Run DES from an Existing RANS Simulation
Computational efficiency is a critical concern in modern engineering simulation workflows. Running high-fidelity simulations like Detached Eddy Simulation (DES) can be computationally expensive, often requiring significant mesh refinement and solver time. Fortunately, modern meshing and simulation tools provide innovative approaches to streamline this process and reduce computational overhead. One such tool, bramble, allows engineers to leverage existing Reynolds-Averaged Navier-Stokes (RANS) simulations as a foundation for DES workflows. This approach not only saves time but also reduces computational costs by eliminating the need to redo mesh generation or repeat the RANS solve.
The key to this efficiency is the Donor Solve workflow, a feature that allows a DES simulation to build directly on an existing RANS solution. To take advantage of this functionality, you must have the Donor Solve workflow enabled on your account. If it is not currently active, we recommend contacting bramble support at info@bramblecfd.com to have this feature activated. Since these settings are applied account-wide, it is important to exercise caution when making changes. As a best practice, it is safer to add new configurations rather than modify existing ones to avoid inadvertently affecting other simulations.
Understanding the donor solve workflow
The Donor Solve workflow is designed to streamline the transition from RANS to DES. It functions in a manner similar to the Donor Mesh workflow, but instead of cloning only the mesh, it allows the DES simulation to inherit the RANS solution. This method ensures that all pre-existing solver data, such as velocity and turbulence fields, are efficiently reused, minimising redundant computation.
Step 1: Define attitudes
The first step involves setting up a map that contains two attitudes: 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: Configure the simulations
After defining the attitudes, create a new run using the map. Within the CFD Setup tab, configure the RANS attitude using the standard workflow, just as you would for any RANS simulation. For the DES attitude, select the DES Donor Solve workflow (e.g., TSFoam DES 1806C Donor Solve) and ensure that a DES template case is chosen.
Step 3: Launching the simulations
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.
Common Setup Errors
While the Donor Solve workflow simplifies the RANS-to-DES process, it is essential to avoid common setup errors. There must be exactly one donor attitude – the one configured with a standard workflow. Any additional attitudes should use donor workflows. bramble will prevent simulations from launching if this rule is violated, either due to the absence of a standard workflow or multiple standard workflow attitudes. In such cases, an error message will appear in the CFD Setup tab, alerting users to the issue.
By following these steps, engineers can leverage existing RANS simulations to efficiently run DES analyses. This approach not only reduces the computational load but also accelerates the overall simulation workflow, enabling faster design iterations and improved productivity. Tools like bramble make it easier than ever to optimise high-fidelity simulations without sacrificing accuracy or detail.
