# Rotational Models

# Sliding Interfaces

# The signed RPM for the rotation interface

The RPM (revolutions per minute) should be positive if the rotation follows the right-hand rule with respect to the axis of rotation (thumb pointing towards axis). If the rotation follows the left-hand rule, the RPM must be negative.

# Actuator Disks

Actuator Disk is a lower-fidelity steady-state model for simulating propellers. See here (opens new window) for more details. The data can be uploaded in JSON format or CSV format.

# JSON format:

See example below:

"forcePerArea": {
    "radius": [0, 1, 10],
    "thrust": [1, 2, 1],
    "circumferential": [0, 20, 1]
}

# CSV format:

Header is not requred, if present it must read radius, thrust, circumferential. See examples below:

radius, thrust, circumferential
0, 1, 0 
1, 2, 20
10, 1, 1

or:

0, 1, 0 
1, 2, 20
10, 1, 1

# Other parameters

If the below parameters are found in the JSON file, they will be populated. Otherwise you must provide them in the provided fields.

# Center of Rotation:

Where in the mesh would you like to put this particular AD disk. This is in Mesh units

# Axis of rotation:

Rotational axis of the AD disk, i.e. (+) thrust axis

# Thickness:

This parameter dictates over what thickness (in mesh units) the extra momentum is applied to the mesh nodes. Practically speaking this value should be near the thickness of the propeller along the thrust axis. It is important that the mesh have enough nodes (we recommend at least 20 nodes) in the thrust axis direction across that thickness. If the mesh refinement is too coarse then the extra momentum added by the AD disk implementation is divided across too few nodes and this may cause the solution to diverge. The more momentum the propeller adds to the flow the more this becomes important.

# Blade Element Theory Disks

Flow360 offers the ability to simulate propellers using a range of different fidelity models. We find that Blade Element Theory (BET) is a great compromise between accuracy and cost. See details here: Blade Element Theory Model (opens new window).

# Flow360 BET disk native format:

You can upload the BET configuration as a JSON file following the Flow360 native format. (opens new window).

# required

  • twists
  • chords
  • sectionalPolars
  • sectionalRadiuses
  • alphas
  • MachNumbers
  • ReynoldsNumbers

# BET disk translators

We provide two different readers that accept common input files from either xrotor (opens new window) or DFDC (opens new window) and converts the contents of those files into the BET disk input data required by Flow360. More information on the data required by Flow360 to run a BET disk simulation can be found in the documentation (opens new window)

# XROTOR translator

Xrotor is a very common low fidelity rotor analysis code that provides high level performance insights for isolated rotors. A logical next step in the design process is to use Flow360's BET disk functionality. To that end we have provided an easy translator that extracts all the propeller features (blade geometry, twist and chord distribution, 2D foil sectional polars etc...) from the xrotor input file and converts them into the data format required by Flow360. Please note that certain information required by Flow360 is not provided by the xrotor input file and needs to be entered. Also, Certain parameters are defined both in the Flow360 input file and in the xrotor input file (i.e. Freestream inflow speed, number of blades, RPM etc...). In that case the xrotor input values are ignored.

# DFDC translator

Since xrotor and dfdc are both from the same family of codes, their input formats are very similar. Everything mentioned above for xrotor is also valid for dfdc. Please note that dfdc is meant to simulate ducted fans. The duct part of the DFDC input file will NOT be used. If you want to simulate a ducted fan with a BET disk in Flow360 then you will need to mesh the duct geometry and position the BET disk in the appropriate location inside the duct.

# The extra inputs required by Flow360

# Center of Rotation:

Where in the mesh would you like to put this particular BET disk. This is in Mesh units

# Axis of rotation:

Rotational axis of the BET disk, i.e. (+) thrust axis

# Rotation Direction rule:

Does the propeller rotate around the axis of rotation using the right hand rule or the left hand rule?

# RPM:

Revolutions per minute of the propeller. The value defined in the xrotor or dfdc input files are ignored.

# Number of Blades:

The value defined in the xrotor or dfdc input files are ignored.

# Radius:

Propeller radius in mesh units

# Thickness:

This parameter dictates over what thickness (in mesh units) the extra momentum, calculated by the BET implementation, is applied to the mesh nodes. Practically speaking this value should be near the thickness of the propeller along the thrust axis. It is important that the mesh have enough nodes in the thrust axis direction across that thickness(we recommend at least 20 nodes). If the mesh refinement is too coarse, then the extra momentum added by the BET disk implementation is divided across too few nodes and this may cause the solution to diverge. The more momentum the propeller adds to the flow the more this becomes important.

# Chord Ref:

In mesh units. This is the reference chord used in the BET output information to get sectional loadings. See the BET loading output (opens new window) section of the documentation.

# nLoadingNodes:

Number of spanwise nodes used to compute the sectional thrust and torque coefficients defined in the BET loading output (opens new window). Recommended value is 20.

# Tip Gap:

This parameter affects the tip loss effect. It is the non-dimensional distance between the blade tips and multiple peripheral instances, e.g. duct, shroud, cowling, nacelle, etc. The peripheral structures must be effective at reducing blade tip vortices. Being close to a fuselage or to another blade does not affect this parameter, because they won’t effectively reduce tip loss. tipGap=0 means there is no tip loss. It is infinity by default for open propellers. An example with finite tipGap would be a ducted fan.

# Is steady?:

Steady state vs unsteady, i.e. time accurate run. Select steady for blade-disk analysis, for blade-line analysis select unsteady.

# Blade Line Chord (unsteady):

Chord (in mesh units) to use if performing an unsteady blade-line (as opposed to steady blade-disk) simulation. Recomended value is 1-2x the physical mean aerodynamic chord (MAC) of the blade for blade line analysis.

# Initial Blade Direction (unsteady):

Orientation of the first blade in the blade-line model. Must be specified if performing blade-line analysis.

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