Numerical study of the rounded corners effect on flow past a square cylinder

2015 ◽  
Vol 25 (4) ◽  
pp. 686-702 ◽  
Author(s):  
Sajjad Miran ◽  
Chang Hyun Sohn
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Lift Coefficient ◽  
Numerical Results ◽  
The Body ◽  
Square Cylinder ◽  
Content Type ◽  
Flow Past ◽  
Corner Radius

Purpose – The purpose of this paper is to numerically investigate the influence of corner radius on flow past a square cylinder at a Reynolds number 500. Design/methodology/approach – Six models were studied, for R/D=0 (square cylinder), 0.1, 0.2, 0.3, 0.4, and 0.5 (circular cylinder), where R is the corner radius and D is the characteristic dimension of the body. The transient two-dimensional (2D) laminar and large eddy simulations (LES) models were employed using finite volume code. The Strouhal number, mean drag coefficient (CD), and root mean square (RMS) value of lift coefficient (CL,RMS), for different R/D values, were computed and compared with experimental and other numerical results. Findings – The computational results showed good agreement with previously published results for a Reynolds number, Re=500. It was found that the corner effect on a square cylinder greatly influences the flow characteristics around the cylinder. Results indicate that, as the corner radius ratio, R/D, increases, the Strouhal number increases rapidly for R/D=0-0.2, and then gradually rises between R/D=0.2 and 0.5. The minimum values of the mean drag coefficient and the RMS value of lift coefficient were found around R/D=0.2, which is verified by the time averaged streamwise velocity deficit profile. Originality/value – On the basis of the numerical results, it is concluded that rounded corners on a square cylinder are useful in reducing the drag and lift forces generated behind a cylinder. Finally, it is suggested that with a rounded corner ratio of around R/D=0.2, the drag and oscillation of the cylinder can be greatly reduced, as compared to circular and square cylinders.

Flow Past Square Cylinders of Different Size With and Without Corner Modification

2015 ◽  
Author(s):  
Y. T. Krishne Gowda ◽  
Ravindra Holalu Venkatdas ◽  
Vikram Chowdeswarally Krishnappa
Keyword(s):  
Drag Coefficient ◽  
Flow Velocity ◽  
Strouhal Number ◽  
Lift Coefficient ◽  
Research Work ◽  
Tall Buildings ◽  
Convergence Criterion ◽  
Square Cylinder ◽  
Square Cylinders ◽  
Flow Past

In many mechanical engineering applications, separated flows often appear around any object such as tall buildings, monuments, and towers are permanently exposed to wind. Similarly, piers, bridge pillars, and legs of offshore platforms are continuously subjected to the load produced by maritime or fluvial streams. These bodies usually create a large region of separated flow and a massive unsteady wake region in the downstream. The highly asymmetric and periodic nature of flow in the downstream has attracted the attention of physicists, engineers and CFD practitioners. A lot of research work is carried out for a square cylinder but flow past square cylinders with and without corner modification work is not taken up. This motivated to take up the task of flow past two different sized square cylinders, numerically simulated. A Reynolds number of 100 and 200 is considered for the investigation. The flow is assumed to be two dimensional unsteady and incompressible. The computational methodology is carried out once the problem is defined the first step in solving the problem is to construct a geometry on which the simulation is planned. Once the geometry is constructed, proper assignment of its boundaries in accordance to the actual physical state is to be done. The various boundary options that are to be set. After setting the boundary types, the continuum type is set. The geometry is discretized into small control volumes. Once the surface mesh is completed, the mesh details are exported to a mesh file, then exported to Fluent, which is CFD solver usually run in background mode. This helps to prioritize the execution of the run. The run would continue until the required convergence criterion is reached or till the maximum number of iterations is completed. Results indicate, in case of chamfered and rounded corners in square cylinder, there is decrease in the wake width and thereby the lift and drag coefficient values. The form drag is reduced because of a higher average pressure downstream when separation is delayed by corner modification. The lift coefficients of Square cylinder with corner modification decreases but Strouhal number increases when compared with a square cylinder without corner modification. Strouhal number remains same even if magnitude of oscillations is increased while monitoring the velocity behind the cylinder. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. As the centre distance between two cylinders i.e., pitch-to-perimeter ratio is increased to 6,the behavior of the flow almost approaches to that of flow past a square cylinder of with and without modification of same condition. When the perimeter of the upstream cylinder with and without modification is larger than the downstream cylinder, the size of the eddies is always bigger in between the cylinders compared to the downstream of the second cylinder. The flow velocity in between the cylinders with and without corner modification are less compared to the downstream of the second cylinder. As the distance increases, the flow velocity in between the cylinders become almost equal to the downstream of the second cylinder. The results are presented in the form of streamlines, flow velocity, pressure distribution. drag coefficient, lift coefficient and Strouhal number.

