Rotating Region Materials

Rotating Regions are part of the Motion Module, and allow for the analysis of rotating machinery such as pumps, turbines, and mixers.

The rotating region is an envelope that surrounds a spinning device. Throughout the analysis, the rotating region rotates about its center-line, and any solids within the region will rotate as well.

It is better to use a Rotating Region instead of an Internal Fan or Centrifugal Pump/Blower if you your focus is on the real performance of the fan, the blade design, or blade-interaction effects.

There are three ways to define the rotation of a rotating region:

• Rotational speed
• Driving torque
• Flow-driven (free spinning)

For more about setting up and running Rotating analyses

To Assign a Rotating Region

To assign a rotating region, select Rotating Region from the Type drop down of the Material Task dialog.

1. Open the Material quick edit dialog. There are several methods:

   • Left click on the part, and click the Edit icon on the context toolbar.
   • Right click on the part, and click Edit...
   • Right click on the part name under the Materials branch of the Design Study bar, and click Edit....
   • Click Edit in the Materials context panel.

2. Select one or more parts.

3. Select the database from the Material DB Name menu.

4. Select Rotating Region from the Type menu.

5. Select the material from the Name menu.

6. To specify the axis of rotation, open the pop-out dialog on the Axis of Rotation line, and select either the Global X, Y, or Z axes. Alternatively, click the Select Surface button, and select a surface. The axis is normal to the selected surface.

7. Click Apply.

The center of rotation is calculated automatically based on the geometry of the rotating region. For this reason, it is important that the rotating region and the solid (or cut-out) rotor have the same center.

Example showing assignment of a Rotating Region Material

To Create and Edit a Rotating Region

1. To open the Material Editor, click Material Editor on the Materials context panel.
2. Click the List button.
3. Right click on a custom database, and select New material. Select Rotating Region. Specify a Name.
4. Select the Analysis type: Known Rotational Speed, Known Driving Torque, or Free Spinning.
5. Click the property button that is to be defined.
6. For each property: Select the Variation method, enter the appropriate value and units, and click Apply.
7. Optionally, click Save.
8. Click OK. The new material is available when the Materials quick edit dialog is opened.

The Default material database contains at least one instance of every material type. A convenient way to create a new material is to use a Default material as an example. Because these materials are read-only, use the Material Editor to copy the original into a custom database, and modify the copy. For more about creating a material from an existing material...

Example showing creation of a Rotating Region Material

Analysis Types

The parameters that define a Rotating Region are based on the type of analysis to be run. There are three different scenarios: Known Rotational Speed, Known Driving Torque, and Free Spinning. The type is selected from the drop menu as described in Step 3, above.

Analysis Type--Known Rotational Speed

Enter the rotational speed of the rotor in either radians per second or RPM.

A variable rotational speed can be entered by changing the Variation Method to Table, and entering data points for rotational speed vs. time.

Analysis Type--Known Driving Torque

This method is useful for modeling a device that is rotated by a known driving torque (such as from a motor). Torque can be entered as a constant value or as varying with time or RPM using a piece-wise linear data table.

(The direction of applied torque is set as the rotational direction on the main Material Task dialog.)

If there is a resistive torque acting on the device, subtract that from the Known Torque value. For example, if the known motor torque is 100 N-m, and the resistive torque is 5 N-m, then apply a value of 95 N-m.

In addition to torque, enter the inertia of the rotating device. This is commonly the rotational inertia of the rotor and shaft and anything that is connected to the shaft (such as a motor or flywheel if the rotating device is a turbine). An easy way to determine an approximate inertia is to multiply the combined mass of the rotor, shaft, and shafted accessories by the average radius squared. This approach is reasonable if the intent of the analysis is to run the device to a steady state condition.

If the intent of the analysis is to obtain a detailed time history of the rotational speed, then a more precise value of inertia is necessary.

Analysis Type--Free Spinning

In this case, the rotor starts with no rotational speed, and will “spin up” based on the applied fluid loading. Specify the inertia of the mechanical components and the rotor. The steady rotational speed will occur when the net hydraulic torque is zero.

If the device is free spinning, but a known resistive torque exists:

1. Set the Analysis Type to Known Driving Torque,
2. Apply the resistive torque as a negative value.

This will cause the device to spin up due to the surrounding flow, and will find a steady rotational speed when the net hydraulic torque is zero.