Norman Arnold Turnquist

Fundamental Design Issues of Brush Seals for Industrial Applications

Advanced seals have been applied to numerous turbine machines over the last decade to improve the performance and output. Industrial experiences have shown that significant benefits can be attained if the seals are designed and applied properly. On the other hand, penalties can be expected if brush seals are not designed correctly. In recent years, attempts have been made to apply brush seals to more challenging locations with high speed (>400 m/s), high temperature (>650 °C), and discontinuous contact surfaces, such as blade tips in a turbine. Various failure modes of a brush seal can be activated under these conditions. It becomes crucial to understand the physical behavior of a brush seal under the operating conditions, and to be capable of quantifying seal life and performance as functions of both operating parameters and seal design parameters. Design criteria are required for different failure modes such as stress, fatigue, creep, wear, oxidation etc. This paper illustrates some of the most important brush seal design criteria and the trade-off of different design approaches.

Advanced Seals for Industrial Turbine Applications: Dynamic Seal Development

The ongoing need for higher performance industrial turbines has lead to extensive efforts to improve various components of gas turbines, steam turbines, compressors, and generators. One area being addressed is improved seals to reduce parasitic leakage flows. Major progress has been made to implement advanced dynamic seals into industrial turbines with resulting performance gains. Brush seals have significantly decreased labyrinth seal leakages in gas-turbine compressors and turbine interstages, steam-turbine interstage and end packings, industrial compressor shaft seals, and generator seals. Abradable seals are being developed for blade-tip locations in various turbine locations. The development and implementation of advanced seals in industrial turbines is summarized and with a focus on dynamic seals.

Improved Steam Turbine Leakage Control With A Brush Seal Design.

Brush seal designs offer improved leakage control over conventional labyrinth seals by applying a compliant bristle with very tight clearance over the rotating shaft. Originally developed for the aircraft engine industry, brush seals have also been applied in land-based gas turbines. More recently, brush seals have been applied in steam turbines. The steam turbine environment adds some unique design considerations that must be addressed to assure a robust and effective brush seal design, and to minimize the impact on the steam turbine as a system. This paper discusses the performance benefits of the brush seal and the design considerations important to a robust design in a steam turbine. The paper also addresses the system characteristics important to 33 IMPROVED STEAM TURBINE LEAKAGE CONTROL WITH A BRUSH SEAL DESIGN

Wear Prediction of Strip Seals Through Conductance

Labyrinth seal assemblies are often used to reduce gas and/or steam leakage in turbines. Caulked-in continuous strip seals are one of the common forms of seals employed on both the rotating and stationary components of turbines. Labyrinth seals perform best when minimum clearances are achieved during the steady state operation of the turbine. However, the design of the turbine and its operation during transient periods of start-up, shut-down and hot re-start often result in interference between the seal components. In the case of the strip seals, this leads primarily to wear of the strip, which in effect adds to leakage. The aim of this paper is to show that strip tip heating and melting during the rub is the main mechanism of wear in the strip. Hence thermal conductivity through the strip and into the body mass in which it is caulked is the primary controlling factor in seal wear. This paper will discuss the use of thermal conductivity and geometry of the strip in predicting wear during high speed rubs against a proprietary material. A close correlation between calculated and experimental strip seal wear data with a number of seal alloys will be demonstrated. Test data will indicate that material properties such as tensile strength and hardness have a minor effect on the wear behavior of continuous seal elements during high-speed rubs.Copyright

High Pressure Subsonic Nucleation in 1D Nozzles — An Experimental Study

The presence of moisture in steam turbines is known to cause blade erosion and reduce turbine performance. As a result, nucleating wet steam flow has been the topic of both academic and engineering research for many decades. However, almost all of the previous experimental studies on steam nucleation have been carried out under low pressure supersonic flow conditions, either in converging-diverging (Laval) nozzles or in supersonic airfoil cascades. Some recent experimental studies conducted droplet size/wetness measurements within actual turbines, but these tests in general only give qualitative assessment on the nucleation phenomena. They are not intended to study the mechanisms of the nucleating steam flow.In this paper, an experimental study of nucleating wet steam flow under high-pressure subsonic flow conditions is presented. In particular, the world’s first high-pressure subsonic nucleation test rig was designed and built at the GE Global Research Center. This advanced test rig takes high pressure (up to 1000 psia) clean steam with controlled inlet superheat and expands it through 1D subsonic nozzles. The Wilson line location and the length of the nucleation zone are controlled through different combinations of inlet steam pressure and superheat, and overall pressure ratios.An advanced optical measurement system was developed and used to measure the Wilson line, the ensuing condensation zone, and the droplet size and number density generated from nucleation. The flow path in the nozzle is visible through specially designed sapphire windows. The optical system is essentially comprised of two laser-photodiode pairs (405 nm and 689 nm wavelength), which can be traversed along the length of the nozzle.The experiment data have indicated that significant differences exist between high pressure subsonic nucleation and low pressure supersonic nucleation. Further, an in-house 1D analytical tool as well as a 3D multiphase CFD have been used to model the test runs, and reasonable agreements have been obtained. This study has direct application in the design of Nuclear and Concentrated Solar high pressure steam turbines.© 2014 ASME

