Blade Tip Timing Sensor Natural Frequency Extraction
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Solution Overview
Problem
Traditional contact methods for detecting rotor blade vibrations in high-speed, high-pressure environments are impractical for real-time monitoring, as they require shutdown and result in undersampling issues with blade tip timing sensors, leading to inaccurate natural frequency identification and increased measurement costs.
Innovation Solution
A method using a single or uniformly distributed blade tip timing sensor to extract natural frequency differences by converting arrival time differences into displacement data, performing discrete Fourier transforms, and calculating frequency remainders to obtain natural frequency differences without additional sensors or complex signal reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple blade tip timing sensors are used to reduce aliasing influence, then measurement precision is improved, but device complexity and installation difficulty increase
Solution Approach 1:
The patent segments the blade tip timing measurement process into multiple discrete steps: data acquisition from uniformly distributed sensors, arrival time difference calculation, discrete Fourier transform processing, and frequency remainder extraction. This segmentation allows a single sensor to perform measurements that would traditionally require multiple sensors, reducing installation complexity while maintaining measurement precision through systematic data processing
Solution Approach 2:
The patent introduces an intermediary processing method that uses uniformly distributed sensor data combined with discrete Fourier transform and frequency remainder calculation. This intermediary approach acts as a mediator between the limited sensor configuration and the desired high-precision natural frequency measurement, enabling accurate results without requiring complex multi-sensor arrangements
2Measurement precision
If traditional modal parameter identification methods are used on blade tip timing data, then natural frequency can be identified, but the algorithms involve large number of operations preventing online real-time detection
Solution Approach 1:
The patent extracts only the essential frequency information from the blade tip timing data by focusing on arrival time differences and their discrete Fourier transform. Instead of performing comprehensive modal parameter identification, the method extracts specifically the frequency remainders that directly indicate natural frequency differences, significantly reducing computational operations while maintaining identification accuracy and enabling real-time detection
Solution Approach 2:
The patent applies partial action by performing discrete Fourier transform only on the arrival time difference data rather than analyzing the complete vibration signal. This partial processing approach focuses computational resources on extracting the critical frequency information needed for natural frequency identification, reducing overall computational burden while maintaining measurement precision
3Productivity
If blade tip timing measurement is performed during operation, then online monitoring is achieved, but undersampling occurs due to limited sensor mounting positions
Solution Approach 1:
The patent applies dynamics by utilizing the rotational motion of the blade itself as part of the measurement system. The blade's rotation provides the timing reference, and the arrival time of different blades at the sensor position is measured dynamically during operation. This dynamic approach converts the rotational speed and blade spacing into a natural sampling mechanism that avoids undersampling issues while enabling online monitoring
Solution Approach 2:
The measurement system uses the blade's own rotational characteristics to provide the sampling mechanism. The uniformly distributed blades naturally provide timing intervals as they pass the sensor, and the rotational speed information is derived from the blade passage timing itself. This self-service approach eliminates the need for external high-speed sampling systems, achieving adequate sampling resolution during online operation
Data Source
AI summary
The present disclosure discloses a method for extracting a natural frequency difference between blades by a single blade tip timing sensor or uniformly distributed blade tip timing sensors. The method includes the following steps: acquiring actual arrival time of a rotating blade by using a single blade tip timing sensor or uniformly distributed blade tip timing sensors, and converting a difference between theoretical arrival time and the actual arrival time into displacement data of a blade tip according to a rotational speed and a blade length of the rotating blade; selecting displacement data of blade tips of two rotating blades with the same blade length at the same rotational speed; intercepting the displacement data, performing discrete Fourier transform respectively, and making a sampling frequency approximate to an average rotational speed to obtain spectrum data.