Gas Turbine Technology

Transcription

1 Gas Turbine Technology Gas turbines are a versatile, cost-effective source of electricity, mechanical power, and propulsion. Gas turbines continually challenge engineers to design, construct, and operate reliable and efficient turbines that meet market needs and respect the environment. Southwest Research Institute (SwRI), now represented in Brazil per TSS Consultoria Técnica, works with users, suppliers, and manufacturers of gas turbines, providing technical services, expertise, and research facilities to meet the challenge. Our broad range of capabilities includes the outlined topics below and more: Materials Evaluation and Testing Failure Analysis Life Management, Stress Analysis, and Structural Analysis Nondestructive Evaluation Fluid Dynamics and Heat Transfer System and Component Testing Gas Turbine Monitoring Testing, Diagnosis, and Support Computer-Based Training Artificial Intelligence Air Pollution Control Fuels, Lubricants, and Combustion Technology Advanced Materials and Technology The Solar gas turbine drives a compressor with spiral-grooved dry gas seals to provide circulation in the only world-class gas transmission metering research facility in the United States. The exhaust heat recovery unit of the Gas Technology Institute facility provides hot oil as the heat source for a rapid response gas temperature control system. The facility was designed by, and is operated and located at Southwest Research Institute. Materials Evaluation and Testing The Institute's gas turbine materials technology program spans super-alloys, including directionally solidified and single crystal alloys, coatings, titanium alloys, composites, ceramics, intermetallics, and polymers, as well as conventional ferrous and nonferrous materials. SwRI metallurgical laboratories provide scanning electron microscopy, transmission electron microscopy, acoustic microscopy, atomic force microscopy, optical microscopy, scanning Auger spectroscopy, energy dispersive spectroscopy, X-ray diffraction, and specimen preparation facilities. Mechanical testing facilities include servo-hydraulic, servo-electric, creep, and impact machines, augmented by computerized control and data acquisition. The Institute can perform the most exacting high temperature testing,

2 including thermo-mechanical fatigue, creep crack growth, and effects of aggressive environments. Standard and advanced fracture mechanics, fatigue, creep, and impact tests are conducted to ASTM standards over a temperature range from the cryogenic regime to more than 3,000 degrees Fahrenheit (1,650 degrees Celsius). SwRI designs and assembles specialized test equipment to meet unique test requirements. Failure Analysis SwRI conducts metallurgical failure analyses on a wide range of gas turbine materials and equipment. The Institute responds rapidly to field failures and the need for timely analysis, and interacts with OEMs and suppliers. Our experienced staff uses extensive metallurgical facilities to identify failure mechanisms and root causes. Analyses draw on the Institute's multidisciplinary capabilities in stress analysis, life management, mechanical and vibration analysis, materials testing, and nondestructive evaluation. An SwRI scanning electron microscope is coupled to energy dispersive spectroscopic and image analysis systems, instrumentation routinely used in failure analyses to determine fracture morphology, microstructural anomalies, and chemical compositions. Metallurgical failure analysis of broken blades to determine cause and sequence of fracture is supplemented with mechanical analysis to determine the root cause of failure.

3 This crack extends from the leading edge to the inside cooling surface and follows the grain boundaries of the cast nickel-base superalloy. Examination by optical and scanning electron microscopy showed that cracking was assisted by environmental attack. Analysis from the Electric Power Research Institute gas turbine life management system, developed by SwRI, showed the cracking was due to thermal fatigue caused by excessively hard engine operation. Life Management, Stress Analysis, and Structural Analysis The Institute develops algorithms and computerized programs for life prediction, life management, and life extension of gas turbine engines to increase component usage, maximize engine availability, and reduce maintenance costs. We apply the most current technology, including finite element and boundary element methods, to the stress analysis of gas turbine components. The Institute is a pioneer in probabilistic structural mechanics, which integrates computational mechanics and probabilistic methods to manage distribution of material properties, dimensions, and loads. Computational facilities include a central VAX computer, distributed workstations, and access to CRAY supercomputers. Available numerical codes include ABAQUS, ANSYS, and NASTRAN. Air-cooled gas turbine blades have complex temperature and stress profiles. Temperatures are shown in the upper figure and longitudinal stresses are below. This analysis, performed for the Electric Power Research Institute (EPRI), uses a generalized plane strain finite element methodology.

