Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

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Two-dimensional laminar flow around three side-by-side rectangular prisms placed between two parallel walls is numerically investigated at a Reynolds number Re = 100. The cross-sectional aspect ratio of each prism is b/h = 3, where b and h are the prism width and height, respectively. The gap spacing (g) between the two adjacent prisms and between the wall and the outer prism is varied from g* (= g/h) = 0.8 to 3.4. The focus is given on the influence of g* on flow structures, Strouhal number (St), and fluid forces. Three distinct flow regimes are identified, namely single vortex street (0.8 ≤ g* &lt; 1.1), twin vortex streets (1.1 &lt; g* &lt; 2.1), and triple vortex streets (2.1 &lt; g* ≤ 3.4). Lift forces on the outer prisms are attractive for single vortex street and repulsive for twin and triple vortex streets. The St being identical for the three prisms exponentially declines from 0.39 to 0.18 with g* increasing from 0.8 to 3.4. Fluctuating lift and time-mean drag also shrink with increasing g*, time-mean drag becoming higher for the middle prism than for the outer prisms. Empirical relations of St and forces are obtained as a function of g*. © 2019 Elsevier Ltd

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Ocean Engineering

Effect of side walls on flow around prisms

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 (C′L), 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 CD , C′L, and St all vary greatly with the change in L and/or P. The CD and C′L 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 (&lt; 2) and more sensitive to L for a larger P (&gt; 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. © 2018 Techno-Press, Ltd.

Wind and Structures, An International Journal

Couette-Poiseuille flow based non-linear flow over a square cylinder near plane wall

A numerical investigation is conducted on the flow around and vibration response of an elastic square cylinder (side width ) in the wake of a stationary cylinder at Reynolds numbers of and 200 based on and the free-stream velocity. The downstream cylinder, referred to as the wake cylinder, is allowed to vibrate in the transverse direction only. The reduced velocity is varied from 1 to 30. Cylinder centre-to-centre spacing ratios of and 6 are considered. Simulations are also conducted for a single isolated cylinder, and the results are compared with those for the wake cylinder. The focus is given to vibration response, frequency response, fluctuating lift force, phase relationship between the lift and displacement, work done and the flow structure modification during the cylinder vibration. The results reveal that the dependence of the Strouhal number on can distinguish different branches more appropriately than that of the vibration amplitude on. The vibration response of the single cylinder at is characterized by the initial, lower and desynchronization branches. On the other hand, that at undergoes initial, lower and galloping branches. The galloping involves the characteristics of both the initial and the lower branches or the initial and the desynchronization branches depending on. For the wake cylinder, the gap flow has a significant impact on the vibration response, leading to (i) the absence of galloping at either and, (ii) the presence of an upper branch at, and (iii) an initial branch of different characteristics at,. The different facets are discussed in terms of wake structures, work done and phase lag between lift and displacement. © 2018 Cambridge University Press.

Journal of Fluid Mechanics

Vibrations of a square cylinder submerged in a wake

A numerical study is made of the shear flow past a square cylinder (of height A*) near a wall (at a gap height 0.5A*) in presence of a vortex generating upstream rectangular cylinder (of different heights a* and widths b*) placed at a fixed height 1.25A* in an offset tandem arrangement. Influence of fluctuating aerodynamic forces of the vortex generator (VG) on the downstream cylinder (DSC) is investigated based on parameters: spacing between the cylinders S(=D*/A*), ratio of heights r2=a*/A* (≤1), aspect ratio r1=b*/a* (≤1) and Reynolds number Re (based on A*). A formula is derived for local Rel=Re×(L+r2/2)×r2 to calculate the effective Re for the VG placed at height L. The critical Reynolds number Rer1-1.25 (at which the VG of r1=0.1, 0.5 and 1.0 starts to shed the vortices) is predicted (using the formula for Rel and the Lagrange interpolation based on the previous data for single cylinder) and validated in the present study of tandem arrangement. A linear relation between Rer1-1.25 and r1 is established to predict Rer1-1.25 and finally a region of finite volume in the r1ReS-space (for the values of r1, Rer1-1.25 and critical spacing Scr for fixed value of r2) is proposed in order to generate the unsteadiness in the steady flow of the DSC at lower Re. The governing unsteady Navier-Stokes equations are solved numerically through a finite volume method on a staggered grid system using QUICK scheme for convective terms. The results for the present case of offset arrangement are compared with that for the case of inline arrangement highlighting some of the major issues: generating the vortices by the VG, the appearance of multiple peaks in the spectra of fluctuating lift coefficient, and the deviation of the aerodynamic characteristics of the DSC from that of the isolated square cylinder. © 2016 Elsevier Ltd.

