Component Synthesis of Multi-Case, Rotating Machinery Trains by the Generalized Receptance Approach

A method is presented for computing the eigenvalues of multicase, coupled, rotating machinery trains. The method is based on a synthesis technique which utilizes generalized receptance formulas, previously derived by the authors. These formulas improve the accuracy of the computed receptances when only an incomplete set of modes is available. A nonsynchronous, gyroscopic, two rotor example is examined to illustrate the synthesis procedure.

Squeeze-Film Damper Technology: Part 1 — Prediction of Finite Length Damper Performance

Squeeze-film dampers are commonly used in gas turbine engines and have been applied successfully in a great many new designs, and also as retrofits to older engines. Of the mechanical components in gas turbines, squeeze-film dampers are the least understood. Their behavior is nonlinear and strongly coupled to the dynamics of the rotor systems on which they are installed. The design of these dampers is still largely empirical, although they have been the subject of a large number of past investigations. To describe recent analytical and experimental work in squeeze-film damper technology, two papers are planned. This abstract outlines the first paper, Part 1, which concerns itself with squeeze-film damper analysis. This paper will describe an analysis method and boundary conditions which have been developed recently for modelling dampers, and in particular, will cover the treatment of finite length, feed and drain holes and fluid inertia effects, the latter having been shown recently to be of great importance in predicting rotor system behavior. A computer program that solves the Reynolds equation for the above conditions will be described and sample calculation results presented.

Strain Isolated Ceramic Coatings

The durability of thermally shocked high tempererature ceramic coatings on metal substrates can be dramatically improved using a fiber metal strain isolator between ceramic and metal. The fiber metal strain isolator is a compliant, porous and low modulus material which yields to control the stress on the ceramic coating during thermal cycling. Plasma sprayed strain isolated ceramic coatings .060” (1.5 mm) thick have shown excellent durability in thermal shock testing. The strain isolated ceramic coating is an excellent thermal barrier since both the ceramic and fiber metal are good insulators. Applications include ceramic thermal barrier coatings for gas turbine engine seals and turbine components, combustors, MHD electrodes, and internal combustion engine insulation.

Stiffness Derivative Finite Element Technique to Determine Nodal Weight Functions With Singularity Elements

The use of the stiffness derivative technique coupled with “quarter-point” singular crack-tip elements permits very efficient finite element determination of both stress intensity factors and nodal weight functions. Two-dimensional results are presented in this paper to demonstrate that accurate stress intensity factors and nodal weight functions can be obtained from relatively coarse mesh models by coupling the stiffness derivative technique with singular elements. The principle of linear superposition implies that the calculation of stress intensity factors and nodal weight functions with crack-face loading, σ(rs), is equivalent to loading the cracked body with remote loads, which produces σ(rs) on the prospective crack face in the absence of crack. The verification of this equivalency is made numerically, using the virtual crack extension technique. Load independent nodal weight functions for two-dimensional crack geometry is demonstrated on various remote and crack-face loading conditions. The efficient calculation of stress intensity factors with the use of the “uncracked” stress field and the crack-face nodal weight functions is also illustrated. In order to facilitate the utilization of the discretized crack-face nodal weight functions, an approach was developed for two-dimensional crack problems. Approximations of the crack-face nodal weight functions as a function of distance, (rs), from crack-tip has been successfully demonstrated by the following equation: h a , r s = A a √ r s + B a + C a √ r s + D a r s Coefficients A(a), B(a), C(a) and D(a), which are functions of crack length (a), can be obtained by least-squares fitting procedures. The crack-face nodal weight functions for a new crack geometry can be approximated using cubic spline interpolation of the coefficients A, B, C and D of varying crack lengths. This approach, demonstrated on the calculation of stress intensity factors for single edge crack geometry, resulted in a total loss of accuracy of less than 1%.

Torsional Analysis of Partially Closed Open Section

The torsional stiffness of a thin walled closed section is many times greater than that of the corresponding open section. The structure consisting of a thin walled open section partially closed along its length by beams is an intermediate case and studies have been carried out to analyze the torsional behavior of such structures. The continuous medium method, in which the intermediate connecting beams are replaced by an equivalent continuous medium, is applied for the torsional analysis. Basically, Vlasov’s theory is applied for the torsional analysis and for the determination of axial warping stresses. Expressions to determine the angle of twist and warping stresses are obtained. Design charts are developed to determine the response for various stiffnesses of intermediate connecting beams. Comparisons between completely open and partially open sections are made for angle of twist and warping stresses. Also, the warping stresses are compared with bending stresses and it is shown that the warping stresses could be very significant.

Distributed Microprocessor-Based Control Systems for Industrial Turbine Applications

The use of powerful 16-bit microprocessors and associated components, together with control and sequencing orientated high level languages has enabled flexible and economical turbine control systems to be developed. This paper describes the architecture, hardware, software and programming methods of a system designed specifically for the control of a range of gas turbines and associated plant.

Condition Monitoring at Bulls Bridge Power Station

The Station chosen for the trial was Bulls Bridge Gas Turbine Station, sited near London Airport. (See Fig 1-1). Bulls Bridge contains 4, 70 MW sets; each 70 MW unit being powered by 4 Industrial Olympus gas generators, two at either end of a central alternator, (See Fig 1-2). At each end of the alternator, power is supplied via a clutch, to a shaft on which is mounted two power turbines, each driven by a single Olympus gas generator. Thus gas paths are separate between intake and final exhaust, and therefore each gas generator/power turbine assembly can be analysed without being unduly affected by associated plant.

Effect of Grinding Variables on Strength of Hot Pressed Silicon Nitride

An experimental study was conducted to evaluate the effect of several grinding variables on the room temperature strength of Norton NC-132 hot pressed silicon nitride. The grinding variables studied included diamond grit size, diamond concentration, type of diamond bond, downfeed rate and type of cut. Significant effects on strength were noted for all variables except diamond concentration.

Vibration Analysis of Radial Compressor Impellers

There are many problems facing the designers of turbomachines with the demand for ever increasing capabilities and reliability. One problem that requires considerable attention is the vibration characteristics of some components. It is object of this work to determine the dynamic behavior, namely natural frequencies, mode shapes of a centrifugal impeller which are being important design parameters in order to avoid costly failures in the development phase. This work divides into three sections. First, a Finite Element structural dynamic analysis is presented. Then experimental procedure used to determine the natural frequencies and mode shapes is described together with the comparison of the results obtained both theoretically through FEM and experimentally. Finally, interferometric holography technique is used as a means for obtaining the dynamic behavior of the impeller.

Squeeze-Film Damper Technology: Part 2 — Experimental Verification Using a Controlled-Orbit Test Rig

This paper is a companion to “Squeeze-Film Damper Technology, Part 1,” which covered an analytic approach and computer program for squeeze-film damper performance prediction. This paper describes a series of damper tests in which a controlled-orbit rig is used to explore squeeze-film damper behavior for representative gas turbine damper geometries and to verify and calibrate the damper analysis program. Test results for both locally end-sealed (hole fed and drained) and globally sealed (groove fed and drained) dampers are presented, along with performance predictions for those test points made using the software analysis. In particular, the effects of feeder hole flow resistance, feed groove geometry, and fluid inertia on damper performance are discussed and illustrated.