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Abstract In the present study, flow behind a square cylinder is investigated using control rods. The control rods are placed in the shear layer and studied using particle image velocimetry, hotwire anemometry and flow visualization techniques. Experiments are conducted in a low-speed wind tunnel for three different Reynolds numbers 485, 805 and 1290. However, detailed analysis of flow is only presented at a Reynolds number of 485. The aim is to modify the wake behind a square cylinder for possible suppression of vortex Street and drag reduction. The control rod diameter is kept constant as 0.2 times of the cylinder diameter. Depending upon the gap between control rods and the cylinder, the flow structure, vortex dynamics, the distance of the shear layer roll up behind the cylinder is modified. An attempt is made to correlate the different flow structures with corresponding drag forces. Several parameters such as time-averaged drag coefficient, Strouhal number, recirculation length, fluctuating velocity, turbulence intensity, and Reynolds stress are measured. To understand the flow phenomena and its intricate structure, flow visualization images are also captured in the same setup with smoke visualization. Maximum up to 22% drag reduction is observed at a particular control rod position. Highlights • Wake modification behind a square cylinder using control rods. • Particle image velocimetry (PIV), hotwire anemometer and flow visualization techniques are used to characterize the flow. • Effect of control rod position on the flow structure, vortex shedding and the drag coefficient. • The maximum reduction in drag coefficient (up to 22%) is observed for particular control rod position in the shear layer. • The flow visualization images give a clear picture of flow structure modification and suppression of vortex shedding. [ABSTRACT FROM AUTHOR]

This study focuses on the computational implementation of structured non-uniform finite volume method for the 2-D laminar flow of viscoelastic fluid past a square section of cylinder in a confined channel with a blockage ratio 1/4 for Re = 10-4, 5, 10 and 20. Oldroyd-B model (constant viscosity with elasticity) and the PTT model (shear-thinning with elasticity) are the constitutive models considered. In this study effects of the elasticity and inertia on the drag coefficients and stress fields around the square cylinder are obtained and discussed in detail. With an increase elasticity, drag coefficients get smaller due to stronger shear thinning effects for PTT fluid, however, the drag coefficients show slightly enhancement for the Oldroyd-B fluid. [ABSTRACT FROM AUTHOR]

The confined flow of a Newtonian fluid around a square cylinder mounted in a rectangular channel was investigated both numerically and experimentally. Ratio between the pipe and channel height, the blockage ratio, is kept constant at 1/4. The flow variables including streamlines, vorticity and drag coefficients were calculated at 0 = Re = 50 using finite volume method. The velocity terms in the momentum equations are approximated by a higher-order and bounded scheme of Convergent and Universally Bounded Interpolation Scheme for the Treatment of Advection (CUBISTA). Particle Image Velocimetry (PIV) was also used to obtain the twodimensional velocity field. The flow measurements were conducted for 1 = Re = 50. Streamline and vorticity results obtained by PIV are compared with those of the numerical simulation. Based on this comparison, good agreement is found between the numerical and experimental results in a qualitative manner. [ABSTRACT FROM AUTHOR]

Dynamic responses of four rigidly-connected square cylinders in a square con- figuration subjected to two-dimensional steady ow of a constant property Newtonian uid were investigated numerically. The focus of the present study is to investigate the effects of the angle of attack α on the dynamic responses by varying α from 0° to 15° in intervals of 2:5° at a fixed L = 4 (L is the non-dimensional center-to-center distance between two adjacent square cylinders, normalized by the side length of the square cylinder B). For each α, the reduced velocity (Vr) ranges from 1 to 40. The Reynolds number Re, mass ratio m* and structural damping ratio maintain constants of 180, 10 and 0, respectively. Numerical results show that the angle of attack α has a significant inuence on the dynamic response. When α ≤ 5°, galloping occurs in addition to vortex-induced vibration (VIV), while it weak- ens for α = 7:5° and 10°, and finally disappears as α = 12:5° and 15°, leaving only VIV response. The effects of L on the responses of the four-square-cylinder oscillating system were also examined for Re = 180, Vr = 40, and α = 2:5°. Numerical results show that L affects not only the response displacement but also the vortex shedding mode. Galloping with large response amplitude can happen at either large L = 4 or small L = 1:5 and 2. The response amplitude is relatively small as 2:5 ≤ L ≤ 3:5 due to the inuence of the ow in the gap between the square cylinders. For the particular case of L = 3:5, a combined vortex shedding mode is identified, where the vortex shedding from the top row square cylinders behaves as that from an elongated single body while the vortex shedding from the bottom row cylinders presents a co-shedding mode. [ABSTRACT FROM AUTHOR]

Simulation of uniform flow past a square cylinder undergoing rotational oscillations at various frequencies is performed using the ANSYS Fluent CFD package. The frequency ratios FR chosen for the study are 0.4, 0.8 and 1.0. At each frequency ratio, a number of angular amplitudes are selected, and the simulations are performed using a dynamically deforming mesh. The results are obtained from the simulations in terms of the nondimensional drag and lift forces, vorticity contours, power spectral density plots of lift coefficients and Strouhal number. A general increase in lift and drag coefficients with increasing frequency ratios as well as with increasing amplitudes at a particular frequency ratio, except a few anomalies, is seen. The flow features in the wake and the vicinity of the cylinder are compared for the various parameters. The use of convective boundary condition for the problem is demonstrated. [ABSTRACT FROM AUTHOR]

Traveling waves generated on the side surfaces of a square cylinder are employed to suppress the oscillating wake for improving the flow behavior around a square cylinder; this method is termed the traveling wave wall (TWW) method. This study aimed to evaluate the influence of the key parameters of TWW on the control of aerodynamic forces and the oscillating wake of the flow around a square cylinder. Unsteady numerical analyses at a low Reynolds number (Re) of 100 were performed using a two-dimensional CFD simulation. First, the grid independence and time step independence tests of the simulation were conducted to verify the rationality of the solving parameter settings, and the validation of flow around the fixed square cylinder at Re =100 was carried out. Subsequently, the lift and drag coefficients and the vortex shedding modes under different combinations of three TWW control parameters, including wave velocity, wave amplitude, and wavenumber, were analyzed in detail. The results show that TWW can remarkably reduce the mean value of drag coefficient and the RMS value of the lift coefficient by more than 12% compared to the method involving a standard square cylinder. Two peaks occur in the lift coefficient spectrum, with the low frequency corresponding to the vortex shedding frequency in the wake of the flow around the square cylinder and the high frequency corresponding to the traveling wave frequency. The vorticity contours show that the alternating vortices in the wake of the square cylinder are not completely suppressed under the selected control parameters. [ABSTRACT FROM AUTHOR]

