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


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 lock-in 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 fluid-elastic 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 publication2008 Proceedings of the NoiseCon/ASME NCAD, NCAD 2008
Number of pages13
StatePublished - 2009
Event2008 NoiseCon/ASME NCAD, NCAD 2008 - Dearborn, MI, United States
Duration: Jul 28 2008Jul 30 2008

Publication series

Name2008 Proceedings of the NoiseCon/ASME NCAD, NCAD 2008


Other2008 NoiseCon/ASME NCAD, NCAD 2008
Country/TerritoryUnited States
CityDearborn, MI

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Acoustics and Ultrasonics


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