Development of Ultrasonic Tests for Super Ceramics

Critical flaw sizes in ceramic turbine parts are very small, especially for dynamic applications. Detection of these small (< 30 μm) internal flaws are almost exclusively in the realm of ultrasonics, wherein 30 to 100 MHz test frequencies are required. Satisfactory transducers for this purpose are not available from commercial suppliers. These devices are now being developed and will be discussed together with problems of signal strength, focussing, penetration and defect signal characterization in ceramics containing both real and artificial defects.

A Frictionally Induced Bladed Disk/Shaft Instability: Physical Explanation of an Experimental Fan Failure

A light weight fan with a novel tip damper, designed and rig tested in the sixties, sustained a cataclysmic vibratory failure during a test with consistently smooth running and an explanatory dynamic mechanism was not found. It is now shown that instability potentially could have been induced in a synchronous backward wave by phase shift due to difference between kinetic and static friction in the damper. Moreover, the same mechanism could have augmented the steady forward harmonic wave recorded by Campbell in the twenties.

Omar Hill-300 MW Cogeneration Plant for Enhanced Oil Recovery

The paper describes a gas turbine based cogeneration plant producing a nominal 300 MWe and 1.8 MM lb/h (0.82 MM kg/h) of 80 percent quality steam for enhanced oil recovery. The plant, which has been in commercial operation since August 18, 1985 is located in the Kern River Oil Field near Bakersfield, California. The plant is owned by the Kern River Cogeneration Company. The paper describes the plant design philosophy as well as the major system operating parameters. The discussion of the overall project schedule highlights the major project milestones.

NDE of Structural Ceramics

Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus x-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions, and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.

Telemetry Measurement of Combustion Turbine Blade Vibration in a High Temperature Environment

Rotating component measurements in a combustion turbine continues to be a most difficult instrumentation problem. Measurements in the turbine high temperature environment makes the problem even more challenging. This paper presents an approach in overcoming the difficulties of acquiring accurate stress data from turbine blades during full load operation. Through the application of existing electronics, which were adapted for these special hostile conditions, a reliable telemetry technique for obtaining dynamic strain gage data of combustion turbine blading is demonstrated.

Experimental Investigations of a Gas Turbine as an Object of Speed and Temperature Control

The examinations of the stationary and frequency characteristics of the two-shaft aviation type gas turbine are described in this paper.

Computational Engine Structural Analysis

A significant research activity at the NASA Lewis Research Center is the computational simulation of complex multidisciplinary engine structural problems. This simulation is performed using computational engine structural analysis (CESA) which consists of integrated multidisciplinary computer codes in conjunction with computer post-processing for “problem-specific” application. A variety of the computational simulations of specific cases are described in some detail in this paper. These case studies include (1) aeroelastic behavior of bladed rotors, (2) high velocity impact of fan blades, (3) blade-loss transient response, (4) rotor/stator/squeeze-film/bearing interaction, (5) blade-fragment/rotor-burst containment, and (6) structural behavior of advanced swept turboprops. These representative case studies were selected to demonstrate the breadth of the problems analyzed and the role of the computer including post-processing and graphical display of voluminous output data.

Considerations in Retrofitting Gas Turbine Governors

The paper examines some aspects which should be examined in specifying and selecting replacement gas turbine governors. It explores the subject from the point of view of the engine manufacturer in his investigations and studies of the original supplied governor. It examines some aspects of the liaison required between the governor engineer, the User and the mechanical, combustion, performance and heat transfer engineers to define governor functions. Having established functional requirements it then considers aspects such as reliability, failure mode, documentation and a plan for the retrofit.

Limitations of Thermocouples Used in Hot Zones in Gas Turbines

Thermocouples are extensively used for controlling as well as safeguarding gas turbines. Some thermocouples have found their way into environments where their life expectancy could not be fulfilled. The literature provides very little information on thermocouple used beyond 3000 hours and yet in gas turbines, 30 000 h expectancy is not uncommon. In the hottest zones, deterioration takes place in spite of special precautions in shielding. A test was developed to find troubles which could not be revealed by calibration or other means of testing. Thermocouples thus identified had lives of less than half the design value and restrictions have been placed on the time span a thermocouple is considered useful. The paper follows a practical approach to a practical problem.

More Effective Control for Centrifugal Gas Compressors Operating in Parallel

Parallel Operating centrifugal gas compressors are major elements in the chemical industry, in oil production and in natural gas gathering, injection, separation, transmission and LNG production. Large energy savings, reduced repairs and improved automation are possible with more effective solutions for compressor station control. The authors suggest an improved definition of compressor energy efficiency. They analyze several common approaches to control of parallel compressors and evaluate them in terms of energy efficiency, stability of control, equipment protection and level of automation. An improved system developed by one of the authors will be described theoretically and with an example from field operation.