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  • Author: Wojciech Pawlak x
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Abstract

Various types of damages to gas-turbine components, in particular to turbine blades, may occur in the course of gas turbine operation. The paper has been intended to discuss different forms of damages to the blades due to non-uniformity of the exit flow temperature. It has been shown that the overheating of blade material and thermal fatigue are the most common reasons for these damages. The paper presents results from numerical experiments with use of the computer model of the aero jet engine designed for simulations. The model has been purposefully modified to take account of the assumed non-homogeneity of the temperature field within the working agent at the turbine intake. It turned out that such non-homogeneity substantially affects dynamic and static properties of the engine considered as an object of control since it leads to a lag of the acceleration time and to increase 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 nonhomogeneity within the working agent at the turbine intake lead to huge fluctuation of the turbine rpm for the idle run.

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.

Abstract

Basalt fibers and fabrics made of these are characterized by excellent thermal and mechanical properties. Therefore, basalt fabrics, due to a good resistance to high temperatures, are frequently applied in the personal protection equipment (PPE). In order to improve their thermal properties and, above all, the contact heat resistance, the process of physical vapor deposition was proposed. The process of Physical Vapor Deposition (PVD) involves producing a coating on a specific substrate as a result of physical deposition of molecules, ions or atoms of the selected chemical compounds. The method selected for the test is the magnetron sputtering. It involves depositing a uniform film of chromium on the surface of the basalt fabric. In order to improve the thermal properties – especially the contact heat resistance, two values of thickness of the chromium layer deposited on the basalt fabric surface were adopted for the test. Covering 1 μm and 5 μm with the chromium layer did not fulfil the expectations and the research will be continued.

Abstract

The paper presents a non-destructive test method that makes it possible to assess condition of gas turbine blades based on the analysis of their images acquired in visible light. The results of high temperature’s influence on the condition of blades are revealed. The direct relationship between the temperatures of blades and discoloration of their surfaces is demonstrated. These relationships have been found out by the analysis of images in the form of first order statistical parameters derived wherefrom. The studies revealed alterations of the blade superalloy microstructures entailed by the effect of high temperature, hence the results in the form of first order statistical parameters could be correlated against alterations of the blade superalloy microstructures. Eventually, the variations of first order statistical parameters as well as variations of the blade superalloy microstructures could be determined as the functions of temperature. These relationships make it possible to assess how much the alloy microstructure is altered due to high temperature merely by discoloration of the blade surface. The innovative method can be used for in-flight evaluation of the superalloy overheating for gas turbine blades in operation.

Abstract

This work initiates a series of reports aimed at a construction of rugate optical filters based on silicon rich materials of alternating gradients of refractive index n with the help of plasma enhanced chemical vapor deposition (PECVD) technique, The idea is to start deposition of high refractive index SixNy type of material using hexamethyldisilazane (HMDSN) vapor and nitrogen rich atmosphere, and then to gradually replace nitrogen with oxygen in that atmosphere in order to lower n down to a minimum characteristic of SixOy type of material. A return to initial gas composition should increase the index back to its maximum. In the present work, thin SixNyCz films were synthesized from a mixture of HMDSN vapor with gaseous NH3 and N2. The effect of NH3/N2 ratio on the coating morphology, its elemental composition, chemical bonding and optical properties was studied using scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultra-violet absorption spectroscopy and variable angle spectroscopic ellipsometry. The results show that films of the highest index of refraction and the lowest extinction coefficient have been deposited from the gas mixture containing 90 % of ammonia. These coatings are also characterized by the lowest carbon and the highest nitrogen contents.