Abstract Shear-inflow effects on flows past a rounded-corner square cylinder is investigated when Reynolds number (Re) increases from subcritical regimes (Re=2.2 × 104) to supercritical regimes (Re=1.0 × 106), with a focus on the latter Re in this study. The dimensionless shear parameter K ranges from 0 to 1.0. Results show that shear inflows have different effects on the aerodynamic characteristics of the cylinder in two Re regimes, and generally shear effects are smaller when Re is in the supercritical region. Specifically, mean and r.m.s pressure distributions remain in the same shapes under all shear inflows tested at supercritical Re; however they witness strong dependency on K at subcritical Re. Moreover, the directions of mean lifts at supercritical Re are opposite to those at subcritical Re. Correspondingly, the mean flow patterns observed in the uniform flow are overall preserved in shear flows at the supercritical Re: the free stream flows along the cross section and separates from the trailing corners on both sides of the cylinder, despite of the existence of small-degree asymmetry in the near-wake. However, the flow patterns are significantly changed at the subcritical Re by the sufficiently high shear inflows: the shear layer in suspension tends to reattach on the side wall of the high-velocity side and eventually separates from the trailing edge while the other on the low-velocity side becomes farther from the side wall. It results in the near-wake forming along an axis rotated in the clockwise direction from the horizontal axis, being opposite to the anticlockwise direction at supercritical Re. The mechanism for Re effects is further explored. The preservation of overall flow pattern at supercritical Re even under the strong shear effects is suggested mainly due to the greater favorable pressure gradient and the induced greater velocity acceleration before flow separation on the low-velocity side. Graphical abstract Highlights • Planar shear-inflow effects are investigated on a rounded-corner square cylinder. • Re dependency is discovered from subcritical to supercritical regime. • Shear effects are smaller and nearly symmetry is preserved at supercritical Re. • Strong asymmetry on two sides of cylinder is found at subcritical Re. • The mechanism for Re dependency under shear inflows is explored. [ABSTRACT FROM AUTHOR]

Turbulent uniform flows past a two-dimensional square cylinder are investigated numerically. By varying the turbulence intensity and turbulence length scale of the approaching flow, the flow effect of the cylinder are compared to that in a laminar approaching-flow case. In addition, the variations of drag and lift coefficients with respect to the changes of turbulence intensity and turbulence length scale are analyzed on a systematic basis. In the large eddy simulations, the approaching-flow turbulence is generated by a spectral method according to Kármán spectrum. Two levels of turbulence intensities (5% and 10%) and three turbulence length scales (0.25, 0.50 and 1.0 times of the cylinder width) are selected in the study to examine the effect on the cylinder. Results show that the Strouhal number remains almost unchanged when the uniform approachingflow changes from a laminar state to a turbulent one. The approaching-flow turbulence has noticeable effect in promoting the resulting drag and lift fluctuations. However, its effect on the mean drag appears negligible. In contrast, an increase of the approaching-flow turbulence length scale leads to mild increases of the mean and root-mean-square values of drag. On the other hand, the resulting lift fluctuation is insensitive to the change of the turbulence length scale. [ABSTRACT FROM AUTHOR]

Flow around an isolated generic sharp-edged object with varying height ratio (β = 0–1) i.e. height from the rear end of the object to the front end ( β = H 2 / H 1 ) has been investigated in cross-flow configuration covering steady and periodic regimes at Reynolds number ( Re ) from 1 to 150 using air as a working fluid. Flow separation is delayed with a decrease in β. Wake formed is the highest for β = 1 (square object) and progressively decreases with the decrease in β. The vortex shedding effect has been demonstrated on the heat transfer phenomena around the objects. For all the cases of height ratios, as Re increases the flow undergoes supercritical Hopf bifurcation to periodic state as steady-state condition loses its stability. Stuart-Landau theory has been used to determine the value of critical Re or the onset of vortex shedding for all the cases of height ratios. As β increases from 0 to 0.7, the value of critical Re increases. Influence of surface vorticity and surface pressure on the overall drag coefficient ( C D ) has been explored. Effect of β on the Strouhal number ( St ) has been investigated and the findings are in agreement with previous results. Finally, correlations relating Lr , C D , Nu ‾ and St with Re and β have been developed. [ABSTRACT FROM AUTHOR]

Abstract In this study, a two-dimensional Immersed Boundary Lattice Boltzmann Method (IB-LBM) is employed to investigate computationally effect of flow past a pair of square cylinders in side-by-side arrangement at Re = 100 , for various corner radii. Numerical simulations were performed simultaneously by varying center to center distance between two cylinders (1.5–5.0 D) in the transverse direction and by changing the corner radius (R) from R/D = 0.0 (square) to 0.5 (circular) with 0.1 increment. Aerodynamic characteristics, including the lift and drag coefficients, were quantitatively calculated and compared with each other. Vorticity contours were used as visualization aids to understand the wake pattern and underlying mechanism. The results indicate different features in lift and drag time histories and in wake patterns for a selected range. The numerical results reveal that the flow characteristics and vortex shedding depend significantly on the corner radius and gap spacing. A square cylinder exhibited the maximum average drag value, and the inverse was observed in the case of a circular cylinder. Furthermore, aerodynamic forces were reduced by rounding the corner radius. [ABSTRACT FROM AUTHOR]

The prospect of harvesting energy from flow-induced vibration using an elastic square cylinder with a detached flat plate is experimentally investigated. The feasibility of flow-induced vibration to supply an adequate base excitation for micro-scale electrical power generation is assessed through a series of wind tunnel tests. The current test model of a single square cylinder is verified through a comparable pattern of vibration amplitude response with previous experimental study and two-dimensional numerical simulations based on the unsteady Reynolds averaged Navier–Stokes (URANS). In addition, a downstream flat plate is included in the wake of the square cylinder to study the effects of wake interference upon flow-induced vibration. A downstream flat plate is introduced as the passive vibration control to enhance the magnitude of flow-induced vibration and simultaneously increases the prospect of harvesting energy from the airflow. The study is conducted by varying the gap separation between the square cylinder and flat plate for 0.1≤ G/D ≤3. The highest peak amplitude is observed for the gap G/D = 1.2 with yrms/D = 0.46 at UR = 17, which is expected to harvest ten times more energy than the single square cylinder. The high amplitude vibration response is sustained within a relatively broader range of lock-in synchronization. Meanwhile, for G/D = 2 the vibration is suppressed, which leads to a lower magnitude of harvested energy. Contrarily, the amplitude response pattern for G/D = 3 is in agreement with the single square cylinder. Hence, the flat plate has no significance to the wake interference of the square cylinder when the gap separation is beyond 3D. [ABSTRACT FROM AUTHOR]

