Józef Błachnio

Damageability of Gas Turbine Blades – Evaluation of Exhaust Gas Temperature in Front of the Turbine Using a Non-Linear Observer

A turbine is a fluid-flow machine that converts enthalpy of the working agent, also referred to as the thermodynamic agent (a stream of exhaust gas, gaseous products of decomposition reactions or compressed gas) into mechanical work that results in the rotation of the turbine rotor. This available work, together with the mass flow intensity of the working agent, define power that can be developed by the turbine and subsequently used to drive various pieces of equipment (e.g. compressors of turbojet engines). The basic advantages of gas turbines include: possibility to develop high power at rather compact dimensions and low bare weight, relatively high efficiency of the energy conversion process, simple design and high reliability of operation (Blachnio, 2004, 2007; Kroes et al., 1992; Sieniawski, 1995). On the other hand, the drawbacks are: high operating temperatures of some components, sophisticated geometrical shapes of the components, e.g. blades and vanes, which makes the manufacturing process difficult, as well as high working speeds of rotors that impose the need to apply reduction gears, e.g. when turbine-power receivers show limited rotational speeds. Because of the direction of flow of the exhaust gas, turbines are classified as axial-flow and radial-flow systems. Each turbine is made up of two basic subassemblies that compose the turbine stage.  A stationary rim with profiled vanes fixed co-axially (axial-flow turbines) or in parallel (radial-flow turbines), i.e. the so-called turbine nozzle guide vanes, or shortly, the stator;  A moving rim (one or several ones) with profiled blades fixed circumferentially (axialflow turbines) or on the face surface (radial-flow turbines) of a rotating disk seated on the shaft, i.e. the turbine blade rim.  Depending on the distribution of the inlet energy of exhaust gases among basic subassemblies, turbines are classified as:  action (impulse) turbines, the exhaust gases are subject to decompression exclusively in turbine nozzle guide vanes,  reaction turbines the exhaust gases are decompressed by both the guide vanes (stator vanes) and in the turbine rotor.

Analysis of causes of decohesion of a gas turbine blade made of EI 867‐WD alloy

Purpose – The purpose of this paper is to present results of laboratory testing work on causes of a service failure/damage to an aircraft turbojets gas‐turbine blade made of the EI 867‐WD alloy.Design/methodology/approach – The tests comprised comparing the microstructure of a service‐damaged blade with microstructures of specimens drawn from a similar all‐new blade, both subjected to temperatures of different values for different annealing times.Findings – Findings based on the comparison of experimentally gained results of microstructure examination of both the gas‐turbine blades were: the change in the microstructure of a damaged blade results from the growth and cuboidal‐to‐lamellar change of shape of the reinforcing phase γ′ (Ni3Al); and the size and shape of this phase are comparable to those of the phase γ′ of a new blade subjected to annealing at temperature exceeding 1,223 K for 1 h. The results gained allowed for drawing the conclusion that the damaged turbine blade was operated in the exhaust‐...

New Non-Destructive Methods of Diagnosing Health of Gas Turbine Blades

The illuminated blade/vane surface can be recognized by a light-sensitive detector (a CCD matrix with an optical system – an optoelectronic device) owing to the fact that the surface becomes a secondary source of light (Zhang et al., 2004; Rafalowski, 2004; Tracton, 2006, 2007). Therefore, it is possible to diagnose the examined object in an indirect way by the processing and analysis of information acquired as digital images (Bogdan; 2008; Blachnio & Bogdan, 2010). Only a very tiny portion of an incident light beam is absorbed by metallic surfaces. Most of the light (90-95%) is reemitted from the reflecting surface as visible light with the same wavelength as the incident light. The remaining 5-10% of the absorbed energy is dissipated as heat (according to the rule of energy conservation). Chemical composition of the coating matter that covers surfaces of metallic objects decides the attenuation of some wavelengths in the spectrum of illuminating light, whilst the mixture of light that is selectively reflected from a specific surface is decisive for the perception of colours (some metals may exhibit specific colours due to selective reflection of light, e.g. gold, copper) (Zhang et al., 2004; Tracton, 2006). The CCD matrix is a set of many light-sensitive sensors, where each sensor is capable to record and then reproduce an electric signal that is proportional to the amount of light that has illuminated the surface (the photoelectric effect – emission of electrons as a consequence of their absorption of energy from photons that reach the matter; the diagram of such energy conversion and the associated losses are shown in Fig. 1). The image-recording devices usually incorporate colour filters that are installed just upstream the light sensors and enable the intensity of a particular bandwidth within the light spectrum (a certain bandwidth of visible electromagnetic waves) to be recorded at a given location of the matrix. After processing by the central unit (CPU) the acquired information can be stored as digital images (graphic files) (Rafalowski, 2004). The analysis of histograms of digital images is very useful since it provides a great amount of information about the image that has been processed, including information about the range of brightness levels and the number of levels represented in the images. In the case of images acquired under suitable illumination conditions the histogram includes also quantitative information about the brightness of the image acquired for the photographed object. On the other hand, the 2-D co-occurrence matrices presented by Haralick in his studies (Haralick & Shanmugam, 1973; Haralick & Shapiro, 1992) are used for analyses of

