scholarly journals Secondary Vortex Street in the Wake of a Thin Rectangular Cylinder

2020 ◽  
Author(s):  
Hongyi Jiang ◽  
Xiaoying Ju ◽  
Yucen Lu
Keyword(s):  
Vortex Street ◽  
Secondary Vortex ◽  
Rectangular Cylinder

A Numerical Study of Heat Transfer Enhancement by a Rectangular Cylinder Placed Parallel to the Heated Wall

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
J. F. Derakhshandeh ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Vortex Dynamics ◽  
Numerical Study ◽  
Vortex Street ◽  
Heated Wall ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Single Row ◽  
Rectangular Cylinder ◽  
Maximum Heat Transfer

The flow around a rectangular cylinder mounted in the vicinity of a hot wall is numerically studied at a Reynolds number of 200. While the cylinder chord-to-height ratio C/W is varied from 2 to 10, the gap distance G from the wall to the cylinder is changed from 0.25 to 6.25. The focus of this study is given on the dependence of G/W and C/W on the heat transfer from the wall and associated physics. The variation in the Strouhal number is presented as a function of C/W. It is observed that the effect of G/W on the vortex dynamics and heat transfer is much more than that of C/W. Based on the dependence of the vortex dynamics and heat transfer on G/W, we have identified four distinct flows: no vortex street flow (G/W < 0.75), single-row vortex street flow (0.75 ≤ G/W ≤ 1.25), inverted two-row vortex street flow (1.25 < G/W ≤ 2.5), and two-row vortex street flow (G/W > 2.5). At the single-row vortex street flow, the two opposite-sign vortices appearing in a jetlike flow carry heat from the wall to the wake and then to the freestream. The maximum heat transfer is achieved at the single-row vortex street flow and 8% increase occurs at C/W = 2, G/W = 0.75–1.25.

Mechanism underlying Kármán vortex street breakdown preceding secondary vortex street formation

2016 ◽  
Vol 28 (5) ◽  
pp. 054101 ◽  
Author(s):  
G. Ya. Dynnikova ◽  
Ya. A. Dynnikov ◽  
S. V. Guvernyuk
Keyword(s):  
Vortex Street ◽  
Secondary Vortex ◽  
Karman Vortex Street ◽  
Kármán Vortex Street ◽  
Karman Vortex

On the origin of the secondary vortex street

2012 ◽  
Vol 711 ◽  
pp. 641-666 ◽  
Author(s):  
Bhaskar Kumar ◽  
Sanjay Mittal
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Vortex Shedding ◽  
Linear Stability Analysis ◽  
Broad Band ◽  
Vortex Street ◽  
Secondary Vortex ◽  
Primary Vortex ◽  
Near Wake ◽  
Far Wake

AbstractThe origin of the secondary vortex street, observed in the far wake in the flow past a circular cylinder, is investigated. The Reynolds number, based on the diameter of the cylinder, is 150. The von Kármán vortex street, which originates in the near wake, decays exponentially downstream of the cylinder. Beyond the region of decay, a broad band of frequencies are selectively amplified, leading to the formation of a secondary vortex street consisting of packets of large-scale vortex structures. The streamwise location of the onset of the instability, frequency of the generation of packets and their convection speed are estimated via direct numerical simulation (DNS). Global linear stability analysis of the time-averaged flow reveals the presence of unstable convective modes that travel at almost the same speed and have a structure similar to the packet-like disturbances as observed in the DNS. Sensitivity analysis of the global convective modes to structural perturbations is carried out to locate the region of the wake that is most significant in generating the modes responsible for the appearance of the secondary vortex street. This information is utilized to control the flow. By placing a ‘slip’ splitter plate along the wake centre line, in the overlap region of the direct and the adjoint modes, the oscillations in the far wake are significantly reduced, though the oscillations related to the primary vortex shedding in the near wake are not. It is also found that suppression of the primary vortex shedding leads to annihilation of the secondary vortex street as well. Linear stability analysis of the steady-state flow does not yield any modes that can explain the appearance of the secondary vortex street. The steady and time-averaged wake profiles, for the $\mathit{Re}= 150$ flow, are compared to bring out the differences in the two. The effect of free-stream oscillations on the evolution of the secondary vortex street is investigated. By reducing the amplitude of inlet excitation, a gradual transition from ordered shedding in the far wake to the appearance of a broad-band spectrum of frequencies, as in the unforced wake, is observed. All the computations have been carried out using a stabilized finite element method.