The unsteady flow past a square cylinder with rounded leading corners is predicted at Re = 2600 by large eddy simulations (LES). The corner radius r is fixed at 3 mm and the cylinder width D is 12.7 mm, resulting in r /D = 0.236. Detailed comparisons are made between the two-dimensional (2D) and the three-dimensional (3D) results with previous experimental measurements [32, 33]. The results show that the Strouhal number agrees well with previous measurement [33], indicating that both 2D and 3D LES are capable of capturing the shedding of large-scale vortical strutures. The statistical quantities (e.g., the drag and lift coefficients, the time-averaged streamwise velocity, the root-mean-square of streamwise velocity and the Reynolds stress) were calculated and validated against experimental results [32, 33]. The 3D LES results show reasonable agreement with the experimental measurement [32, 33], while the results predicted by 2D LES deviate far from the experimental measurement [32, 33]. It is further demonstrated that the recirculation length and the vortex formation length are consistent with experimental results [33], while it is greatly shortened in 2D LES. [ABSTRACT FROM AUTHOR]

This study deals with the flow induced vibrations of a freely vibrating circular cylinder in tandem arrangement with sharp edge square and diamond upstream cylinders. Spacing ratios of 4, 8 and 11 are examined. The lateral displacements, lift forces and the pressure data in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 1.5 × 10 3 to 3.7 × 10 4 . The overall transverse response of a circular cylinder in the wake of a sharp edge cylinder look like a VIV type of response. The ever increasing type of transverse oscillations for tandem circular cylinders at low spacing ratios no longer exists. It is concluded that in general, the wake from the upstream sharp edge cylinder has mitigated (around 40%) the lift force coefficient on the downstream cylinder. The oscillations and pressure frequencies occur primarily at the upstream sharp edge cylinder shedding frequency. It appears that the upstream wake is much stronger than the vortices past the downstream cylinder, so they take control of the downstream circular cylinder oscillations and shedding. [ABSTRACT FROM AUTHOR]

A numerical study on the flow over a square cylinder in the vicinity of a wall is conducted for different Couette-Poiseuille-based non-uniform flow with the non-dimensional pressure gradient P varying from 0 to 5. The nondimensional gap ratio L (=H*/a*) is changed from 0.1 to 2, where H* is gap height between the cylinder and wall, and a* is the cylinder width. The governing equations are solved numerically through finite volume method based on SIMPLE algorithm on a staggered grid system. Both P and L have a substantial influence on the flow structure, time-mean drag coefficient CD, fluctuating (rms) lift coefficient (CL'), and Strouhal number St. The changes in P and L leads to four distinct flow regimes (I, II, III and IV). Following the flow structure change, the C d , C i , and S t all vary greatly with the change in L and/or P. The CD and CL' both grow with increasing P and/or L. The St increases with P for a given L, being less sensitive to L for a smaller P (< 2) and more sensitive to L for a larger P (> 2). A strong relationship is observed between the flow regimes and the values of CD, CL' and St. An increase in P affects the pressure distribution more on the top surface than on bottom surface while an increase in L does the opposite. [ABSTRACT FROM AUTHOR]

A numerical investigation is carried out to analyze the flow patterns, drag and lift coefficients, and vortex shedding around a square cylinder using a control circular bar upstream and downstream. Lattice Boltzmann method (LBM) was used to investigate flow over a square cylinder controlled by upstream and downstream circular bar, which is the main novelty of this study. Compared with those available results in the literature, the code for flow over a single square cylinder proves valid. The Reynolds number (Re) based on the width of the square cylinder () and diameter of circular bar () are 100 for square cylinder, 30 and 50 for different circular bars. Numerical simulations are performed in the ranges of and , where and are the center-to-center distances between the bar and cylinder. Five distinct flow patterns are observed in the present study. It is found that the maximum percentage reduction in drag coefficient is 59.86% by upstream control bar, and the maximum percentage reduction in r.m.s. lift coefficient is 73.69% by downstream control bar. By varying the distance ratio for the downstream control bar, a critical value of distance ratio is found where there are two domain frequencies. [ABSTRACT FROM AUTHOR]

The phenomenon of flow-induced vibration (FIV) over a square cylinder at Reynolds numbers, Re = (3.6–12.5 × 10 3 ) is numerically studied. This current study provides a detailed explanation of the behaviour of transverse motion of square cylinder with the mass damping ratio, m ζ *  = 2.48. The computation of FIV is conducted by numerical simulation based on the Unsteady Reynolds Navier-Stokes (URANS) flow field using OpenFOAM software. The first part of the numerical simulation consists of an isolated square cylinder to validate the solution with previous studies. The computation of FIV with a total number of cells, N = 101,662 have shown a comparable pattern of amplitude curve. The coexistence of vortex-induced vibration (VIV) and galloping is observed for a single isolated cylinder. A downstream flat plate is introduced in the second part of the work. Different gaps separation between the cylinder and flat plate (0.1  ⩽ G/D ⩽ 3) are simulated. Based on the amplitude curve against reduced velocities 4 ⩽ U R ⩽ 20, four regimes are identified. According to the power estimation, the optimum gap separation is G/D = 0.1. The harnessed power is higher than a single isolated square cylinder while preserving the robustness for the remote harvesting purpose. [ABSTRACT FROM AUTHOR]

