Anthony J. Smalley

Measuring Rotor and Blade Dynamics Using an Optical Blade Tip Sensor

This paper describes an optical measurement system for monitoring combustion turbine blade tips. The sensor measures distance to a blade tip using triangulation of reflected laser light. The system accomplishes triangulation using an optical position sensing device and high speed data acquisition. In this way, it is able to monitor not only average and minimum blade tip clearances, but to monitor the variations of individual blade tip clearances. By appropriate signal processing, it is possible to determine rotor vibration at the probe axial location, variations in shaft DC position, transient losses in blade tip clearance, the potential for tip and seal rubs, vibrations of individual blades in the tangential direction, and rotor torsional vibration at the probe location. Some aspects of blade and torsional vibrations would require more than one probe. The paper presents static calibration data for the measurement system, showing its degree of linearity and range. The paper also presents data obtained on a dynamic blade test rig with tip passing speeds and blade widths comparable to those encountered in high performance industrial combustion turbines. Data from this rig have been processed to show rotor vibration, shift in shaft average position, blade-to-blade tip clearance variation, and variation with speed of minimum blade tip clearance. The measurement system is designed to produce data suitable for use in the monitoring of advanced combustion turbine durability and the diagnosis of turbine functional problems, static and dynamic.© 1990 ASME

Development of a Knowledge Based Advisory System Based on Vibration of a Peaking Gas Turbine

This paper describes the process of knowledge development and interpretation for a particular model of power generation combustion turbine and generator. The knowledge derives from three sources: fundamental understanding of rotordynamics; the experience of experts in troubleshooting this particular turbine; and in-depth analysis of vibration data acquired during every start-up and run of several examples. The data acquisition system is operated via modem from any phone tine to provide operational data for review.The knowledge is to be applied in two ways. A Post Trip Analysis will provide the operator with advice on what to do when the unit trips, based upon the data obtained during the tripped run and previously acquired characteristics. The Post Trip Analysis will have knowledge which, when compared with the acquired data factors about vibration, and historical characteristics of the specific machine or the fleet, will give a recommended action. This application is designed to be available moments after the trip has occurred.The second application of knowledge is for health assessment. A software module will automatically analyze each day’s data when the file is completed. The volume of data is reduced to a smaller, very descriptive set of data which is saved and compared with previous runs. These analyses are to be performed at the two critical speeds of the turbine and generator, as well as the normal running speed. One planned test for health assessment is to seek deviations: characteristics which fall outside the statistically normal range for the unit in question; characteristics which fall outside the desirable range based on expert opinion; and distinct unexplained changes during a run.The paper illustrates the development and application of the knowledge base.Copyright

Spray Automated Balancing of Rotors: Concept and Initial Feasibility Study

This paper describes a new balancing concept: Spray Automated Balancing Of Rotors (SABOR). The Fuel Air Repetitive Explosion (FARE) process of metal film deposition is used to apply discrete amounts of metallic or ceramic particles to a spinning rotor at a controlled angular location on the rotor. The system design and control for implementing SABOR are described. The method is used to balance a spinning disk without stopping it. Results are presented which show that the bond strengths of materials deposited by the FARE process for use in small gas turbine engines are acceptable for the level of centrifugal stresses expected

Remote Condition Monitoring of a Peaking Gas Turbine

This paper illustrates how software and hardware for telecommunications and data acquisition enable cost-effective monitoring of peaking gas turbines using personal computers. It describes the design and evaluation of a system which transmits data from each start-up and shutdown over 1,500 miles to a monitoring computer. It presents system structure, interfaces, data content, and management. The system captures transient sequences of acceleration, synchronization, loading, thermal stabilization, steady operation, shutdown and cooldown; it yields coherent sets of speed, load, temperature, journal eccentricity, vibration amplitude, and phase at intervals appropriately spaced in time and speed. The data may be used to characterize and identify operational problems.© 1991 ASME

Dynamic Characteristics of the Diverging Taper Honeycomb-Stator Seal

This paper introduces a variant on the honeycomb-stator seal, which can extend the already strong stabilizing influence of this seal geometry for centrifugal compressors. The paper presents predicted and measured dynamic characteristics, demonstrating how a clearance, which diverges axially from inlet to outlet, increases the maximum effective damping of a honeycomb-stator seal, even though the average clearance is increased. The results also show a strong negative direct stiffness at zero and low frequency for this seal geometry (termed the “Diverging Taper Honeycomb Seal (DTHCS)”). The predictions are made with ISOTSEAL, software developed at The Texas A&M Turbomachinery Laboratory. The test data, also obtained at the Turbomachinery Laboratory, confirms the nature and magnitude of both these dynamic characteristics with close fidelity. However, measured leakage falls significantly below predicted leakage. The frequency dependence of the seal dynamic characteristics and the strong negative static stiffness require careful attention in rotor dynamics analysis.Copyright

Tools for Diagnosing Case Deflections and Alignment on a Power Utility Combustion Turbine

This paper discusses development, installation, and analysis of instrumentation systems for reliably measuring casing, thermal distortion, and alignment deviation on a large combustion turbine in power utility service. A variety of redundant measurement systems were installed to document casing distortion during the cool-down period after firing. The operating principles of each measurement system are described and presented with the rationale developed for installing and locating sensors. A vertical deflection sensor used for casing bow and bearing misalignment measurements is highlighted in the paper to illustrate its potential for use in other investigations. Additional sensors used include an array of shaft proximity probes, blade tip proximity probes, thermocouples, and axial growth probes, blade tip proximity probes, thermocouples, and axial growth probes. A measurement system for casing ovalization was developed using LVDTs mounted from a thermally stabilized ring. An automated data acquisition system was developed and installed to facilitate the recording of turbine cool-down events over the complete operating season without the need for constant on-site attention. Preliminary results define the turbine cylinder bow and ovalization response during the cool-down event following normal unit operation and correlated casting distortions with thermal gradients.

