scholarly journals A Numerical Investigation of Turbulent Flow Over Single and Tandem Square Cylinders

2021 ◽  
Vol 40 (4) ◽  
pp. 724-746
Author(s):  
Mahrukh Mahrukh ◽  
Usman Allauddin ◽  
Mohammed Ehteshamul Haque ◽  
Naseem Uddin ◽  
Ahmed Hussain
Keyword(s):  
Three Dimensional ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Shear Stresses ◽  
Square Cylinder ◽  
Tandem Arrangement ◽  
Square Cylinders ◽  
Contour Plots ◽  
Tandem Square Cylinders ◽  
Lift And Drag

This paper presents the three-dimensional flow investigations over the square cylinders placed in the tandem arrangement. Two different flow configurations were investigated in detail; one comprising of a single square cylinder and the other comprising of three square cylinders placed in a tandem arrangement with the spacing of six times the width (w) of each square cylinder. The Reynolds number based on the width of the square cylinder (w) and free stream velocity (Uo) is 22,000. The problem was solved numerically using an Unsteady Reynolds-Averaged Navier-Stokes (URANS) based model and Large Eddy Simulation (LES) based model. Strouhal Number, lift, and drag coefficients were computed for each configuration. By comparing both the models using contour plots of pressure, velocity and vorticity it is found that the LES model is more accurate to capture the turbulence around single and tandem square cylinders. In the tandem arrangement, complex periodic vortex shedding was observed in the wake of each square cylinder. The production of turbulent kinetic energy was also investigated to understand the roles of stresses during flow over the cylinders. The analysis showed that the production of turbulence by normal stresses is higher than that of shear stresses. Furthermore, it was observed that the flow over the first cylinder arranged in tandem is quite identical to that of the single square cylinder. Moreover, the upstream cylinder experienced a higher lift in comparison to the downstream cylinders.

Numerical Simulations of Turbulent Flow Over Two Surface-Mounted Tandem Square Cylinders

2017 ◽  
Author(s):  
Yukun Dai ◽  
Hong Wang ◽  
Cai Tian
Keyword(s):  
Turbulent Flow ◽  
Numerical Simulations ◽  
Wake Flow ◽  
Navier Stokes ◽  
Square Cylinder ◽  
Wake Effect ◽  
Simple Method ◽  
Square Cylinders ◽  
Tandem Square Cylinders ◽  
Turbulence Effect

Numerical simulations of wake flow generated by a surface-mounted square cylinder over a subsequent square cylinder are presented for incompressible low-Re turbulent flow. The behaviors of the square cylinder in the wake flow are investigated. A developed numerical method — Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) is adopted to solve the governing equations in steady state. Turbulence effect is modelled by Reynolds Averaged Navier Stokes (RANS) equations with a standard k-ω turbulence model. The k-ω SIMPLE method is validated by comparison with experimental data. The results show that in wake flow, the square cylinder produces a much weaker wake effect and is subjected to an inverse drag force.

Three-Dimensional Numerical Prediction of the Hydrodynamic Loads and Motions of Offshore Structures

2000 ◽  
Vol 122 (4) ◽  
pp. 294-300 ◽  
Author(s):  
Karl W. Schulz ◽  
Yannis Kallinderis
Keyword(s):  
Flow Structure ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Structural Response ◽  
Offshore Structures ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Hydrodynamic Loads ◽  
Drag Coefficients ◽  
Lift And Drag

A generalized numerical method for solution of the incompressible Navier-Stokes equations in three-dimensions has been developed. This solution methodology allows for the accurate prediction of the hydrodynamic loads on offshore structures, which is then combined with a rigid body structural response to address the flow-structure coupling which is often present in offshore applications. Validation results using this method are first presented for fixed structures which compare the drag coefficients of sphere and cylinder geometries to experimental measurements over a range of subcritical Reynolds numbers. Additional fixed structure results are then presented which explore the influence of aspect ratio effects on the lift and drag coefficients of a bare circular cylinder. Finally, the spanwise flow variations between a fixed and freely vibrating cylindrical structure are compared to demonstrate the ability of the flow-structure method to correctly predict correlation length increases for a vibrating structure. [S0892-7219(00)00904-3]