This study investigated vortex-induced vibrations of a slender square-section cylinder inclined from the vertical direction by a series of angles experimentally. Both aeroelastic tests and pressure measurements were performed on the cylinder with forward inclinations (inclined to the upwind direction), a vertical attitude, and backward inclinations (inclined to the downwind direction) in a wind tunnel. The cylinder was kept stationary in the pressure measurement tests. The aeroelastic test results show that vortex-induced responses of the cylinder decrease considerably as increasing the forward inclination angle. By contrast, the effect of the backward inclination on the vortex-induced vibration varies. Not all the backward inclined cylinders exhibit crosswind responses smaller than those of the vertical cylinder does. The responses of the cylinder with a small backward inclination are significantly larger, whereas the cylinder with a large backward inclination exhibits lower responses than those of the vertical case. The variation in the vortex-induced vibration response with the inclination is explained by performing power spectral analyses on the pressure data on the side face over the cylinder span, which reveals local vortex shedding characteristics. The findings provide significant guidance to the wind-resistant design of an inclined slender structure. [ABSTRACT FROM AUTHOR]

The natural ocean/river currents energy can be harvested using Flow Induced Motion (FIM) phenomena. The effect of damping-ratio and mass-ratio on Flow Induced Motion energy harnessing of a square cylinder are numerically investigated for Reynolds number 15500 < Re < 232000 (0.2 m/s < flow velocity <3.0 m/s). Four typical regions can be observed in the Flow Induced Motion responses, including Vortex Induced Vibration (VIV) Initial Branch, Vortex Induced Vibration Upper Branch, Vortex Induced Vibration-Galloping Transition and Galloping. Results indicate that as the velocity increases, the number of vortices shed per cycle increases, and the harnessed power increases without upper limit. The energy conversion efficiency increases up to the highest value until the Vortex Induced Vibration upper branch. Then, it starts decreasing and tends to a relatively small value in the galloping region. Increasing mass-ratio will shorten the velocity range of Vortex Induced Vibration. High damping-ratio has a negative impact on oscillation amplitude, but provides a boost for energy harnessing. In all tests, the power (143 W) is considerable at damping-ratio = 0.6. As the damping-ratio reaches up to 0.8 (nearing critical damping), galloping will no longer occur. [ABSTRACT FROM AUTHOR]

In the present study, the effect of corner modifications on fluid flow and heat transfer characteristics across a square cylinder has been analyzed numerically in an effort to improve thermohydraulic parameters. Two-dimensional simulations have been carried out for laminar flow across a square cylinder with sharp, round, chamfered and recessed corners for Reynolds number range 55–200. Corner variations have been made for dimension c/D = 0.125, where c and D indicate corner size and cylinder diameter respectively. When compared with the sharp-cornered cylinder, the results illustrated that corner modifications lead to significant drag reduction, however, the penalty in terms of Strouhal number increment is comparatively low. Deflected flow from upstream modified corners promotes flow separation from downstream corners in contrast to the sharp-cornered cylinder results in narrow wake width with intense fluid circulations, farther vortex shedding location and consequently reduced pressure drag as well as improved heat transfer coefficients. Recirculating fluid inside the upstream corner cut of recessed corners additionally contributes towards drag increment as compared to other corner configurations. Results also indicate that upstream corners modifications are more influential in amelioration of thermohydraulic characteristics as compared to downstream corners. Moreover, a new correlation for the average Nusselt number has been developed as a function of Reynolds number. [ABSTRACT FROM AUTHOR]

In this study, the flow characteristics around two tandem square and equilateral triangle cylinders have been experimentally investigated. Experiments were conducted in an open-circuit subsonic wind tunnel with maximum free-stream turbulence level of 0.3%. Investigations for tandem arrangement were performed by moving the downstream square cylinder along the flow direction at various distances from the upstream triangular cylinder. Measurements were performed using 32-channel pressure transducer, three-component balances and hotwire anemometer. Square cylinder was placed at various distances from the upstream triangular cylinder and the flow Reynolds numbers were chosen to be 26000, 37000, 46000, and 51000. In this study, the mean and fluctuating lift and drag forces were measured for square cylinder at different spacings. Also, the distribution of mean and fluctuating surface pressure on the two-cylinders were measured. The vortex shedding frequency was measured by using both hotwire and surface pressure fluctuations on both cylinders and the results obtained by these two different measurement methods were compared. One of the most important outcome of the present study is the observation of two different flow patterns. It is noticed that the vortex shedding from the upstream cylinder was eliminated for cylinder distances lower than the critical spacing while for distances more than the critical spacing, the vortex shedding occurs from both triangular and square cylinders. The critical distance for this arrangement was obtained to be around three times of the length of the side length of the cylinders. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the distributed blowing control of the flow around a square cylinder at a low Reynolds number of R e = 200. The air holes are placed at the windward or leeward stagnation points. The control effect of the unsteady aerodynamic forces is notably different with different spanwise distributions of air holes, which is represented by the dimensionless air hole area ratio G. The simulation results indicate that the windward blowing control (WBC) shows better control effect than the leeward blowing control (LBC) in reducing the time-averaged drag coefficient C d ¯ of the square cylinder while the fluctuating lift coefficient C l ′ can be significantly suppressed by the LBC. Besides, the surface pressure distribution, the turbulence kinetic energy (TKE) and Reynolds shear stress (RSS) distributions and the shedding vortices in the wake are analysed and compared in detail under different control conditions. Finally, through the instantaneous 3D vortex structures and the spanwise fluctuating velocity w ′ distribution in the flow field, the suppression of the unsteady aerodynamic forces is mainly related to the 3D vortex pairs induced by the blowing jet. • Distributed blowing was employed to control the flow around a square cylinder. • The spanwise distribution of air holes notably affected the steady blowing flow control. • A 'Six-Vortices Type' vorticity distribution appeared in the flow field under windward blowing control. [ABSTRACT FROM AUTHOR]

Based on the fact that the drag coefficient is relatively insensitive to the Reynolds number in many experiments on the flow past a sharp-edged bluff body (SEBB) at high Reynolds numbers, it is speculated that the effect of the wall viscosity on the aerodynamics of the SEBB can be neglected to some extent. To validate this hypothesis for the large-eddy simulation (LES), the slip-wall boundary condition was applied to the SEBB, and this LES was termed slip-wall LES (SWLES). The flow past a square cylinder was chosen to validate the SWLES. The aerodynamic parameters, such as the drag coefficient and Strouhal number, agreed well with the experimental data and those of the traditional wall-resolved LES (WRLES). The surface pressure distributions and energy spectra were close to those of the WRLES. The Kelvin–Helmholtz instability structures, flow separation, and von Kármán vortex shedding were captured accurately by the SWLES. The computational cost was compared with that of the WRLES. An interpretation of the SWLES was discussed based on flow visualizations. After the validation, the SWLES was applied to the flow past a photovoltaic system. The wind loads of the system were compared with the wind tunnel experimental data at different incident angles. The surface pressure distributions, flow structures, and wake were analyzed. The present study demonstrated that the SWLES has potential applications for the flow around an SEBB with a much lower cost than that of the WRLES. • Slip-wall large-eddy simulation (SWLES) is proposed for the flow past a sharp-edged bluff body at high Reynolds numbers. • The SWLES was validated via the flow past a square cylinder. • The SWLES was applied on the flow past a photovoltaic system. • SWLES obtained an accuracy similar to that of the wall-resolved large-eddy simulation with much lower computational cost. [ABSTRACT FROM AUTHOR]

