Model Building - Blades

Articles on this page:

• Polar inertia
• Changing an Airfoil file
• Pre-cone definition
• Transferring aerofoil database between Bladed versions
• Partial span pitch control
• More than three blades
• How are blade mass and inertia values calculated?

Problem

Is the polar inertia per unit of the blades defined in the multibody definition of blades referred to the centre of mass of the section?

Solution

It is about the Zm axis, which is the axis joining the centres of mass at each blade section.

Keywords

Polar inertia; Blades; Centre of mass

Problem

I want to make some changes to the airfoil datasets. I have double clicked a line of the airfoil parameter set and entered new values, after saving this process I closed the window but after opening the window again the old values are still displayed.

Solution

1. Load the airfoil dataset that you wish to change.
2. Select the row of data that you wish to alter and select Edit. (This then loads the data into the boxes at the bottom right of the window.)
3. Once you have edited the data select Add.
4. Bladed will ask you if you want to overwrite existing data, select Yes.
5. Save the modified aerofoil by clicking Save. Rename the aerofoil first if you do not wish to overwrite the previous dataset.

Keywords

Airfoil; Dataset

Problem

How is the pre-cone defined in Bladed?

Solution

The pre-cone is an additional rotation of the blade, outboard of the pitch bearing, as illustrated below.

With the blade at zero pitch position, the axis of pre-cone rotation is the same as the axis for cone rotation.

Note that without blade pre-cone, the blade root Z axis and the pitch axis are identical.

Keywords

Cone; Pre-cone; pre cone

Problem

Is there a way to transfer the aerofoil database completely between Bladed versions without having to transfer the aerofoils separately?

Solution

It's possible to transfer the aerofoil database from one version of Bladed to another if you copy the file garrhas2.mdb from the installation directory of the older Bladed version which you were using to the installation directory of the most recent version of Bladed.

Keywords

Aerofoils

Problem

How do you define a partial span pitch control blade in Bladed?

Solution

To define a partial span pitch control blade you first need to click on the blade station where you would like the partial pitch to begin and then press the 'split' button (see screenshot below).

You will then be free to define the outer section of the blade to pitch by choosing 'moving' in the Moving/Fixed row. You should also notice that Bladed will have automatically updated the pitch control in the Blade information tab to 'partial span'.

Keywords

Blade; Partial span pitch control

Problem

How do I run simulation with more than three blades, are what are the limitations?

Solution

More than three blades can be modelled through "Additional Items" in Bladed 4.8 and later.

There are some known limitations when using this functionality:

• Mass totals in GUI:
  The Bladed GUI can calculate mass totals for information. They are not used by any Bladed calculation. The GUI only knows about 3 blades so, will not add the mass from any additional blades
• Iced blades:
  There is some complex behaviour relating to adding the mass of ice to Blades. This is done in the GUI, which again only knows about 3 blades.
• Post-processing of extreme blade loads (maximum over three blades):
  You will still be able to calculate the extremes for each blade individually, and then manually check which blade has the highest load.

Keywords

More than three blades

Problem

How are the blade mass and inertia values, that are output into the Turbine Info window, calculated from the information entered in the Blade screen?

Solution

There is a downloadable zip package containing a set of equations (scanned image) that explain the derivation of the 1st moment figure. It also contains a spreadsheet showing a worked example from the demo_a project that illustrated the steps to replicate these figures. The mass is calculated using a trapezoidal integration scheme and the 1st moment is calculated as per the equations supplied.

Keywords

Blade; Mass; Inertia