Ryszard Szczepanik

Turbine Engine Health/Maintenance Status Monitoring with Use of Phase-Discrete Method of Blade Vibration Monitoring

The intended aim of the paper was to present a short review of more than 15 years of experience of ITWL in the field of applying the signal of actual rotational speed (aperiodic and oscillation components thereof) to the expert diagnosing of aero-engines, including identification of low- and high-cycle fatigue (LCF, HCF) of critical structural members. What has been presented is some essential metrological bearings of the non-contact technique of measuring the engine’s rpm with some flexible key phasors (i.e. vibrating compressor/turbine blades). Also, methods of numerical analysis of measuring signals, in use nowadays, have been discussed. With the jet engine of the SO-3 type (in use on the TS-11 “Iskra” combat trainer) as an example, are discussed algorithms of both the identification of disadvantageous aeromechanical effects (energy state of the engine - i.e. the source of accelerated HCF wear of structural components) and the early detection of symptoms of fatigue failures to compressor blades and the bearing system. The discussed problems have been illustrated with examples selected as to emphasise practicalities of applying a new source of diagnostic information to ‘actively’ control the process of fatigue wear (HCF + LCF) of engine components and to forecast the engine health/maintenance status.

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

Analysis of Middle Bearing Failure in Rotor Jet Engine Using Tip-Timing and Tip-Clearance Technique

The reported problem is the failure of the middle bearing in an aircraft rotor engine. Tip-timing and tip-clearance and variance analyses are carried out on a compressor rotor blade in the seventh stage above the middle bearing. The experimental analyses concern both an aircraft engine with a middle bearing in good working order and an engine with a damaged middle bearing. A numerical analysis of the seventh stage blade free vibration are conducted to explain the experimental results. This appears to be an effective method of predicting middle bearing failure. The blade vibration variance increases when there is bearing failure.© 2014 ASME

On-Line Prediction of Temperature and Stress in Steam Turbine Components Using Neural Networks

Considered here are Nonlinear Auto-Regressive neural networks with exogenous inputs (NARX) as a mathematical model of a steam turbine rotor used for the on-line prediction of turbine temperature and stress. In this paper on-line prediction is presented on the basis of one critical location in a high pressure steam turbine rotor, according to power plant common measurements, i.e., turbine speed, turbine load as well as steam temperature and pressure before turbine control valve. In order to obtain neural networks that will correspond to the temperature and stress the critical rotor location, an FE rotor model was built. Neural networks trained using the FE rotor model not only have FEM accuracy, but also include nonlinearity related to nonlinear steam turbine expansion, nonlinear heat exchange inside the turbine and nonlinear rotor material properties during transient conditions. Simultaneous neural networks are algorithms which can be implemented in turbine controllers. This allows for the application of neural networks to control steam turbine stress in industrial power plants.Copyright

Online Prediction of Temperature and Stress in Steam Turbine Components Using Neural Networks

Considered here are Nonlinear Auto-Regressive neural networks with exogenous inputs (NARX) as a mathematical model of a steam turbine rotor used for the on-line prediction of turbine temperature and stress. In this paper on-line prediction is presented on the basis of one critical location in a high pressure steam turbine rotor, according to power plant common measurements, i.e., turbine speed, turbine load as well as steam temperature and pressure before turbine control valve. In order to obtain neural networks that will correspond to the temperature and stress the critical rotor location, an FE rotor model was built. Neural networks trained using the FE rotor model not only have FEM accuracy, but also include nonlinearity related to nonlinear steam turbine expansion, nonlinear heat exchange inside the turbine and nonlinear rotor material properties during transient conditions. Simultaneous neural networks are algorithms which can be implemented in turbine controllers. This allows for the application of neural networks to control steam turbine stress in industrial power plants.Copyright

Non-intrusive Diagnostic of Middle Bearing of Aircraft Engine

Failure of the middle bearing in an aircraft rotor engine was reported. Tip-timing and tip-clearance analyses were carried out on a compressor rotor blade in the seventh stage above the middle bearing. The experimental analyses concerned both an aircraft engine with a middle bearing in good working order and an engine with a damaged middle bearing. A numerical analysis of the free vibration of the seventh stage blade was conducted to explain the experimental ones. Proposed in this paper is a method to prevent middle bearing failure.