The present work is an experimental investigation of flow control over a square cylinder using an attached splitter plate. The experiments are mainly conducted at a Reynolds number of 485. A splitter plate of varying length from 0 to 6 times of the cylinder width is attached to the rear side of the square cylinder to control the flow. The thickness of the splitter plate is kept constant at 10% of cylinder width. The flow interference of a square cylinder with an attached splitter plate is observed using PIV, Hot wire and flow visualization techniques. The primary focus is given on the flow structure and related forces. From the experiments, it has been observed that a secondary vortex appears at the tail edge of the plate after a particular length of the splitter plate. This vortex rotation is opposite to the main vortex and it influences the primary vortex shedding as well as shear layer formation. As a result, the plate modifies the wake size and flow structure behind the cylinder. The drag coefficient and the Strouhal number decrease with an increase in splitter plate length. A correlation is found between the splitter plate length, Reynolds number, and the drag coefficient. The effect of the splitter plate length on the flow field is also studied in terms of velocity, vorticity, streamlines, recirculation length, and turbulence statistics. [ABSTRACT FROM AUTHOR]

A numerical study has been carried out to elucidate the effects of rounding the sharp edges on flow-induced forces on a square cylinder immersed in a laminar cross flow. Rounding reduces both the upstream stagnation pressure and the downstream base pressure. Consequently, competition between these two pressure reductions yields the minimum drag on the cylinder when its edges are partially rounded. It was also found that the leading-edge rounding is mainly responsible for the topological change thus the drag reduction, while the trailing- edge rounding alone just enhances lift fluctuation. However, trailing-edge rounding plays a role of stabilizing the flow when all of the four edges are rounded. [ABSTRACT FROM AUTHOR]

The mixed convective momentum and heat transfer phenomena of confined square cylinders in non-Newtonian nanofluids are numerically investigated. The experimental thermophysical properties of alumina-water-based nanofluids are adopted from literature and these nanofluids obey shear-thinning power-law type non-Newtonian behavior. The square cylinder is confined in a vertical channel with a confinement ratio of 0.1333. The flow is assumed to be two-dimensional and the fluid is allowed to flow in upward direction across the confined square cylinder in the vertical channel. The aiding/opposing buoyancy in the flow is incorporated in terms of Richardson number ( Ri) in the range of -2 to 2. The ranges of other dimensionless parameters considered are: Reynolds number, Re: 1 to 40; and volume fraction of nanoparticles, ϕ: 0.005 to 0.045. This range of volume fraction of nanoparticles (i.e., ϕ = 0.005 to 0.045) corresponds to the power-law index ( n) of a non-Newtonian nanofluid in the range of n = 0.88 to 0.5, respectively. Prior to obtaining new results, the solution methodology is validated with existing literature counterparts. Finally, effects of the Reynolds number, Richardson number, and the rheology of non-Newtonian nanofluids on streamline patterns, surface pressure, surface vorticity, drag coefficients, isotherm contours, local and average Nusselt numbers are delineated. [ABSTRACT FROM AUTHOR]

In Large Eddy Simulation (LES), the cost of resolving the boundary layer on a solid wall boundary is high. One way to overcome this difficulty is to employ a wall model that can provide the approximate wall boundary conditions into the LES solution. In addition to the wall model, selecting a proper sub-grid model in the LES solution can affect computational time. In this study, the applicability of the Smagorinsky sub-grid model and of a simple wall model was investigated by simulating the turbulent flow past the square and circular cylinders, which are relevant case-studies for marine structures supported by piles. The simple wall model is based on the turbulent boundary layer equations. A solution procedure was developed to solve the set of the flow equations and then calculations were performed by considering different values of the Smagorinsky coefficient and different definitions to compute the spatial filter width scale. The corresponding numerical results are in good agreement with those extracted from available experimental and numerical data at different cylinder Reynolds numbers. The solution procedure used in this study has low computational cost such that all calculations could be performed on a single computer in a short period of time. [ABSTRACT FROM AUTHOR]

Three-dimensional unsteady flow and heat transfer from an isothermal square cylinder subjected to crossflow of air is numerically investigated. The governing continuity, momentum and energy equations are solved using implicit fractional step method. The first order spatial derivatives are discretized using a third-order upwind scheme while the second order derivatives from the viscous terms are discretized by central-difference formula. The momentum equations are solved separately using Crank-Nicholson time-stepping method. The Poisson type equations are solved using Jacobi method with Chebyshev acceleration procedure. The heat transfer characteristics of a square cylinder subjected cross flow of air and the three-dimensionality of the flow and its effects are assessed. Three dimensional instantaneous isotemperature surfaces and in the wake region and local Nusselt number variations on the cylinder surfaces along z-axis were provided. The time histories of the Nusselt numbers at the cylinder surfaces are obtained. Also instantaneous and mean deviation of the local Nusselt numbers on the cylinder surfaces both in spanwise direction and x-y plane are provided for Re = 185 and 250 which are representative of typical A-mode and B-mode vortex structures in spanwise direction respectively. [ABSTRACT FROM AUTHOR]

