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Run a DES with MeanCalc

MeanCalc watches the forces while a DES runs. It detects the end of the initial transient, averages over as much of the remaining data as it can, and stops the solve once the averages meet your accuracy target.

Before you start

  • Your Account needs the MeanCalc methodology and workflow. Account admins see a MeanCalc tag on the Account Settings page when a MeanCalc workflow is enabled. If you don't have one, contact support@bramblecfd.com to have it enabled for your Account.
  • MeanCalc is a DES workflow, so it helps to know how to run a DES.

Set up the Template Case

  1. Copy or open a Template Case. In the editor's header card, click Edit. In Update Template Case:

    • set Methodology group to OpenFoam
    • add the MeanCalc workflow to Workflows, for example TSFoam v1806F DES + MeanCalc

    Click Update. The Meancalc Settings and MC Stopping Criteria tables only appear on the Solutions tab once the MeanCalc workflow is selected. If they don't appear, contact support@bramblecfd.com.

  2. On the Solutions tab, in Solution Stage, set Solution to Transient and fill in RANS Iterations, DES Solution Time (s) and DES Time Step, as for any DES.

    DES Solution Time is the maximum run time

    With MeanCalc, DES Solution Time is the longest the DES can run. MeanCalc stops it earlier once the accuracy target is met, so set it generously.

  3. In Meancalc Settings, choose a Preset:

    Preset Effect
    Fast or Precise Uses recommended settings for the minimum sample time and the accuracy targets. Min Sample Time and Relative Accuracy Target are disabled
    Custom Uses your Min Sample Time (s) and Relative Accuracy Target values. An empty Min Sample Time is saved as 0

    Min Sample Time is the shortest averaging window MeanCalc may use.

  4. In MC Stopping Criteria, click New and add a row for each force direction to converge:

    • Direction: Drag Force, Side Force or Lift. Each direction can appear only once ("Direction must be unique for Meancalc cases").
    • Relative Accuracy Target: the ratio of random error to standard deviation, between 0.07 and 0.15. The placeholder is 0.1.

    MeanCalc monitors the all force group. Each row sets the target for one direction.

  5. Click Save in the header.

Set up and launch the Run

  1. On the Run's CFD Setup tab, click the edit icon next to an Attitude's name.
  2. In CFD Attitude Setup, choose the MeanCalc Methodology and Workflow, and your MeanCalc Template Case.
  3. Click Save, or Save to All.
  4. Launch the Run.

Check the settings

The pre-check Check Meancalc settings runs on MeanCalc Attitudes. If it fails, Reset the Attitude, fix the Template Case (or a copy of it, if it's locked), and launch again.

Message What to do
"A target accuracy is set outside of the recommended range of 0.07 - 0.15." Change Relative Accuracy Target in MC Stopping Criteria
"The current minimum sample time of … s is insufficient. According to MeanCalc best practices, a minimum sample time of at least … s is strongly recommended for this case." Increase Min Sample Time. The recommendation is 10 convective time units
"The maximum run time (… s) must be greater than the calculated minimum run time (… s). Please increase the maximum run time (DES Solution Time). …" Increase DES Solution Time
"Stopping columns must be a subset of detection columns." Contact support@bramblecfd.com
"includeDictTransient fieldAverages is required, and writeInterval should be set." Contact support@bramblecfd.com

Results

  • Check Convergence shows MeanCalc's run-control plots on the Run Checks tab, instead of the usual force plots. It fails with "Meancalc runControl post-run graphs not found" if MeanCalc produced none.
  • Check End Time checks that the solve ended between MeanCalc's minimum and maximum run times.

Forces and postpro are then produced as for any other DES.

Related: Run a DES · Checks reference · Template Case editor reference