# Actuator Disk Model

The Actuator Disk model in Flow360 provides a simplified representation of a propulsor using a momentum source term distributed across a disk-shaped region.

# 📝 Actuator Disk Configuration

The Actuator Disk model implements a pressure jump or force distribution across a disk to model thrust-producing devices like propellers, fans, or rotors. It's simpler than the BET Disk model and doesn't require detailed blade geometry or airfoil data.

# 📋 Available Parameters

Parameter Description Unit
Entities Cylinder entity defining disk location and dimensions
Force Per Area Force distribution across the disk with radius, thrust and circumferential components
- Radius Radial positions for force distribution length (e.g., m)
- Thrust Axial force per area at each radial position pressure (e.g., Pa)
- Circumferential Tangential force per area at each radial position pressure (e.g., Pa)

# 🔍 Detailed Descriptions

# Entities

The cylinder entity that defines the location and dimensions of the disk. The cylinder's center, axis, height, and outer radius are used as the actuator disk's center, thrust axis, thickness, and radius respectively.

  • Default: None (required parameter)
  • Example: Cylinder(name="actuator_disk", center=(0,0,0), axis=(-1,0,0), height=30, outer_radius=5.0)
  • Notes: The cylinder axis defines the direction of the thrust. Ensure the cylinder is sized appropriately for your application.

# Force Per Area

Specifies the distribution of forces across the actuator disk as a function of radius.

  • Default: None (required parameter)
  • Example: ForcePerArea(radius=[0, 1], thrust=[4.1, 5.5], circumferential=[4.1, 5.5])
  • Notes:
    • Arrays for radius, thrust, and circumferential must all have the same length
    • Positive thrust means the axial force follows the same direction as the thrust axis
    • Positive circumferential force follows the same direction as the thrust axis with the right hand rule
    • In the GUI, you can either input values directly or upload JSON/CSV files with the distribution data

# Force Per Area - File Upload Options in the GUI

In the Flow360 GUI, you can upload Force Per Area data in either JSON or CSV format:

JSON Format:

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

CSV Format: CSV files can be uploaded with or without headers. If headers are present, they must be: radius, thrust, circumferential

Example with headers:

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

Example without headers:

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

# - Radius

Radius of the sampled locations in grid units where force values are defined.

  • Default: None (required as part of Force Per Area)
  • Example: [0, 0.25, 0.5, 0.75, 1.0] * u.m
  • Notes: Values must be non-negative. Usually starting at hub (0) and extending to tip (maximum radius).

# - Thrust

Dimensional force per area in the axial direction.

  • Default: None (required as part of Force Per Area)
  • Example: [100, 150, 200, 150, 100] * u.Pa
  • Notes: Positive values produce thrust in the direction of the cylinder axis.

# - Circumferential

Dimensional force per area in the circumferential direction.

  • Default: None (required as part of Force Per Area)
  • Example: [0, 25, 50, 25, 0] * u.Pa
  • Notes: Controls swirl/rotational effects in the wake. Can be set to zero for pure thrust models.

💡 Tips

# When to Use Actuator Disk Model

  • For propellers or fans where detailed blade modeling is unnecessary
  • In preliminary design studies requiring quick turnaround
  • When only the thrust and torque effects matter, not detailed wake structures
  • For wind turbine analysis where detailed blade aerodynamics are less important
  • In applications where the general influence of a propulsor on flow is needed, but not blade-specific phenomena

# Comparison with BET Disk Model

Feature Actuator Disk BET Disk
Complexity Lower Higher
Setup Time Fast Moderate
Computational Cost Lower Higher
Accuracy Basic More detailed
Wake Prediction General structure Blade-specific effects
Required Inputs Thrust/pressure Detailed blade geometry

# Common Applications

  • Propeller/Fan Simulation: Aircraft propulsion, marine propulsors, cooling fans, HVAC systems
  • Wind Turbine Analysis: Single turbine performance estimation, wind farm wake interactions, site assessment studies
  • General Flow Control: Modeling jet fans in tunnels, representing flow accelerators, simplified representation of thrust-producing devices

# Implementation Tips

  • Consider upgrading to BET Disk for more accurate wake prediction
  • Ensure adequate mesh resolution around the disk
    • Typically 10-20 cells across the disk radius
    • Maintain refined mesh downstream to capture wake development
  • Start with uniform loading for initial studies
  • Base thrust and pressure values on experimental or analytical data when possible
  • For accurate flow-field predictions, include swirl effects

# Limitations

  • Cannot capture blade-specific effects
  • Simplified wake structure
  • No inherent modeling of performance variation with flow conditions
  • Less accurate than BET Disk or fully-resolved blade simulations
  • May oversimplify flow-field effects in cases with complex inflow conditions

❓ Frequently Asked Questions

  • When should I use Actuator Disk instead of BET Disk?

    Use Actuator Disk for preliminary design studies requiring quick turnaround, cases where detailed wake structures aren't needed, or applications where only the thrust and torque effects matter. Use BET Disk when blade-specific aerodynamics are important.

  • How do I determine appropriate thrust values?

    Thrust values can be determined from experimental data, analytical calculations, or known performance metrics of your propulsor. Typically, you'd convert a known thrust to a pressure by dividing by the disk area.

  • Can I model non-uniform loading?

    Yes, by specifying different thrust values across the radial positions, you can create custom radial distributions to model tip effects or other non-uniform loading patterns.

  • Does the actuator disk model capture tip vortices?

    Not directly. The model produces a simplified wake structure without capturing detailed blade-specific phenomena like tip vortices. For those effects, consider the BET Disk model or fully-resolved blade simulations.

  • How does this model handle different flow conditions?

    The model applies the specified force distribution regardless of inflow conditions. It doesn't inherently account for performance variations with flow speed or angle. You would need to manually update the force distribution for different operating conditions.

  • Can I use this model for contra-rotating propellers?

    Yes, by creating two actuator disk models with opposite swirl directions, positioned in sequence along the flow path.

  • How do I import data from existing propeller analysis?

    You can prepare your data in CSV or JSON format and upload it through the GUI. This is useful when you have force distributions from other analysis tools or experimental data.

🐍 Python API Usage Example

Below is an example of how to configure an Actuator Disk model using the Flow360 Python API:

# Example (for reference only, not included in GUI documentation)
actuator_disk = fl.ActuatorDisk(
    entities = fl.Cylinder(
        name="actuator_disk",
        center=(0,0,0)*fl.u.mm,
        axis=(-1,0,0),
        height = 30 * fl.u.mm,
        outer_radius=5.0 * fl.u.mm,
    ),
    force_per_area = fl.ForcePerArea(
        radius=[0, 1] * fl.u.mm,
        thrust=[4.1, 5.5] * fl.u.Pa,
        circumferential=[4.1, 5.5] * fl.u.Pa,
    )
)

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