Vortex Dynamics in the Turbulent Wake of a Single Step Cylinder

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
C. Morton ◽  
S. Yarusevych
Keyword(s):  
Vortex Dynamics ◽  
Turbulent Wake ◽  
Single Step ◽  
Cylinder Wake ◽  
Near Wake ◽  
Vortex Interactions ◽  
Direct Cross ◽  
Half Loop ◽  
Turbulent Vortex Shedding ◽  
Different Diameters

The turbulent wake development of a circular cylinder with a single stepwise discontinuity in diameter was investigated experimentally using flow visualization and two-component Laser Doppler Velocimetry (LDV). A single step cylinder is comprised of two cylinders of different diameters (D and d). Experiments were performed at a Reynolds number (ReD) of 1050 and a diameter ratio (D/d) of two. A combination of hydrogen bubble and laser induced fluorescence techniques allowed visualization of complex vortex dynamics in the near wake. The results show that turbulent vortex shedding from a single step cylinder occurs in three distinct cells of constant shedding frequency. The differences in frequency and strengths between vortices in the cells lead to complex vortex interactions at the cell boundaries. The results demonstrate that vortex splitting, half-loop vortex connections, and direct cross-boundary vortex connections occur near the cell boundaries. A comparative analysis of flow visualizations and velocity measurements is used to characterize the main vortex cells and the attendant vortex interactions, producing a simplified model of vortex dynamics in the step cylinder wake for ReD = 1050 and D/d = 2.

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.

Bistable Phenomenon of the Aerodynamic Forces on a Square Prism with the Aspect Ratio of 5

2012 ◽  
Vol 256-259 ◽  
pp. 844-849
Author(s):  
Han Feng Wang
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Side Surface ◽  
Shear Layers ◽  
Cylinder Wake ◽  
Near Wake ◽  
Square Prism ◽  
Bistable Phenomenon ◽  
Side Walls ◽  
Simulation Results

The flow around a finite-length square prism with aspect ratio of 5 is numerical investigated using LES at Red = 3900. The prism is mounted on a flat wall, with one end free. Based on the simulation results, it is found that the near wake is highly three dimensional under the effects of free-end downwash flow. The shear layers from prism side walls and free end form an arch-type structure. There are two typical flow modes presence in the near wake: first, the spanwise vortices are staggered arranged similar to that in 2D cylinder wake; second, the spanwise vortices are quasi-symmetrically arranged. These two modes occur alternately and intermittently. When the first mode occurs, the pressure on the prism side surface fluctuates periodically, corresponding to large values of drag and fluctuating lift coefficients; when the second modes occurs, there is no obvious pressure fluctuation on prism side surfaces, and the correspond drag and fluctuation life coefficients are significantly smaller than those for the first mode.

scholarly journals Stabilizing effect of flexibility in the wake of a flapping foil

2012 ◽  
Vol 710 ◽  
pp. 659-669 ◽  
Author(s):  
C. Marais ◽  
B. Thiria ◽  
J. E. Wesfreid ◽  
R. Godoy-Diana
Keyword(s):  
Symmetry Breaking ◽  
Vortex Dynamics ◽  
Momentum Balance ◽  
Near Wake ◽  
Low Speed ◽  
Flapping Foil ◽  
Balance Calculation ◽  
Stabilizing Effect ◽  
Dynamical Features ◽  
Regime Transitions

AbstractThe wake of a flexible foil undergoing pitching oscillations in a low-speed hydrodynamic tunnel is used to examine the effect of chordwise foil flexibility in the dynamical features of flapping-based propulsion. We compare the regime transitions in the wake with respect to the case of a rigid foil and show that foil flexibility inhibits the symmetry breaking of the reverse Bénard–von Kármán wake reported in the literature. A momentum balance calculation shows the average thrust to be up to three times greater for the flexible foil than for the rigid foil. We explain both of these observations by analysing the vortex dynamics in the very near wake.

Near wake vortex dynamics of a hovering hawkmoth

2008 ◽  
Vol 25 (1) ◽  
pp. 23-36 ◽  
Author(s):  
Hikaru Aono ◽  
Wei Shyy ◽  
Hao Liu
Keyword(s):  
Vortex Dynamics ◽  
Wake Vortex ◽  
Near Wake

On the Intrinsic Mechanism of Wakes Interference Past Two Cylinders Towed Beneath a Free Surface

2013 ◽  
Author(s):  
Dominique R. Rajaona ◽  
Toky Ramanakoto
Keyword(s):  
Free Surface ◽  
Maximum Velocity ◽  
Ccd Camera ◽  
Cylinder Wake ◽  
Near Wake ◽  
Interference Phenomenon ◽  
Flow Past ◽  
Intrinsic Mechanism ◽  
Drag And Lift ◽  
Horizontal Cylinders

An experimental study of the flow past a set of two horizontal cylinders is presented. The cylinders are towed in a uniformly accelerated and decelerated motion in a visualization tank in order to enhance the vortex effects. The main cylinder (D = 0.04 m; L/D = 16) is placed in the flow past a front one (d = 0.002m; L/D = 16). They are towed beneath the free surface and the drag and lift forces are measured. The main cylinder wake pattern is visualized by an embarked CCD camera. The Reynolds number based on the maximum velocity is from 0 to 14000 and the Froude number based on the main cylinder immersion from 0.2 to 1.2 for an acceleration value of 0.15m.s-2. It is shown that the near wake is made of a combination of the main cylinder Von Karman vortices and those of the front cylinder. The interference phenomenon and the free surface effects are studied by varying the depth parameter and the two cylinders arrangements.

A Combined Experimental and Numerical Study of Flow Past a Single Step Cylinder

2010 ◽  
Author(s):  
Chris R. Morton ◽  
Serhiy Yarusevych
Keyword(s):  
Vortex Shedding ◽  
Numerical Study ◽  
Experimental Tests ◽  
Numerical Approach ◽  
Single Step ◽  
Wake Flow ◽  
Cylinder Wake ◽  
Flow Topology ◽  
Single Vortex ◽  
Flow Past

The current study investigates flow past a step cylinder for ReD = 1050 and D/d = 2 using both experimental and numerical methods. The focus of the study is on the vortex shedding and vortex interactions occurring in the step cylinder wake. Flow visualization with hydrogen bubble technique and planar Laser Induced Fluorescence has shown that three distinct spanwise vortex cells form: a single vortex shedding cell in the wake of the small cylinder and two vortex shedding cells in the wake of the large cylinder. Vortex connections form between the spanwise vortices in these cells downstream of the step, and vortex dislocations occur at cell boundaries. Complementary to the experimental tests, an LES-RANS hybrid numerical simulation is used to model the flow development. A comparison of the experimental and numerical results indicates that the numerical approach adequately models vortex dynamics in the wake of a step cylinder and, thus, may be used to analyze time dependent, three-dimensional flow topology which is difficult to characterize quantitatively using experimental methods.

scholarly journals Energy contents and vortex dynamics in Mode-C transition of wired-cylinder wake

2013 ◽  
Vol 25 (5) ◽  
pp. 054103 ◽  
Author(s):  
I. Yildirim ◽  
C. C. M. Rindt ◽  
A. A. van Steenhoven
Keyword(s):  
Vortex Dynamics ◽  
Cylinder Wake
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