Analysis of the Feasibility to Investigate Condition of Gas Turbine Vanes by Means of the Radiographic Method

Analysis of the Feasibility to Investigate Condition of Gas Turbine Vanes by Means of the Radiographic Method Operation of avionic turbine engines is always associated with possibility of various defects that may happen to turbine components, in particular to its vanes. The basic examination method intended to assess condition of the turbine vanes is the metallography, a destructive testing technology. The paper deals with the non-destructive test method of X-ray computer tomography (CT) that is chiefly used in medicine but is also suitable to diagnose how far the process of turbine vanes wear and tear is advanced. The computer tomography (CT) is the transmission diagnostic technique that makes it possible to obtain images of various layers within the investigated object. Application areas of this technique include also the quality control in manufacturing of technical facilities. The study presents results of assessments for gas turbine vanes with the use of the X-ray computer tomography after a specific period of the turbine operation. It was found out that the radiographic method, owing to availability of 3D images (including also internal defects) makes it possible to detect types of defects, their sizes and locations. Analiza możliwości badania stanu łopatek turbiny gazowej matodą radiograficzną W procesie eksploatacji lotniczych silników turbinowych występują różnego rodzaju uszkodzenia elementów turbin, a zwłaszcza ich łopatek. Podstawową metodą oceny stanu łopatek są badania metalograficzne - metoda niszcząca. W artykule omówiono stosowaną obecnie, głównie w medycynie, rentgenowską tomografię komputerową (angielski skrót: CT) oraz możliwości jej wykorzystania do diagnozowania zmian stanu łopatek turbin, jako metodę badań nieniszczących. CT jest transmisyjną techniką diagnostyczną umożliwiającą uzyskiwanie warstwowych obrazów obiektów badań. Wykorzystywana jest między innymi w procesie kontroli jakości produkcji obiektów technicznych. Przedstawiono wyniki oceny stanu eksploatowanych łopatek turbiny gazowej rentgenowską tomografia komputerową. Stwierdzono, że metoda radiologiczna wygenerowując przestrzenny obraz stanu (wad wewnętrznych) łopatek umożliwia rozpoznanie ich rodzaju, wielkości i umiejscowienia.

ON THE NEED TO MAINTAIN HOMOGENOUS TEMPERATURE FIELD WITHIN THE WORKING AGENT AT THE INTAKE OF A JET ENGINE TURBINE

The paper presents results from numerical experiments with use of the computer model of the SO-3 engine designed for simulations. The model has been purposefully modified to take account of the assumed nonhomogeneity of the temperature field within the working agent at the turbine intake. It turned out that such nonhomogeneity substantially affects dynamic and static properties of the engine are considered as an object of control since it leads to a lag of the acceleration time and to increasing in fuel consumption. The summarized simulation results demonstrate that the foregoing properties of a jet engine are subject to considerable deterioration in pace with gradual increase of the assumed non-homogeneity of the temperature field, The simulations made it possible to find out that variations of the temperature field non-homogeneity within the working agent at the turbine intake lead to huge fluctuation of the turbine rpm for the idle run, which enables a new look to the role of the so-called idle run valve and importance of that component within the supply and control system of the SO-3 engine.

