Gas Turbine Cleaning Upgrade (Compressor Wash)

The influence of gas turbine degradation on operating costs is high. Gas turbine cleaning is one of many actions taken for power recovery and is considered preventive maintenance. It is generally performed within the industrial and occasionally within the aero sector. Following a survey about potential for cost reduction in gas turbine operation the cleaning issue appears to be overlooked from an engineering point of view and there is a large potential for efficiency improvements. Engine development with corresponding high blade loads and ever-increasing temperatures require more efficient and careful cleaning methods. Together with emission taxes and environmental regulations, optimized cleaning methods will play an ever-growing role in future gas turbine operation. In order to achieve cost effectiveness regarding hardware, man-hour and consumables a new cleaning method has been evaluated for a standard process. The economic evaluations show that a standardisation of cleaning with the new method would enable the aviation sector to perform engine cleaning on a routine basis as well as the stationary sector to make significant cost savings in equipment purchase and operation.

Vibration of Skew Sandwich Plates With Laminated Facings

A Rayleigh-Ritz analysis is presented for the free vibration of skew sandwich plates composed of an orthotropic core and laminated facings. By proposing a set of Ritz functions consisting of the product of mathematically complete polynomial functions and the the boundary equations raised to appropriate powers, the Rayleigh-Ritz method can be automated to handle such composite plates with any combination of edge conditions. For convenience and better accurarcy, the Ritz formulation was derived in the skew coordinate system. Vibration frequencies of rectangular plates (a special case of skew plates) obtained via this method have been found to be in good agreement with previous researchers results. Owing to length limitation, only sample vibration frequencies for skew sandwich plates are presented.

Analysis on Response of Blades With Friction Damping Interconnection Using a New Friction Model

Blades with damper structures have been widely used in gas and steam turbines. Operation experience indicate that damper structures can reduce the dynamic stress of the blade effectively, so it is essential to predict the oscillating characteristics of damped blade accurately. In this paper, a modified Oden friction model, which can consider the difference between static friction and dynamic friction, for analyzing nonlinear friction damping, is presented and the dynamic equations of motion of blade system is given also. The response of blade group with 5 blades is analyzed using the model presented in this paper. Factors such as the placement of connectors, external exciting force frequency, and normal pressure that influence the blade vibration characteristic are studied. Some results available for reference have been obtained.

A GC2 Joining Procedure for B-Spline Patches in Reverse Engineering

Reconstruction of surface models is a vital part in reverse engineering. Because of the huge amount of data from Coordinate Measuring Machine (CMM), processes for division of data into groups, surface patch reconstruction, and patch joining are inevitable in the CAD systems tailored for reverse engineering applications. Existing techniques of surface patch joining have the disadvantages, such as computational complication or lack of desired geometric continuity. A GC2 joining technique for B-spline surface patches by utilising a Bezier patch joining technique was proposed in this paper. This method possesses the merits in which only the control vertices near the joining boundaries of patches are modified and no additional blending surfaces at the joints of patches are created.

Electromagnetic Vibration Control of Secondary Structures

A new active controller for vibration reduction of secondary structures is studied. The secondary structure is exemplified by a steel Euler beam. The output electromagnetic force from an electric current whirling machine is used as controller force. The excitation is given by a shake table to represent earthquake ground motion. The effectiveness of the controller is examined by varying the phase angle and electromagnetic force amplitude of the electric current whirling machine. We quantify the effectiveness as equivalent added modal damping of the Euler beam.

Flaw Detection and Characterization Using Shearography

Shearography is a laser interferometric method developed originally for full field observation of surface strains of components. Since flaws usually induce strain concentrations around them, shearography can be employed to detect the flaws. Conventional shearography involves exposing high resolution films before and after the components are loaded. The exposed films are developed and then viewed via a high-pass filtering optical setup. Though the images obtained are good, this method is time-consuming. With the advent of high-speed computers, associated sophisticated imaging hardware and software, the Digital Speckle Shearing Interferometry (DSSI) method which employs a CCD (charged-coupled device) camera and computer image processing to produce the interferometric fringe patterns has been developed. In contrast with the conventional shearography, the electronic version does not require any film and is faster. The techniques are used to detect and characterise (a) flaws simulating delaminations in composites and (b) thinning in pipes.

