Frequency Lock-In of a Cylinder Oscillating In-Line with and Transverse to the Flow

Background

Vortex-induced vibration is a fluid instability occurring in various areas, including offshore platforms, turbomachinery, and airplane wings. Under certain circumstances, the vortices created by the presence of secondary flows induce high amplitude response of an elastic structure. The structure experiencing these continuous large vibrations may be subject to material fatigue and eventual failure. The lack of understanding of the underlying lock-in phenomenon make it difficult to predict these vibrations without the use of computationally expensive fluid dynamic simulations.

 

About this Project

This work presents a novel way to calculate the limit cycle oscillation (LCO) response amplitude of an elastically supported cylinder experiencing vortex-induced vibrations. The method couples a computational fluid dynamic model of the shedding vortex flow to a spring-mass-damper structural model representation of the elastically supported cylinder. The aerodynamic forces on the cylinder are calculated using a harmonic balance, frequency domain solver. Three cases are considered: the cylinder vibrating transversally to the flow, in-line with the flow, and with both degrees of freedom. The alternate shedding pattern is identified as the source of primary lock-in for both in-line and cross-flow vibrations while the secondary lock-in region for the in-line vibration is defined by symmetric shedding. It appears the in-line degree of freedom does not have a significant effect on the cylinder cross-flow response, except at really low mass-damping parameters.

 

 

 

 

Group Members Involved