In the present research aeroacoustic characteristics of flow over a finite height wall mounted square cylinder at different angles of attack is investigated. The aspect ratio of the model and the boundary layer thickness were 7 and훿⁄퐷 = 4.27, respectively. The experiments were done in an acoustically improved aerodynamic wind tunnel. The purpose of this study is to identify correlation between the fluid and the acoustic fields. The flow-induced noise was measured using single microphone. The measured noise is related to aerodynamic characteristics of the flow using a single hot wire. The flowinduced noise of the cylinder is characterized in terms of frequency and magnitude. A sharp peak was observed in the far-field pressure at the vortex shedding frequency which was measured with hot wire anemometer. So, it could be concluded that vortex shedding is a source of aerodynamic noise generation. The Strouhal number obtained from two devices was almost equal to 0.11 which is in agreement with previous studies. Also, maximum vortex shedding frequency was measured for 훼 = 15°. It is observed that sound pressure level is increased with increasing upstream velocity. The overall sound pressure level ranged between 84.2 and 110.95 (dB) for upstream velocities in the range of 5-15 (m/s). The angle of attack has no important effect on overall sound pressure level. [ABSTRACT FROM AUTHOR]

The reduction in the drag and lift forces on a square cylinder is obtained by attaching an extended solid (thorn) with it positioned at the front stagnation point and at the rear stagnation point separately at low Reynolds number, Re = 40, 100 and 180. The effect of variation of thorn length ( l′ = 0.2, 0.4 and 0.6) and inclination angle ( θ = 5°, 10°, 15° and 20°) on the drag, lift and this effect is forecasted by the ANN (artificial neural network) and GEP (gene expression programming). The required input and output data to train the ANN and GEP models have been taken from the available published results of the present authors (Dey and Das in Eng Sci Technol 18:758-768 [2015]; in Ain Shams Eng J 6:929-938 [2015]). It is found that the drag and lift are minimized by 16 and 46 % for Re = 100, respectively, and 22 and 60 % for Re = 180 compared to a square model. It has been perceived that both the prediction tools (ANN and GEP) can forecast the aerodynamic behavior correctly and quickly within the given range of the training data than simulation, which takes much longer time to complete the computation. It is further observed that the GEP model is much efficient than the ANN model. [ABSTRACT FROM AUTHOR]

A detailed numerical investigation of the flow behind a square cylinder at a Reynolds number of 21,400 is conducted to assess the ability of the delayed detached-eddy simulation (DDES) modeling approach to accurately predict the velocity recovery in the wake of a bluff body. Three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) and DDES simulations making use of the Spalart-Allmaras turbulence model are carried out using the open-source computational fluid dynamics (CFD) toolbox OpenFOAM-2.1.x, and are compared with available experimental velocity measurements. It is found that the DDES simulation tends to overestimate the averaged streamwise velocity component, especially in the near wake, but a better agreement with the experimental data is observed further downstream of the body. The velocity fluctuations also match reasonably well with the experimental data. Moreover, it is found that the spanwise domain length has a significant impact on the flow, especially regarding the fluctuations of the drag coefficient. Nonetheless, for both the averaged and fluctuating velocity components, the DDES approach is shown to be superior to the URANS approach. Therefore, for engineering purposes, it is found that the DDES approach is a suitable choice to simulate and characterize the velocity recovery in a wake. [ABSTRACT FROM AUTHOR]

The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already known that a sharp edge square cylinder would undergo galloping if it is subjected to uniform flow. In this study the influence of the wake of a fixed circular cylinder on the response of a downstream square cylinder at different spacing ratios ( S/D = 4, 8, 11) is experimentally investigated. The subject appears not to have received previous attention. The lateral displacements, lift forces and the pressure data from gauges mounted in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 7.7 × 10 2 to 3.7 × 10 4 . In contrast to that for two circular cylinders in tandem arrangement, the freely mounted downstream square cylinder displays a VIV type of response at all spacing ratios tested. There is no sign of galloping or wake induced galloping with the square cylinder. With increase at the spacing ratio the cross-flow oscillations decrease. It is shown that the vortices arriving from the upstream fixed circular cylinder play a major role on the shedding mechanism behind the downstream square cylinder and cause the square cylinder to shed vortices with frequencies above Strouhal frequency of the fixed square cylinder (St = 0.13). The VIV type of oscillations in the downstream square cylinder is most probably caused by the vortices newly generated behind the square cylinder. [ABSTRACT FROM AUTHOR]

An unsteady two-dimensional laminar forced convection heat transfer around a square cylinder with the rounded corner edge is numerically investigated for Re = 80-180 and non-dimensional corner radius, r = 0.50-0.71 at Pr = 0.71 (Air). A structured non-uniform mesh is used for the computational domain discretization, and the finite-volume-method-based commercial code FLUENT is used for numerical simulation. The heat transfer characteristics over the rounded corner square cylinder are analyzed with average Nusselt number ( Nu ) at various Re and various corner radii. The heat transfer characteristic is predicted by gene expression programming (GEP), and the GEP-generated explicit equation of Nu is utilized in particle swarm optimization to optimize the corner radii for maximum heat transfer rate. The data required for the training the GEP model have been collected from the authors' recent published article (Neural Comput Appl, 2015. doi:). It is found that the heat transfer rate of a circular cylinder can be enhanced 12 % by introducing a new cylinder geometry of corner radius r = 0.51. [ABSTRACT FROM AUTHOR]

A numerical study of the consequence of the corner roundness of a square cylinder and nanofluid volume fraction on the warmth transmission and fluid flow phenomenon were studied at low Re (Re = 100). The existing nanofluid is made by blending the water with copper nanoparticles, and the blending percentage is in the range of 0-15 % and the corner radius is varying from 0.5 D (circle) to 0.71 D (square). The numerical solution is accomplished by a FVM-based code. The fluid flow and the warmth transmission characteristics of the sharp and curved surrounded square chamber were considered with the vorticity, isotherm contours, drag and lift coefficients, local Nusselt number (Nulocal) and average Nusselt number (Nuavg) at various volume fractions and for several corner roundness. It is found that the heat transfer amount is maximum at r = 0.51, whereas at r = 0.50, the fluid forces are least for the every volume fractions. [ABSTRACT FROM AUTHOR]