Vortex Shedding From Two Surface-Mounted Prismatic Obstacles in Lock-in Regime

2003 ◽  
Author(s):  
Robert J. Martinuzzi ◽  
Brian Havel
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Front Face ◽  
Thin Boundary Layer ◽  
Tandem Arrangement ◽  
Freestream Velocity ◽  
Square Cylinders ◽  
Shedding Frequency ◽  
Lock In

Periodic vortex shedding from two surface-mounted cubes, of height H, in tandem arrangement placed in a thin boundary layer is investigated for a spacing 2H using phase-averaged laser Doppler velocimetry measurements. Tests were conducted for a Reynolds number of 22000, based on H and the freestream velocity, and an approximately 0.07H thick laminar boundary layer. For this obstacle spacing, the shedding frequency scales linearly with the obstacle spacing. It is shown that in this lock-in regime, periodic shedding is triggered by the displacement of the vertical flow along the front face of the downstream obstacle and is thus different from that observed for two-dimensional cylinders in uniform streams. The existence of this three-dimensional effect is then used to explain why lock-in cannot be observed for square cylinders in tandem arrangement.

scholarly journals Prediction of Turbulent Flow Around a Square Cylinder With Rounded Corners

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
S. S. Dai ◽  
B. A. Younis ◽  
H. Y. Zhang
Keyword(s):  
Turbulent Flow ◽  
Vortex Shedding ◽  
Turbulence Closure ◽  
Navier Stokes ◽  
Square Cylinder ◽  
Mean Flow ◽  
Drag Forces ◽  
Turbulence Closures ◽  
High Reynolds ◽  
Lift And Drag

Predictions are reported of the two-dimensional turbulent flow around a square cylinder with rounded corners at high Reynolds numbers. The effects of rounded corners have proved difficult to predict with conventional turbulence closures, and hence, the adoption in this study of a two-equation closure that has been specifically adapted to account for the interactions between the organized mean-flow motions due to vortex shedding and the random motions due to turbulence. The computations were performed using openfoam and were validated against the data from flows past cylinders with sharp corners. For the case of rounded corners, only the modified turbulence closure succeeded in capturing the consequences of the delayed flow separation manifested mainly in the reduction of the magnitude of the lift and drag forces relative to the sharp-edged case. These and other results presented here argue in favor of the use of the computationally more efficient unsteady Reynolds-averaged Navier-Stokes approach to this important class of flows provided that the effects of vortex shedding are properly accounted for in the turbulence closure.

scholarly journals Three-Dimensional Hydro-Magnetic Flow Arising in a Long Porous Slider and a Circular Porous Slider with Velocity Slip

Mathematics ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 748 ◽  
Author(s):  
Naeem Faraz ◽  
Yasir Khan ◽  
Amna Anjum ◽  
Muhammad Kahshan
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Frictional Resistance ◽  
Mhd Flow ◽  
Velocity Slip ◽  
Convergent Series ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Homotopy Analysis ◽  
Lift And Drag

The current research explores the injection of a viscous fluid through a moving flat plate with a transverse uniform magneto-hydrodynamic (MHD) flow field to reduce sliding drag. Two cases of velocity slip between the slider and the ground are studied: a long slider and a circular slider. Solving the porous slider problem is applicable to fluid-cushioned porous sliders, which are useful in reducing the frictional resistance of moving bodies. By using a similarity transformation, three dimensional Navier–Stokes equations are converted into coupled nonlinear ordinary differential equations. The resulting nonlinear boundary value problem was solved analytically using the homotopy analysis method (HAM). The HAM provided a fast convergent series solution, showing that this method is efficient, accurate, and has many advantages over the other existing methods. Solutions were obtained for the different values of Reynolds numbers (R), velocity slip, and magnetic fields. It was found that surface slip and Reynolds number had substantial influence on the lift and drag of the long and the circular sliders. Moreover, the effects of the applied magnetic field on the velocity components, load-carrying capacity, and friction force are discussed in detail with the aid of graphs and tables.