Reverse Engineered Part Development

Reverse engineering proceeds in the reverse of conventional manufacturing order, based on the pull system instead of the traditional push system. This paper is concerned with applying the reverse engineering concept to the development of parts. With this procedure the development of parts involves an iterative reverse process from the scanning of a developmental prototype towards the design model. The focus is on the use of two set-ups of network in providing computerized data of the prototype that are exchangeable among Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) systems. The first set-up applies a direct approach to manipulate the scanned data in the CAM environment for generating Numerical Control (NC) programs used for machining the workpiece. The second set-up applies an indirect approach to manipulate the scanned data in a CAD environment prior to generating the NC programs. The major benefits gained from the reverse engineering application in the development of parts are also described.

Internal Combustion Steam Cycle (G.I.S.T. Cycle): Thermodynamical Feasibility and Plant Lay-Out Proposals

In this paper a new kind of steam cycle provided with internal combustion is proposed. The internal combustion of natural gas and compressed air inside the steam flow has been conceived to carry out a steam heating (SH a/o RH) until TIT (Turbine Inlet Temperature) much higher than those of the conventional steam power plants. By this internal combustion it seems possible to overcome the present limits to TIT in steam plants which are, as known, especially related to the technological problems of the superheater tube materials in the conventional external combustion steam boilers. The proposed cycle has been named with the acronym GIST (Gas Injection STeam) since the hot gases resulting from a combustion close to stechiometric conditions are injected inside the steam flow. This paper provides a first critical approach to these new kinds of thermodynamical cycles. At the first the thermodynamical and technological problems related to the combustion inside steam are explained and discussed. Then, different plant lay-out solutions are proposed with a critical discussion on their overall performance. At the last two GIST solution have been defined that seem very interesting: the first is an hybrid plant scheme (i.e. provided with multi-fuel supply) which involves performances higher than conventional steam power plants (net electric efficiency of about 47%); the second is a plant scheme with full natural gas supply (i.e. without multi-fuel steam boiler) wich involves very relevant performances (net electric efficiency of about 57%).

Evaluation of Delaminations in Aluminium Honeycomb Structures Using the Mechanical Impedance Technique

This paper describes an evaluation of the capability of a mechanical impedance instrument, for detecting delamination defects in aluminium honeycomb structures. The resonant frequency was found to decrease as the centre of a defect was approached. The defects have been found to be accurately represented by a model for a vibrating plate, which is rigidly clamped at its edges. It was also possible to use resonant frequency to determine the size of the defects in the specimens used in this paper. An irregularly shaped defect showed that the rate of drop in resonant frequency across an extremity of the defect was affected by the radius at the extremity and the proximity to the main central area of the defect. An important result was that an ellipsoidal shaped defect would be sized as a circular defect of diameter equal to the minor diameter of the ellipse. Also a boron skinned honeycomb was found to behave similarly to a glass fibre skinned honeycomb.

Computational and Experimental Study of Turbulent Flow Past an Array of Bluff Bodies Aligned Along the Channel Axis

Computations and measurements of time mean velocities, total fluctuation intensities, and Reynolds stresses are presented for spatially periodic flows past an array of bluff bodies aligned along the channel axis. The Reynolds number based on the channel hydraulic diameter and cross-sectional bulk mean velocity, the pitch to rib-height ratio, and the rib-height to channel-height ratio were 2 × 104, 10, and 0.133, respectively. The unsteady phase-averaged Navier-Stokes equations were solved using a Reynolds stress model with wall function and wall-related pressure strain treatment to reveal the feature of examined unsteady vortex shedding flow. Laser Doppler velocimetry measurements were performed to measure the velocity filed. Code verifications were performed through comparisons with others’ measured developing single-rib flow and our measured fully developed rib-array flow. The computed results and measured data are found in reasonable agreement, which justifies the turbulence model adopted. The calculated phase-averaged flow field clearly displays the vortex shedding behind the rib and is characterized in terms of shedding Strouhal number, vortex trajectory, vortex celerity, and vortex travelling distance in a phase cycle. Furthermore, the difference between the computed developing single-rib flow and fully developed rib-array flow is addressed.