Degradation of the gas turbine blade coating and its influence on the microstructure state of the superalloy

The technical condition of the blades has a critical influence on the reliability and life span of a gas turbine and an engine into which it is built in. The main causes of blade damage are overheating, creeping, thermal fatigue, high temperature corrosion, etc. It is often caused by adverse operational conditions or manufacturing defect, e.g. using insufficiently durable types of heat-resistant protective coatings or applied in an improper manner on the blade material. Reaction of coatings and blade material to mechanical and thermal loads depends mainly on the operating temperature of the turbine. Selection of a protective coating and material to manufacture a blade with an assumed strength must take into account its mechanical and thermal properties at maximum aerofoil temperature. The article presents characteristic forms of operational damages to the gas turbine blades of a turbojet aero engine. Distinguished were operational factors and their influence on the technical condition of coatings during the engine operation period. An influence of excess exhaust gas temperature on the condition of the heat-resistant blade layer was shown. Shown were also results of morphology tests of coating degradation types. Results of micro-structure tests of the blade superalloy after damage to the heat-resistant coating were also presented.

The Attempt To Assess The Technical Condition Of A Gas Turbine Blade When Information On Its Operating Condition Is Limited

Abstract The paper discloses a non-invasive method of visual inspection based on processing of images taken for blade surfaces in the spectrum of visible light and then analyzed with the use of a computer-aided technology. The method of computer-aided analysis of images for blade surfaces is presented in details along with the obtained outcome, whilst the results from metallographic investigation of the blade superalloy are disclosed as well. The comparison is made between the results obtained from the analysis of images for blade surface and the results from the metallographic investigation of their structures. Finally, the relationship is established between parameters of digital images taken for surfaces of gas turbine blades in the visible spectrum of electromagnetic waves and microstructural parameters of the turbine blade metal. The completed investigations and analyses reveal that troubleshooting of gas turbine blades, which employs digital processing of images taken for its surface, offers new opportunities to determine the condition of blades after a long-term impact of a working agent at high temperature.

Welds’ Quality of Aluminium Alloy Components of Military Aircraft Executed by Arc Welding Method

Abstract The paper presents the problems arising in the process of repairs of aircraft (AC) components made of aluminium alloys during arc welding with the TIG (tungsten inert gas) method. The paper provides information on the rules applicable in the welding process qualification. The procedure algorithm when qualifying the welding process was presented in accordance with PN-EN ISO 15614-2. The main causes and factors affecting the formation of defects and welding imperfections were described and classified. The principles of preparing the components for welding and selection of a binder were discussed. The issue of effect of the welding parameters on the formation of defects and welding imperfections in relation to PN-L-01426 standard was raised. The application of computed tomography in assessment of the welded joints was described and tomograms from tests of butt welds of aluminium alloys made of the AW 5754 grade aluminium alloy were presented. On the example of the tomograms, the welding imperfections and defects formed in the tested joints were discussed. The usefulness of computed tomography in assessment of the welds’ quality was shown.

Scopus as a Meta-Source of Knowledge About Turbine Blade Damage in the Aspect of Designing an Expert Diagnostic System

Abstract The paper presents the concept of using the Scopus as a meta-source of knowledge about turbine blade damage in the aspect of designing an expert diagnostic system. In the first stage, the search was limited to the scope of the general term “turbine engine”, followed by a refinement of the search terms within the area of rotary machines components degradation including their construction, manufacturing, repair technology and diagnostic methods. By using EndNote software in semi-automatic mode, specific issue groups have been designated. In the second stage, a query focused on the main causes of turbine blade damage and diagnostic methods was proposed. Using the Scopus-based search and archiving tools, one can systematically update the knowledge.

Assessment of the technical condition of welds from Al alloy grade en an 5754 using the computed tomography method

Abstract The article presents selected results of tests conducted using the X-ray method with the application of a computed tomography device with a panel detector. The tests embraced samples of butt welds using aluminium alloy grade EN AN 5754, classified as an alloy for plastic processing with very good welding properties. The welds were executed using the TIG (Tungsten Inert Gas) method – arc welding using a non-consumable electrode in shielding gas. As a result of modernising the current welding process, it was possible to obtain better results of the welds’ technical condition assessed according to the number of welding defects.