Body Force Propeller Reference

To fully define the body force propeller method, the corresponding child nodes need to be defined. These can be found within the Virtual Disk > Virtual Disks > Virtual Disk node.

A virtual disk defined using the body force propeller method provides the following sub-nodes:
Propeller Curve
Specifies the propeller performance curve based on the data that you provide for thrust coefficient Kt, torque coefficient Kq, and propeller efficiency as a function of advance ratio J. You can provide this data either as polynomial functions or as a table.
Method Child Node
Polynomial (J)Define a polynomial for each quantity.
Polynomial (J)
For each of the properties Kt = f(J), Kq = f(J), and Eta = f(J), define the characteristic polynomial using the editor dialog that appears when you click the custom editor .
Table (J)
Table (J)
After choosing the correct imported table in Table, match the Table: J, Table: Kt, Table: Kq, and Table: Eta properties with their respective columns in the chosen table.
Disk Geometry
See Virtual Disk Model Reference.
Radial Distribution Option
The single property, Thrust and Torque Distribution, allows you to choose between using the Same Distribution for both thrust and torque definitions, or using a Different Distribution for each.
When you choose Different Distribution, the Thrust and Torque Specification node is replaced by individual nodes for Thrust Specification and Torque Specification.
Thrust and Torque Specification, Thrust Specification, and Torque Specification
These nodes all function in the same way. After selecting the Method by which to set the distribution, complete the properties on the corresponding child node.

For all methods, the radial thrust and torque distributions must be specified as function of the dimensionless normalized disk span r * as given by Eqn. (4978).

Method Value Nodes and Properties
Field Function Distribution
Field Function Distribution
Set Scalar Function to a user-defined field function that defines the the radial force distribution in terms of the field function that represents the normalized disk span r * (see Virtual Disk Field Functions. For example, to specify the Goldstein distribution as a user-defined field function:

${VirtualDiskNormalizedSpanStar1} * sqrt(1.0 -${VirtualDiskNormalizedSpanStar1})
Goldstein's Optimum Distribution
Goldstein's Optimum Distribution
Distributions are calculated by using the Goldstein Optimum distribution. For more information, see Body Force Propeller Method. No additional properties.
Polynomial Distribution
Polynomial Distribution
Define the Polynomial using the usual methods. See Setting Values Using a Polynomial.
Tabular Distribution
Tabular Distribution > Table (r*)
Set Input Table to the name of the table under the Tools > Tables node that contains the torque or thrust data. Complete the setup by assigning the respective table columns to Table: Data and Table: Normalized Span Star. You can optionally activate Cubic Interpolation.
Inflow Specification
The inflow specification defines how Simcenter STAR-CCM+ samples the velocity upstream of the virtual disk. If the operation point is set to Thrust (T) or Torque (Q), the inflow density value is also required.
Method Value Node Properties
Constant Inflow Values
Typical use: towing tank with single velocity.

You specify the inflow velocity vector and the inflow density directly as single values. The inflow values remain constant throughout the simulation. This setup leads to a fixed advance ratio and corresponding fixed K t and K q . Constant inflow values correspond to a fixed operating point on the user-specified propeller performance curve.

This method is not compatible with motion—that is, with dynamic fluid body interaction, moving reference frames, or rigid-body motion.

Inflow Velocity
Constant inflow velocity vector.
Inflow Density
Constant inflow density.
Coordinate System
The inflow velocity vector is specified with respect to this coordinate system.
Inflow Velocity Boundary
Typical use: towing tank with varying inflow velocities.

The velocity and density values on the selected inflow velocity boundaries are area-averaged over the boundary. The area-averaged velocity vector is then projected onto the local coordinate system of the virtual disk.

Inflow Boundary
Inflow boundary surfaces over which the boundary face velocities and boundary face densities are area-averaged to obtain a single value inflow velocity vector and an inflow density. The inflow velocity vector is projected onto the local coordinate system of the virtual disk.
Inflow Velocity Plane
Typical use: self-propulsion; averaged local behavior.

The inflow velocity plane is located upstream of the virtual disk and is always oriented with respect to the direction of the virtual disk normal.

You can switch on/off the associated velocity correction using the Induced Velocity Correction Option control.

The velocity components and the density of the fluid approaching the virtual disk are volume-averaged over the inflow velocity plane. The averaged velocity components are then projected onto the normal plane of the virtual disk to yield one average velocity vector value.

Inflow Plane Radius
Radius of the inflow velocity plane. You are advised to use a value that is approximately 10% larger than the virtual disk radius.
Inflow Plane Offset
Offset in the normal (z) direction of the virtual disk. You specify the offset with respect to the virtual disk origin.

For the Body Force Propeller method, you are advised to use an offset of between 1% to 10% of the virtual disk diameter.

Local Coordinate System
Reference to the local virtual disk coordinate system (read-only).
Sampled Velocity Plane
(Body Force Propeller Method only)

Typical use: self propulsion; capture local velocity behavior. Also used for cross-flow or with coaxial propellers.

The sampled velocity plane is located upstream of the virtual disk and is always oriented with respect to the direction of the virtual disk normal. The local velocity components of the inflow plane are mapped to the cells on the disk during each iteration.

You can switch on/off the associated velocity correction using the Induced Velocity Correction Option control.

With this option, the velocity at each cell is used to calculate the local values of K t and K q .

When selected, the sampled local velocity is not averaged, but is instead used to calculate the advance ratio J locally, for all of the cells across the virtual disk. Therefore, the influence of the local velocity field on the propeller is better captured with this method.

For optimum results, it is recommended that the mesh on the cross section of the sampled inflow plane and virtual disk are identical.

Sampled Plane Radius
Radius of the sampled velocity plane. This is a read-only property that is set equal to the disk outer radius.
Sampled Plane Offset
Offset in the normal (z) direction of the virtual disk. You specify the offset with respect to the virtual disk origin.

For the body force propeller method, you are advised to use an offset of between 1% to 10% of the virtual disk diameter.

Local Coordinate System
As per the Inflow Velocity Plane method.
Induced Velocity Correction Option
Controls the usage of the induced velocity correction—the automatic iterative correction for the propeller-induced effects.

The propeller-induced velocity has an impact on either the averaged inflow velocity (for Inflow Velocity Plane method) or the sampled inflow velocity (for Sampled Velocity Plane method). For the latter, the correction is applied on a cell-by-cell basis using the local velocity.

The default setting is ON. To switch off the induced velocity correction, set Induced Velocity Correction to Off.

Propeller Handedness Option
Choose between right-handed or left-handed orientation. For a definition of the propeller handedness and how it affects the direction of rotation, see Propeller Handedness. Set Option to:
  • Right Handed: A right-handed propeller always rotates in the counter-clockwise direction with respect to the positive z-axis of the local coordinate system of the virtual disk.
  • Left Handed: A left-handed propeller always rotates in the clockwise direction with respect to the positive z-axis of the local coordinate system of the virtual disk.
Operation Point Input Option
The operation point defines where on the specified propeller performance curve you want to perform the simulation. A corresponding value node appears alongside on which you set the value for the chosen quantity.
Option Corresponding Value Node
Rotation Rate (n)
Rotation Rate
Set Rotation Rate to the required operation point.
Thrust (T)
Thrust
Set Thrust to the required operation point.
Torque (Q)
Torque
Set Torque to the required operation point.