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(searched for: doi:10.1017/s0001925900009768)
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, Amirhossein Mohammadkhani, Hamed Ahani
Published: 23 April 2021
Journal of Hydrodynamics, Volume 33, pp 301-310; https://doi.org/10.1007/s42241-021-0027-7

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Published: 1 March 2021
Experiments in Fluids, Volume 62, pp 1-17; https://doi.org/10.1007/s00348-021-03143-5

Abstract:
The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1 $$\times$$ × 10 $$^{5}$$ 5 $$\le$$ ≤ Re $$_{D}$$ D $$\le$$ ≤ 1 $$\times$$ × 10 $$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4 $$\times$$ × 10 $$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0 $$^{\circ }$$ ∘ , −22.5 $$^{\circ }$$ ∘ and −45 $$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1 $$\times$$ × 10 $$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10 $$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract
, S. Ajith Kumar, K. Arun Kumar
Lecture Notes in Mechanical Engineering pp 189-197; https://doi.org/10.1007/978-981-15-7831-1_18

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Pankaj Kumar,
Journal of Ocean Engineering and Science, Volume 5, pp 173-179; https://doi.org/10.1016/j.joes.2019.10.002

Abstract:
The paper aimed to study the flow structure at the wake of the bluff body with altered blockage ratio (BR) keeping the fixed aspect ratio (AR). The study was conducted by a finite volume technique using commercial software Ansys-Fluent. The CFD analysis of the bluff body is mainly subjected to the lower subcritical Reynolds number range (5000 to 15,000) along with blockage ratio as an important factor. The flow parameters such as drag coefficient, pressure, and kinetic energy variations are analyzed here for the Reynolds number (Re) and BR. It was observed that at fixed Re, the drag coefficient (CD) increases with an increase in the BR while decrease with increasing Re for a fixed value of BR.
F. Wang, , G.B. Zu, L. Cheng
Journal of Wind Engineering and Industrial Aerodynamics, Volume 188, pp 175-193; https://doi.org/10.1016/j.jweia.2019.02.019

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Published: 18 August 2018
Nonlinear Dynamics, Volume 94, pp 2685-2696; https://doi.org/10.1007/s11071-018-4518-1

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Gongbo Zu,
Advances in Structural Engineering, Volume 21, pp 2241-2258; https://doi.org/10.1177/1369433218770822

Abstract:
Vortex shedding from a tall building is known to be responsible for the quasi-periodic across-wind force exerted on the building. This article unveils the exact relationship between the vortex shedding pattern and the fluctuating across-wind force. Simultaneous particle-image velocimetry and pressure measurements are carried out on a square-plan tall building model in the wind tunnel toward an understanding of the velocity–pressure–force relation for across-wind force generation on the building. A collection of instantaneous wind flow patterns and synchronized wind pressure distributions suggests the existence of full periods of vortex shedding from the building. The results are further analyzed using the conditional sampling method by which the roles of development and shedding of large-scale vortices in the building wake on the generation of peak across-wind forces are evidently found. Furthermore, quasi-periodicity of across-wind excitation is clearly confirmed with Hilbert transform of the across-wind force signal. The phase averaging technique is applied to the particle-image velocimetry flow fields and distinct vortex shedding patterns from the building are observed for most of the measurement time, together with an evident phase relationship with the across-wind forces.
Meraj Mohebi, Phillip Du Plessix, Robert J. Martinuzzi,
Physical Review Fluids, Volume 2; https://doi.org/10.1103/physrevfluids.2.064702

