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Numerical Investigation of Vapor and Gaseous Cavitation in Squeeze-Film Damper Bearings

Sarkar, Snigdha
http://orcid.org/0000-0003-3980-085X
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523636346718425

Abstract Details

2018, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
Squeeze-film dampers (SFDs) are used in high-speed turbomachinery to provide viscous damping, reduce vibrations and improve machine stability. However, often the presence of cavitation can significantly hinder the damping capability of the bearing, and also cause damage to the bearing surface. The purpose of this study is to numerically model cavitation in squeeze-film damper bearings, understand the resulting impact of cavitation on damper performance, and conduct a parametric study to determine the effect of varying parameters on the onset and extent of cavitation. A commercial Computational Fluid Dynamics (CFD) solver, ANSYS Fluent 18.2, is used to model lubricant flow in squeeze-film dampers using the moving reference frame formulation that renders this transient problem steady. The mixture multiphase model is used, in conjunction with the Schnerr-Sauer and Singhal et al. cavitation, to simulate vapor and gaseous cavitation, respectively. The numerical solution is verified using the half Sommerfeld solution. The comparison between CFD and analytical results shows a nominal 2.87% difference in the damping forces. Next, the cavitation model is validated using experimental results. Simulations are run for a partially sealed damper with varying amounts of air mixed with the lubricant. Vapor cavitation is modeled for the zero void fraction case using the Schnerr-Sauer cavitation model. Comparisons in the cavitated zone show 4.3% difference between experimental and computational peak pressures. For the gaseous cavitation case, computational peak pressures are compared with the average experimental peak pressures over consecutive whirl cycles. The computational peak-to-peak pressures for gaseous cavitation cases with low to moderate void fractions are in very good agreement with the experimental results. However, the experimental film pressures seem to be non-repetitive and unstable during successive whirl motions in higher void fraction cases. This leads to a high margin of error in the averaged experimental peak pressures. As a result, comparisons between computational and experimental peak pressures yield a maximum difference of 9% for gaseous cavitation cases. Verification and validation results show that the computational model can predict the extent of cavitation and damper response in SFD bearings within reasonable limits. For the parametric study, we vary void fraction, supply pressure, speed and eccentricity. Computational results show that higher void fractions cause a considerable decline in the damping capability of the bearing. A sufficiently high supply pressure can inhibit the occurrence of cavitation. As speed is increased, damping and stiffness remain constant for uncavitated conditions. However, at high speeds the bearing experiences cavitation, leading to a significant reduction in the damping capability. The stiffness increases in magnitude as the bearings become severely cavitated. The otherwise outward radial force due to inertia starts acting inward as soon as cavitation sets in. This causes a stiffening effect during severely cavitated conditions, which leads to an overly restrictive system. The damping and stiffness trends clearly indicate the effect of cavitation on the SFD performance. Overall, the present work demonstrates the successful usage of a cavitation model to capture multiphase cavitation physics, and numerically predict damper response in cavitated SFD bearings.
Urmila Ghia, Ph.D. (Committee Chair)
Jay Kim, Ph.D. (Committee Member)
Tod Steen, MSME (Committee Member)
80 p.
Mechanical Engineering
Multiphase Flows; Cavitation; Squeeze Film Damper; Moving Reference Frame; Tribology; Vapor Cavitation

Recommended Citations

Citations

  • Sarkar, S. (2018). Numerical Investigation of Vapor and Gaseous Cavitation in Squeeze-Film Damper Bearings [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523636346718425

    APA Style (7th edition)

  • Sarkar, Snigdha. Numerical Investigation of Vapor and Gaseous Cavitation in Squeeze-Film Damper Bearings. 2018. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523636346718425.

    MLA Style (8th edition)

  • Sarkar, Snigdha. "Numerical Investigation of Vapor and Gaseous Cavitation in Squeeze-Film Damper Bearings." Master's thesis, University of Cincinnati, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523636346718425

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.