The finite-length square cylinder near wake

2009 ◽  
Vol 638 ◽  
pp. 453-490 ◽  
Author(s):  
H. F. WANG ◽  
Y. ZHOU
Keyword(s):  
Flow Visualization ◽  
Flow Structure ◽  
Finite Length ◽  
Laser Doppler Anemometry ◽  
Three Dimensional ◽  
Width Ratio ◽  
Stream Velocity ◽  
Cylinder Wake ◽  
Square Cylinder ◽  
Near Wake

This paper reports an experimental investigation of the near wake of a finite-length square cylinder, with one end mounted on a flat plate and the other free. The cylinder aspect ratio or height-to-width ratio H/d ranges from 3 to 7. Measurements were carried out mainly in a closed-loop low-speed wind tunnel at a Reynolds number Red, based on d and the free-stream velocity of 9300 using hot-wire anemometry, laser Doppler anemometry and particle image velocimetry (PIV). The planar PIV measurements were performed in the three orthogonal planes of the three-dimensional cylinder wake, along with flow visualization conducted simultaneously in two orthogonal planes (Red = 221). Three types of vortices, i.e. the tip, base and spanwise vortices were observed and the near wake is characterized by the interactions of these vortices. Both flow visualization and two-point correlation point to an inherent connection between the three types of vortices. A model is proposed for the three-dimensional flow structure based on the present measurements, which is distinct from previously proposed models. The instantaneous flow structure around the cylinder is arch-type, regardless of H/d, consisting of two spanwise vortical ‘legs’, one on each side of the cylinder, and their connection or ‘bridge’ near the free end. Both tip and base vortices are the streamwise projections of the arch-type structure in the (y, z) plane, associated with the free-end downwash flow and upwash flow from the wall, respectively. Other issues such as the topological characteristics, spatial arrangement and interactions among the vortical structures are also addressed.

A smoke visualization study of the flow over a square cylinder at incidence and tandem square cylinders

2015 ◽  
Vol 18 (4) ◽  
pp. 687-703 ◽  
Author(s):  
A. Sohankar ◽  
S. Mohagheghian ◽  
A. A. Dehghan ◽  
M. Dehghan Manshadi
Keyword(s):  
Square Cylinder ◽  
Smoke Visualization ◽  
Square Cylinders ◽  
Tandem Square Cylinders

Intermittency effects in a numerical simulation of stationary three-dimensional turbulence

1978 ◽  
Vol 86 (3) ◽  
pp. 567-592 ◽  
Author(s):  
Eric D. Siggia ◽  
G. S. Patterson
Keyword(s):  
Isotropic Turbulence ◽  
Probability Distributions ◽  
Longitudinal Velocity ◽  
Strain Tensor ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Spectral Simulation ◽  
Simulation Code ◽  
Contour Plots

A Navier-Stokes direct spectral simulation code was modified to produce stationary and nearly isotropic turbulence in three dimensions. An approximate$-\frac{5}{3}$energy spectrum was maintained over the entire range of wavenumbers by simultaneously driving the fluid and supplementing the ordinary viscosity with a subgrid-like energy sink in the last 15% of the spectrum. Half-tone and contour plots of the fluctuations in the vorticity, rate-of-strain tensor and helicity show increasing ‘spottiness’ as the system evolves in time. Probability distributions and cross-correlations among these three quantities were also obtained. The flatness factor of the longitudinal velocity derivative, the longitudinal structure functions and the fluctuations in the locally averaged dissipation rate are consistent with some degree of intermittency, but do not unambiguously demonstrate its presence in the simulated flows.

Wake-Boundary Layer Interactions Behind a Square Cylinder for a Reynolds Number in Periodic Vortex Shedding Regime

2015 ◽  
Author(s):  
Arti Pal ◽  
Sudipto Sarkar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Navier Stokes Equation ◽  
Ansys Fluent ◽  
Boundary Layer Interaction

Flow over a square cylinder in proximity to a wall for different gap-to-diameter ratios (G/D = 0 to 2, where G is the gap between the cylinder and flat plate and D is the side of the square cylinder) has been studied extensively for a Reynolds Number (Re = U∞D/v, where v is the kinematic viscosity of the fluid and U∞ is the free stream velocity) in the periodic vortex shedding regime. Ansys Fluent is used to solve two-dimensional (2-D), time dependent, incompressible Navier-Stokes equation by SIMPLE [1] algorithm implemented in finite volume method. Interesting flow features and changes in vortex dynamics can be seen by the present simulation, when the cylinder approaches very close to the plate. The boundary layer formed over the flat plate changes its characteristics for these low gap-ratios. Also the modification of the aerodynamic forces and the vortex shedding frequency are thoroughly described to understand the physics behind wake-boundary layer interaction at low Reynolds Number.

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