# 8.2.8. volumeZones#

## 8.2.8.1. referenceFrame#

The referenceFrame section describes the parameters for moving volume zones.

### 8.2.8.1.1. axisOfRotation#

The rotation of a rotating volume zone follows the right hand rule. The fingers follow the spinning of the rotating volume zone and the thumb points to the axisOfRotation. Left handed rotations can be simulated by entering a negative omega.

### 8.2.8.1.2. omega#

For convenience, there are two options for prescribing the nondimensional rotation speed in the Flow360.json file. Users can either input omegaRadians or omegaDegrees according to the units of their physical rotation speed $$\Omega$$:

(8.2.5)#\begin{align}\begin{aligned}\text{omegaRadians} = \Omega \ \text{(rad/s)} \cdot \frac{L_\text{gridUnit}}{C_\infty}\\\text{omegaDegrees} = \Omega \ \text{(deg/s)} \cdot \frac{L_\text{gridUnit}}{C_\infty}\end{aligned}\end{align}

See this example showing how to obtain nondimensional omega from RPM and this tutorial for an unsteady isolated rotor case using a rotating volume zone.

### 8.2.8.1.3. parentVolumeName#

The parentVolumeName is required for nested rotational volume zones. If zoneA is a rotational zone and zoneB rotates relative to zoneA, zoneB is treated as a nested rotational volume zone. In such a scenario, zoneB’s frame of reference is built upon zoneA’s frame of reference, so in zoneB’s configuration, the parentVolumeName:"zoneA" is required in the referenceFrame.

Caution

If a volume zone rotates with respect to the inertial frame of reference, the parentVolumeName should not be specified in its referenceFrame. An example can be found at XV15 rotor tutorial. Any volume zone, assigned as parent of another volume zone, has to be a rotational volume zone, otherwise the validation during case submission will report errors.

In the following configuration, the frame of reference of FLUID-MIDDLE-BLOCK rotates with respect to the inertial frame of reference, so the parentVolumeName is not specified. The frame of reference of FLUID-INNER-BLOCK rotates with respect to the FLUID-MIDDLE-BLOCK’s frame of reference, so its parentVolumeName is required to be specified as FLUID-MIDDLE-BLOCK.

 1"volumeZones": {
2    "FLUID-OUTER-BLOCK": {
3        "modelType": "FluidDynamics"
4    },
5    "FLUID-MIDDLE-BLOCK": {
6        "modelType": "FluidDynamics",
7        "referenceFrame":{
9            "centerOfRotation": [1,2,3],
10            "axisOfRotation": [1,0,0]
11        }
12    },
13    "FLUID-INNER-BLOCK": {
14        "modelType": "FluidDynamics",
15        "referenceFrame":{

Flow360 does not support simulations containing two adjacent volume zones, which are both stationary. If you want to do simulations in such a scenario, a referenceFrame with omega:0 can be assigned to either of them.