Stiffness Measurement for Pressure-Loaded Brush Seals

Brush seals are widely used as flexible seals for rotor-stator and stator-stator gaps in power generation turbo-machinery like steam turbines, gas turbines, generators and aircraft engines. Understanding the force interactions between a brush seal bristle pack and the rotor is important for avoiding overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness (i.e. brush seal force per unit circumferential length per unit incursion of the rotor) is usually measured and characterized at atmospheric pressure conditions. However, the inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack change in the presence of a pressure loading, thereby changing the stiffness of the brush seal in the presence of this pressure loading. Furthermore, brush seals exhibit different hysteresis behavior under different pressure loading conditions. Understanding the increased brush seal stiffness and the increased hysteresis behavior of brush seals in the presence of a pressure loading is important for designing brush seals for higher pressure applications. In this article, we present the development of a test fixture for measuring the stiffness of brush seals subjected to a pressure loading. The fixture allows for measurement of the bristle pack forces in the presence of a pressure loading on the seal while the rotor is incrementally pushed (radially) into the bristle pack. Following the development of this test fixture, we present representative test results on three sample seals to show the trends in brush seal stiffness as the pressure loading is increased. Specifically, we study the effect of different brush seal design parameters on the stiffness of brush seals over a wide range of pressure loadings. These test data can be used for developing predictive models for brush seal stiffness under pressure loading. Furthermore, we demonstrate the utility of this fixture in studying the hysteresis exhibited by brush seals along with the importance of the backplate pressure balance feature present in several brush seal designs. The test results validate the bilinear force-displacement curves previously reported in the literature.Copyright

Active Retractable Seals for High-efficiency Steam Turbines

*† ‡ § ** Rotor end leakage at the high-pressure section accounts for about 20% of the total leakage loss in a steam turbine. Advanced sealing technology at end packing locations can bring about significant improvement in overall turbine efficiency. In this paper, we propose an active seal, which can be retracted during rotor transients. As a result, tighter clearances can be designed and preserved during the life of the turbine. The concept is an extension of commonly used Variable Clearance Positive Pressure Packing technology, where the seal opens and closes depending on the pressure differential across it. The proposed extension involves the addition of a bypassing mechanism across the seal, which can actively control the pressure differential and hence the opening and closure of the seal. The design concept was initially demonstrated in a subscale test rig. Operational validation was performed through extensive testing on a full-scale rig.

An optical method for measuring Metal Surface temperature in Harsh environment conditions

Commercially available instruments for measuring and monitoring surface temperature of metal parts are very limited and often unsuitable for applications at harsh environment conditions. Another major challenge is to measure temperature of a rotating surface, as it is very difficult to take an electrical signal out from rotating parts. A novel optical reflectance based non-contact temperature measurement technique is discussed which can be used for temperature measurement on metal surfaces. The optical reflectivity of metals is known to depend on metal temperature and wavelength of the incident light. An increase in metal temperature resulted in the change (increase or decrease depending on particular metal properties) of reflected laser power from the metal surface. This also depends on the surface geometries of the metal surface being measured. We have shown that the sensitivity of the temperature measured depends on the angle of incidence, surface topology and surface properties of the object.

Latest Developments In Wear Prediction of Strip Seals Through Conductance

This paper discusses the latest developments in the ability to predict wear of strip seals in turbine engines. Caulked-in continuous strip seals are a common form of seals employed on both the rotating and stationary components of gas and/or steam turbines. These seals perform best when minimum clearances are achieved during the steady state operation of the turbine, and when a sharp tip profile can be maintained. However, interference between the stationary and rotating seal components often occurs during transient periods of startup, shutdown and hot re-start. In the case of the strip seals, this leads primarily to wear of the strip, which increases leakage and reduces turbine performance. The aim of this paper is to present the latest findings showing that thermal conductivity through the strip and into the body mass in which it is caulked are the primary factors in controlling seal wear within the range of materials and parameters tested. This paper will discuss the latest experimental validation of a model that uses thermal conductivity and geometry of the strip in predicting wear during high speed rubs against a proprietary material.