Secondary vortex street in the wake of two tandem circular cylinders at low Reynolds number

2010 ◽  
Vol 81 (3) ◽  
Author(s):  
Si-ying Wang ◽  
Fang-bao Tian ◽  
Lai-bing Jia ◽  
Xi-yun Lu ◽  
Xie-zhen Yin
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Secondary Vortex ◽  
Low Reynolds

Secondary vortex street in the intermediate wake of a circular cylinder

2018 ◽  
Vol 59 (7) ◽  
Author(s):  
S. L. Tang ◽  
L. Djenidi ◽  
R. A. Antonia ◽  
Y. Zhou
Keyword(s):  
Circular Cylinder ◽  
Vortex Street ◽  
Secondary Vortex

Flow Structures and Vortex Dynamics in the Wake of Three Tandem Prisms

2018 ◽  
Author(s):  
Qinmin Zheng ◽  
Md. Mahbub Alam
Keyword(s):  
Bluff Body ◽  
Decomposition Analysis ◽  
Vortex Street ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Secondary Vortex ◽  
Primary Vortex ◽  
Mode Decomposition ◽  
Inherent Frequency ◽  
Bluff Body Flow

A study of the flow around three tandem square prisms may provide us a better understanding of complicated flow physics related to multiple closely spaced structures. In this paper, a numerical investigation on the flow around three tandem prisms at Reynolds number Re = 150 is conducted for L/W = 1.2 ∼ 10.0, where L is the prism center-to-center spacing and W is the prism width. Four distinct flow regimes and their ranges are identified, viz., single bluff-body flow (L/W < 3.0), alternating reattachment flow (3.0 < L/W < 4.3), synchronized coshedding flow (4.3 < L/W < 7.3) and desynchronized coshedding flow (7.3 < L/W ≤ 10.0). The synchronized coshedding flow can be further subdivided into two regimes: single St flow (4.3 < L/W < 5.1) and dual St flow (5.1 < L/W < 7.3). A secondary vortex street following the primary vortex street is observed for the dual St flow and the desynchronized coshedding flow. The detailed physics of the evolution of the primary vortex street to the secondary is imparted. The inherent frequency associated with the secondary vortex street is smaller than that with the primary. The evolution process of the primary vortex street to the secondary leads to a tertiary frequency. The DMD (dynamic mode decomposition) analysis for the first time is proposed as a useful and quantitative tool to identify the secondary vortex street and its onset position.

scholarly journals Transition to the secondary vortex street in the wake of a circular cylinder

2019 ◽  
Vol 867 ◽  
pp. 691-722 ◽  
Author(s):  
Hongyi Jiang ◽  
Liang Cheng
Keyword(s):  
Circular Cylinder ◽  
Transverse Velocity ◽  
Broad Band ◽  
Flow Characteristics ◽  
Vortex Street ◽  
Bluff Bodies ◽  
Secondary Vortex ◽  
Frequency Spectra ◽  
Vortex Streets ◽  
Merging Process

Instabilities and flow characteristics in the far wake of a circular cylinder are examined through direct numerical simulations. The transitions to the two-layered and secondary vortex streets are quantified by a new method based on the time-averaged transverse velocity field. Two processes for the transition to the secondary vortex street are observed: (i) the merging of two same-sign vortices over a range of low Reynolds numbers ($Re$) between 200 and 300, and (ii) the pairing of two opposite-sign vortices, followed by the merging of the paired vortices into subsequent vortices, over a range of $Re$ between 400 and 1000. Single vortices may be generated between the merging cycles due to mismatch of the vortices. The irregular merging process results in flow irregularity and an additional frequency signal $f_{2}$ (in addition to the primary vortex shedding frequency $f_{1}$) in the two-layered and secondary vortex streets. In particular, a gradual energy transfer from $f_{1}$ to $f_{2}$ with distance downstream is observed in the two-layered vortex street prior to the merging. The frequency spectra of $f_{2}$ are broad-band for $Re=200$–300 but become increasingly sharp-peaked with increasing $Re$ because the vortex merging process becomes increasingly regular. The ratio of the sharp-peaked frequencies $f_{2}$ and $f_{1}$ is equal to the ratio of the numbers of vortices observed after and before the merging. The general conclusions drawn from a circular cylinder are expected to be applicable to other bluff bodies.

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