Ｗｉｔｈ ｔｈｅ ｄｅｖｅｌｏｐｍｅｎｔ ｏｆ ｏｆｆｓｈｏｒｅ ｅｎｇｉｎｅｅｒｉｎｇ， ｉｎｃｒｅａｓｉｎｇ ａｔｔｅｎｔｉｏｎ ｈａｓ ｂｅｅｎ ｄｅｖｏｔｅｄ ｔｏ ｔｈｅ ｓａｆｅｔｙ ｏｆ ｔｈｅ ｕｎｄｅｒｗａｔｅｒ ｓｔｒｕｃｔｕｒｅｓ， ｓｕｃｈ ａｓ ｔｈｅ ｂｏｔｔｏｍ⁃ｓｕｐｐｏｒｔｅｄ ｐｉｌｅｓ ｏｆ ｏｆｆｓｈｏｒｅ ｏｉｌ ｄｒｉｌｌｉｎｇ ｐｌａｔｆｏｒｍｓ ａｎｄ ｏｆｆｓｈｏｒｅ ｐｅｔｒｏｌｅｕｍ ｐｉｐｅｌｉｎｅｓ． Ｆｏｒ ｉｎｔｅｒｎａｌ ｓｏｌｉｔａｒｙ ｗａｖｅｓ （ＩＳＷｓ） ｅｘｅｒｔ ａ ｎｅｇｌｅｃｔｅｄ ｉｎｆｌｕｅｎｃｅ ｏｎ ｔｈｅ ｓａｆｅｔｙ ｏｆ ｕｎｄｅｒｗａｔｅｒ ｓｔｒｕｃｔｕｒｅｓ， ｓｔｕｄｙｉｎｇ ＩＳＷ ｆｏｒｃｅｓ ａｃｔｉｎｇ ｏｎ ｃｙｌｉｎｄｅｒｓ ｉｓ ｈｉｇｈｌｙ ｓｉｇｎｉｆｉｃａｎｔ． Ｏｎｌｙ ａ ｆｅｗ ｓｔｕｄｉｅｓ ｈａｖｅ ｂｅｅｎ ｃｏｎｄｕｃｔｅｄ ｏｎ ＩＳＷ ｆｏｒｃｅｓ ａｃｔｉｎｇ ｏｎ ｃｙｌｉｎｄｅｒｓ， ａｎｄ ｓｔｕｄｉｅｓ ｔｈａｔ ｃｏｍｐａｒｅ ｔｈｅ ｆｏｒｃｅｓ ａｃｔｉｎｇ ｏｎ ｃｉｒｃｕｌａｒ ａｎｄ ｓｑｕａｒｅ ｃｙｌｉｎｄｅｒｓ ｉｎ ａ ｓｔｒａｔｉｆｉｅｄ ｆｌｕｉｄ ｅｎｖｉｒｏｎｍｅｎｔ ａｒｅ ｓｃａｒｃｅ． Ｅｘｐｅｒｉｍｅｎｔａｌ ｉｎｖｅｓｔｉｇａｔｉｏｎｓ ｏｆ ｔｈｅ ｆｏｒｃｅｓ ｅｘｅｒｔｅｄ ｂｙ ＩＳＷｓ ｏｎ ｃｉｒｃｕｌａｒ ａｎｄ ｓｑｕａｒｅ ｃｙｌｉｎｄｅｒｓ ａｒｅ ｐｅｒｆｏｒｍｅｄ ｉｎ ａ ｓｔｒａｔｉｆｉｅｄ ｆｌｕｉｄ ｔａｎｋ ｕｓｉｎｇ ａ ｎｅｗ ｄｅｖｉｃｅ ｔｏ ｇｅｎｅｒａｔｅ ＩＳＷｓ ａｎｄ ａ ｍｅａｓｕｒｅｍｅｎｔ ｓｙｓｔｅｍ ｆｏｒ ＩＳＷｓ ｌｏａｄｓ． Ｃｏｍｐａｒｉｓｏｎｓ ｏｆ ＩＳＷ ｆｏｒｃｅ ｂｅｈａｖｉｏｒｓ ｉｎ ｔｈｅ ｔｗｏ ｃｙｌｉｎｄｅｒｓ ａｒｅ ｓｔｕｄｉｅｄ ａｔ ｖａｒｉｏｕｓ ＩＳＷ ａｍｐｌｉｔｕｄｅｓ． Ｒｅｓｕｌｔｓ ｓｈｏｗ ｔｈａｔ ｔｈｅ ｆｏｒｃｅｓ ｅｘｅｒｔｅｄ ｏｎ ｔｈｅ ｃｉｒｃｕｌａｒ ａｎｄ ｓｑｕａｒｅ ｃｙｌｉｎｄｅｒｓ ｉｎｃｒｅａｓｅ ｗｉｔｈ ｉｎｃｒｅａｓｉｎｇ ｗａｖｅ ａｍｐｌｉｔｕｄｅｓ． Ａｔ ｔｈｅ ｓａｍｅ ｗａｖｅ ａｍｐｌｉｔｕｄｅ， ｔｈｅ ＩＳＷ ｆｏｒｃｅｓ ｏｎ ｔｈｅ ｓｑｕａｒｅ ｃｙｌｉｎｄｅｒ ａｒｅ ｌａｒｇｅｒ ｔｈａｎ ｔｈｏｓｅ ｏｎ ｔｈｅ ｃｉｒｃｕｌａｒ ｃｙｌｉｎｄｅｒ． Ｔｈｉｓ ｓｔｕｄｙ ｐｒｏｖｉｄｅｓ ｇｕｉｄａｎｃｅ ｆｏｒ ｃｙｌｉｎｄｅｒ ｄｅｓｉｇｎ ａｎｄ ｓａｆｅｔｙ ｅｖａｌｕａｔｉｏｎ ｉｎ ａ ｓｔｒａｔｉｆｉｅｄ ｆｌｕｉｄ ｅｎｖｉｒｏｎｍｅｎｔ． [ABSTRACT FROM AUTHOR]

Passive control of vortex shedding behind a square cylinder at incidence has been conducted experimentally by using a stationary splitter plate for the Reynolds numbers of 3.0×10 4 . The splitter plate was located at the center of the rear face of the square cylinder in tandem. The width of the cylinder and the plate were both chosen to be 30 mm and the incidence angle of the square cylinder was rotated between 0° to 45°. In this study, the combined effects of the splitter plate and angle of incidence on the pressure distributions and vortex-shedding phenomenon were investigated. Vortex shedding frequency was obtained from velocity measurements and aerodynamic force coefficients acted on the cylinder were calculated from pressure distributions. Characteristics of the vortex formation region and location of the flow attachments, reattachments and separation were observed by using the smoke–wire flow visualization technique. For the case with the plate, there is a sudden jump in the Strouhal number in the vicinity of 13° which corresponds to a minimum value of the drag coefficient. At zero angle of incidence, Strouhal number and a drag coefficient of the square cylinder decreased about 20% by means of the splitter plate. Drag reduction was minimum at about 13° and reached its maximum value at about 20°. [ABSTRACT FROM AUTHOR]

