Aerodynamic Properties

QuarterChordCoordinateSystem

The QuarterChordCoordinateSystem represents the quarter-chord point along the chord line of the aerofoil. The chord line is the straight line connecting the aerofoil’s leading edge (front) to its trailing edge (rear). The Y-axis of the QuarterChordCoordinateSystem points from the leading edge to the trailing edge of the aerofoil and the RotationAboutReferenceZ rotates the aerofoil in relation to the reference Z-axis.

The associated property group AerodynamicProperties defines the relevant aerodynamic properties for this aerofoil section, including the specification of the associated polar data.

Figure 1: Illustration and orientation of the QuarterChordCoordinateSystem.

Note

It can be seen from this that the orientation of the aerofoil in relation to the root system will thus depend on both the orientation of the ReferenceCoordinateSystem and the subsequent rotation of the QuarterChordCoordinateSystem. The customer can choose a modelling strategy which best suits their approach, but should be aware that the orientation in relation to the root system is not directly equivalent to QuarterChordCoordinateSystem->RotationAboutReferenceZ unless the reference system is oriented the same as the root system.

Would you prefer a different aerodynamics coordinate system? Let us know about it.

AerodynamicProperties

The AerodynamicProperties are defined in the QuarterChordCoordinateSystem.

The AerodynamicProperties properties are:

• Chord: The chord of the blade at this section, measured from leading to trailing edge. The section will be positioned such that the aerofoil's quarter chord position will lie on the aerodynamic axes origin.
• ThicknessToChordRatio: The ratio between the thickness and the chord length at the section. This would be 1.0 for a cylinder, and in the order of 0.1 (or 10%) for a typical slender aerofoil section.
• AerodynamicSection: A reference to an aerofoil from the Aerofoil Library or a reference to an Interpolated Aerofoil Library to use for this section.

Example of the properties in JSON format where the AerodynamicSection is assigned a fixed aerofoil from an Aerofoil Library. This type of assignment disregards the ThicknessToChordRatio of the aerofoil and whether or not it matches the ThicknessToChordRatio of the blade's AerodynamicSection and the computed Reynolds during the simulation:

"AerodynamicProperties": {
    "Chord": 4.260,
    "ThicknessToChordRatio": 0.288,
    "AerodynamicSection": "DNV_Foil_5"
}

As an alternative an Interpolated Aerofoil Library can be assigned to an AerodynamicSection in the JSON input deck just like a single aerofoil would. In this case, the aerofoils on the set are interpolated by ThicknessToChordRatio before the simulation starts and then are interpolated by Reynolds Number of the blade section at every time step during the simulation:

"AerodynamicProperties": {
    "Chord": 4.260,
    "ThicknessToChordRatio": 0.288,
    "AerodynamicSection": "Interpolated_aerofoil_library_1"
}