Hard core and pure Computational Fluid Dynamics (CFD) still remains one of the most complex fields within engineering. Yet, it is incredibly valuable, especially in a world where optimisation is becoming more necessary, not only for cost reduction but to make products even more efficient every day. 

October 11, 2016

Fortunately, technological developments in computers have enabled software to perform even better and to have much simpler interfaces for users to perform their tasks. In the case of CFD used for industrial applications, this means that it is a lot easier to validate fluid behaviour today.

The 3DEXPERIENCE platform is definitely not alien to this evolution, and it offers exceptional tools for Fluid Validation. In this example we go through the process of applying an external flow around a simplified car surface. The idea is to check if the design is capable of generating any downforce.

To create a basic Fluid Simulation you need to go to the Fluid Mechanics Validation application under My Simulation Apps on the 3DEXPERIENCE compass.

Once you are in the app, the Flow Simulation Assistant aids you in the setup of the analysis by showing which steps are missing or have been incompletely defined throughout the process. The way in which it does this is by showing a green tick on all the steps which have been defined properly.

If the definition of a step is invalid or incomplete, a red exclamation mark appears. If a step has not been defined yet but it can be defined, there will be a red empty circle. If it can’t be defined yet because previous steps have to be completed previously, there will be a red “no entry” sign. A green empty square means you can skip that step if it is not required for the simulation.

The first step in this case, is to define the Fluid Domain, in which the Part involved in the simulation, Exterior Boundaries (if any), Regions, and Openings (for example: in case of internal flow) are defined.

A general step in creating a CFD analysis in different analyses packages is that the object around which the flow is going is usually subtracted from the fluid domain. Fluid Validation in 3DEXPERIENCE does not explicitly require for this to be done by the user. Although it can be done if preferred, it rather recognizes the part around which the flow is going to move and automatically meshes around it without needing to subtract it from the fluid domain. This is made possible by specifying the Regions on the model, in which only a face of the solid needs to be selected in order for 3DEXPERIENCE to automatically recognize it as the object interacting with the flow.

After the steps to define the Fluid Domain have been completed you can proceed with the Simulation Setup, in which the increment size and number of increments can be specified.

Later, the Mesh Setup allows you to easily define minimum and maximum mesh sizes, plus the number and size of Boundary Layers. The rest of the meshing process is done automatically and, as mentioned earlier, 3DEXPERIENCE automatically identifies the object around which its meshing and the Fluid Domain to be meshed.

You can visualise the mesh by going back to the original Part from which the simulation is being created and Show the “Nodes and Elements” node in the tree under the Finite Element Model.

Then, if you have not defined any materials prior to the simulation, they can be defined and applied to the Regions in the model. Until the Material Definition, you stay in the Setup tab from the Action Bars.

Following this step, the Boundary Conditions can be specified accordingly by going to the Flow tab in the Action Bars. In here, conditions like Walls, Velocity Inlets, and Pressure Outlets can be specified and configured.

Proceeding then to the Results tab from the Action Bars, you can finish the process of creation by requesting Field or History Outputs of the variables you are most interested in visualising later when post processing the simulation. Since this simulation is about observing whether there is downforce or not, you can request a History Output to obtain FORCE, which gives you the force magnitudes and components on the walls you specify. This would allow to also obtain the total Drag from this model.

Since the simulation has been Setup now, it can be run using the “Simulate” icon. In the same tab the results can all be visualised later on after the simulation has finished running.