Numerical Analysis of Two Square Cylinders of Different Sizes With and Without Corner Modification

2016 ◽  
Author(s):  
Y. T. Krishne Gowda ◽  
Holalu Venkatdas Ravindra ◽  
Vikram Chowdeswarally Krishnappa
Keyword(s):  
Drag Coefficient ◽  
Flow Velocity ◽  
Strouhal Number ◽  
Lift Coefficient ◽  
Research Work ◽  
Convergence Criterion ◽  
Back Side ◽  
Square Cylinder ◽  
Square Cylinders ◽  
Flow Past

Flow past square cylinders has attracted a great deal of attention because of its practical significance in engineering e.g., High rise buildings, monuments and towers. Similarly, bridge pillars, and legs of offshore platforms are continuously subjected to the load produced by maritime or fluvial streams. The presence of separated flows, reattachment, formation the vortices, un steadiness of flow, mass and momentum transfer across shear layer makes the flow field quite complex. Many research work was carried out for a single square cylinder and flow past two square cylinders, but with corner medications in square cylinder of different size arranged in tandem was not taken up. This has motivated to take up the flow past two different sized square cylinders i.e., smaller in upstream and larger in downstream which is numerically simulated by using Fluent software. Reynolds number of 100 and 200 is considered for the investigation. The flow is assumed to be two dimensional, unsteady and incompressible. The computational methodology is carried out once the problem is defined, the first step in solving the problem is to construct a geometry then proper assignment of boundaries are set. After setting the boundary types, the geometry is discretized into small control volumes. Once the surface mesh is completed by using Gambit software, the mesh along with boundary conditions are exported to fluent, which is CFD solver usually run in background mode. The run would continue until the required convergence criterion is reached or till the maximum number of iterations is completed. Results indicate, in case of chamfered and rounded corners in square cylinders of different size, there is decrease in the wake width and thereby the lift and drag coefficient values. The lift coefficients in Square cylinders of different size with corner modifications decreases but Strouhal number increases when compared with a single square cylinder without corner modifications. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. As the centre distance between two square cylinders i.e., PPR (pitch to perimeter ratio) with and without corner modifications is increased to 6, the flow velocity almost approaches to flow past a single square cylinder with and without modifications for same condition. When the size of the upstream square cylinder with and without modifications is smaller than that of the downstream square cylinder, the size of the eddies is always smaller in between the cylinders compared to the downstream of the second cylinder. The flow velocity in between the cylinders with and without corner modifications are less compared to the downstream of the second cylinder. Pressure on the downstream side of the cylinder is smaller than that on the upstream side of the cylinder for with and without corner modifications. Also, the front portion of the cylinder is experiencing highest pressure compared to the second cylinder for all the three cases i.e., PPR = 2, 4 and 6. Pressure at the upper side, bottom side and back side of square cylinder with and without corner modifications is of negative pressure, it is because of vortices generated at that surfaces. The downstream cylinder is found to experience higher lift compared to the upstream cylinder. The results are presented in the form of while the downstream cylinder is found to experience higher drag compared to the streamlines, flow velocity, pressure distribution, drag coefficient, lift coefficient and strouhal number.

