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QBlade ForumQBlade: Bugs and ErrorsUnexpected behavior of rotor with …

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Unexpected behavior of rotor with blade damage

#1 · 22. January 2025, 17:16

Quote from IvanRigel on 22. January 2025, 17:16
Hello!
I am trying to analyze the effect of rotor icing on tower and foundation loads. Among other things, I need to consider the case of 2 out of 3 blades icing, for which I wanted to use the blade damage to give reduced aerodynamic characteristics on the individual blades.
To check the correctness of my actions, I decided to first model the rotor with icing on all 3 blades in two ways: A) by setting the icing polars directly for the blade stations, B) by setting the same polars for all 3 blades using blade damage (Fig. 1). Also, for comparison purposes, the rotor in its original form.
Here’s what I found:
1) As I thought blade damage in steady BEM should be ignored, but I got 3 different results, with the difference between the original rotor and case A seems correct to me, but the difference between cases A and B is inadequate, although they should be identical. How does blade damage work in steady BEM? (Fig. 2)
2) Also in Turbine Simulation module (without considering the structural model) I got very different results for cases A and B (all settings are identical except the rotor). Maybe I did something wrong? Why cases A and B are not the same? (Fig. 3)
3) When exporting a blade with damage in *.bld form, the blocks with damage description are different from the data entered into the program. The station numbers in the exported file are reduced by 1, and the same polar is assigned for two stations (although Qblade set different polars for two stations with the expectation of interpolation) (Fig.4). When this file is imported back, the stations are read correctly (as they were in the original version), but each fault has the same polar for both stations, and the blade number is increased by 1 compared to the *.bld file, which results in the faults being assigned to blades 2, 3, 4 instead of 1, 2, 3. (Fig. 5)
I realize that I can easily use the structural model description to account for ice mass, but I am confused and don’t understand how I can correctly model the change in aerodynamic properties when 2 out of 3 blades are iced. I really hope for your help, thanks in advance!

Hello!

I am trying to analyze the effect of rotor icing on tower and foundation loads. Among other things, I need to consider the case of 2 out of 3 blades icing, for which I wanted to use the blade damage to give reduced aerodynamic characteristics on the individual blades.

To check the correctness of my actions, I decided to first model the rotor with icing on all 3 blades in two ways: A) by setting the icing polars directly for the blade stations, B) by setting the same polars for all 3 blades using blade damage (Fig. 1). Also, for comparison purposes, the rotor in its original form.

Here’s what I found:

1) As I thought blade damage in steady BEM should be ignored, but I got 3 different results, with the difference between the original rotor and case A seems correct to me, but the difference between cases A and B is inadequate, although they should be identical. How does blade damage work in steady BEM? (Fig. 2)

2) Also in Turbine Simulation module (without considering the structural model) I got very different results for cases A and B (all settings are identical except the rotor). Maybe I did something wrong? Why cases A and B are not the same? (Fig. 3)

3) When exporting a blade with damage in *.bld form, the blocks with damage description are different from the data entered into the program. The station numbers in the exported file are reduced by 1, and the same polar is assigned for two stations (although Qblade set different polars for two stations with the expectation of interpolation) (Fig.4). When this file is imported back, the stations are read correctly (as they were in the original version), but each fault has the same polar for both stations, and the blade number is increased by 1 compared to the *.bld file, which results in the faults being assigned to blades 2, 3, 4 instead of 1, 2, 3. (Fig. 5)

I realize that I can easily use the structural model description to account for ice mass, but I am confused and don’t understand how I can correctly model the change in aerodynamic properties when 2 out of 3 blades are iced. I really hope for your help, thanks in advance!

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#2 · 22. January 2025, 17:23

For your familiarization I attach the file with models

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#3 · 23. January 2025, 19:39

Hi Ivan,

You are absolutely correct to question the blade damage functionality. I found two issues that slipped our automatic tests:

When a damaged blade section is defined with two different polars, the associated interpolation function is incorrect and produced nonsensical results, as reflected in your plots.
When exporting to and reimporting from ASCII, polarA was incorrectly used for both sections, and the blade number was incremented erroneously, as you observed.

I have addressed these issues, along with some other minor fixes, and pushed an update (2.0.8.2) that should now work correctly with your model files.

The primary intent behind the blade damage feature is to enable modeling of blades with nonuniform damages across different blades. If all blades have experienced the same damage (or, as in your case, icing) condition, this can be modeled by simply replacing all polars of the blade with the damaged (or iced) ones.

One small distinction to note, however, is the following: When a section with a blade damage or AFC element is defined, the Cl, Cd, and Cm characteristics of that element are used only when an aerodynamic evaluation point lies fully within the element definition (i.e., between both stations). In contrast, when assigning damaged sections directly to a blade, their Cl, Cd, and Cm characteristics are also used during interpolation between these stations and adjacent blade stations.

In the Steady BEM Analysis, the damaged blade sections will correctly contribute to the overall turbine performance. This means that if damage is assigned only to blade 2 or 3, the impact will be appropriately reflected in the simulated performance. However, when viewing the blade graphs, these will only display the respective distributions (Cl, Cd, AoA, etc.) for blade 1. This limitation exists because, during the initial development, a uniform rotor was always assumed, and individual blade data was not generated.

BR,

David