Aerodynamic Properties

Sections of the tower exposed to the air are subject to both aerodynamic loading and also alter the flow pattern around the tower. These flows introduce additional forces on the structure, that may be modelled in Bladed.

Coefficient of Drag

The aerodynamic properties of a support structure are represented by the aerodynamic drag coefficient \(C_d\). A single value of \(C_d\) is used for the aerodynamic load computation on all tower sections exposed to air.

Tower shadow

The tower represents an obstacle to the incident air flow altering the flow pattern around the tower and generating a wake downwind of the tower. A tower shadow model is used to represent the reduction in wind velocity in front of the tower and speed up around the sides. When using this option the correction to air velocity is applied to the blade load calculation. More details about the available models for flow obstruction may be found in the tower shadow theory section. The available models are PotentialFlow and Powles.

Potential Flow

The potential flow only depends on a single dimensionless value, called the CorrectionFactor.

A simple example for aerodynamic properties with a PotentialFlow tower shadow model is given below.

"AerodynamicProperties": {
    "CoefficientOfDrag": 0.6,
    "TowerShadow": {
      "PotentialFlow": {
        "CorrectionFactor": 1.0
        }
    }
}

Powles

The Powles-model for tower shadow relies on three parameters. These are:

• ShadowWidthProportion: The horizontal extent of the tower shadow, relative to the size of the obstruction. It is a dimensionless factor.
• MaximumDeficit: The maximum deficit in the wind flow caused by the tower shadow. It is given in \(m/s\).
• LengthReference: The maximum length of the wake in a downwind direction. This value is given as a dimensionless multiple of the local obstruction.

A simple example of aerodynamic properties with a Powles-model is provided below.

"AerodynamicProperties": {
    "CoefficientOfDrag": 0.6,
    "TowerShadow": {
      "Powles": {
        "ShadowWidthProportion": 2.0, 
        "MaximumDeficit": 0.5, 
        "LengthReference": 5.0, 
        }
    }
}