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WORKSHOP - Flow Simulation within a pipe.

The following instructions will allow the user to set up and run the simulation of gas in a pipe using VR. Initially, the domain is filled with a solid, and the pipe is then 'carved' out by making the pipe sections from a fluid material.

The flow is three-dimensional and its geometry is shown below:

 

Accessing PHOENICS-VR.

From the system level:

To enter the PHOENICS-VR environment, click on the PHOENICS icon on the desktop, or click on Start, programs, PHOENICS, PHOENICS.

In PHOENICS-VR 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.

To enter VR Editor:

This is the default mode of operation.

 

Within VR Editor.

Set the domain size, activate solution of variables and set the domain material:

Click on 'Main Menu' and set 'Pipe flow' as the Title.

Click on 'Geometry'.

Change the X-domain Size to 1.5 m.

Change the Y-domain size to 0.3 m.

Change the Z-domain size to 2.0 m.

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

Click on 'Models'.

Leave the 'solution for velocities and pressure' ON.

Select the LVEL Turbulence model in 'Turbulence Models'. This turbulence model is based on distance to the nearest wall, and is suitable for confined flows where the grid is fairly coarse.

Click on 'Properties'.

Click on the button next to 'The current domain material is'. Select 'Gases', then 'Carbon Dioxide at 27 deg C, 1 atm'.

Click on 'Top menu' then on 'OK'.

The domain no longer fits the screen. To resize the view so that it does fit, click on the pull-down next to the 'R' icon on the toolbar then 'Fit to Window'.

reset1.gif (3045 bytes)

Create the objects making up the scene

Click on the 'Object Management' button ( on the toolbar or image172.gif (1000 bytes) on the hand set). This will display a (currently empty apart from the domain) list of objects.

Create a solid to fill the domain:

Click on 'Object', 'New', 'New object'  on the top bar menu of the Object management Dialog to bring up the object specification dialog box.

Change name to SOLID.

Click on 'Size' and set SIZE of object as:

Xsize: tick the 'to end' box

Ysize: tick the 'to end' box

Zsize: tick the 'to end' box

Click on 'General'

Click on 'Shape' and in 'Geometry', select PUBLIC\SHAPES\BOX and then click on 'Open'. We use the 'box' shape to ensure that the Earth solver will be able to subtract the flowing pipe segments from the solid correctly.

Click on 'Options' and then tick 'Hide object'. The solid will no longer obscure the rest of the geometry.

Click on 'OK' to close the Object Specification Dialogue box.

Create the first horizontal pipe segment:

Click on 'Object', 'New', 'New object'.

Change name to PIPE-1.

Click on 'Size' and set SIZE of object as:

Xsize: 0.3

Ysize: 0.3

Zsize: 0.3

Click on 'General'.

Click on 'Shape' and in 'Geometry', select PUBLIC\SHAPES\CYLINDER and then click on 'Open'.

Click on 'General'.

Define Type: Blockage (default).

Click on 'Attributes', click on 'Other materials', 'Domain material'.

Click on 'Options', 'Rotation options', then on 'Rotate object face' until the cylinder has the right orientation: the axis is in X-direction.

Click on 'OK' to exit the attributes menu, and click on 'OK' to close the Object Dialogue box.

Create the second horizontal pipe section by duplication from PIPE-1:

Click on 'Duplicate object or group' image27.gif (931 bytes) or on 'Object', 'Copy objects' on the top bar of the Object Management Dialog, then 'OK' to confirm the duplication. A new object will appear at the bottom of the object list.

Click on 'X position up' until the copy object has moved as far as possible in X (Xpos=1.2)

Click on 'Z position up' until the copy object has moved as far as possible in Z (Zpos=1.7)

Double click on the copy object to bring up the object specification dialog box and change name to PIPE-2.

Click on 'OK' to close the Object specification dialog box.

Create the vertical pipe section:

Click on 'Object', 'New', 'New object'.

Change name to PIPE-3.

Click on 'Size' and set SIZE of object as:

Xsize: 0.3

Ysize: 0.3

Zsize: 0.8

Click on 'Place' and set Position of object as:

Xpos: 0.6

Ypos: 0.0

Zpos: 0.6

Click on 'General'.

Click on 'Shape' and in 'Geometry', select PUBLIC\SHAPES\CYLINDER and then 'Open'.

Click on 'General'.

Define Type: Blockage (default).

Click on 'Attributes', then on 'Other materials', 'Domain material'.