Abstract:
The dynamics of the nearly periodic highly modulated turbulent wakes of two-dimensional rectangular cylinders normal to a uniform flow are investigated experimentally for thickness-to-chord ratios between 0.05 and 1.92 at Reynolds numbers around 6600. Measurements were conducted using planar, time-resolved stereoscopic particle image velocimetry. A generalized phase average analysis, which invokes elements of mean-field theory to relate the temporal modal coefficients of the fundamental harmonic and slow-varying base-flow drift, provided a statistically significant representation of the coherent cycle-to-cycle variation of the shedding process. It is shown that the characteristics of the wake velocity fluctuations change as a function of the thickness-to-chord ratio and can be related to structural differences in the wake topology. Moreover, the trajectory of shed vortices plays an important role in distinguishing the dynamics observed for different fluctuation-amplitude cycles. Based on differences in amplitude modulation characteristics and the vortex formation region topology, three flow regimes can be defined: a thin-plate regime, for which the feedback between forming vortices and base pressure is important; a cylinder-like thick-plate regime for which the obstacle afterbody suppresses the feedback; and a long-plate regime for which wake periodicity is not associated with the classical Kármán shedding process. The present analysis highlights the importance of the feedback mechanism for the thin-plate regime and helps reconcile differences in the reported critical thickness values between regimes. DOI:https://doi.org/10.1103/PhysRevFluids.2.064702 ©2017 American Physical Society
R. Ajith Kumar, , B. H. Lakshmana Gowda
Journal of Mechanical Science and Technology, Volume 29, pp 527-541; https://doi.org/10.1007/s12206-015-0113-2

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J. F. McClean,
Journal of Fluids Engineering, Volume 136; https://doi.org/10.1115/1.4027138

Abstract:
The flow around a surface-mounted finite-height square prism was investigated using a low-speed wind tunnel. The experiments were conducted at a Reynolds number of Re = 7.3 × 104 for prism aspect ratios of AR = 3, 5, 7, 9, and 11 and incidence angles from α = 0 deg to 45 deg. The thickness of the boundary layer on the ground plane relative to the side length was δ/D = 1.5. Measurements of the vortex shedding frequency were made with a single-component hot-wire probe, and measurements of the mean drag and lift forces were obtained with a force balance. For all aspect ratios and incidence angles, the mean drag coefficient and Strouhal number were lower than those of an infinite prism, while the mean lift coefficient was of nearly similar magnitude. As the aspect ratio was increased from AR = 3 to 11, the force coefficients and Strouhal number slowly approached the infinite-square-prism data. The mean drag coefficient and Strouhal number for the finite prism were less sensitive to changes in incidence angle compared to the infinite square prism. The critical incidence angle, corresponding to minimum mean drag coefficient, minimum (most negative) mean lift coefficient, and maximum Strouhal number, shifted to a higher incidence angle compared to the infinite square prism, with values ranging from αcritical = 15 deg to 18 deg; this shift was greatest for the prisms of higher aspect ratio. The behavior of the force coefficients and Strouhal number for the prism of AR = 3 was distinct from the other prisms (with lower values of mean drag coefficient and mean lift coefficient magnitude, and a different Strouhal number trend), suggesting the critical aspect ratio was between AR = 5 and AR = 3 in these experiments. In the wall-normal direction, the power spectra for AR = 11 and 9 tended to have weaker and/or more broad-banded vortex shedding peaks near the ground plane and near the free end at α = 0 deg and 15 deg. For AR = 7 to 3, well-defined vortex shedding peaks were detected along the entire height of the prisms. For AR = 11 and 9, at α = 30 deg and 45 deg, vortex shedding peaks were absent in the power spectra in the upper part of the wake.
Shun C. Yen, Chen W. Yang
Journal of Fluids Engineering, Volume 134; https://doi.org/10.1115/1.4004904

