# Cylinder

A cylinder is a three-dimensional geometric shape with a circular cross-section, defined by its center, axis direction, height, and radius.

# Available Options

Option Description Applicable
Name Identifier for the cylinder always
Center Three-dimensional coordinates of the center point always
Axis Direction vector defining the cylinder orientation always
Radius Distance from central axis to outer surface always
Inner radius Distance from central axis to inner surface always
Height Length along the central axis always

# Detailed Descriptions

# Name

Identifier for the cylinder volume entity.

  • Required

Note: Names are not required to be unique, but using descriptive unique names is recommended.

# Center

Three-dimensional coordinates (X, Y, Z) defining the center point of the cylinder.

  • Required
  • Units: Length

Note: The center is located at the midpoint of the cylinder's height.

# Axis

Direction vector (X, Y, Z) defining the orientation of the cylinder's central axis.

  • Required

Notes:

  • The vector is normalized internally
  • The height extends equally in both directions from the center along this axis

# Radius

The distance from the central axis to the outer cylindrical surface.

  • Required
  • Units: Length

# Inner radius

The distance from the central axis to the inner cylindrical surface, creating a hollow cylinder (annulus).

  • Default: 0 (solid cylinder)
  • Units: Length

Notes:

  • Set to 0 for a solid cylinder
  • Must be less than the radius
  • Use non-zero values to create donut-shaped (annular) volumes

# Height

The total length of the cylinder along its central axis.

  • Required
  • Units: Length

Note: The cylinder extends height/2 in each direction from the center along the axis.

💡 Tips
  • Use cylinders for rotation zones around propellers, rotors, or fans
  • For actuator disk or BET disk models, align the cylinder axis with the disk normal
  • Create hollow cylinders (annulus) by setting inner radius > 0 to exclude a central hub region
  • Ensure the cylinder fully encloses the rotating geometry with some margin

❓ Frequently Asked Questions

  • How do I create a hollow cylinder?

    Set the inner radius parameter to a value greater than 0 and less than the outer radius.

  • Where is the center located relative to the cylinder?

    The center is at the geometric center of the cylinder, midway along its height.

  • Can I use a cylinder for non-rotating refinement?

    Yes, cylinders can be used for any cylindrical refinement region, not just rotation zones.

🐍 Python Example Usage

 
import flow360 as fl

# Solid cylinder for a rotor disk
rotor_cylinder = fl.Cylinder(
    name="rotor_zone",
    center=(0, 0, 0) * fl.u.m,
    axis=(0, 0, 1),
    outer_radius=1.5 * fl.u.m,
    height=0.2 * fl.u.m
)

# Hollow cylinder (annulus) excluding a hub
annular_cylinder = fl.Cylinder(
    name="propeller_zone",
    center=(0, 0, 0) * fl.u.inch,
    axis=(1, 0, 0),
    outer_radius=12 * fl.u.inch,
    inner_radius=2 * fl.u.inch,
    height=3 * fl.u.inch
)

← Axisymmetric volume →