Thermoelastic Steam Turbine Rotor Control Based on Neural Network

Considered here are Nonlinear Auto-Regressive neural networks with eXogenous inputs (NARX) as a mathematical model of a steam turbine rotor for controlling steam turbine stress on-line. In order to obtain neural networks that locate critical stress and temperature points in the steam turbine during transient states, an FE rotor model was built. This model was used to train the neural networks on the basis of steam turbine transient operating data. The training included nonlinearity related to steam turbine expansion, heat exchange and rotor material properties during transients. Simultaneous neural networks are algorithms which can be implemented on PLC controllers. This allows for the application neural networks to control steam turbine stress in industrial power plants.

Analysis of 1st stage compressor rotor blade stress and vibration amplitudes in one-pass jet engine

This paper considers 1 st stage compressor blade dynamics in the one-pass jet engines of trainer aircraft. Research was carried out on an engine test bench using the SAD system and its results were compared with those obtained using the tensometric approach. In this paper presented basic dynamic properties of rotor blades, bench test of rotor blade dynamics, Bench tests of the dynamic behaviour of blades subjected to external impacts and then Comparison of strain gauge and SAD tip-timing results. Then discusses the results of tests assessing the accuracy of the 1987 ITWL device by comparing strain gauge signals with those recorded by SAD apparatus in a running engine. It also presented simultaneous vibration readings of all the rotor blades at selected rotation speeds. Also shows that increased stress in these blades may be due to repeated engine surges, normal and hot engine surges, entry into the engine of a foreign object. Among others selection and layout of rotor blades in the 1 st stage of a one-pass engine compressor, stress amplitudes for rotor blade, stress in rotor blade, stress amplitudes, free inlet flow and smooth engine acceleration, vibration amplitudes, asynchronous vibrations are presented in the paper.

Studies on unsteady operation of a turbojet engine and an intake channel of a supersonic aircraft

The paper explains how to analyse possible disturbances in the intake air stream and their impact on engine operation. The introduction outlines possible reasons that induce disorders in the intake air stream. Then the substantial differences in operational characteristics between a centrifugal and an axial compressor are enlightened. The phenomenon of an unsteady compressor, referred to as the compressor stall, is explained through presentation of the process phases when air stream detaches from the surfaces of the compressor blades. Then the paper presents how disturbances in the air stream propagate down subsequent stages of the engine compressor with the emphasis on the fact that the air stream is not able to affect the full height of blades but usually only a portion of them. In addition, the mechanism of the unsteady operation of the engine (compressor) is presented on the graph that shows fuel consumption Q as a function of the engine rpm n. Attention is drawn to the fact that the phenomenon of the engine unsteady operation is associated with the so called rotating areas of air detachments that revolute in the same direction as the engine rotor itself but their rotation speed is lower than the rotor rpm. Consequently, flame downstream the area of detachment may go out for a moment and then quickly reappear, since air is kept supplied at quite high rates. If the foregoing process fails to go in phase with the rotating areas of air detachment, it may even lead to a total flameout of the engine. Then the unsteady operation of the intake channel is discussed in details, as it is frequently mismatched with the compressor stall. The mechanism of the phenomenon origination and the consequences it entails is presented with adequate details by means of appropriated graphs. In addition, the paper explains the phenomenon of beats in the intake channel, which is a result of detachment of the wall-adjacent layer of air flow just downstream the perpendicular shock wave in the intake channel. The effect of beats frequency often leads to the engine stall. The paper ends up with conclusions, in which it is emphasized that studies on the phenomenon and familiarity with the process are extremely important for the safety of flights.

EARLY DETECTION OF FATIGUE CRACKS IN TURBINE AERO-ENGINE ROTOR BLADES DURING FLIGHT

The author shows results of research done in the Air Force Institute of Technology concerning design, development and implementation of modern diagnostic systems for aero-engines. The papers gives brief description of a project of a new advanced monitoring system basing on non-contact blade-vibration measurement. Recent monitoring systems for engines offer a great potential to reduce the high maintenance costs of aircraft while increasing reliability and safety. These systems check for abnormal engine responses to detect failures, saving lives and reducing secondary damage to the aircraft. A phenomenon of dynamic change of an aero-engine compressor blades natural frequency in course of fatigue cracks propagation in their roots on the example of a Polish turbojet engine is described. On the ground of this phenomenon main working principles of a device, which measures vibrations of turbine engine rotor blades with application of the noninterfering discrete method (MDPh), used for early detection of first stage compressor blade cracks are discussed. Typical representation of the first stage compressor blades vibration during engine acceleration, representation of the first stage blades vibration during engine acceleration and deceleration with steady-state stator distortions, crack initiation and propagation symptoms in blades, comparison of blade vibration spectra of the same blades for different conditions are presented in the paper.