties of current material'

Click on Density dialogue box and select the INVERSE-LINEAR option. Click on OK.

Set Variable to: C1

Set A to : 1/1.189 = 0.841

Set B to : (1.189 - 2*1.189)/(2*1.189*1.189) = -0.4205

Set Storage for density to : ON

Click on Previous panel/Top Menu/OK.

 

Running the Solver.

In the PHOENICS-VR environment, click on 'Run', 'Solver'(Earth), and click on 'OK'; to confirm running Earth.

 

Using the VR Viewer.

In the PHOENICS-VR environment, click on 'Run', 'Post processor',then GUI Post processor (VR Viewer) , and view the velocity vectors, contours and isosurfaces.

Click on the 'C' button and select C1 to display the contaminant distribution.

Click on the 'C' button and select DEN1 to display the density distribution.

The density contours plot from this case is:

contam2.gif (8785 bytes)

 

Saving the results.

In the PHOENICS-VR environment, click on 'Save as a case', make a new folder called 'CONTAMIN' (e.g.) and save as 'CASE2' (e.g.).