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.
The reliability of thermal energy meters is analysed using the Markov model which describes the operation of these meters in a large number of apartments and offices by a media accounting company. The data has been extracted from a relational database storing information on the operation, installation and exchange of these measures from the last 10 years. The built Markov model turned out to be ergodic, which allowed determining its limiting distribution. In addition, the probability distributions for the cumulated consumption were determined in the work - separately for all meters and meters’ failures.
Composite fan blades are more and more common both in aviation and ground applications. This work aims to characterize the vibration parameters of plastic blades installed in a wind tunnel fan by a non-contact method, namely blade tip timing (BTT). Blade dynamics was predicted with finite element modelling (FEM) and confirmed experimentally by tip timing measurements and analysis of data. BTT results were acquired and compared in two different configurations. A good agreement between predicted and measured frequency values was obtained for the fundamental mode. Significant differences were observed for the second and third modes due to material anisotropy and contact effects which could not be modelled because necessary material data were unavailable.
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 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.
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.
The result of operating the military helicopters in a dusty environment is a loss of performance and premature failures of gas paths of the engines. The efficient protection of the power plant against dust ingestion is tough, especially in the desert. The article summarises the experience accumulated while operating the military helicopters under harsh conditions in Poland and during foreign missions. There were characterised the types of conducted missions, operated helicopters, protection methods of engines and common failures. It was stated that the performance of TV3-117 engines and their particle separation systems was insufficient in the mountains and on the desert (Iraq and Afghanistan). The deterioration of gas paths resulted in the loss of helicopters’ performance and substantially contributed to the few aircraft incidents. The experience gained during foreign missions is used in training the crews and ground personnel and in the programmes of modernisation and renewal of the helicopter fleet.
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
The main goal of the work reported here was to expand the capability of the NRC-Aerospace spin rig by adding an on-line damage detection, discrimination and tracking system, and to develop necessary expertise that will allow for optimizing the NDE inspection periods of gas turbine engine components in this facility and minimizing undetected crack nucleation and growth and possibility of catastrophic failures. Passive eddy-current sensors and a data acquisition system able to simultaneously measure blade deflection and tip clearance were selected to monitor health of rotating components. Before application of the system in the spin rig, the system was tested with a rotor rig to check sensor responses to deliberately induced changes in blade tip positions in both radial and circumferential directions. The monitored disc had 12 bolts simulating aerofoils that could be turned into threaded holes to extend or shorten the protruding parts of the bolts. On the other hand, bolt vibration was not excited and analysed during the experiment. Lessons learned on the rotor rig are used to prepare and plan spin tests in vacuum chamber.