1. PhD student: Jia Sun Supervisor: Leif Kari MWL/AVE/ KTH 2009-04-23
COMPRESSOR TECHNOLOGY
Project COMP (WP3): Development and validation of numerical tools for prediction of damping (WP3)
PhD student: Jia Sun
Supervisor: Leif Kari
MWL/AVE/ KTH

2. Structural damping (WP3)
Aero damping
Aero forcing
Material fatigue
Structural damping

3. Outline Part I Overview Part II Damping Measurement
Part III Design the damping treatment
Part IV Analysis of the vibration characteristic of the rotating turbine blade
Conclusion

4. Part I Overview Goal: Structural Damping with coating treatments
The concept of damping
In practice, the loss factor is defined as the energy relation with physical meanings

5. Part I Overview Measurement methods for different damping materials:
The reverberation time method
Light damping, having enough decay time
The vibration decay method
Heavy damping
Half power method
Only measuring damping at the resonance frequency

6. Part II Damping Measurement
Goal: Measuring material damping for turbine blade
Two base materials with three different coating layers including eight different material’s configurations

7. Test Object Test Specimens Specimens Dimension
Free-Free Non Rigid Body modes of the turbine blade from Siemens
Titanium: Hz
Stainless Stell: Hz

8. Method Test method: Reverberation time method
In practice, the decay curve can not reach 60dB reduction. Approximate 20dB reduction can give the sufficient accuracy.
The linear regression method is used to calculate the reverberation time T60.

9. Measurement setting Test configuration
The suspending points are at 0.132L and 0776L; no force acts at the two points;
Sensor Selection: Microphone

10. Measurement setting
Exciter
Equipments

11. Results
Test Results

12. Further Measurement
How to measure the damping for the base material with the coating layer?
The coating material has the higher damping than base material
Reverberation time method doesn't work
Vibration decay method will be used

13. Measurement for the real turbine blades
Damping measurement of two types of the turbine blade from Siemens Industrial Turbomachinery AB.
Test the material damping of the turbine blade in air and vacuum condition.
Titanium
Stainless Steel

14. Method The reverberation method
Accelerometer, electro-magnetic exciter

15. Part III Design the damping treatment
The definition of the loss factor
Design the damping layer
The quasi-longitudinal waves are hard to be damped
Only consider to damp the bending wave
Energy lost per cycle of vibration
Reversible Energy

16. Coating Models The loss factor for bending wave
Case one: treatment on one side
Case two: treatments on both sides

17. Procedure for designing the treatment
The procedure for determining the configuration of the damping treatment:
First measurement
Decide the loss factor of the coating material
Suggest the proper treatment configuration according to the requirement
Input this loss factor into the equation to calculate the combined damping
Measurement to verify our design

18. Part IV Analysis of the vibration characteristic of the rotating turbine blade
Comsol Multiphysics gives the numerical solution for the eigenfrequency analysis of a rotating blade
Since stress stiffness is an effect of the stationary stress field
1st step: calculating the stationary deformation due to rotating effect
Convert centrifugal force to a loading force
2nd step: calculating the eigen mode for this prestressed blade
Introduce the damping into numerical model
The damped eigenfrequency analysis can induce the loss factor in turbine blade model.
Two options can be selected: Rayleigh damping (viscous model) or the loss factor (structural or material damping)

19. Conclusion Describing the damping concept and measurement methods
Damping measurements are made and further experiments will continue to take measure the damping of specimens with different damping layers
Developing an analytical method to design the damping treatment and the validation will be made by experimental results
FEM analysis about the vibration characteristic of the rotating blade is being worked by Comsol and the further task is to integrate this treatment model into our FEM analysis

20. Thank you for your attention