Waqas Abbasi | COMSATS Institute of Information Technology (original) (raw)

Papers by Waqas Abbasi

Computational Particle Mechanics

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Mathematical Problems in Engineering, 2021

In this work, numerical simulations are performed in order to study the effects of aspect ratio (... more In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag forc...

In this research numerical simulations are performed, using the multi-relaxation-time lattice Bol... more In this research numerical simulations are performed, using the multi-relaxation-time lattice Boltzmann method, in the range 3 ≤ β = w[d] ≤ 30 at Re = 100, 200 and 300, where β the blockage ratio, w is the equispaced distance between centers of cylinders, d is the diameter of the cylinder and Re is the Reynolds number, respectively. Special attention is paid to the effect of the equispaced distance between centers of cylinders. Visualization of the vorticity contour visualization are presented for some simulation showing the flow dynamics and patterns for blockage effect. Results show that the drag and mean drag coefficients, and Strouhal number, in general, decrease with the increase of β for fixed Re. It is found that the decreasing rate of drag and mean drag coefficients and Strouhal number is more distinct in the range 3 ≤ β ≤ 15. We found that when β > 15, the blockage effect almost diminishes. Our results further indicate that the drag and mean drag coefficients, peak value...

A systematic study for the flow past four square cylinders in an in-line square configuration is ... more A systematic study for the flow past four square cylinders in an in-line square configuration is carried out in this paper at a Reynolds number of 150 using the Lattice Boltzmann method. The main agenda of the present study is to fully investigate the effect of gap spacing between the four cylinders on the vortex shedding mechanism and wake structure. The selected separation ratios we considered are 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 3.0, 4.0 and 6.0. Five different kinds of flow patterns are observed depending on the separation ratio: a single bluff-body pattern, shielding pattern, wiggling shielding pattern and anti-phase and in-phase vortex shedding pattern. These five different kinds of flow patterns mainly depend on the primary vortex shedding frequency and the secondary cylinder interaction frequencies. At small separation ratio the secondary frequencies play a major role and the jet flow between cylinders dominate the shielding pattern of flow. On the other hand, for intermediate and higher separation ratio the primary vortex shedding frequency dominates the flow (wiggling shielding and anti-phase and in-phase vortex shedding patterns) and the secondary frequencies almost disappear.

Journal of Mechanical Science and Technology, 2014

In this paper two-dimensional (2-D) numerical investigation of flow past four square cylinders in... more In this paper two-dimensional (2-D) numerical investigation of flow past four square cylinders in an in-line square configuration are performed using the lattice Boltzmann method. The gap spacing g=s/d is set at 1.0, 3.0 and 6.0 and Reynolds number ranging from Re=60 to 175. We observed four distinct wake patterns: (i) a steady wake pattern (Re=60 and g=1.0); (ii) a stable shielding wake pattern (80≤Re≤175 and g=1.0); (iii) a wiggling shielding wake pattern (60≤Re≤175 and g=3.0) and (iv) a vortex shedding wake pattern (60≤Re≤175 and g=6.0). At g=1.0, the Reynolds number is observed to have a strong effect on the wake patterns. It is also found that at g=1.0, the secondary cylinder interaction frequency significantly contributes for drag and lift coefficients signal. It is found that the primary vortex shedding frequency dominates the flow and the role of secondary cylinder interaction frequency almost vanish at g=6.0. It is observed that the jet between the gaps strongly influenced the wake interaction for different gap spacing and Reynolds number combination. To fully understand the wake transformations the details vorticity contour visualization, power spectra of lift coefficient signal and time signal analysis of drag and lift coefficients also presented in this paper.

Mathematical Problems in Engineering

This article is concerned with the numerical analysis of reduction of fluid forces (drag and lift... more This article is concerned with the numerical analysis of reduction of fluid forces (drag and lift) and suppression of vortex shedding around two side-by-side square cylinders using the lattice Boltzmann method. For this purpose, a passive flow control methodology is adopted in which a flat plate (termed as the control plate) is placed at the upstream position of cylinders. The gap ratio ( g ) between the cylinders and the plate is varied from 0 to 4 while the height of the control plate is varied from 0.2 to 0.8 at fixed Reynolds number of 150. Different flow patterns are found in this study depending on the gap ratios and different heights of the control plate. These flow patterns are single bluff body flow, flip-flopping flow, and antiphase vortex shedding flow patterns. The narrow gap ratio ( g = 0.5) is found to have more impact in terms of force reduction and flow control as compared to larger gap ratios. This article also shows that the fluid flow parameters such as the mean ...

International Journal of Modern Physics C, 2020

World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, 2014

Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-... more Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann method at Reynolds number 150. The effects of upstream locations, downstream locations and blockage are investigated systematically. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The results had shown that the upstream, downstream and height of the computational domain are at least 7.5, 37.5 and 12 diameters of the cylinder, respectively. Keywords—Grid independence, Multi-relaxation-time lattice Boltzmann method, Physical quantities, Square cylinder, Vorticity c...

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Numerical investigation of flow around a square cylinder are presented using the multi-relaxation... more Numerical investigation of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann methods at different Reynolds numbers. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations, streamlines and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The Reynolds numbers affected the physical quantities. Keywords—Code validation, Force statistics, Multi-relaxationtime lattice Boltzmann method, Reynolds numbers, Square cylinder.

