scholarly journals Unsteady dynamics in the streamwise-oscillating cylinder wake for forcing frequencies below lock-on

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
Maysam Shamai ◽  
Scott T. M. Dawson ◽  
Igor Mezić ◽  
Beverley J. McKeon
Keyword(s):  
Cylinder Wake ◽  
Oscillating Cylinder

Three-dimensional transition in the wake of a transversely oscillating cylinder

2007 ◽  
Vol 577 ◽  
pp. 79-104 ◽  
Author(s):  
JUSTIN S. LEONTINI ◽  
M. C. THOMPSON ◽  
K. HOURIGAN
Keyword(s):  
Bluff Body ◽  
Oscillation Amplitude ◽  
Three Dimensional ◽  
Base Flow ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Oscillating Cylinder ◽  
Single Vortex ◽  
Spatio Temporal ◽  
Mode A

A Floquet stability analysis of the transition to three-dimensionality in the wake of a cylinder forced to oscillate transversely to the free stream has been undertaken. The effect of varying the oscillation amplitude is determined for a frequency of oscillation close to the natural shedding frequency. The three-dimensional modes that arise are identified, and the effect of the oscillation amplitude on their structure and growth rate quantified.It is shown that when the two-dimensional wake is in the 2S configuration (which is similar to the Kármán vortex street), the three-dimensional modes that arise are similar in nature and symmetry structure to the modes in the wake of a fixed cylinder. These modes are known as modes A, B and QP and occur in this order with increasing Re. However, increasing the amplitude of oscillation causes the critical Reynolds number for mode A to increase significantly, to the point where mode B becomes critical before mode A. The critical wavelength for mode A is also affected by the oscillation, becoming smaller with increasing amplitude. Elliptic instability theory is shown also to predict this trend, providing further support that mode A primarily arises as a result of an elliptic instability.At higher oscillation amplitudes, the spatio-temporal symmetry of the two-dimensional wake changes and it takes on the P + S configuration, with a pair of vortices on one side of the wake and a single vortex on the other side, for each oscillation cycle. With the onset of this configuration, modes A, B and QP cease to exist. It is shown that two new three-dimensional modes arise from this base flow, which we call modes SL and SS. Both of these modes are subharmonic, repeating over two base-flow periods. Also, either mode can be the first to become critical, depending on the amplitude of oscillation of the cylinder.The emergence of these two new modes, as well as the reversal of the order of inception of the three-dimensional modes A and B, leads to the observation that for an oscillating cylinder wake there are four different modes that can lead the transition to three-dimensionality, depending on the amplitude of oscillation. Therefore this type of flow provides a good example for studying the effect of mode-order inception on the path taken to turbulence in bluff-body wakes.For the range of amplitudes studied, the maximum Re value for which the flow remains two-dimensional is 280.

Numerical study of an oscillating cylinder in uniform flow and in the wake of an upstream cylinder

1992 ◽  
Vol 237 ◽  
pp. 457-478 ◽  
Author(s):  
Jing Li ◽  
Jiong Sun ◽  
Bernard Roux
Keyword(s):  
Numerical Study ◽  
Vortex Formation ◽  
Uniform Flow ◽  
Driving Frequency ◽  
Cylinder Wake ◽  
Oscillating Cylinder ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Response State ◽  
Lock In

Direct numerical simulation is carried out to study the response of an oscillating cylinder in uniform flow and in the wake of an upstream cylinder. It is found that the response of the cylinder wake is either a periodic (lock-in) or a quasi-periodic (non-lock-in) state. In the lock-in state, the vortex shedding frequency equals the forcing frequency. In the non-lock-in state, the shedding frequency shows a smooth variation with the driving frequency. For a cylinder oscillating in uniform flow, a lock-in diagram of different forcing amplitude is computed. However, no clear chaotic behaviour is detected near the lock-in boundary. For a cylinder oscillating in the wake of an upstream cylinder, the response state is strongly influenced by the distance between the two cylinders. By changing cylinder spacing, two different flow regimes are identified. In the ‘vortex formation regime’, found at large spacings, the vortex street develops behind both the upstream and downstream cylinders. The strength of the naturally produced oscillation upstream of the second cylinder becomes important compared to the forced oscillation and dominates the flow, leading to a very small or even indistinguishable zone of synchronization. However, in the ‘vortex suppression regime’, observed at small spacings, the oncoming flow to the downstream cylinder becomes so weak that it hardly affects its vortex wake, and therefore a large zone of synchronization is obtained. The numerical results are in good agreement with available experimental data.