Effects of Corner Cutoffs on Flow Past Two Square Cylinders in a Tandem Arrangement

2012 ◽  
Author(s):  
Y. T. Krishne Gowda ◽  
H. V. Ravindra ◽  
C. K. Vikram
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Two Dimensional ◽  
Square Cylinder ◽  
Tandem Arrangement ◽  
Square Cylinders ◽  
Flow Past

Flow past the two square cylinders with and without corner modification in a tandem arrangement has been simulated using a CFD code FLUENT. A Reynolds number of 100 and pitch to perimeter ratios (PPR) of 2,4 and 6 are considered for the investigation. The flow is assumed to be two dimensional unsteady and incompressible. The obtained results are presented in the form of streamlines, pressure distribution, monitored velocity, lift coefficient and Strouhal number. Results indicate, in case of chamfered and rounded corners, there is decrease in the wake width and thereby the lift values. For the square cylinders of same perimeters with and without corner modification, the size of the eddy and the monitored velocity in between the square cylinders increases with increase in PPR. Frequency of vortex shedding is same in between the cylinders and in the downstream of the cylinder. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. The lift coefficient of square cylinder with corner modification decreases but Strouhal number increases when compared with a square cylinder without corner modification.

scholarly journals Numerical Analysis of the Aerodynamic Characteristics of NACA-4312 Airfoil

2020 ◽  
Vol 01 (02) ◽  
pp. 29-36
Author(s):  
Md Rhyhanul Islam Pranto ◽  
Mohammad Ilias Inam
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Numerical Results ◽  
Ansys Fluent ◽  
Coefficient Increase ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aim of the work is to investigate the aerodynamic characteristics such as lift coefficient, drag coefficient, pressure distribution over a surface of an airfoil of NACA-4312. A commercial software ANSYS Fluent was used for these numerical simulations to calculate the aerodynamic characteristics of 2-D NACA-4312 airfoil at different angles of attack (α) at fixed Reynolds number (Re), equal to 5×10^5 . These simulations were solved using two different turbulence models, one was the Standard k-ε model with enhanced wall treatment and other was the SST k-ω model. Numerical results demonstrate that both models can produce similar results with little deviations. It was observed that both lift and drag coefficient increase at higher angles of attack, however lift coefficient starts to reduce at α =13° which is known as stalling condition. Numerical results also show that flow separations start at rare edge when the angle of attack is higher than 13° due to the reduction of lift coefficient.

The predominant frequency for viscous flow past two tandem circular cylinders of different diameters at low Reynolds number

2019 ◽  
Vol 234 (2) ◽  
pp. 534-546
Author(s):  
Ming-ming Liu
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Viscous Flow ◽  
Lift Coefficient ◽  
Circular Cylinders ◽  
Predominant Frequency ◽  
Flow Past ◽  
Gap Ratio ◽  
The Mean ◽  
Different Diameters

Viscous flow past two circular cylinders in tandem arrangement is numerically investigated at a typical Reynolds number of 200 which is based on the diameter of the downstream cylinder. The non-dimensional diameter of the downstream cylinder D is fixed to be 1.0, while the non-dimensional diameter of the upstream cylinder d varies from 0.1 to 1.0 with an interval of 0.1. Moreover, the minimal non-dimensional distance between the two cylinders changes from 0.1 to 4.0. The numerical results show that continuous variation of the mean drag coefficient, the lift coefficient, and the lift frequency is observed with the increase in the gap ratio for d/ D = 0.1 and 0.2. Discontinuities are found for the mean drag coefficient, the lift coefficient, and the lift frequency of the downstream cylinder with the increase in gap ratio for d/ D = 0.9 and 1.0. Multiple lift oscillating frequencies of the downstream cylinder can be detected for d/ D = 0.3–0.8 at special gap ratios. Special attention is paid on d/ D = 0.4, which is a typical example for d/ D = 0.3–0.8. The predominant lift frequency of the downstream cylinder is observed to change from fL-1 to fL-2 as the increase in the gap ratio for d/ D = 0.4, which have not been previously detected. However, the predominant drag frequency of the downstream cylinder is found always to be fD-3 in present investigation scope. Moreover, a conclusion that fD-3 =  fL-1 +  fL-2 can be obtained.