Turning Gear Operation: Its Influence on Combustion Turbine Rotor Eccentricity and Starting Dynamics

This paper presents an experimental program which investigates how turning gear operation influences thermal distortion and start quality of a power generation combustion turbine. It presents results which quantify how taking a turbine off turning gear under hot or cold conditions influences rotor distortion. It further shows how time on turning gear reduces rotor eccentricity. This paper uses available unbalanced sensitivity data and rotor eccentricity measured on turning gear to estimate the margin for vibration trip on start-up. The paper discusses how rotor eccentricity data can be independently obtained with limited additional non-intrusive instrumentation, and how the data can help guide turning gear operational strategies for different utility load profiles.Copyright

Prototype Development of a Novel Radial Flow Gas Turbine

A prototype of a novel gas turbine concept is being developed to demonstrate the technical feasibility of a gas turbine design based on a straight radial flow with no axial flow turning. The prototype gas turbine consists of only two structural elements — a rotor disk and a stator shroud. The rotor consists of a centrifugal compressor and high impulse radial outward-flow turbine connected to an electric generator. The stator shroud contains the combustor and nozzles. The difference between this novel design and conventional radial gas turbine is that the compressor and turbine section are installed on the same side of the rotating wheel, while the combustor and nozzle are mounted on the stationary shroud. Thus, the entire assembly consists of two components. Technical advantages are: • Single Rotating Disk; • Compact Two-Piece Construction; • Ease of Repair and Maintenance; • High Power to Weight Ratio. This paper discusses the test set-up, instrumentation, and initial mechanical testing of the radial gas turbine. Performance predictions, rotordynamics analysis, and aerodynamic component verification are also discussed.Copyright

A Novel Centrifugal Flow Gas Turbine Design

A centrifugal gas turbine is developed based on a straight radial flow design with no axial flow turning. The geometry contains only two major elements — a rotor disk and a stator shroud. The rotor consists of a centrifugal compressor and high impulse radial outward-flow turbine connected to an electric generator. The stator shroud contains the combustor and nozzles. Fuel lines are attached to the shroud, ducted directly into the combustor. The difference between this novel design and conventional radial gas turbine is that the compressor and turbine section are installed on the same side of the rotating wheel, while the combustor and nozzle are mounted on the stationary shroud. Thus, the entire assembly consists of two components. Technical advantages are: • Single Rotating Component; • Short Axial Span; • Compact Two-Piece Construction; • Ease of Maintenance/Repair Access. Aerodynamic design, performance, and structural analysis of this design are discussed.Copyright

Methods for and Benefits of Centrifugal Compressor Design Audits

As gas pipeline and industrial compressors become more powerful and more complex, it has become beneficial to conduct technical audits of these machines in the design stage. Detailed analysis of critical or advanced compressors by independent evaluators have identified operating limitations, resonant responses, potential vibrations, weak components, the onset of stall, and other instabilities, and have recommended ways to eliminate a variety of potential problems before the compressor is placed in operation. The suitability of a compressor and its driver for the planned service should be thoroughly evaluated, so that each component and the system not only satisfy the design conditions, but also extreme operating conditions. This paper presents a description of the tools available for design audits and gives examples of benefits that have resulted from recent audits. The rotordynamics of any large high-speed compressor should be carefully evaluated to identify potential instabilities, high vibration levels, and even destructive responses of the machine. Powerful rotordynamic analysis tools and specific knowledge exists to accurately predict bearing and seal stiffness and damping, lateral critical speeds, and damped forced responses. Some examples of significant results obtained from rotordynamic evaluations are presented, and typical problems that have been identified and eliminated are highlighted. Torsional vibration analyses for compressor trains are an essential aspect of a design audit that have identified vibration problems and weak components. Examples of torsional vibration responses and problems that can be identified and corrected are included in this paper. The aerodynamics of a compressor is a design audit topic to which attention should be paid. Thermophysical properties of the process gas, as it is compressed, are important quantities which can be accurately determined by modern equations of state. The internal velocity distribution and pressure rise per impeller and diffuser can be evaluated to identify areas of excess loss, poor work transfer, or restrictions within a compressor. Flow angles such as at the impeller and diffuser entrances can be predicted and evaluated. The diffuser inlet flow angle is a critical indicator of the onset of rotating stall. This type of aerodynamic analysis also provides important input for performance test planning and evaluation. This paper concludes with a summary of benefits of design audits for pipeline and industrial compressors.Copyright