Design strength of ceramics for use in elements of gas-turbine engines

Strength of Materials -     

Basis of engineering specifications for a gas-turbine engine rotor

The main elements of a methodology are described that make it possible by mathematical modelling of the condition of a flexible rotor in the design stage to evaluate the effect of the main manufacturing and assembly parameters, and to prescribe their main limits in order to provide prescribed vibrational activity.     

Examination of the causes of a bucket wheel fracture in a bucket wheel excavator

A bucket wheel excavator failure occurred in a brown-coal mine. The failure was caused by a fractured shaft of the bucket wheel. An attempt to determine the causes of the bucket wheel shaft fracture has been made. To that end, the character of changing loads and their maximum amplitudes has been determined by performing measurements on the excavator. A discreet model of the shaft was built and a numerical simulation of the shaft operation using the FEM method was achieved. An analysis of the materials in the fracture area was also implemented. Macroscopic and microscopic images of the fracture area are provided. The shaft fracture was mainly caused by a non-metallic inclusion located below the surface of the shaft as a result of its being rolled. Moreover, it was discovered that the shaft had not been heat-treated.     

Stress concentration in sloping cooling circuits of a disk of a gas-turbine engine

The stressed state and stress concentration in sloping cooling circuits of the rim part of a disk of a gas-turbine engine are studied by using a three-dimensional finite-element model. It is shown that the numerical values of the stress concentration factors do not exceed their designed values. Translated from Problemy Prochnosti, No. 3, pp. 78–82, May–June, 1998.     

Matrix method for calculating inelastic strain kinetics for a gas-turbine disk

Strength of Materials -     

Analytical modeling of a desiccant wheel

A simple integral model is presented for a desiccant wheel. The original governing equations for a desiccant wheel were simplified to a set of linear ordinary differential equations and an analytical solution was obtained. A brief analysis is given about the solution regarding the non-dimensional numbers that decide the behavior of a desiccant wheel. From the solution, algebraic expressions were obtained for time-averaged heat and mass transfer rates and the results were compared with a numerical model and a set of experimental data in the literature. In comparison with the numerical model, relative error was found less than 12% at 120 °C regeneration temperature and 10% standard deviation was observed with the experimental data. The analytical model is considered capable of describing a symmetric desiccant wheel realistically.     

Metallurgical failure analysis for a blade failed in a gas-turbine engine of a power plant

The failed gas-turbine blades (first stage blades) (type Siemens V94.2 KWU) were acquired from TNB Research Sdn. Bhd: a subsidiary of Malaysian power-generation industry (TNB, Malaysia). The blades were sectioned for metallographic investigations. The microstructural characterization involved use of both optical as well as electron microscopes including application of EPMA technique. The Microstructures were compared for three spots selection i.e. leading edge of the blade (transverse and longitudinal), trailing edge of the blade (transverse and longitudinal), and centre (near the platform of the blade) (transverse and longitudinal). The material properties and behavior at high temperature were interpreted on the basis of the observed microstructures and the phases present in the alloy. The interpretations were related to the operating conditions of the turbine blade; and main cause of failure was found to be creep damage. Recommendations have been made for improved material performance.     

Design and performance of an internal heat exchange desiccant wheel

A fundamental limitation in the dehumidification performance of adiabatic desiccant wheels occurs due to heating of the air stream to be dried. This results from both the carry-over of heat stored in the wheel and the release of the adsorption heat. Previous authors have identified an isothermal dehumidification process as theoretically superior, though the practicalities of constructing such a wheel have meant that demonstrating the benefit is difficult. Recently experimental data from testing of an internally cooled wheel was published. Here we use this data to calibrate a mathematical heat and mass transfer model of the internally cooled heat exchange desiccant wheel. The model is then used to estimate the performance for selected modifications to the design and materials. The results show that more than a 40% improvement is possible relative to the previously tested cooled wheel. The results have application to the development of desiccant air-conditioners.     

地铁车轮不圆度多点非接触检测系统设计

为准确、快速测量地铁车轮不圆度数据,设计一种多点激光检测系统。系统采用非接触检测方式,利用三个激光位移传感器实现对车轮踏面的多点检测。三个激光传感器同时测量可以提升维保检测效率,检测结果能更全面地评估车轮状态。采用最小二乘法拟合圆确定车轮几何圆心,通过小波滤波去除信号中的高频噪声,结果表明此方法在处理车轮不圆度这类随机信号时,可以快速去除信号中的高频噪声,筛选出有效信号。检测设备具有体积小、质量轻、操作简单等优势,可为车轮维护工作提供依据。     

Experience with repair of stationary gas-turbine blades –view of a turbine manufacturer

Abstract

Repair procedures for stationary gas–turbine blades, both established practices and techniques which have yet to find wide application, are described. Special attention is paid to quality assurance – making sure that repaired parts do not reduce reliability. Of the various repair techniques, only regenerative heat treatment (including hot isostatic pressing, or hipping) and recoating can be performed as standard procedures. Machining (e.g. grinding) changes the geometry of the blade and requires an exact knowledge of design tolerances. Straightening has to be done very carefully and should be followed by a hipping treatment. The greatest number of restrictions apply when fusion and deposition techniques such as brazing, welding, inserting, sintering, and plasma deposition are used. These techniques are used at present only if it is absolutely necessary to restore heavily worn blades.

MST/101