Blade Section Property Coordinate Systems

The blades in Bladed are defined as a finite series of 2D sections along the blade's span, using the neutral axes system relative to the blade root axes system.

Each section has an aerofoil that is oriented according to the Aerodynamic twist, with an associated chord axes system origin located at the leading edge as shown in Figure 1. The aerofoil must be positioned relative to the neutral z-axis, which passes through the elastic centre of each blade section. This is done by defining the location of the elastic centre as a percentage of the Chord length, measured from the aerofoil leading edge along the chord axes that follow the Aerodynamic twist:

• Elastic centre (x')
• Elastic centre (y')

Figure 1: Blade section principal elastic axes coordinate system

Details on the orientation of the local element frame relative to the blade root axes can be found in Blade Local Element Axes.

Each section then allows for the definition of additional property systems that describe the structural and aerodynamic properties of the blade.

Note

Not all coordinate systems are relevant in every model; their inclusion depends on the model's complexity. For example, the principal shear axes coordinate system is not needed if Shear stiffness is omitted.

Table 1: Blade section coordinate systems in Bladed

Coordinate System	Description
Root axes	Fixed to the blade root, and it does not rotate with twist or blade deflection but rotates about the z-axis with pitch.
Chord axes	Located at the leading edge of the aerofoil and follows the Aerodynamic twist.
Principal elastic axes	Located at the Elastic centre and follows the Principal elastic axes orientation (xe, ye).
Principal shear axes	Located at the Shear centre and follows the Principal shear axes orientation (xs, ys).
Principal inertia axes	Located at the Mass centre and follows the Principal inertia axes orientation (xm, ym).
User axis	Located at the User axis, specified by the user for additional loads output. See Loads Outputs at User Axes for details.

Figure 2: Overview of blade section coordinate systems in Bladed.

Definition of Centre Locations and Axes Orientations

The centres, including the Elastic centre, Shear centre, Mass centre and User axis, are all defined with respect to the chord axes, which are controlled by the Aerodynamic twist. The locations of these centres are specified as a percentage of the chord length measured from the aerofoil leading edge. An example of this is illustrated in Figure 3 for the Shear centre definition.

Figure 3: Top: Definition of Shear centre (x'). Bottom: Definition of Shear centre (y').

Furthermore, the orientations of the Aerodynamic twist, Principal elastic axes orientation (xe, ye), Principal shear axes orientation (xs, ys), and Principal inertia axes orientation (xm, ym) are all defined with respect to the root axes and are positive in the clockwise direction as shown in Figure 4. In the GUI, the unit of the inputs is in degrees, whereas in the project file, it is in radians.

Figure 4: Definition of various property axes orientations in Bladed.

Overview of Blade Section Inputs and Associated Coordinate Systems

This section provides an overview of the structural properties defined in the various coordinate systems. For more details, see Blade Section Stiffness and Blade Section Mass.

Principal Elastic Axes

The following blade section input properties are defined in the principal elastic axes coordinate system:

• Bending stiffness about xe
• Bending stiffness about ye
• Shear stiffness along xe
• Shear stiffness along ye
• Axial stiffness
• FlapEdgeCStiff
• TorsionFlapCStiff
• TorsionEdgeCStiff

Principal Shear Axes

The following blade section input property is defined in the principal shear axes coordinate system:

• Torsional stiffness

Principal Inertia Axes

The following blade section input properties are defined in the principal inertia axes coordinate system:

• Mass/unit length
• Polar mass moment of inertia/unit length
• Radii of gyration ratio

Chord Axes

The following blade section input properties are defined in the chord axes coordinate system:

• Chord
• Thickness
• Foil section

Last updated 16-12-2024