Browsing by Author "Wilkes, Jason C."

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    An Overview of the Design and Performance Testing of a 275 BAR Integrally Geared Supercritical CO2 Compressor for Power Generation
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2022) Wilkes, Jason C.; Pelton, Robert; Wygant, Karl
    An integrally geared compressor-expander (compander) for supercritical CO2 (sCO2) was developed to convert thermal energy to electricity. With operating pressures of 275 bar, this turbomachine represents the state of the art in integrally geared machine architecture, hitting compressor inlet densities of 600 kg/m3 and discharge pressures of 275 bar. The product development was funded by the Department of Energy’s Energy Efficiency and Renewable Energy Office under EE0007114 to advance the state of the art in concentrated solar power applications; however, the technology itself is agnostic to heat source, and is predicted to achieve a thermal-to-electric conversion efficiency of 50% for any indirect heat source capable of providing turbine inlet temperatures of 700°C or greater. While the program encompassed the design and testing for the compressor and turbine elements, this paper will focus on the compressor design and operation. The paper will begin with an introduction to the cycle design and analysis of an indirectly heated integrally geared sCO2 compander, a discussion of the mechanical and aerodynamic design of the compressor that is a two stage radial compressor operating subcritically at 27,512 rpm, and will then proceed to describe the test facility and measured data to characterize the performance and robustness of the machine. The paper will conclude with a discussion on lessons learned throughout the course of commissioning and testing. Practical aspects of testing a compressor operating near the dome including complications relating to obtaining an accurate compressor flow map, efficiency calculations, flow unsteadiness, and associated measurement uncertainties will be discussed.
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    Manufacturing and Testing Experience with Direct Metal Laser Sintering for Closed Centrifugal Compressor Impellers
    (Texas A&M University. Turbomachinery Laboratories, 2014) Allison, Timothy C.; Rimpel, Aaron M.; Moore, J. Jeffrey; Wilkes, Jason C.; Pelton, Robert; Wygant, Karl; Turbomachinery Symposium (43rd : 2014)
    Direct Metal Laser Sintering (DMLS) is an additive manufacturing process that utilizes a high-powered laser to build up a metal part by selectively melting thin layers of metal powder. This process is attractive for the manufacturing of parts with complex geometry such as closed centrifugal compressor impellers. DMLS allows closed impellers to be made in a single piece and eliminates the shroud joint that results from two-piece manufacturing processes. Using a monolithic impeller can allow higher tip speeds with improved fatigue characteristics compared with two-piece and three-piece designs. Prototype parts can be made more economically than investment casting when considering the tooling costs. Manufacturing costs for DMLS parts are marginally higher than for two-piece machined impellers, but qualification efforts for the braze/weld joint at the cover are circumvented. The DMLS process introduces several factors that must be considered in the impeller design to achieve a successful build with the proper strength and surface finish. This paper describes the authors’ experience with manufacturing and testing multiple closed impeller designs constructed from Inconel 718, 17-4 PH Stainless Steel, and Titanium 6Al-4V. A detailed discussion of design factors and manufacturing experience with a DMLS vendor is included for the various metals. Dimensional, post-test destructive inspection, and material test results are provided showing that the DMLS process can produce an impeller with good dimensional accuracy, surface finish, and material strength. Finally, overspeed test results up to maximum tip speeds of over 1400 ft/s (425 m/s) and aerodynamic performance test results are presented and discussed.
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    A PERSPECTIVE ON THE NUMERICAL AND EXPERIMENTAL CHARACTERISTICS OF MULTI-MODE DRY-FRICTION WHIP AND WHIRL
    (2010-01-16) Wilkes, Jason C.; Childs, Dara W.; Palazzolo, Alan B.; Cizmas, Paul G.
    The present work investigates the nature of dry-friction whip and whirl through experimental and numerical methods. Efforts of the author, Dyck, Pavalek, and coworkers enabled the design and construction of a test rig that demonstrated and recorded accurately the character of multi-mode dry-friction whip and whirl. These tests examined steady state whip and whirl characteristics for a variety of rub materials and clearances. Results provided by the test rig are unparalleled in quality and nature to those seen in literature and possess several unique characteristics that are presented and discussed. A simulation model is constructed using the Texas A and M University (TAMU) Turbomachinery Laboratory rotordynamic software suite XLTRC2 comprised of tapered Timoshenko beam finite elements to form multiple degree of freedom rotor and stator models. These models are reduced by component mode synthesis to discard highfrequency modes while retaining physical coordinates at locations for nonlinear interactions. The interaction at the rub surface is modeled using a nonlinear Hunt and Crossley contact model with coulomb friction. Dry-friction simulations are performed for specific test cases and compared against experimental data to determine the validity of the model. These comparisons are favorable, capturing accurately the nature of dryfriction whirl. Experimental and numerical analysis reveals the existence of multiple whirl and whip regions spanning the entire range of frequencies excited during whirl, despite claims of previous investigations that these regions are predicted by Black's whirl solution, but are not excited in simulations or experiments. In addition, spectral analysis illustrates the presence of harmonic sidebands that accompany the fundamental whirl solution. These sidebands are more evident in whip, and can excite higher-frequency whirl solutions. Experimental evidence also shows a strong nonlinearity present in the whirl frequency ratio, which is greater than that predicted by the measured radius-toclearance ratio at the rub location. Results include whirl frequencies 250% of that predicted by the measured radius-to-clearance ratio.