The influence of flow instability on the lock-in of distributed elastic resonators

Kristin Lai Fook Cody, Stephen A. Hambric, Martin L. Pollack, Michael L. Jonson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Lock-in occurs between many different types of flow instabilities and structural-acoustic resonators. Factors that describe the coupling between the fluid and structure have been defined for low flow Mach numbers. This paper discusses how different flow instabilities influence lock-in experimentally and analytically. A key concept to the lock-in process is the relative source generation versus dissipation. The type of fluid instability source dominates the generation component of the process, so a comparison between a cavity shear layer instability with a relatively stronger source, for example wake vortex shedding from a bluff body, will be described as a coupling factor. In the fluid-elastic cavity lock-in case, the shear layer instability produced by flow over a cavity couples to the elastic structure containing the cavity. In this study, this type of lockin was not achieved experimentally. A stronger source, vortex shedding from a bluff body however, is shown experimentally to locks into the same resonator. This study shows that fluidelastic cavity lock-in is unlikely to occur given the critical level of damping that exists for a submerged structure and the relatively weak source strength that a cavity produces. Also in this paper, a unified theory is presented based on describing functions, a nonlinear control theory used to predict limit cycles of oscillation, where a self-sustaining oscillation or lock-in is possible. The describing function models capture the primary characteristics of the instability mechanisms, are consistent with Strouhal frequency concepts, capture damping, and are consistent with mass-damping concepts from wake oscillator theory. This study shows a strong consistency between the analytical models and experimental results.

Original languageEnglish (US)
Title of host publicationASME 2008 Noise Control and Acoustics Division Conference, NCAD 2008
Pages17-29
Number of pages13
DOIs
StatePublished - Dec 1 2008
EventASME 2008 Noise Control and Acoustics Division Conference, NCAD 2008 - Dearborn, MI, United States
Duration: Jul 28 2008Jul 30 2008

Publication series

NameAmerican Society of Mechanical Engineers, Noise Control and Acoustics Division (Publication) NCAD

Other

OtherASME 2008 Noise Control and Acoustics Division Conference, NCAD 2008
CountryUnited States
CityDearborn, MI
Period7/28/087/30/08

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Acoustics and Ultrasonics

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  • Cite this

    Cody, K. L. F., Hambric, S. A., Pollack, M. L., & Jonson, M. L. (2008). The influence of flow instability on the lock-in of distributed elastic resonators. In ASME 2008 Noise Control and Acoustics Division Conference, NCAD 2008 (pp. 17-29). (American Society of Mechanical Engineers, Noise Control and Acoustics Division (Publication) NCAD). https://doi.org/10.1115/NCAD2008-73016