4 Flow diagram shows the tasks required to develop a life management system for determining the life of gas turbine components. SwRI is one of the few organizations capable of performing each step in the development of these systems. Predictions of thermal-mechanical fatigue life of first stage blades from the EPRI life management system, developed by SwRI, correlate well with field data. Results are used to determine inspection intervals and to modify engine operation for longer blade life. Nondestructive Evaluation The Institute continues to develop new techniques and improved equipment for nondestructive evaluation of gas turbines and jet engines. We apply acoustic emission, ultrasonics, eddy current, electric current perturbation, magnetic flux leakage, and radiometrics to detect flaws in turbines for power and propulsion. The Institute designs specialized sensors for difficult geometries or confined spaces and makes full use of computercontrolled scanning, data acquisition, and display to achieve efficient and reliable detection and discrimination. An eddy current inspection system developed by SwRI uses a threeaxis scanner to inspect small blades of space shuttle APUs. A space shuttle APU blade crack is imaged and measured by an eddy current inspection system developed at SwRI. Two-

5 dimensional display of the processed eddy current signal is shown at left. Fluid Dynamics and Heat Transfer Fluid dynamics, heat transfer, and fluid-structure interaction are essential disciplines to the effective design, application, and performance evaluation of gas turbines. The Institute maintains a variety of commercial and SwRI-developed computational fluid dynamics codes to meet specific needs. A number of flow facilities are used in conjunction with computational methods to support comprehensive simulation and understanding of fluid flows and their interactions with structures. Flow visualization techniques enhance this capability. Facilities include: High pressure (2,500 psi), large volume (750 ft 3 ) N 2 gas blowdown system Low pressure (to 200 psia) natural gas recirculating loop (to 6MMSCFD) High pressure (to 1,400 psi) natural gas recirculating loop (to 165MMSCFD) 0-25,000 gpm 30-inch-diameter water tunnel 0-6,000 gpm low turbulence water tunnel Pressure contours and velocity vectors for flow through first stage blades are determined from computational fluid dynamics codes. Boundary element codes determine heat transfer coefficients that are then used in thermal and stress analysis of the blades. Results shown were obtained with the FLOW-3D computer code modified by SwRI. Computational modeling is used to analyze temperature distribution in fuel nozzles. System and Component Testing Optimum performance and reliability of gas turbines in aeropropulsion, electrical power generation, and compressor or pump drives is achieved by careful balancing of conflicting demands that include low seal leakage without rubs, low weight without excessive vibration, high temperatures with long life, and blades free of vibration over a range of flow and speed conditions. The ability to test components and systems is important to achieving this balance. SwRI has a variety of vibration, flow, noise, and environmental qualification testing facilities that are effectively used, often under conditions of realistic pressure, flow, speed, and size, in a variety of applications of critical concern to users and manufacturers of gas turbines. Environmental test facilities investigate the

