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ANALYS OFF VIBRATORY STRESS

OF ISB FOR MECHANICAL DRIVESTEAM TURBINE

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ADVANCED INTEGRAL SHROUD BLADE

• Blades are continuously coupled by blade

deformation due to centrifugal force.

• Applied to control as well as intermediate stage

 blades.

Operation concept of Control Stage

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INTEGRAL SHROUD BLADE – cont.

•Assembling : Each blade inserted into the groove on the slant.

•Blades coupled during rotation

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ANALYSIS OF VIBRATORY STRESS

DUE TO NOZZLE BLADE INTERACTION

CAUSES OF VIBRATORY STRESS

Excitation force due to interaction between nozzle and

 bladesResonant response of the blade due to nozzle wake

excitation force calculated using 3D CFD and FEA.

Resonant condition and stress due to nozzle wake

excitation force given by:

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•Pressure fluctuation on the blade surface obtained in the form of time history wave

using unsteady 3D CFD.

•

Magnitude and phase of pressure fluctuation with the fundamental frequency (rotorspeed x vane count) – calculated by Fourier analysis.

•Eigen value analysis of bladed disk carried out by 3D FEA.

•Resonant stress calculated by an equation.

•Magnitude and phase of the excitation force obtained by pressure fluctuation x effective

area . Calculated value used for blade damping

ANALYSIS OF VIBRATORY STRESS – cont.

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• Natural frequencies of the system and the Campbell diagram can be obtained

using the FE software.

•Using the information, blade designer can identify dangerous vibration modes in

the operating speed range.

ANALYSIS OF VIBRATORY STRESS – cont.

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DUE TO NOZZLE SHOCK LOADCause: due to rapid load increase and

decrease during partial admission

ANALYSIS OF VIBRATORY STRESS – cont.

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ANALYSIS OF VIBRATORY STRESS – cont.

SAMPLE ANALYSIS

•Analysis carried out for ISB structure and

Conventional grouped blades structure.

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Pressure fluctuations during the

operation of the control stage blades

Safety Factor Comparison of ISB andGrouped Blade structure for shock loads for

25 % Steam admission.

ANALYSIS OF VIBRATORY STRESS – cont.

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VERIFICATION OF THE ANALYTICAL

METHOD FOR VIBRATORY STRESS

•Rotating Vibratory test carried out verify the analytical methods

•Setup consisted of rotor with 3 ISB structures

•Blades excited by air jet to completely measure resonating stress

• Natural frequency of blades measured by Conventional telemetry system.

•Campbell diagram measured in

the test, almost matches the

Campbell diagram predicted by

FEAAnalysis.

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CONCLUSION

•CFD & FEA Software is a useful tool to analyze the

Vibratory stresses induced in the turbine blades.

•The Shock load strength / resistance to shock loads of the

ISB structure was compared with the conventional Grouped

 blade structure and was found superior.

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REFERENCE

•Yasutemo Kaneko (Senior Engineering Research

Manager), Kazushi Mori (Chief Research Engineer),

Toshihiro Miyawaki (Senior Research Engineer) – 

Mitsubishi Heavy Industries Ltd (Hyogo, Japan) &

Satoshi Hata (Group Manager-Turbomachineryengineering D0epartment, Mitsubishi Heavy Industries

Ltd., Hiroshima, Japan), 2007, “ ANALYSIS OF

VIBRATORY STRESS OF INTEGRAL SHROUD

BLADE FOR MECHANICAL DRIVE STEAM

TURBINE”, Proceedings of the thirty sixth

turbomachinery symposium.