There are situations when the different attitudes in a run will end up using a duplicated mesh, i.e, speed sweeps.  In these instances, bramble can clone the mesh from one of the attitudes and use it on the others.  This saves on computational costs as the meshing stage doesn’t need to be repeated.

Similarly, it is also possible to get bramble to clone a RANS solution and run it on using a DES workflow.  This again saves computation costs as both the meshing and RANS solve do not have to be repeated.

For these to work, the “Donor Mesh” and “Donor Solve” workflows need enabling on your account.  If they are unavailable, please contact bramble support to have them enabled on your account.

These settings are global to the account, so be sure that any changes won’t impact the post-processing being generated for other programmes and projects.  If you are unsure, it is safer to add new options rather than editing existing ones.

Donor Mesh Workflow

Step 1

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

Step 2

The first attitude in the simulation should be configured as normal (i.e. using a standard RANS or DES workflow) (1).  The 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

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.  No further intervention is required by the user.

Donor Solve Workflow

Step 1

A Donor Solve workflow is used to run a DES simulation on from a RANS one.  This is configured in a very similar method to the Donor Mesh workflow.

Begin by defining a map that has two attitudes defined, one with a name identifying it as the RANS run and the other identifying it as being DES (1).  All other parameters should be identical (2).

Step 2

Create a run using this map, and then from the CFD Setup tab, configure the RANS attitude using the standard workflow.  The DES attitude should have a DES Donor Solve workflow selected, e.g. TSFoam DES 1806C Donor Solve.

Additionally, ensure that the DES attitude has a DES template case selected.

Once configured, the attitudes can be launched as normal.  As with the Donor Mesh workflow, it is only possible to press Mesh & Solve on the RANS simulation.  The DES simulation will be launched automatically when the RANS simulation completes.

Errors in the Setup

When running a donor type workflow, there should be only one donor attitude, i.e. one that has a standard workflow and the remainder that have donor ones.

bramble will prevent the simulations from being launched if this isn’t the case and there is either no standard workflow attitude, or multiple attitudes with standard workflows.  Additionally, an error message will appear in the CFD Setup tab alerting you to the problem.