Abstract:
The flow behaviors around a square cylinder were modulated using the passive mesh fence. The effects of Reynolds number (Re) and rotation angle (θ) on the square-cylinder flow fields using different turbulence intensity (TI) were also investigated. Additionally, various steel mesh fences with different mesh densities were installed between the nozzle outlet and the test-section inlet to adjust the free-stream TI. The Reynolds number and turbulence intensity used in this investigation are 3.0 × 104 ≤ Re ≤ 1.0 × 105 and 0.32% ≤ TI ≤ 0.82%. The flow fields are visualized using the surface oil-flow visualization scheme. Furthermore, the flow patterns are classified as—leading-edge bubble, separation bubble, separation, leading-edge separation, and boundary-layer attached modes. Specifically, the leading-edge bubble mode does not exist while θ and TI are low. Moreover, a hot-wire anemometer was placed in the wake to detect the vortex-shedding frequency. The experimental results indicate that Strouhal number (St) decreases with increasing the free-stream TI while TI < 0.45%. However, St approaches a constant as TI > 0.45%. Furthermore, the surface pressure was detected using a pressure scanner and the drag coefficient (CD) was obtained using the surface-pressure profile. The experimental results also reveal that CD decreases with increasing the free-stream TI. However, the change rate of CD for TI < 0.45% exceeds that for TI > 0.45%.
R. F. Huang, B. H. Lin
Journal of Mechanics, Volume 27, pp 347-355; https://doi.org/10.1017/jmech.2011.37

Abstract:
The pressure distributions around a square cylinder in a crossflow were experimentally studied in a wind tunnel. The subject of study was conventional, but the results presented new findings. The experiments were performed by using a home-made linear pressure scanner. The ranges of Reynolds number and incidence angle were 2 × 104- 9.4 × 104and 0° - 45°, respectively. According to the topological flow patterns, the flows around the square cylinder at incidence showed three characteristic regimes: The subcritical, supercritical, and wedge flows. A critical incidence angle αcri= 15° separated the regimes of subcritical and supercritical modes. The results of current study provided information regarding the effects of the topological flow patterns on surface pressure distribution, drag, and lift characteristics. The pressure distributions, drag, and lift presented different characteristics in different characteristic flow regimes and had close correlations with the flows. At the critical incidence angle 15° which separated the subcritical and supercritical regimes, the surface-averaged pressure coefficient on each face displayed local extreme value—The drag coefficient attained a minimum of 1.6, the lateral force coefficient reached a maximum of 0.9. The appearance of the minimum drag at the critical incidence angle was attributed to the reduction of wake width which was induced by two surface flow phenomena: (1) reattachment of the separated boundary layer on the lateral surface facing windward at the critical incidence angle and (2) flow pattern change on the lateral surface facing leeward.
, Jeng Cha Cheng, , Ching Min Hsu
Journal of Fluids Engineering, Volume 133; https://doi.org/10.1115/1.4004091

Abstract:
The flow, vortex shedding, and surface pressure of a square cylinder at incidence were manipulated by means of a self-sustained vibrating rod placed around the leading edge of the upwind-facing lateral face of the square cylinder. The flow patterns on the cylinder surface were studied by using the surface-oil flow method for a Reynolds number between 4.5 × 104 and 1.1 × 105 as the incidence angle varied from 0° to 45°. Vortex-shedding characteristics were measured by means of a single-component hot-wire anemometer, and surface-pressure distributions were detected by using a linear-pressure scanner. The results show that owing to the influence of the rod vibration, the flow pattern on the agitated face changed from its natural state of a dual-ring bubble to the mode of boundary-layer separation. The critical incidence angle separating the dual-ring bubble and single-ring bubble modes was advanced to 11° from its natural state of 15°. The locations of the characteristic points on the cylinder surface were altered by the rod vibration, implying that the whole flow field surrounding the square cylinder was modified by the vibrating rod installed around the leading edge of the upwind-facing lateral face. The Strouhal numbers of wake instability of the controlled and uncontrolled cylinders did not present significant difference. The variations of the pressure coefficients induced by the rod vibration were closely related with the modification of the flow field on the cylinder surface. The decreases in the pressure coefficients on the upwind-facing faces and on the leeward-facing faces lead to drag reduction of the controlled cylinder by ∼25% when compared with the uncontrolled cylinder.
N. Jamshidi, M. Farhadi, K. Sedighi
The International Journal of Multiphysics, Volume 4, pp 11-20; https://doi.org/10.1260/1750-9548.4.1.11

