Using the Time-Accurate Approach with the Virtual Disk Trim Option

When using the Blade Element Method with the Virtual Disk Trim Option, the trim solver calculates the control inputs—the required collective pitch, lateral cyclic pitch, and longitudinal cyclic pitch to achieve the desired thrust and moments you specify.

The trim solver in Simcenter STAR-CCM+ works robustly and precisely with the following workflow.


To create a reasonable initialization, you first run the virtual disk simulation with time-average approach using steady time model.
  1. Specify the virtual disk geometrical properties, which describe the blade geometry. See Blade Element Method Reference.
  2. To pre-run the steady simulation:
    1. Right-click on the Continua > [physics continuum] > [Models] node, select Select Models and switch the time model to Steady.
    2. Select the Virtual Disk > Time Option node and set Source Term Distribution to Time Average.
    3. Select the Virtual Disk > Disk Stick Specification node, set the initial pitch angles and activate the Virtual Disk Trim Option with only thrust or with thrust and moments. See Disk Stick Specification.
    To visualize the solution, you are advised to create a single plot with the following reports with iteration as monitor trigger. See 报告虚拟盘体结果 and Virtual Disk Report Reference.
    • Virtual Disk Force report in the Z direction of the disk coordinate system for thrust (lift force).
    • Virtual Disk Moment reports in the Y direction of the disk coordinate system for the pitch moment and in the X direction for the roll moment.
    • Virtual Disk Angle reports for the collective pitch, cyclic pitch: cosine component, and cyclic pitch: sine component.


  3. Run the steady simulation until convergence.
After convergence, you modify the settings to use unsteady time model with time-accurate approach.
  1. Right-click on the Continua > [physics continuum] > [Models] node, select Select Models and replace the time model with Implicit Unsteady.
  2. Select the Solvers > Implicit Unsteady node and set the properties as follows:
    Property Setting
    Time-Step A value, which corresponds to 1 degree rotation per time-step.
    Temporal Discretization 2nd-order
  3. Create another set of reports for thrust and moments. For all the reports, activate Average Force/Moment.
    This option averages the report value over one revolution:


  4. If required, create a Cyclic Time Unit to record the number of revolutions:
    1. Right-click the Tools > Units node and select New > Cyclic Time Units.
    2. In the new generated [CT] node, set the Units to rev and Rotation Rate to the virtual disk rotation rate.
    3. After the creation of the Cyclic Time Unit, you find the following four reports generated within the Reports node:
      • CT
      • CT Cumulative
      • CT Cycle Length
      • CT Cycle Number

      You apply the CT Cumulative as the X axis of a plot to represent the revolution number or create stopping criteria with respect to the revolution number.

You switch to the Time Accurate approach and continue running the simulation:
  1. Select the Time Option node and set Source Term Distribution to Time Accurate.
  2. Select the Time Accurate Trim Specification node and set the properties described in Disk Stick Specification.
  3. Run the simulation.

    The plot of the thrust report is shown as follows:



    The averaged signal is zero during the first revolution. The trim solver updates the values at the end of each revolution with the average of values collected during the last revolution.