scholarly journals Large Eddy Simulation of Flow Past a Stationary and Controlled Oscillating Circular Cylinder at Re=5500

2013 ◽  
Author(s):  
Sunghan Kim ◽  
Philip A. Wilson ◽  
Zhi-Min Chen
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Large Eddy Simulation ◽  
Accurate Method ◽  
Excitation Amplitude ◽  
Uniform Flow ◽  
Cylinder Wake ◽  
Oscillating Cylinder ◽  
Eddy Simulation ◽  
Large Eddy

Vortex shedding from a stationary cylinder and transversely oscillating circular cylinder in a uniform flow at a Reynolds number of 5500 is numerically studied by three-dimensional Large Eddy Simulation (LES). The filtered equations are discretised using the finite volume method with an O-type structured grid and a second-order accurate method in both time and space. Firstly, the main wake parameters of a stationary cylinder are examined and compared for different grid resolutions. Secondly, a transversely oscillating cylinder with a constant amplitude in a uniform flow is investigated. The cylinder oscillation frequency ranges between 0.75 and 0.95 of the natural Kármán frequency, and the excitation amplitude is 50% of the cylinder diameter. Comparisons with the available experimental data indicate that the present study has properly predicted the flow statistics of the cylinder wake for both the fixed and oscillating cylinder case, and numerically captured the vortex switching phenomenon, which is characterized by changes in forces and wake mode of shedding observed in the previous experiments at high values of Reynolds number.

Wake Flow of Single and Multiple Yawed Cylinders

2004 ◽  
Vol 126 (5) ◽  
pp. 861-870 ◽  
Author(s):  
A. Thakur ◽  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Wake Flow ◽  
Upstream Region ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Dimensional Approximation ◽  
The Face ◽  
Drag And Lift

An experimental and computational study is performed of the wake flow behind a single yawed cylinder and a pair of parallel yawed cylinders placed in tandem. The experiments are performed for a yawed cylinder and a pair of yawed cylinders towed in a tank. Laser-induced fluorescence is used for flow visualization and particle-image velocimetry is used for quantitative velocity and vorticity measurement. Computations are performed using a second-order accurate block-structured finite-volume method with periodic boundary conditions along the cylinder axis. Results are applied to assess the applicability of a quasi-two-dimensional approximation, which assumes that the flow field is the same for any slice of the flow over the cylinder cross section. For a single cylinder, it is found that the cylinder wake vortices approach a quasi-two-dimensional state away from the cylinder upstream end for all cases examined (in which the cylinder yaw angle covers the range 0⩽ϕ⩽60°). Within the upstream region, the vortex orientation is found to be influenced by the tank side-wall boundary condition relative to the cylinder. For the case of two parallel yawed cylinders, vortices shed from the upstream cylinder are found to remain nearly quasi-two-dimensional as they are advected back and reach within about a cylinder diameter from the face of the downstream cylinder. As the vortices advect closer to the cylinder, the vortex cores become highly deformed and wrap around the downstream cylinder face. Three-dimensional perturbations of the upstream vortices are amplified as the vortices impact upon the downstream cylinder, such that during the final stages of vortex impact the quasi-two-dimensional nature of the flow breaks down and the vorticity field for the impacting vortices acquire significant three-dimensional perturbations. Quasi-two-dimensional and fully three-dimensional computational results are compared to assess the accuracy of the quasi-two-dimensional approximation in prediction of drag and lift coefficients of the cylinders.

scholarly journals Energy transfer mechanisms and resolvent analysis in the cylinder wake

2021 ◽  
Vol 6 (2) ◽  
Author(s):  
Bo Jin ◽  
Sean Symon ◽  
Simon J. Illingworth
Keyword(s):  
Energy Transfer ◽  
Cylinder Wake ◽  
Transfer Mechanisms

Aspects of Flow Structure During a Cylinder Wake-Induced Laminar/Turbulent Transition

AIAA Journal ◽  
10.2514/2.613 ◽  
1999 ◽  
Vol 37 (10) ◽  
pp. 1197-1205 ◽  
Author(s):  
N. K. Kyriakides ◽  
E. G. Kastrinakis ◽  
S. G. Nychas ◽  
A. Goulas
Keyword(s):  
Flow Structure ◽  
Cylinder Wake ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition
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