Dam Break - CFD Simulation CFD Software Tutorial

In this tutorial, we will demonstrate a common free surface flow with a Volume of Fluid approach. We will examine the multiphase, immiscible flow of water and air. Increasing the water level will lead to a water flow through the dam. Using ParaView, we will be able to visualize the resulting flow and its effects.

SimFlow is a general purpose CFD Software

To follow this tutorial, you will need SimFlow free version, you may download it via the following link:
Download SimFlow

Open SimFlow and create a new case named dam break

Firstly we need to Download GeometryDam

The STL geometry format does not store the unit in which the geometry was created. Geometry size shows the overall size of the model in each direction, which is helpful for unit selection. In our case, the default unit meter is correct.

After importing geometry, it will appear in the 3D panel.

Now we need to enable meshing for the newly imported geometry.

Now we are going to define the computational domain in the Base Mesh panel.

To be able to define different conditions on each boundary of the domain we need to assign an individual name to each side of the base mesh.

We need to tell the meshing algorithm where the mesh should be retained.

Everything is now set up for meshing

After meshing process is finished the mesh will be loaded and displayed. To show what is inside of mesh, we can zoom in, or hide other meshes.

You can toggle the visibility of different objects to examine desired ones.

To analyze water flow over a dam we will use Inter (interFoam) solver. This solver is able to model two-phase flow with a free surface.

At the inlet, we will apply a constant water flow rate in order to simulate water supplied by a river.

We will modify the default phase fraction boundary condition to properly interact with the velocity boundary condition.

On the outlet we want the water to freely flow out of the domain.

We want sides to be impermeable but did not provide any friction.

As an initial state, we want some water to already be behind the dam. For this purpose, we need to create geometry defining the initial location of water.

The gray box behind the broken dam geometry indicates the water we have created for the initialization part

We will use the water_init geometry to select the region where water phase fraction should be applied.

Usually, we do data postprocessing when the computation is finished. However, it is handy to be able to see a preview of the results during the calculation. To do this, we need to use the Monitors panel where we might sample data in a specified point or section plane. In this tutorial, we will add a section plane, going through the center of our mesh.

Finally, we need to choose which data should be sampled on the section plane.

For multiphase simulations, we usually want the solver to automatically determine the proper time step. This should lead to good stability and reduce simulation time.

In some situations, it might be necessary to use smaller time step values than the one provided by default configuration. To force solver reducing it you need to change the Max Co [-] (Courant Number). This property is used by the solver to automatically estimate the desired time step value.

Before we will start computations we will specify intervals for writing data.

To speed up the calculation process, take advantage of parallel computing and increase the number of CPUs based on your PC’s capability. The free version allows you to use only one processor (serial mode). To get the full version, you can use the contact form to Request 30-day Trial

Estimated computation time for serial mode: 35 minutes

When the calculation is finished we should see a similar residual plot.

When the calculation is started SimFlow will automatically open the Residuals plots tab. When data is written to the disk for the first time new tab Slices will appear next to Residuals . Under this tab, we can preview results on the defined slice plane.

When the computations are finished start the ParaView software.

You might also start ParaView when the simulation is still in progress to observe intermediate results

After opening the ParaView, we have to load the results of the simulation from SimFlow.

We want to show how the water surface looks like. Additionally, we want the water surface to be colored based on the local velocity to better understand the flow behavior.

After the clip is created we can color water surface with velocity and choose color scale preset. While being still in the Properties panel.

We can now select Color Preset of your choosing.

After correctly defining configuration you should be able to see similar results in the graphics 3D view.

We can also add an opacity attribute to surface colors.

This concludes the tutorial, covering all the aspects we intended to showcase. For a finely tuned presentation of the results, you may take advantage of the more advanced features.

In ParaView, you can display streamlines, contour plots, vector fields, line or time plots, calculating volume or surface integrals and create animations.

To familiarize yourself with the ParaView capabilities, it’s worth checking out our video tutorial, Paraview CFD Tutorial - Advanced Postprocessing in ParaView, in which we demonstrate some of the most commonly used post-processing techniques.

Paraview CFD Tutorial - Advanced Postprocessing in ParaView