To model multi-rotor concepts with many rotors where the user is primarily concerned with support structure loads, Bladed offers the pseudo-rotor model.

Bladed can model multiple rotors using the full dynamic model for every rotor. This is more appropriate for a small number of rotors.

Functionality

Pseudo-rotors offer a way for users to model concepts with many rotors on one support structure. Bladed can model each rotor as a much-simplified pseudo-rotor model. These consist of simple look-up tables of forces and moments based on flow speed and angle between the rotor and the flow. The forces and moments are then applied to the support structure allowing design loads on the structure to be simulated. Power output and rotor speed are also calculated based on look-up tables and output, but they are not used in the model of structural loading.

Limitations:

Rotor dynamics

Rotor dynamics are not modelled. The look-up tables assume instantaneous following of the steady state. In reality the coupled structural and aerodynamic behaviour and control action result in a response that has an overshoot and settling time.

Periodic loading

There is no model of loading and power variation caused by the blade passing frequency.

Rotor disk averaging of flow speed and direction

Hub centre flow speeds are used by Bladed pseudo-rotors. In reality, the global rotor loads and power output reflect an average flow over the rotor area.

Rotor faults or shutdowns

No rotor faults or shutdowns can be simulated

Direction of flow misalignment

The direction of the misalignment is not taken into consideration by Bladed pseudo-rotors i.e. the effect of a flow yaw misalignment or upflow angle on the loads, power and rotor speed is identical. For power and rotor speed it is reasonable to expect a yaw misalignment to have the same effect as an up-flow. However, the user should be aware that the off-axis forces and moments cannot be modelled well using this approach.

Yaw position

The pseudo-rotors do not reflect any yaw angle defined by Bladed. The pseudo-rotors are always initially aligned with the global x-axis.

Integration with steady operational loads

Although the GUI has a field for specifying a path to a data file, the functionality of importing look-up tables from Steady Operational Loads results has not be implemented. The user must enter the tables manually.

User Guide

To define a pseudo-rotor, follow these steps:

1. From the main Bladed menu Go to Specify -> Pseudorotors…
2. Create a new PseudoRotorDefinition
   1. There should be one PseudoRotorDefinition for each different type of rotor on the support structure. If there are several identical rotors they can share one PseudoRotorDefinition.
   2. Ignore the Data folder
   3. Give it a name. You will need to reference to the name later
   4. For each lookup,

                                                               i.      select Edit Matrix

                                                             ii.      enter the size of the lookup table that you wish to use in the Dimensions. The first dimension is the number of wind speed points, the second dimension is the angle to the flow

                                                           iii.      enter the values for the lookup in the table. The wind speeds (in m/s) should be entered as the axis values down the left-hand side of the table. The angles to the flow should be entered (in radians) across the top of the table.

                                                           iv.      For Forces and Moments, you will need to use the third Visible Slice drop-down to enter values for X, Y, and Z loads.

1. Create a new PseudoRotor
   1. Add as many PseudoRotors as desired. Bladed will still model one rotor using the full dynamic model, so you may choose to only use pseudo-rotors for all but one of the rotors on the device.
   2. Give each PseudoRotor a unique name.
   3. Specify the node on the support structure where it is to be located. This corresponds to tower station numbers for axisymmetric towers.
   4. Reference the PseudoRotorDefinition by copying the correct name string into PseudoRotorName