Dynamics and stability of gap-flow interference in a vibrating side-by-side arrangement of two circular cylinders

Abstract

In this work, the coupled dynamics of the gap flow and the vortex-induced vibration (VIV) on a side-by-side (SBS) arrangement of two circular cylinders is numerically investigated at moderate Reynolds number 100Re 800. The influence of VIV is incorporated by allowing one of the cylinders to freely vibrate in the transverse direction, which is termed as a vibrating side-by-side (VSBS) arrangement. A comparative analysis is performed between the stationary side-by-side (SSBS) and the VSBS arrangements to investigate the characteristics of the complex coupling between the VIV and the gap flow in a three-dimensional flow. The results are also contrasted against the isolated stationary and the vibrating configurations without any proximity and gap flow interference. Of particular interest is to establish a relationship between the VIV, the gap flow and the near-wake instability behind bluff bodies. We find that the kinematics of the VIV regulates the streamwise vorticity concentration, which accompanies with a recovery of two-dimensional hydrodynamic responses at the peak lock-in stage. On the other hand, the near-wake instability may develop around an in-determinant two-dimensional streamline saddle point along the interfaces of a pair of imbalanced counter-signed vorticity clusters. The vorticity concentration difference of adjacent vorticity clusters and the fluid momentum are closely interlinked with the prominence of streamwise vortical structures. In both SSBS and VSBS arrangements, the flip-flopping frequency is significantly low for the three-dimensional flow, except at the VIV lock-in stage for the VSBS arrangement. A quasi-stable deflected gap flow regime with negligible spanwise hydrodynamic (i.e., two-dimensional) response is found at the peak lock-in stage of VSBS arrangements. Owing to the gap-flow proximity interference, a high streamwise vorticity concentration is observed in its narrow near-wake region. The increase of the gap-flow proximity interference tends to stabilize the VIV lock-in, which eventually amplifies the spanwise correlation length and weakens the streamwise vortical structures. We employ the dynamic mode decomposition procedure to characterize the space-time evolution of the primary vortex wake.

On wake modulation and interaction features of a pair of dual-step circular cylinders in side-by-side arrangements

“…For instance, the DMD mode for the pitchfork bifurcation has a frequency of the switching gap flow, while the DMD mode for the Hopf bifurcation has a frequency of the vortex shedding. Such features were also reported in Liu and Jaiman 34,35 , where a DMD analysis was employed for the FF flow behind two uniform cylinders. Further, the vorticity distributions of these DMD modes are reasonably similar to those in Mizushima and Ino 50 where a strict bifurcation analysis was performed.…”

“…By performing a linear global stability analysis, Carini et al 32,33 found that the FF flow stems from an instability in the gap region out of an in-phase synchronized vortex shedding. This is supported by the Dynamic Mode Decomposition (DMD) analysis in Liu and Jaiman 34,35 .…”

Secondary lock-in of vortex-induced vibration and energy transfer characteristics of a vibrating cylinder subject to cross buoyancy

“…In contrast, the energy transfer is almost suppressed during pre-and post-lock-in regions for a vibrating cylinder in isothermal flow. 46 In this article, we further noticed a secondary VIV lock-in-state and an enhanced kinetic energy transfer between fluid and structure subject to cross buoyancy in mixed convective. It is again confirmed in this study that the maximum kinetic energy transfer occurs for the phase angle difference of 90 between lift force and transverse vibration.…”

“…Furthermore, the kinetic energy transfer between fluid and structure is a primary concern in hydropower harvesting. Liu and Jaiman 46 recorded that the maximum energy transfer occurs at about 90 phase angle difference between the lift force and transverse vibration during VIV lock-in. For 90 phase angle difference, the transverse motion acquires the maximum acceleration from the lift force.…”

Effect of Gap Flow on the Characteristics of Flow-Around and Flow-Induced Vibration for Two Circular Cylinders with Roughness Strips

“…When the gap flow mechanism was induced, the amplitude of the VIV was greater than that of the one degree of freedom VIV. Liu and Jaiman [32,33] simulated the FIV response of two parallel cylinders and found that the near wake instability was closely related to the gap flow and VIV.…”