The Emergence of Compliant Foil Bearing and Seal Technologies in Support of 21st Century Compressors and Turbine Engines

Abstract

For energy independence to become a reality, whether through the more effective use of US natural resources such as natural gas or through the continued development of the hydrogen economy, efficient and reliable large-scale compressors are needed to enhance the existing pipeline infrastructure that moves energy storing gases from production sites to end user locations. Oil-free, non-contacting seal and bearing technologies are critical to the successful development of new high efficiency and power dense compressors. Similarly with increasing emphasis on energy conservation, power and propulsion gas turbine engines will require advanced low leakage seals and may take advantage of efficiencies offered by compliant foil gas bearings. When properly applied these oil-free, non contacting technologies will have a positive impact on the operating efficiency and life of compressor and gas turbine engine systems. The overall objective of this paper is to present recent advances in compliant foil bearings and seals that make them attractive for a wide array of systems. The paper documents the design approach that includes analytical trade off studies to establish overall requirements followed by an experimental program to demonstrate the ability of the identified foil technology to meet the machine requirements. A summary of advancements in foil bearing load carrying capacity, size scaling from 6 mm to 150 mm in diameter, the ability to operate under shock loads greater than 40 g as well as under steady side loads with two different gases and finally the ability to operate at temperatures greater than 750 C will be presented. Data will also be presented showing the application of foil bearings to several different machines. Similarly, results from design, fabrication and testing of compliant foil radial and axial face seals will be discussed. Data from axial face seals testing at differential pressures, surface velocities, and normal loads greater than 675 kPa, 350 m/s, and 1100 N respectively will be presented to demonstrate non-contacting performance. Results of subcomponent testing will also be presented to demonstrate the capability of the face seal to accommodate axial excursions of up to 3.8 mm. Compliant foil radial seal testing in sizes ranging from approximately 60 to 215 mm in diameter under differential pressures to 690 kPa and surface velocities to 340 m/s will be presented and compared to prediction. The culmination of the work presented supports the application of compliant foil bearings and seals in a wide array of advanced machinery.

Study on Sealing Characteristics of Compliant Foil Face Gas Seal under Typical Hypervelocity Gas Effects

“…Under extreme operating conditions such as high rotating speed and high medium pressure, the rigid surface of end face gas seal is prone to rubbing and crushing. Compliant foil face gas seal (CFFGS) with gas as the lubricating medium shows important application value in the shaft end seal of centrifugal compressors, aero-engines, and other turbomachinery, with its significant advantages such as high temperature resistance, impact resistance, excellent leakage control, and strong adaptability [4,5].…”

“…Muson et al [11,12] verified that CFFGS has excellent adaptability and leakage control performance under extremely highspeed and high-temperature conditions. The test results of Heshmat et al [4,13] based on aircraft air circulation machines and hydrogen centrifugal compressors show that CFFGS is a high-efficiency gas sealing technology with low leakage and low wear. Research by Muson [5] shows that CFFGS has important applications in turbine shaft-end seals.…”

Flow field and sealing performance analysis of compliant foil face gas seal

“…Heshmat and Walton 17 put forward a theoretical prediction formula for the leakage rate of CFFGS, and experimentally explored the influence of structural parameters on the leakage rate. Heshmat et al 18 explored the coordination between film pressure and foil deformation based on finite difference and finite element analysis, and experimentally proved that CFFGS is a low-leakage and high-efficiency gas face sealing technology for new hydrogen centrifugal compressors. Muson, 19 in a test based on the Rolls-Royce gas turbine platform, found CFFGS to be of great value for applications in gas turbine rotor thrust balance structures and turbine rims.…”

Oil-Free Bearings and Seals for Centrifugal Hydrogen Compressor

“…Both static and dynamic testing were performed on the seals using air and helium at operating speeds up to 60 krpm. The results of these tests, in which various seal parameters were varied, indicated that very low values could be obtained for the flow factors used to characterize seal leakage [41]. It was then demonstrated that performance capabilities of the designed centrifugal hydrogen compressor met the needs for the pipeline delivery of pure hydrogen [42].…”

“…The work of the lead author and his research team is also recognized for its simultaneous developments in the theoretical realm, experimental methods and results, and in the methods needed to successfully apply foil bearings and seals in advanced oil-free rotating machinery. These works have resulted in a better understanding of the performance, design and application methodology of compliant foil bearings/seals, as well as the development of better analytical tools to integrate advanced foil bearings/seals into high performance propulsion and power generation systems [17][18][19][20][21][22][23][24][25][26][27]. These advanced foil bearings with improved load and temperature performance having variable compliant structures in all three dimensions and time-dependant damping and stiffness are designated as 4th generation foil bearings.…”