Useful CFD Tip

Looking for a practical CFD tip to streamline your workflow and save time? One of the most effective ways CFD engineers and aerodynamicists can reduce both computational cost and turnaround time is by reusing existing meshes. For example in scenarios like speed sweeps, where different attitudes in a run will end up using a duplicated mesh. Traditionally, creating a new mesh for each case can be time-consuming and resource-intensive. By reusing meshes, you can avoid duplicating work, while ensuring consistent quality across multiple simulation cases.

In bramble, this can be achieved through mesh cloning, a functionality designed to let one mesh serve multiple simulation cases efficiently. With this approach, you create a single high-quality mesh once, and then reuse it across subsequent simulation runs. This is particularly helpful for simulations that share geometry or boundary conditions, such as speed sweeps, where each attitude of the vehicle may only differ in orientation or operating conditions.

Enabling Donor Mesh Workflow

To take advantage of this functionality, the Donor Mesh workflow must be enabled on your bramble account. If the option is not visible in your interface, you can contact bramble Support at info@bramblecfd.com to have it activated. Once enabled, this workflow provides a systematic way to clone a donor mesh from a base simulation and apply it to other cases without having to regenerate the mesh each time.

It’s important to remember that Donor Mesh settings are global across your account. Any changes made can potentially impact other programs or projects that rely on the same simulation environment. Therefore, before modifying these settings, it’s best to verify that your updates will not affect ongoing simulations. If you’re uncertain, a safer approach is to add new options rather than altering existing configurations. This ensures continuity and avoids unintended disruptions in your workflow.

Step-by-step donor mesh workflow

Step 1: Define your test map

Begin by defining your test map and creating a run as normal.  The example below is a simple speed sweep.

Step 2: Configure the first attitude

The first attitude in the simulation should be configured as normal (i.e. using a standard RANS or DES workflow) (1).  Subsequent attitudes should then use the same CFD Setup, except that the Workflow is updated to use either a RANS or DES Donor Mesh option (2 & 3), e.g. ‘TSFoam RANS 1806C Donor Mesh’.

A number of additional attitudes can be configured to use the Donor Mesh workflow.  To save time, it can be easier to setup the Donor Mesh attitudes first using the ‘Save to all’ option, and then updating the workflow for the ‘standard’ workflow case.

When using Donor Mesh workflows for DES cases, only the mesh is cloned and the RANS solve will be re-run.

Step 3: Lauch the simulations

The attitudes can now be launched as usual. When they reach they reach the ‘mesh & solve’ stage, it will only be possible to launch the standard workflow simulation (1); the ‘mesh and solve’ button will be deactivated for the other attitudes (2).

When the standard workflow simulation completes the mesh and solve stage, it will automatically launch the other attitudes.  The user need not intervene further. 

Next Meshing Tip

For your next CFD tip, you can explore how to run a DES simulation from an existing RANS simulation, further optimising your simulation pipeline and reducing redundant computation.

By incorporating these techniques into your workflow, you can make high-fidelity CFD simulations more efficient and accessible, even for small teams or projects with limited computational resources. Mesh reuse is a simple yet powerful strategy that improves productivity, reduces turnaround time, and allows engineers to focus more on analysing results rather than repeating the same setup steps.

Run DES from an Existing RANS Simulation  →