Blisk Blade Mistuning Detection via Temporary Mass Decoupling
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Solution Overview
Problem
Existing methods for determining blade detuning in integral impellers, such as BLISKs, face challenges in accurately measuring natural frequencies and vibration responses due to incomplete decoupling, especially in designs with a high number of blades, leading to incomplete or complex mode separation and limited applicability.
Innovation Solution
The method involves temporarily attaching identical additional masses to unexamined blades to shift their oscillation frequencies away from natural frequencies, allowing for clear measurement of the examined blade's vibration response and determining the natural frequency distribution of the impeller, using laser vibrometry and transfer functions to assess detuning and fatigue risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If blades are excited one after the other in a decoupled state to measure vibration response, then measurement precision of natural frequencies is improved, but device complexity increases due to the need for bracing and additional masses
Solution Approach 1:
The patent applies segmentation by treating each blade as an independent measurement unit. Additional masses are attached to specific blades to be excited, while other blades are braced to create a decoupled state. This allows the vibration response of individual blades to be measured separately, improving the precision of natural frequency determination without requiring complex global bracing structures.
Solution Approach 2:
The patent changes the mass parameter of specific blades by attaching additional masses. This modifies the oscillation frequencies of unexcited blades, shifting them away from the natural frequencies of excited blades. This parameter change enables clear separation of vibration modes and improves measurement precision while avoiding the need for complex bracing arrangements.
2Stability of the object's composition
If additional masses are attached to unexamined blades to shift oscillation frequencies, then blade decoupling is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by attaching additional masses to blades before the vibration measurement process. This preparatory step shifts the oscillation frequencies of unexamined blades in advance, ensuring stable decoupling during the subsequent measurement. The masses are attached at predetermined locations on the blades, making the process systematic and manageable despite the additional manufacturing step.
3Productivity
If impellers with high number of blades are measured, then productivity is improved, but measurement precision deteriorates due to incomplete mode separation
Solution Approach 1:
The patent applies local quality by applying different conditions to different blades during measurement. Additional masses are attached only to unexamined blades, while the blade being measured remains in its original state. This localized modification allows each blade to be measured with optimal conditions, maintaining high measurement precision even when dealing with impellers that have a high number of blades.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables realistic detection of blade natural frequencies and detuning, providing reliable statements on operational safety and service life by effectively decoupling blades with minimal effort, applicable to both dismantled and installed impellers.
Implementation Method 1
the vibration response of the blade in question is measured
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
To determine manufacturing-related mistuning of integrally manufactured impellers (BLISKs) based on the identification of blade natural frequencies, the individual blades are excited independently, and the vibration response is measured to calculate the respective blade natural frequency and the mistuning. Near the measurement process, the blades not under investigation are further detuned by means of a temporarily attached, identical additional mass. This shifts and thus eliminates interfering coupling effects from the blades' natural frequency range when measuring the vibration response of the excited blade.