Encyclopaedia Index

WORKSHOP - Scalar Equation Method

Overview

The example simulates unsteady, laminar flow over a backward-facing step of 0.13m in a two-dimensional channel of width 0.3m. The length of the channel is 1m. The water is coming through a narrow inlet between the step. The example shows how to activate SEM in VR-Editor for a free surface problem.

 

A complete step-by-step guide, showing how to set the case from the default mode of operation, is provided 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.

From the commander level:

To enter the PHOENICS-VR environment, click on the 'Run vre' icon in the left column.

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 and grid numbers:

Click on 'Menu' (Main Menu) on the VRE-Editor panel; and set 'Flow over a backward-facing step (SEM)' as the Title.

Click on 'Geometry'.

Change 'Steady' to 'Transient'

Click 'Time step settings' button and set

Time at the end of last step to 1 s

Last step number to 1000

Click on 'Apply' and 'OK'.

Change the x-domain size to 1.0.

Change the y-domain size to 1.0.

Change the z-domain size to 0.3.

Set 'number of cells' to 1 in x-direction, 40 in y-direction and 28 in z-direction.

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

Click on 'OK' to exit from 'Menu'.

Click on 'Reset' and then on 'Fit to window'/'OK'.

Activate solution of the required variables and models

Click on 'Menu'; and the on 'Models'.

Leave 'Solution for velocities and pressure' to ON.

Click on 'Turbulence models' and select 'Laminar'/'OK'.

Click on Free-Surface models; and then choose SCALAR_EQUATION.

Leave settings for cut-off values for interface sharpening as default 0.4 and 0.6

Specify properties

Click on 'Properties'.

Leave the default settings for the 'light fluid' and the 'heavy fluid' they are '0 Air at 20 C deg, 1 atm' and '67 Water at 20 deg C' respectively.

Click on Property 'Storage' and set 'ON' for Density and Viscosity, then on 'Previous panel'.

Keep the default setting for Domain initially full of: Light fluid

Sources settings

Click on 'Sources'

Set 'Gravitational forces' ON and click 'OK'.

Set 'Buoyancy model' to CONSTANT

Change 'Gravitational acceleration' to 0.0 in X and Y directions and -9.81 in Z.

Numerical settings

Click on 'Numerics'.

Set 'Total number of iterations' to 10.

Click 'Relaxation control' and set 'Automatic convergence control' to OFF

Set the following values:

Click 'Previous panel'

Output settings

Click Field dump settings button and set 'First step' to 1, 'Last step' to 1000 and 'Step frequency' to 40 and select a letter, say 'N' for PHI.

Click 'Previous panel', and then on 'Top menu' and 'OK' to exit from 'Menu'.

Create Objects and specify boundary conditions

Create a Blockage for the step

Click on 'Settings', 'New' and 'New Object' on the top bar menu.

Change name to BLK .

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

Xsize: 1.0

Ysize: 0.4

Zsize: 0.13

Click on 'General'.

Define Type: Blockage.

Click 'OK' to exit from the Object Dialogue Box.

Create the Inlet

Click on 'Settings', 'New' and 'New Object' on the top bar menu.

Change name to INLET.

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

Xsize: 1.0

Ysize: 0

Zsize: 0.0912

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

Xpos: 0

Ypos: 0.

Zpos: 0.13

Click on 'General'.

Define Type: INLET.

Click on 'Attributes'

Set Inlet density to Heavy

Set velocity in Y-direction at 1.5 m/s.

Click on 'OK' twice to exit from the Object specification Dialogue Box.

Create the outlet

Click on 'Settings', 'New' and 'New Object' on the top bar menu.

Change name to OUT.

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

Xsize: 1.0

Ysize: 0

Zsize: 0.3

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

Xpos: 0

Ypos: 1.0

Zpos: 0.0

Click on 'General'.

Define Type: OUTLET

Click on 'OK' to exit from the Object specification Dialogue Box.

Adjust grid distribution in Z-direction

Click on 'Mesh toggle' button, and the grid will appear on the screen.

Make sure that the grid distribution is uniform in all regions.

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 to display the result.

In the PHOENICS-VR environment, click on 'Run', 'Post processor',then GUI Post processor (VR Viewer)'. Click 'Use intermediate step files' The 'Plot step number' will show 40. Then clcik on 'OK'.

To view:

Turn the Contour display on, then select DEN1 from the 'Select variable' button . Click the animation button to show the evolution of the density contour with time.

A few selected plots at various time steps are shown below.

Time = 0.12 s

Time = 0.2 s
Time = 0.6 Time = 0.8

Source of Further Information

The PHOENICS Encyclopedia contains further details under the headings:

 

Free-Surface-Flow; Scalar-Equation Method

 

Library examples can be found in the multi-Phase flow library, which can be accessed from the VR-Editor ->File menu->Load from libraries ->/Browse/Option library: Advanced multi-phase/Scalar-Equation Model(SEM).

 

References

Jun L, Spalding DB 1988 "Numerical simulation of flows with moving interfaces." PHOENICS Journal of Computational Fluid Dynamics Vol 10, No 5/6, pp 625-637 1988. Published by Pergamon Press

 

Hamill IS, Jun L, Waterson N 1991 "A model for the simulation of three-dimensional mould-filling processes with complex geometries." Presented at the International Conference on Mathematical Modelling of Materials Processing, Bristol, 23-25 September 1991

 

Spalding DB, Jun L 1988 "Numerical simulation of flows with moving interfaces." Published in PCH PhysioChemical Hydrodynamics Vol 10, No. 5/6, pp 625-637 1988

Saving the results.

In the PHOENICS-VR environment, click on 'Save as a case', make a new folder called 'FREES', select the new folder, and save as 'SEM', where n is 1,2,3 or 4 depending on the combustion option.