Dynamic Behavior of a Streamwise Oscillating Heated Cylinder

2021 ◽  
Author(s):  
Ussama Ali ◽  
MD Islam ◽  
Isam Janajreh
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Natural Frequency ◽  
Strouhal Number ◽  
Frequency Ratio ◽  
Lift Coefficient ◽  
Cylinder Wall ◽  
Forcing Function ◽  
Lower Amplitude

Abstract The influence of oscillation and heat transfer on the lift and drag coefficients over a circular cylinder is numerically studied in this work. Temperature difference of 300, 600 and 900 K is used between the cylinder wall and the incoming fluid flow for Reynolds number of 100. Air is used as the fluid and the temperature dependent properties of air are used for the analysis as a significant change in the properties of air incurred. Numerical simulation is done on Ansys/fluent with O-type mesh and the vibration in the circular cylinder is induced using user defined function. The vibration of the cylinder in streamwise direction is induced at a frequency ratio of 0.5, 1, and 2, with the natural frequency of the cylinder being 2.5 Hz marking its Strouhal number. It is observed that for all the induced frequencies, the forcing function interacts with the natural frequency of the system, and the beating phenomenon spectrum is observed, where two distinct frequencies appear which correspond to the sum and difference between the natural and the forcing frequency. At the frequency ratio of 0.5 (1.25 Hz), the spectrum of lift coefficient is characterized with three peaks centered at 2.5 Hz (natural frequency), 3.75 Hz (sum) and 1.25 Hz (difference). Oscillating the isothermal cylinder at a frequency ratio of 0.5 caused a negligible increase in the rms value of the lift coefficient by 2.13%, drag coefficient by 0.17%, and had no effect on the natural frequency of the system, however at a frequency ratio of 2, a drastic increase in the rms value of lift coefficient by 137.4% and drag coefficient by 13.9% occurred, indicating the lock-on regime. As compared to the stationary isothermal cylinder, heating the cylinder 300K above the incoming flow, decreased the rms value of the lift coefficient by 62.7% and the natural frequency by 16%, while increased the drag coefficient by 7.3%. The results show that heating of cylinder in cross-flow is equivalent to running the flow at a reduced Reynolds number and in the laminar region, this is associated with lower Strouhal number and lower amplitude of lift but a higher drag.

Two-Dimensional Study of the Turbulent Wake Behind a Square Cylinder Subject to Uniform Shear

2000 ◽  
Author(s):  
A. K. Saha ◽  
G. Biswas ◽  
K. Muralidhar
Keyword(s):  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Lift Coefficient ◽  
Turbulence Models ◽  
Direct Calculation ◽  
Square Cylinder ◽  
Shear Parameter ◽  
High Reynolds ◽  
Direct Calculations

Abstract The flow past a square cylinder at a high Reynolds number has been simulated through direct calculations and through the calculations using turbulence models. The present investigation highlights significant differences between the two approaches in terms of instantaneous flow, Strouhal number and the aerodynamic forces. The time-averaged drag coefficient and the rms fluctuations due to the direct calculation are higher than those due to the turbulence model. However, Strouhal number is underpredicted in direct calculations. The effect of shear on the flow has also been determined using the turbulence model. The time-averaged drag coefficient is found to decrease with the increase in shear parameter up to a certain value. Then it increases with the further increase in the shear parameter. On the other hand, the lift coefficient increases with the increase in shear parameter. Strouhal number shows a decreasing trend with the increase in shear parameter whereas the rms values of the drag and lift coefficients increase with the shear parameter. Kármán Vortex Street, mainly comprising of clockwise vortices due to shear, decays slowly compared to uniform flow condition.

