Suppression of Wake Transition and Occurrence of Lock-on Downstream of a Circular Cylinder in a Perturbed Flow in the A-mode Instability Regime

AbstractA simple way to decrease the drag and oscillating lift forces in the flow around a circular cylinder consists of positioning a splitter plate in the wake, parallel to the flow. In this paper, the effect of the splitter plate on the wake dynamics, more specifically on the wake transition, is described in detail. First, two-dimensional and three-dimensional direct numerical simulations (DNS) using the spectral element method were used to observe the behaviour of the wake in the presence of the splitter plate. Then, a linear stability analysis based on the Floquet theory was performed in order to obtain information on how the splitter plate changes the instabilities that lead to wake transition. Simulations were carried out for several gaps between the splitter plate and the cylinder, with the Reynolds number varying in the range between 100 and 350, which corresponds to the wake transition in the flow around a circular cylinder. The results of the simulations showed a discontinuity in the Strouhal number curve that is consistent with the results available in the literature. The stability analysis showed how the splitter plate modifies the transition of the flow to a three-dimensional configuration. The splitter plate has a stabilizing effect on the flow for small gaps, delaying the appearance of three-dimensional structures to higher Reynolds numbers. Mode A and a quasi-periodic (QP) mode are observed for such small gaps. As the gap is increased the discontinuity in the Strouhal number curve also caused a clear change in the characteristics of the neutral stability curve, and the existence of an unstable period-doubling mode was observed. The onset characteristics of the unstable modes are analysed and discussed in depth.

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Three-dimensional wake transition for a circular cylinder near a moving wall

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.146 ◽

2017 ◽

Vol 818 ◽

pp. 260-287 ◽

Cited By ~ 10

Author(s):

Hongyi Jiang ◽

Liang Cheng ◽

Scott Draper ◽

Hongwei An

Keyword(s):

Circular Cylinder ◽

Parameter Space ◽

Large Scale ◽

Three Dimensional ◽

Scale Structure ◽

Moving Wall ◽

Local Reduction ◽

Gap Ratio ◽

Wake Transition ◽

Mode A

Three-dimensional (3D) wake transition for a circular cylinder placed near to a moving wall is investigated using direct numerical simulation (DNS). The study covers a parameter space spanning a gap ratio $(G/D)\geqslant 0.3$ and Reynolds number ($Re$) up to 325. The wake transition regimes in the parameter space are mapped out. It is found that vortex dislocation associated with Mode A is completely suppressed at $G/D$ smaller than approximately 1.0. The suppression of vortex dislocation is believed to be due to the confinement of the Mode A streamwise vortices by the plane wall, which suppresses the excess growth and local dislocation of any Mode A vortex loop. Detailed wake transition is examined at $G/D=0.4$, where the wake transition sequence is ‘two-dimensional (2D) $\rightarrow$ ordered Mode A $\rightarrow$ mode swapping (without dislocations) $\rightarrow$ Mode B’. Relatively strong three-dimensionality is found at $Re=160{-}220$ as the wake is dominated by large-scale structure of ordered Mode A, and also at $Re\geqslant 285$, where Mode B becomes increasingly disordered. A local reduction in three-dimensionality is observed at $Re=225{-}275$, where the wake is dominated by finer-scale structure of a mixture of ordered Modes A and B. Corresponding variations in the vortex shedding frequency and hydrodynamic forces are also investigated.

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Low Reynolds number flow around and heat transfer from a heated circular cylinder

International Review of Applied Sciences and Engineering ◽

10.1556/irase.1.2010.1-2.3 ◽

2010 ◽

Vol 1 (1-2) ◽

pp. 15-20 ◽

Cited By ~ 1

Author(s):

B. Bolló

Keyword(s):

Reynolds Number ◽

Circular Cylinder ◽

Lift Coefficient ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Reynolds Number Flow ◽

Two Dimensional Flow ◽

Number Flow ◽

Low Reynolds ◽

Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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