Radosław Przysowa

Tip-Clearance Measurement in the First Stage of the Compressor of an Aircraft Engine

In this article, we report the design of a reflective intensity-modulated optical fiber sensor for blade tip-clearance measurement, and the experimental results for the first stage of a compressor of an aircraft engine operating in real conditions. The tests were performed in a ground test cell, where the engine completed four cycles from idling state to takeoff and back to idling state. During these tests, the rotational speed of the compressor ranged between 7000 and 15,600 rpm. The main component of the sensor is a tetrafurcated bundle of optical fibers, with which the resulting precision of the experimental measurements was 12 µm for a measurement range from 2 to 4 mm. To get this precision the effect of temperature on the optoelectronic components of the sensor was compensated by calibrating the sensor in a climate chamber. A custom-designed MATLAB program was employed to simulate the behavior of the sensor prior to its manufacture.

Inductive sensors for blade tip-timing in gas turbines

Abstract The paper reviews features and applications of the upgraded inductive sensor for BTT, which is able to operate in contact with exhaust gases of temperature even as high as 1200 K. The new design includes metal-ceramic housing ensuring proper heat transfer, magnetic circuit containing set of permanent magnets with various magnetic field values and Curie temperatures, completely redesigned windings and current/voltage converter used instead of an electromotive force amplifier. Its principle of operation is based on electro-dynamical interaction and therefore it may be referred as a passive eddy-current sensor. The sensor technique has been demonstrated on four stages of a surplus military turbofan including the high pressure turbine as part of the engine health monitoring system. We present signal samples and review methods used for online processing of time-of-arrival signals when only a limited number of sensors is available.

Application of Blade-Tip Sensors to Blade-Vibration Monitoring in Gas Turbines

Non-contact blade vibration measurement in turbomachinery is performed during development phase to verify design quality of bladed disk and its structural integrity (Zielinski & Ziller, 2005). The method, referred as blade tip-timing (BTT) or Non-contact Stress Measurement System (NSMS) is applied by mostly all manufacturers as a complement of strain gauges, traditionally used to measure stress levels and blade vibration parameters (Roberts, 2007). Measurement results are usually presented in the function of rotational speed in Campbell diagram, showing vibration modes excited by particular engine orders. Operational stress levels and accumulated fatigue cycles should not exceed material endurance limits. High Cycle Fatigue, occurring at low stress and high vibration frequency is a common reason for blade damage in turbomachinery. HCF has been identified as factor limiting development of more efficient blade designs, affecting safe operation of turbomachinery and causing considerable losses (Nicholas, 2006). US Air Forces initiated HCF Science and technology program in late 1990’s, which launched and supported multidisciplinary efforts for HCF mitigation, continued recently as Engine Prognosis Program. Development of tiptiming instrumentation both for supporting design of fatigue-resistant components and also for online blade crack detection has been one of research priorities and provided new sensors and advanced data analysis methods. NSMS technologies are also developed and successfully applied in power industry (Ross, 2007). Nowadays Blade Tip-Timing using optical sensors is considered as mature technology able to replace strain gauges in development process of fans or compressors (Rushard, 2010; Courtney, 2011). Current research activities concentrate on turbines, which are more demanding environment for tip-timing instrumentation due to high temperature, contamination and lower amplitude of vibration. Development of alternative tip sensors is considered as another priority. Optical sensors despite providing the highest available resolution, require cleaning and ensure quite limited life, which makes them unusable in embedded systems for blade health monitoring. This chapter describes development and application of inductive, eddy-current and microwave tip-timing sensors for gas-turbine blades, carried out in ITWL in last five years. Other sensors’ applications, like measurement of tip-clearance, blade twist and disk

Data Management Techniques for Blade Vibration Analysis

Abstract Well-designed procedures are required to handle large amounts of data, generated by complex measurement systems used in engine tests. The paper presents selected methodologies and software tools for characterisation and monitoring of blade vibration. Common file formats and data structures as well as methods to process and visualise tip-timing data are discussed. Report Generation Framework (RGF) developed in Python is demonstrated as a flexible tool for processing and publishing blade vibration results.

The Analysis Of Synchronous Blade Vibration Using Linear Sine Fitting

Abstract In Blade Tip Timing several sensors installed circumferentially in the casing are used to record times of arrival (TOA) and observe deflections of blade tips. This paper aims to demonstrate methodology of model-based processing of aliased data. It focuses on the blade vibration excited by the forces synchronous with engine rotation, which are called integral responses. The driven harmonic oscillator with single degree of freedom (SDOF) is used to analyse blade vibration measured by tip-timing sensors during engine deceleration. When integral engine order EO is known, the linear sine fitting techniques can be used to process data from sensors to estimate amplitude, phase and frequency of blade vibration in each rotation. The oscillator model is implemented in MATLAB and used to generate resonance curves and simulate blade responses observed with tip sensors, installed in the axial compressor. Generated TOA data are fitted to the sine function to estimate vibration parameters. The validated procedure is then employed to analyze real test data.

Standard Sine Fitting Algorithms Applied To Blade Tip Timing Data

Abstract Blade Tip Timing (BTT) is a non-intrusive method to measure blade vibration in turbomachinery. Time of Arrival (TOA) is recorded when a blade is passing a stationary sensor. The measurement data, in form of undersampled (aliased) tip-deflection signal, are difficult to analyze with standard signal processing methods like digital filters or Fourier Transform. Several indirect methods are applied to process TOA sequences, such as reconstruction of aliased spectrum and Least-Squares Fitting to harmonic oscillator model. We used standard sine fitting algorithms provided by IEEE-STD-1057 to estimate blade vibration parameters. Blade-tip displacement was simulated in time domain using SDOF model, sampled by stationary sensors and then processed by the sinefit.m toolkit. We evaluated several configurations of different sensor placement, noise level and number of data. Results of the linear sine fitting, performed with the frequency known a priori, were compared with the non-linear ones. Some of non-linear iterations were not convergent. The algorithms and testing results are aimed to be used in analysis of asynchronous blade vibration.

Tip timing measurements for structural health monitoring in the first stage of the compressor of an aircraft engine

In this paper the performance of a new optical sensor based on a bundle of optical fibres is analysed. An inductive sensor with proven capacity to carry out blade tip timing measurements in real aircraft engines applications is used as reference. The results of the optical sensor show a good correlation with those provided by the inductive sensor, demonstrating the suitability of the optical sensor to be employed in tip timing measurements and structural health monitoring applications in real working conditions of aircraft engines.

Mathematical Model and Simulator of Rotor With Vibrating Blades Model / Matematyczny I Symulator Stopnia Wirnikowego Z Drgającymi Łopatkami

Abstract The paper presents description of rotating bladed disk mathematical model. Correctly defined mathematical model of rotor allows creation of numerical simulation model which can be used to generate tip-timing data. First of all, the model is necessary to conduct a research on blade response due to input force in form of changing rotational speed. This enables the possibility to determine turbojet engine terminal operating conditions causing its failure Streszczenie Tematem publikacji jest opis modelu matematycznego ułopatkowanej tarczy stopnia wirującego silnika odrzutowego. Poprawnie stworzony model matematyczny wirnika pozwala na stworzenie modelu symulacyjnego, który może posłużyć do generowania danych tip-timing. Przede wszystkim jest on potrzebny do badania odpowiedzi łopatek wieńca wirnikowego na wymuszenie w postaci zmian prędkości obrotowej silnika. Pozwala to na określenie warunków pracy silnika odrzutowego, dla których mogło by nastąpić jego uszkodzenie