6 effects of vibration, shock, temperature, fire, salt fog, and sand and dust erosion on components and systems. Institute analytical resources complement test facilities. Gas Turbine Monitoring Gas turbines are the power source of choice in many applications for mechanical drive of machinery and for electrical power generation. When aero-derivative or large industrial gas turbines experience mechanical vibration, unsatisfactory performance, surge, stall, or thermal distortion, there is need for effective remedies applied on-site. SwRI has developed capabilities for measuring, acquiring, and analyzing the parameters critical to defining and correcting such problems. The Institute's remote data acquisition optimizes the testing process that can require weeks or months to assure coverage of varied operating conditions. SwRI provides all equipment needed on-site, with rapid response, to solve critical availability problems. An SwRI field measurement team installed a specially designed instrumentation system on a 50 mw power generating combustion turbine to measure casing ovalization, casing "banana" distortion, shaft distortion, and individual blade tip clearance changes during thermal transients. Data from this Electric Power Research Institute program was downloaded from the site cross-country via telephone, for analysis and display. On-site testing is complemented by in-house capabilities for analysis of bearing dynamics, critical speeds, unbalance response, stability, and performance. Testing, Diagnosis, and Support Southwest Research Institute control, electronic, manufacturing, and performance capabilities provide broad support for turbine engine design, manufacture, inspection, test, and maintenance. Services include: Development of advanced airborne avionics and engine monitoring systems Development of turbine engine inspection and maintenance methods Design studies, producibility evaluations, and ADA/JOVIAL developments Equipment and programs for diagnostics and testing of turbine engine assemblies Prototype construction ranging from circuit hybrids to airframe structures that permit development of engine modification programs according to U.S. Air Force Regulation 57-4 for Class II and Class IV installations Animated simulation techniques and other SwRI-developed methods for conceptual design of computerintegrated manufacturing facilities Expert system development Computer-Based Training SwRI developed computer-based training for the operation and maintenance of large combustion turbines for the Electric Power Research Institute. Using digital video interactive (DVI ) computers, the course takes operators from cold shutdown conditions through pre-start, cranking, acceleration, synchronization, and load for

7 the Westinghouse 501 gas turbine. A tutorial on the turbine's fuel system is under development. SwRI instructional designers integrate DVI with other advanced technologies to complete a dynamic informational resource for diagnostic training, visual databases, post disturbance analysis, and blade inspection. These resources can be applied as on-site training. Artificial Intelligence The Institute applies artificial intelligence techniques to the gas turbine industry. A number of knowledgebased, or expert, systems has been developed to support the maintenance and life assessment of gas turbine engines, including a system used to recommend protective coatings for gas turbines. Another SwRI system predicts the remaining life of gas turbine nozzle vanes, including estimated crack length, number of hours remaining, and the number of starts left for the nozzle. These systems run on PCs as well as larger computers. Air Pollution Control The many emissions produced by turbines are of great concern environmentally. The Institute has developed, quantified, and validated procedures to characterize and measure regulated emissions that include NO x, SO x, CO, CO 2, O 2, total hydrocarbons, particulates, and more than 20 unregulated emissions. Typical projects involve: New procedures development Particulate characterization Engine modifications evaluation Fuels and fuel properties evaluation Compliance testing Exhaust catalyst and particulate trap development and evaluation Current emissions control technologies application On-site tests of propulsion and stationary turbines are performed conveniently with a mobile emissions laboratory designed and constructed by SwRI that provides continuous hydrocarbon, CO, NO x, CO 2, and O 2 analysis, with additional capabilities for individual hydrocarbon, smoke, and particulate analysis. Fuels, Lubricants, and Combustion Technology The Institute, through fundamental and applied research, seeks to better understand how physical and chemical properties of fuels influence emissions, performance, and durability of engines and fuel systems. SwRI programs support military and civilian aviation and have additional applications for marine and stationary gas turbines. This gas turbine combustor facility was developed to study the effects of fuel properties on flame radiation, liner temperature, exhaust smoke, gaseous emissions, cold weather and altitude ignition, and flame stabilization. Pressure capabilities range from 1/4 to 16 atmospheres at temperatures from -40 degrees to 1,500 degrees Fahrenheit and flow rates to 2.5 pounds per second. Both optical access and advanced laser diagnostics are used to study atomization, mixing, ignition, and combustion processes.

8 Expertise is also directed to solving problems created by high temperature requirements that high performance engines, aircraft, and missiles will place on future fuels, lubricants, and other fluids. Research, development, testing, and evaluation capabilities range from production of test fuels to development of special laboratory and full-scale test rigs to address combustion and non-combustion problems. The program is supported by an analytical chemistry laboratory and a staff experienced in combustion, mechanical and chemical engineering, chemistry, chemical kinetics, and rheology. Advanced Materials and Technology The Institute's vigorous multi-disciplinary gas turbine research and development program, both internally funded and externally sponsored, addresses new analysis methods, processes, materials, and advanced measurement techniques to benefit past, present, and future gas turbines and their applications.