Turbulent Near Wake Behind a Partially Grooved Circular Cylinder

1997 ◽  
Vol 119 (1) ◽  
pp. 19-28 ◽  
Author(s):  
K. W. Lo ◽  
N. W. M. Ko
Keyword(s):  
Circular Cylinder ◽  
Shear Layers ◽  
Near Wake ◽  
Subcritical Regime ◽  
Secondary Vortices

The near wake of a partially V-grooved circular cylinder is investigated. The flow over the smooth half is within the high subcritical regime, while that over the grooved half is within the transcritical regime. Secondary and Strouhal vortices are found in the near wakes of both halves. The formation of the secondary vortices, due to the separated shear layers, is coupled to the formation of the Strouhal vortices. These secondary vortices of the two halves are of the horse shoe type. On the grooved half, another type of secondary vortices is found to be caused by the flow over the triangular blunt end of the V grooves.

At the Upper Transition of Subcritical Regime of a Circular Cylinder

2000 ◽  
Vol 123 (2) ◽  
pp. 422-434 ◽  
Author(s):  
K. W. Lo ◽  
N. W. M. Ko
Keyword(s):  
Circular Cylinder ◽  
Dominant Role ◽  
Sampling Technique ◽  
Streamwise Velocity ◽  
High Energy ◽  
Small Scale ◽  
Primary Vortex ◽  
Subcritical Regime ◽  
Group I ◽  
Secondary Vortices

The present study establishes the transition between the lower and upper subcritical regime of flow over a circular cylinder at 7×103<Re<2×104. Based on a new sampling technique, it is shown that the small-scale secondary vortices, especially those of high energy, play an important role in the transition. Within a primary vortex shedding period, the secondary vortices appear in groups. In a group, the streamwise velocity of secondary vortices exhibits the increase, peak, and decrease pattern associated with the formation of Strouhal vortices. In the lower subcritical regime, the Group I of singular group occurs most frequently, while in the upper subcritical regime, the Group III of three groups is the most frequent. Pairings of successive secondary vortices are found, and the paired vortices also appear in groups. The present model of transition involves the excitation of the separated shear layer at the most amplified mode by the disturbances associated with the secondary and paired vortices. Due to their mutual interference, the higher-energy small-scale vortices affect the primary vortex sheet, which in turn amplifies the former. These higher-energy vortices have enhanced pairings, which also play a dominant role in the later stage of transition.

Mode C flow transition behind a circular cylinder with a near-wake wire disturbance

2013 ◽  
Vol 727 ◽  
pp. 30-55 ◽  
Author(s):  
I. Yildirim ◽  
C. C. M. Rindt ◽  
A. A. van Steenhoven
Keyword(s):  
Circular Cylinder ◽  
Particle Image ◽  
Three Dimensional ◽  
Period Doubling ◽  
Feedback Mechanism ◽  
Near Wake ◽  
Number Range ◽  
Image Velocimetry ◽  
The Wire ◽  
Secondary Vortices

AbstractThe three-dimensional transition of the flow behind a circular cylinder with a near-wake wire disturbance has been investigated experimentally. The asymmetric placement of a wire in the near-wake region of the cylinder causes an unnatural mode of shedding to occur, namely mode C. We performed flow visualization and particle image velocimetry (PIV) experiments to investigate the influence of the wire on various properties of the flow, such as the dynamics of the streamwise secondary vortices. Experiments were performed at the Reynolds number range of Re = 165–300. From these experiments, it can be concluded that mode C structures are formed as secondary streamwise vortices around the primary von Kármán vortices. The spanwise wavelength of those mode C structures is determined to be approximately two cylinder diameters. The presence of the wire also triggered the occurrence of period doubling in the wake. Each new set of mode C structures is out of phase with the previous set, i.e. doubling the shedding period. This period-doubling phenomenon is due to a feedback mechanism between the consecutively shed upper vortices.

scholarly journals The drag-adjoint field of a circular cylinder wake at Reynolds numbers 20, 100 and 500

2013 ◽  
Vol 730 ◽  
pp. 145-161 ◽  
Author(s):  
Qiqi Wang ◽  
Jun-Hui Gao
Keyword(s):  
Circular Cylinder ◽  
Flow Field ◽  
Unsteady Flow ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Adjoint Equations ◽  
Cylinder Wake ◽  
Near Wake ◽  
Navier Stokes Equation ◽  
D 20

AbstractThis paper analyses the adjoint solution of the Navier–Stokes equation. We focus on flow across a circular cylinder at three Reynolds numbers, ${\mathit{Re}}_{D} = 20, 100$ and $500$. The quantity of interest in the adjoint formulation is the drag on the cylinder. We use classical fluid mechanics approaches to analyse the adjoint solution, which is a vector field similar to a flow field. Production and dissipation of kinetic energy of the adjoint field is discussed. We also derive the evolution of circulation of the adjoint field along a closed material contour. These analytical results are used to explain three numerical solutions of the adjoint equations presented in this paper. The adjoint solution at ${\mathit{Re}}_{D} = 20$, a viscous steady state flow, exhibits a downstream suction and an upstream jet, the opposite of the expected behaviour of a flow field. The adjoint solution at ${\mathit{Re}}_{D} = 100$, a periodic two-dimensional unsteady flow, exhibits periodic, bean-shaped circulation in the near-wake region. The adjoint solution at ${\mathit{Re}}_{D} = 500$, a turbulent three-dimensional unsteady flow, has complex dynamics created by the shear layer in the near wake. The magnitude of the adjoint solution increases exponentially at the rate of the first Lyapunov exponent. These numerical results correlate well with the theoretical analysis presented in this paper.

Sign in / Sign up

Export Citation Format

Share Document