Abstract:
This paper presents comparisons between flow fields for turbulent flow over square cylinder with two different angles of incidence in free stream at Reynolds number of Re = 3400. The present numerical results were obtained using a two-dimensional finite-volume code which solves governing equations. The pressure field was obtained with well known SIMPLE algorithm. The central difference scheme was employed for the discretization of convection and diffusion terms. The ν2 f and standard k - ε model were used for simulation of turbulent flow. Time averaged velocity, root mean square velocities and streamlines in the downstream of square cylinders are presented. A number of quantities such as Strouhal number, drag coefficient and the length of the wake are calculated for the case of angle of incidence α = 0°, 45° with two turbulent models. Strouhal number and the length of the wake are larger for the case of α = 45° because of the sharp corners in it which results in more diffusion of turbulence in the downstream of the cylinder. On the other hand, with comparison of results obtained by ν2 f and standard k - ε models with experiment, it is obvious that ν2 f leads to much more accurate results.
Sushanta Dutta, P. K. Panigrahi, K. Muralidhar
Journal of Engineering Mechanics, Volume 134, pp 788-803; https://doi.org/10.1061/(asce)0733-9399(2008)134:9(788)

Abstract:
Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations ( θ=0 , 22.5, 30, and 45°) and two aspect ratios [ AR=16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v -velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied.
Adriana L. Csiba,
Journal of Wind Engineering and Industrial Aerodynamics, Volume 96, pp 1152-1163; https://doi.org/10.1016/j.jweia.2007.06.037

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B.H.L. Gowda,
Published: 6 November 2006
Journal of Sound and Vibration, Volume 297, pp 842-864; https://doi.org/10.1016/j.jsv.2006.05.003

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Flow Measurement and Instrumentation, Volume 17, pp 225-235; https://doi.org/10.1016/j.flowmeasinst.2005.11.005

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A. Roy, G. Bandyopadhyay
The Aeronautical Journal, Volume 110, pp 249-256; https://doi.org/10.1017/s0001924000001226

Abstract:
In the present investigation, a potential flow model based on panel method has been developed for calculation of two dimensional separated flows past square and rectangular cylinders. Free vortex lines are assumed to emanate from the points of separation that converge downstream of the body. The converged wake shape is iteratively obtained by integrating the velocity vectors at the collocation points. For solving separated flow past square and rectangular cylinders, four different versions of the solver have been developed for a wide range of incidence, namely, for zero, low, moderate and high angles of incidence. For validation of computed results, experimental investigations have been carried out in a low speed wind tunnel to obtain the surface pressure distribution on square cylinder and rectangular cylinder over a range of angles of incidence. Comparison is reasonably good.
, Chia-Hung Liu
International Journal of Heat and Fluid Flow, Volume 20, pp 592-597; https://doi.org/10.1016/s0142-727x(99)00047-8

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S.C. Luo, M.G. Yazdani, Y.T. Chew, T.S. Lee
Journal of Wind Engineering and Industrial Aerodynamics, Volume 53, pp 375-399; https://doi.org/10.1016/0167-6105(94)90092-2

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T.G. Zaki, M. S,
Published: 1 January 1994
Journal of Fluids and Structures, Volume 8, pp 555-582; https://doi.org/10.1016/s0889-9746(94)90020-5

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C.W. Knisely
Journal of Fluids and Structures, Volume 4, pp 371-393; https://doi.org/10.1016/0889-9746(90)90137-t

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F.A. Da Matha, Sant' Anna, A. Laneville, J.Y. Trepanier, Z.Y. Lu
Published: 1 January 1988
Advances in Wind Engineering pp 241-250; https://doi.org/10.1016/b978-0-444-87156-5.50034-5

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