Influence of Corner Radius on Flow Past Square Cylinder With Tandem Arrangements

2019 ◽  
Author(s):  
Sajjad Miran ◽  
Furqan Ahmad ◽  
Waseem Arif ◽  
Kamran Nazir
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Aerodynamic Characteristics ◽  
Diameter Ratio ◽  
Square Cylinder ◽  
Total Drag ◽  
Flow Past ◽  
Corner Radius ◽  
Drag And Lift ◽  
Gap Spacing

Abstract The Flow Past square cylinder with tandem arrangement is numerically analyzed using Commercial Finite volume code. The fixed Reynolds number (Re.) 100 is selected for the present study. However, corner radius to diameter ratio, R/D = 0 to 0.5 and L/D = 1.5 to 7.5 spacing between two cylinders is used as a varying parameter. The flow visualization parameters, the drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of corner radius and gap spacing on the behavior of the flow. The obtained results have shown that flow aerodynamic characteristics are strongly influenced by cylinders rounded corners and spacing. It was also found that the total drag force can be reduced for the downstream cylinder when cylinders are placed within L/D ≤ 4.5.

Numerical Simulation of Flow Past an Elliptical Cylinder Undergoing Rotationally Oscillating Motion

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Local Maximum ◽  
Elliptical Cylinder ◽  
Equivalent Diameter ◽  
Lift And Drag ◽  
Oscillating Motion

The finite element method is used to simulate the near-wake of an elliptical cylinder undergoing rotationally oscillating motion at low Reynolds number, 50 ≤ Re ≤ 150. Reynolds number is based on equivalent diameter of the ellipse. The rotationally oscillating motion was carried out by varying the angle of attack between 10 deg and 60 deg, while the considered oscillation frequencies are between St/4 and 4 × St, where St is the Strouhal number of a stationary elliptical cylinder with zero angle of attack. Fluid flow results are presented in terms of lift and drag coefficients for rotationally oscillating case. The details of streamlines and vorticity contours are also presented for a few representative cases. The result indicates that at when the frequency is equal to the Strouhal number, the root-mean-square (RMS) of lift coefficient reaches its local minimum, while the average of drag coefficient reaches its local maximum. Increasing the Reynolds number increases the RMS of lift coefficient and decreases average of drag coefficient.

Two-Dimensional Study of the Turbulent Wake Behind a Square Cylinder Subject to Uniform Shear

2001 ◽  
Vol 123 (3) ◽  
pp. 595-603 ◽  
Author(s):  
A. K. Saha ◽  
G. Biswas ◽  
K. Muralidhar
Keyword(s):  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Lift Coefficient ◽  
Turbulent Wake ◽  
Square Cylinder ◽  
Uniform Shear ◽  
Shear Parameter ◽  
Drag And Lift ◽  
Direct Calculations

The flow past a square cylinder at a Reynolds number of 20,000 has been simulated through direct calculations and through the calculations using turbulence model. The present investigation highlights significant differences between the two approaches in terms of time-averaged flow, Strouhal number, and aerodynamic forces. The time-averaged drag coefficient and the rms fluctuations due to the direct calculations are higher than those due to the turbulence model. However, Strouhal number is underpredicted in the direct calculations. The effect of shear on the flow has also been determined using the turbulence model. The time-averaged drag coefficient is found to decrease with the increase in shear parameter up to a certain value. Then it increases with the further increase in the shear parameter. On the other hand, lift coefficient increases with the increase in shear parameter. Strouhal number shows a decreasing trend with the increase in shear parameter whereas the rms values of drag and lift coefficients increase with the shear parameter. The Ka´rma´n vortex street, mainly comprising clockwise vortices due to shear, decays slowly compared to the uniform flow condition.

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