Computers and Fluids

Aerodynamic forces on square cylinder due to secondary flow by rectangular vortex generator in offset tandem: Comparison with inline

This study focuses on interactions of vortices generated by a family of eddy-promoting upstream rectangular cylinders (of different heights a∗and widths b∗) with the shear layers of a downstream square cylinder (of height A∗) placed near a plane in an in-line tandem arrangement under the incidence of Couette-Poiseuille flow based nonuniform linear/nonlinear velocity profile. The dimensionless operational parameters are cylinders spacing distance S, ratio of heights r2 = a∗/A∗(≤1), aspect ratio r1 = b∗/a∗(≤1), Reynolds number Re (based on the velocity at height A∗for Couette flow), ReU2 (based on the velocity at height 10A∗for Couette-Poiseuille flow), and nondimensional pressure gradient P at the inlet. The governing equations are solved numerically through a pressure-correction-based iterative algorithm (SIMPLE) with the quadratic upwind interpolation for convective kinematics (QUICK) scheme for convective terms. The major issue of appearing multiple peaks in the spectrum of the fluctuating lift coefficient of the downstream cylinder is addressed and justified exhibiting the flow patterns. While considering the rectangular shape (for the upstream cylinder) and nonlinear velocity (at the inlet), the possibility of generating the unsteadiness in the steady wake flow of the downstream cylinder at a Re (based on height a∗) less than the critical Re for the downstream cylinder is documented here. The dependence of flow characteristics of the downstream cylinder on the angle of incident linear velocity at specific S and r1 is also demonstrated here. It is observed that the discontinuous jump in the aerodynamic characteristics (due to a sudden change from one distinct flow pattern to the other in the critical spacing distance regime) is directly proportional to the height of the vortex generator. Increasing P under the same characteristic velocity causes the steady flow of cylinder(s) to convert to a periodic flow and reduces the critical spacing distance for the vortex generator. Copyright © 2015 by ASME.

Journal of Fluids Engineering, Transactions of the ASME

Interactions of vortices of a square cylinder and a rectangular vortex generator under Couette-Poiseuille flow

Numerically simulated results are presented for shear flow past a square cylinder (of height A) near a wall (at a gap height 0.5A) in the presence of a family of upstream rectangular cylinders (of different heights a and widths b≤a) in an offset tandem arrangement (towards the wall) in order to investigate the physical mechanism for the cessation of vortex shedding from the downstream cylinder due to this arrangement and the dependency of the aerodynamic characteristics of the downstream cylinder on the operational dimensionless parameters, Reynolds number Re, gap height L from the wall, spacing distance between the cylinders S, ratio of heights r2=a/A (≤1) and aspect ratio r1=b/a (≤1). The governing unsteady Navier-Stokes equations are solved numerically through SIMPLE algorithm with the QUICK scheme for convective terms. The strong dependency of diversion of the flow (away from the narrow passage between the downstream cylinder×.

Vortex shedding suppression and aerodynamic characteristics of square cylinder due to offsetting of rectangular cylinders towards a plane

Numerically simulated results are presented for shear flow past a square cylinder (of height a) near a wall (at a gap height 0.5a) in presence of eddy promoting rectangular cylinders (of fixed height a with different widths b≤a) to gain a better insight into the dependency of aerodynamic characteristics of both the cylinders on the parameters: spacing distance between the cylinders S (=D/a:0.5≤S≤20) and aspect ratio r (=b/a:0.1≤r≤1.0). The value of Reynolds number Re is kept as Re=100 and 200. The governing unsteady Navier-Stokes equations are solved numerically based on the finite volume method on a staggered grid system using QUICK scheme. The resulting equations are then solved by an implicit, time-marching, pressure correction-based SIMPLE algorithm. The influence of numerical parameters on the validated code used in this study is demonstrated here. The strong dependency of vortex shedding (from both the cylinders) on aspect ratio r and spacing distance S are explored and, hence, a region of finite area in the Sr-plane is proposed in order to generate the unsteadiness in the steady flow of the downstream cylinder. An attempt is made to identify the different flow regimes depending on the flow patterns of the downstream cylinder, associated with the geometrical parameters (S and r). Owing to the differences in the basic shedding frequency of the square (downstream) cylinder from that of the rectangular cylinder (promoter) of different widths, the major issue of appearing multiple peaks in the spectrum of fluctuating lift coefficient of the downstream cylinder is addressed. The thrust force observed on the downstream cylinder in presence of the thinner promoter at closely spaced arrangement is justified presenting the surface pressure distribution. Finally, the present numerical results at large spacing distances are certified with some previous numerical and experimental findings. © 2014 Elsevier Masson SAS.