Click on 'OK' to exit the attributes menu, and click on 'OK' to close the Object Dialogue box.

The cylinder already has its axis in the Z-direction as desired.

Create the lower pipe bend:

Click on 'Object', 'New', 'New object'.

Change name to BPIPE-1.

Click on 'Size' and set SIZE of object as:

Xsize: 0.6

Ysize: 0.3

Zsize: 0.6

Click on 'Place' and set Position of object as:

Xpos: 0.3

Ypos: 0.0

Zpos: 0.0

Click on 'General'.

Click on 'Shape' and in 'Geometry', select PUBLIC\SHAPES\PIPEBEND and then 'Open'.

Define Type: Blockage (default).

Click on 'Attributes', then on 'Other materials', 'Domain material'.

Click on 'OK' to exit the Attributes menu, and click on 'OK' to close the Object Dialogue box.

Rotate the pipe to give it the right direction (clip art rotation 9/24).

Create the second pipe bend by duplication from BPIPE-1:

Click on 'Duplicate object or group' and 'OK'.

Click on the copy object to bring up the object specification dialog box.

Change name to BPIPE-2.

Click on 'Place and set POSITION of object as:

Xpos: 0.6

Ypos: 0.0

Zpos: 1.4

Click on 'Options'.

Click on 'Rotation options' and set value to 3.

Click on 'OK' twice.

Create the fluid inlet by duplication from PIPE-1:

Click on PIPE-1 in the Object management dialog or on screen to select it.

Click on 'Duplicate object or group' and 'OK'.

Click on 'Size' and set SIZE of object as:

Xsize: 0.0

Ysize: 0.3 (already correct)

Zsize: 0.3 (already correct)

Click on 'General'.

Change name to INLET.

Define Type: Inlet.

Click on 'Attributes' to define the inlet conditions.

Set the velocity of the inflow in X-direction at 1.0 m/s.

Click on 'OK' to close the Attributes menu, and on 'OK' in the Object Dialogue Box.

Create the fluid outlet by duplication from PIPE-2:

Click on PIPE-2 in the Object management dialog or on screen to select it.

Click on 'Duplicate object or group' and 'OK'.

Click on 'Size' and set SIZE of object as:

Xsize: 0.0

Ysize: 0.3 (already correct)

Zsize: 0.3 (already correct)

Click on 'Place' and set Position of object as:

Xpos: 1.5

Ypos: 0.0 (already correct)

Zpos: 1.7 (already correct)

Click on 'General'.

Change name to OUTLET.

Define Type: Outlet.

Leave the default values in the Attributes Dialogue box.

Click on 'OK'.

Setting the Probe Location

Before running the solver,it is a good idea to place the probe in a suitable place to monitor the convergence of the solution. Too close to an inlet, and the value will settle down very quickly before the rest of the solution. Placed in a recirculation zone, it may still show traces of change even though the bulk solution is converged. In this case, somewhere downstream of the buildings is fine.

Click on the probe icon on the toolbar or double-click the probe itself, and move the probe to X=0.75, Y=0.15, Z=1.5.

Setting the Grid

Click the mesh toggle meshtog.gif (928 bytes) to display the grid. The orange lines are region boundaries, located at the edges of the objects. The blue lines are 'ordinary' gid lines inserted by the auto-mesher. In this case, the default grid is too coarse. Click on the mesh to display the Grid mesh dialog.

Click 'Edit all regions is X direction'. Turn the auto grid settings to Off. Set the cells for the X regions as follows:

Region Cells
1 5
2 10
3 10
4 10
5 5

Click OK to close the X direction setting dialog.  Click Y-Auto to switch to Y-Manual. Set 'Number of cells' to 10 for Y. As there is only one region in Y, it is not necessary to use the 'All regions' method.

Click 'Edit all regions in Z' Turn the auto grid settings to off. Set the regions as follows:

Region Cells Power Symmetric
1 10 1 No
2 10 1 No
3 15 1.3 Yes
4 10 1 No
5 10 1 No

Click Ok to close the Z direction settings dialog, then OK to close the Grid mesh dialog. The final grid should look like this:

The settings for Z region 3 have made the grid here compress towards the top and bottom of the region, keeping the rate of change of grid size across the region boundary small.

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) 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).

To make the objects see-through, click the 'Wire-frame' toggle (to the right of the Macro button on the second row of buttons).

A typical plot from this case is:

Saving the results.

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