.. _knowledge_base_volumeZones:

:ref:`volumeZones <volumeZonesParameters>`
=======================================================

:code:`referenceFrame`
---------------------------------------------

The :code:`referenceFrame` section describes the parameters for moving volume zones.

:code:`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 :code:`axisOfRotation`. Left handed rotations can be simulated by entering a negative :code:`omega`.

.. grid:: 2

    .. grid-item::
        :columns: 6
        :margin: auto

        .. figure:: ../BETDisks/Figures/left_hand_rule.svg
            :width: 80%
            :align: center

    .. grid-item::
        :columns: 6
        :margin: auto

        .. figure:: ../BETDisks/Figures/right_hand_rule.svg
            :width: 80%
            :align: center

:code:`omega`
^^^^^^^^^^^^^^^^^^

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

.. math::

    \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}

See this :ref:`example <non_dim_omega>` showing how to obtain nondimensional :code:`omega` from RPM and this :ref:`tutorial <sliding_interface>` for an unsteady isolated rotor case using a rotating volume zone.

..
    [TODO]
    Once Qiqi and I figure out the best-practice for the dynamic derivatives, I will add more info on setting up thetaRadians and thetaDegrees

.. _knowledge_base_volumeZones_parentVolumeName:

:code:`parentVolumeName`
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The :code:`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 :code:`parentVolumeName:"zoneA"` is required in the :code:`referenceFrame`. 

.. caution::
   If a volume zone rotates with respect to the inertial frame of reference, the :code:`parentVolumeName` should not be specified in its :code:`referenceFrame`. An example can be found at :ref:`XV15 rotor tutorial <XV15_tutorial_case_config>`. 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 :code:`FLUID-MIDDLE-BLOCK` rotates with respect to the inertial frame of reference, so the :code:`parentVolumeName` is not specified. The frame of reference of :code:`FLUID-INNER-BLOCK` rotates with respect to the :code:`FLUID-MIDDLE-BLOCK`'s frame of reference, so its :code:`parentVolumeName` is required to be specified as :code:`FLUID-MIDDLE-BLOCK`.

.. literalinclude:: ../../../solverConfiguration/Files/volumeZonesExample_2.json
   :linenos:

Miscellaneous
^^^^^^^^^^^^^^^^^^^^

.. attention::
   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 :code:`referenceFrame` with :code:`omega:0` can be assigned to either of them.