In this paper, the numerical investigations for drag reduction and vortex shedding suppression behind a square cylinder are carried out in presence of small control cylinders placed both at upstream and downstream locations of main cylinder. The numerical computations are performed in the ranges of $$80 \le Re \le 200$$ and $$0.5 \le g \le 6$$ , (where Re is the Reynolds number and g is the gap spacing between the control cylinders and main square cylinder, respectively) using a single relaxation time lattice Boltzmann method (SRT-LBM). Firstly, the present code is validated for flow past a single square cylinder at different Reynolds numbers. The effects of Re and g are investigated in terms of vortex shedding frequency, time-history analysis of drag and lift coefficients, energy spectra analysis of lift coefficient, vorticity contours visualization and forces exerted on the cylinder. Three different types of flow patterns are observed at different combinations of Reynolds numbers and gap spacings. The maximum reduction in the mean drag force and root-mean-square value of lift coefficient is found. Furthermore, the applications of SRT-LBM for suppression of vortex shedding and reduction in the drag force are also discussed. [ABSTRACT FROM AUTHOR]

Flow characteristics and sound pressure level in the acoustical far field and on the surface of a square cylinder at incidence are investigated for six angles of attacks. Flow around square cylinder is modeled using large eddy simulation method. The flow simulation is conducted using fluent commercial software. The results of the present study showed good agreement with the available experimental results. The minimum of drag coefficient, mean and root mean squared (rms) value of lift coefficient, and sound pressure level in acoustical far field occurred at 13o angle of attack which is due to the lowest values of fluctuating lift and drag forces at this angle of attack. The induced acoustic field is due to the fluctuating lift force acting on the rod. [ABSTRACT FROM AUTHOR]

The flow around a horizontal square cylinder with uniform suction or injection at the front and rear sides is considered in the present paper. The problem is investigated numerically with a finite volume method using the SIMPLE algorithm. This flow has been investigated in the past for Reynolds numbers greater than 70. In the present work, the investigation is extended to very low Reynolds numbers (up to 0.001, Stokes flow) including eight different cases concerning suction-injection at the two sides. It is found that the drag coefficient takes negative and zero values in many cases and varies linearly at low Re numbers. In all eight cases, the vortices around the cylinder have been calculated. It is found that at low Re numbers, some vortices are symmetrical both about the horizontal and vertical cylinder axes. [ABSTRACT FROM AUTHOR]

A two-dimensional numerical study is carried out to analyze the drag reduction and vortex shedding suppression behind a square cylinder in presence of splitter plate arranged in upstream, downstream and both upstream and downstream location at low Reynolds number (Re = 160). Computations are performed using a Single relaxation time lattice Boltzmann method (SRT-LBM). Firstly, the code is validated for flow past a single square cylinder. The obtained results are compared to those available in literature and found to be in good agreement. Numerical simulations are performed in the ranges of 1 ≤ L ≤ 4 and 0 ≤ g ≤ 7, where L and g are the length of splitter plate and gap spacing between the splitter plate and main square cylinder, respectively. The effect of these parameters on the vortex shedding frequency, time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualization and force exerted on the cylinder are quantified together with the observed flow patterns around the main cylinder and within the gap spacings. The observed results are also compared with a single square cylinder without splitter plate. We found that at some combinations of L and g, the mean drag coefficient and Strouhal number reach either its maximum or minimum value. It is found that the drag is reduced up to 62.2 %, 13.3 % and 70.2 % for upstream, downstream and dual splitter plates, respectively as compared to a single square cylinder (without splitter plate). In addition, in this paper we also discussed the applications of SRT-LBM for suppression of vortex shedding and reduction of the drag coefficients. [ABSTRACT FROM AUTHOR]

Many previous studies have been conducted to investigate wind-induced galloping of slender structures or structural members. While some recent studies have examined the particular problem of galloping involving coupling between vibration components about the principal axes, few occurrences of such vibrations of full-scale structures have been reported. This paper presents a comprehensive investigation that incorporates full-scale and wind tunnel experiments and an analytical formulation to study the galloping oscillation of a type of slender tower. The full-scale and wind tunnel experiments were conducted to assess the characteristics of the oscillations, their correlation with the wind characteristics, as well as the core parameters that influence the interaction between the tower and the wind. Based on the results from the experiments, a state-space model for coupled galloping of slender towers is formulated. This model enables the prediction of the susceptibility of a slender tower to galloping instability through an evaluation of the net damping resulting from the wind-structure interaction. The tower subjected to monitoring in the full-scale study is used as an example structure in an illustrative application of the analytical model. [ABSTRACT FROM AUTHOR]

Numerous works have been conducted to study the wake control of a bluff body and more efficient strategies are still what we seek for. This paper studies the complex fluid–structure interaction (FSI) problem of a square cylinder mounted with dual flexible splitter plates from a new perspective: impinging the vortex core with flapping plate tip. The Reynolds number (Re) based on the side length of the square cylinder is fixed at 332.6. The splitter plates are attached at both sides of the square cylinder. Structural parameters, such as plate length and bending stiffness, are considered to achieve an optimal arrangement of this configuration. Compared to the traditional single splitter plate arrangement, only a short splitter length is needed for this dual splitter plates configuration. Flow visualization indicates that the drag reduction is associated with the increase of base pressure and the lift suppression is related to the inhabitation of the interaction of the shear layer and split effect of the tip vortices. The dimensionless bending stiffness plays a vital role in determining the behavior of the splitter plate. Two vibration modes, i.e., off-center vibration and asymmetry vibration modes are captured and the up and down splitter plates tend to vibration in-phase. The Lissajous trajectories of the free tip mainly exhibits arc-shape and sickle-shape. Given the performance of the square cylinder-dual splitter plates configuration, splitter length of l / L = 1. 5 is an optimal configuration, which is less affected by flexural rigidity. The maximum drag reduction could reach 23.1% and the lift force exerting on this configuration does not increase significantly, which is beneficial for the structural stability. • Wake control from a new perspective: impinging the vortex core with plate tip. • Pronounced drag reduction of a square cylinder with dual splitter plates. • Gap flow plays a vital role in determining the vibration modes. • Mechanism elaboration of the dynamical system. [ABSTRACT FROM AUTHOR]