Defining Imbalances

Mass Imbalance

A mass imbalance can be added to the hub system. The hub body-fixed frame is used to define the position of the mass imbalance in Bladed. The user must specify the mass, radial and azimuthal position of the centre of gravity of the imbalance mass. The radius is measured from the hub centre and lies in the flat rotor plane (without coning) spanned by \(y_b\) and \(z_b\). A positive azimuth angle generates positive rotation about the \(x_b\) axis measured from the positive \(z_b\) axis, as shown by the azimuth angle in the hub geometry section.

Note

The imbalance mass is an additional mass and therefore will affect the mass total and also the moment of inertia of the turbine.

An example of defining a mass imbalance is given below.

"Imbalances": {
        "OutOfBalanceMass": 135.0,
        "RadiusOfMass": 1.0,
        "AzimuthalPositionOfMass": 0.0
}

Set Angle Error

For each blade, specify the error in set angle ErrorInSetAngle \(\phi_{\text{err},i}\). An additional pitch rotation is applied to the blade that is mounted on the hub. A positive value moves the leading edge of the blade towards the nose.

An example of set angle error inputs for a three blade rotor is given below.

"Imbalances": {
        "ErrorsInSetAngle": [
          0.0,
          -0.00523598796404245,
          0.00523598796404245
        ]
}

Error in Azimuth Angle

For each blade, specify the error in azimuthal position for each blade \(\psi_{\text{err}, i}\) using ErrorInAzimuthAngle. The azimuth error is applied to each blade and therefore affects the distal frame. Now the azimuth angle for blade \(i\) is computed using

\[ \begin{equation} \psi = (i-1) \frac{2 \pi}{N_b} + \psi_{\text{err}, i}. \end{equation} \]

An example of azimuth angle error inputs for a three blade rotor is given below.

"Imbalances": {
        "ErrorsInAzimuthAngle": [
          0.0,
          -0.00523598796404245,
          0.00523598796404245
        ]
}