Steady and unsteady flow regimes in two-dimensional mixed convective flow of air past a heated square cylinder

The results of unsteady Reynolds averaged Navier-Stokes (URANS) simulations of flow around a square cylinder using two-dimensional hybrid meshes were presented in this paper. The first part examined the accuracy of various RANS turbulence models, i.e. the standard model, RNG model, realizable model, standard model, SST model, and RSM, by comparing their results with available experimental data. Despite the limits imposed by the RANS approach and the relatively inexpensive two-dimensional computations, the main features of this complex flow can be predicted reasonably well. Among the computations using various RANS models compared here, the SST model shows the best agreement with the experiment. The second part investigated the effects of corner cutoffs on unsteady flow characteristics around a square cylinder by using the SST model. Especially the detailed near-surface flow structure around the cylinder was focused on, aiming at giving an explanation for the drastic modification of the aerodynamic characteristics as the corner shape is slightly changed.

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Effects of heating and free-stream orientation in two-dimensional forced convective flow of air past a square cylinder

International Journal of Thermal Sciences ◽

10.1016/j.ijthermalsci.2016.08.020 ◽

2017 ◽

Vol 112 ◽

pp. 1-30 ◽

Cited By ~ 5

Author(s):

Nadeem Hasan ◽

Adnan Saeed

Keyword(s):

Convective Flow ◽

Free Stream ◽

Two Dimensional ◽

Square Cylinder ◽

Forced Convective Flow

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Flow regimes for a square cross-section cylinder in oscillatory flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.829 ◽

2017 ◽

Vol 813 ◽

pp. 85-109 ◽

Cited By ~ 6

Author(s):

Feifei Tong ◽

Liang Cheng ◽

Chengwang Xiong ◽

Scott Draper ◽

Hongwei An ◽

...

Keyword(s):

Circular Cylinder ◽

Cross Section ◽

Oscillatory Flow ◽

Vortex Formation ◽

Flow Regimes ◽

Oscillation Period ◽

Marginal Stability ◽

Two Dimensional ◽

Square Cylinder ◽

Vortex Formation Time

Two-dimensional direct numerical simulation and Floquet stability analysis have been performed at moderate Keulegan–Carpenter number ($KC$) and low Reynolds number ($Re$) for a square cross-section cylinder with its face normal to the oscillatory flow. Based on the numerical simulations a map of flow regimes is formed and compared to the map of flow around an oscillating circular cylinder by Tatsuno & Bearman (J. Fluid Mech., vol. 211, 1990, pp. 157–182). Two new flow regimes have been observed, namely A$^{\prime }$ and F$^{\prime }$. The regime A$^{\prime }$ found at low $KC$ is characterised by the transverse convection of fluid particles perpendicular to the motion; and the regime F$^{\prime }$ found at high $KC$ shows a quasi-periodic feature with a well-defined secondary period, which is larger than the oscillation period. The Floquet analysis demonstrates that when the two-dimensional flow breaks the reflection symmetry about the axis of oscillation, the quasi-periodic instability and the synchronous instability with the imposed oscillation occur alternately for the square cylinder along the curve of marginal stability. This alternate pattern in instabilities leads to four distinct flow regimes. When compared to the vortex shedding in otherwise unidirectional flow, the two quasi-periodic flow regimes are observed when the oscillation frequency is close to the Strouhal frequency (or to half of it). Both the flow regimes and marginal stability curve shift in the $(Re,KC)$-space compared to the oscillatory flow around a circular cylinder and this shift appears to be consistent with the change in vortex formation time associated with the lower Strouhal frequency of the square cylinder.

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