I Waqas Sarwar Abbasi, CIIT/SP13-PMT-003/ISB, hereby declare that I have produced the work presen... more I Waqas Sarwar Abbasi, CIIT/SP13-PMT-003/ISB, hereby declare that I have produced the work presented in this thesis, during the scheduled period of study. I also declare that I have not taken any material from any source except referred to wherever due that amount of plagiarism is within acceptable range. If a violation of HEC rules on research has occurred in this thesis, I shall be liable to punishable action under the plagiarism rules of the HEC.

Arabian Journal for Science and Engineering, 2021

Numerical investigations are carried out for the flow around two inline square cylinders with a f... more Numerical investigations are carried out for the flow around two inline square cylinders with a flat plate, placed in the wake, using the lattice Boltzmann method. Main emphasis of this work is to find the optimum values of the gap ratio ( L / d ) between cylinders and plate for maximum vortex shedding control and suppression of flow induced forces. The gap ratio between both cylinders as well as between second cylinder and plate is varied in the range 0.5 to 10 by fixing Reynolds number at 150. Three different flow structures are observed by systematically increasing the gap ratio: solo body ( L / d = 0.5), reattachment flow (1 ≤ L / d < 4) and binary vortex flow (4 ≤ L / d ≤ 10). Comparison of results with the case of two inline square cylinders without control plate shows that the fluctuating lift for both cylinders is completely suppressed in the range 0.5 < L / d ≤ 2, resulting in a steady flow pattern due to comprehensive vortex shedding control. Furthermore, the ...

Mathematical Problems in Engineering

The present work is concerned with a comprehensive analysis of hydrodynamic forces, under MHD and... more The present work is concerned with a comprehensive analysis of hydrodynamic forces, under MHD and forced convection thermal flow over a heated cylinder in presence of insulated plates installed at walls. The magnetic field is imposed in the transverse direction of flow. The Galerkin finite element (GFE) scheme has been used to discretize the two-dimensional system of nonlinear partial different equations. The study is executed for the varying range of flow behavior index n from 0.4 to 1.6, Hartmann number Ha from 0 to 100, Reynolds number Re from 10 to 50, Grashof number Gr from 1 to 10, thickness ratio e from 0.5 to 1.0, and Prandtl number Pr from 1 to 10, respectively. A coarse hybrid computational grid is developed, and further refinement is carried out for obtaining the highly accurate solution. The optimum case selection is based on flow patterns, drag and lift coefficients, and pressure drop reduction against cylinder thickness ratios and average Nusselt numbers. Drag coeffici...

AIP Advances

Low-Reynolds-number flow around a wall-mounted square cylinder: Flow structures and onset of vort... more Low-Reynolds-number flow around a wall-mounted square cylinder: Flow structures and onset of vortex shedding

Journal of the Brazilian Society of Mechanical Sciences and Engineering

The present study investigates the wake interference effects for flow around two tandem cylinders... more The present study investigates the wake interference effects for flow around two tandem cylinders under the effect of gap spacing ranging from 0.5 to 10. The flow Reynolds number is fixed at 150, and lattice Boltzmann method is used as a numerical tool for this study. The results show that three different regimes exist depending on gap spacing and flow structure mechanism around cylinders: single cylinder body regime, reattachment regime and co-shedding regime. The results also show that in a particular regime multiple flow patterns may coexist and affect the behavior of fluid forces. This study reveals that there exists a critical value of spacing which alters the fluid flow characteristics abruptly. The drag coefficient of second cylinder is negative until critical spacing and becomes positive after that. It is found that when spacing crosses the critical value, both cylinders start shedding vortices and the drag coefficient oscillates. The wake interference effect is found to be dominant at small spacing values which weakens with increment in spacing between cylinders.

Iranian Journal of Science and Technology, Transactions of Mechanical Engineering

In this paper, numerical simulations are carried out for a laminar, incompressible and Newtonian ... more In this paper, numerical simulations are carried out for a laminar, incompressible and Newtonian fluid flow past three square cylinders in triangular arrangement using the lattice Boltzmann method. Two different arrangements are considered for the present study: In arrangement-I, a square cylinder is placed at the front side of two side-by-side square cylinders and in arrangement-II, a square cylinder is placed at the rear side of two side-by-side square cylinders. The Reynolds number ( Re ) is fixed at 150, and gap ratio ( g ) is varied from 0.5 to 7. It is found that both the arrangements and gap ratios affect the flow characteristics significantly. Four flow patterns are observed for each arrangement, corresponding to different values of g . The numerical results show that in arrangement-I, the downstream two side-by-side cylinders experience larger drag than the upstream single cylinder, while in arrangement-II, the upstream two side-by-side cylinders experience smaller drag than the downstream single cylinder for all g , except at g = 0.5, where the trend reverses. The results also show that with increment in g , the mean drag coefficient of all three cylinders approaches single cylinder mean drag coefficient for both arrangements. In addition, it is also observed that by increasing g the effect of a square cylinder, placed either at upstream position or downstream position of two side-by-side square cylinders, on the force coefficients of these side-by-side square cylinders almost vanishes. As a result, these force coefficients approach two side-by-side cylinders data without an upstream/downstream cylinder.

Mathematical Problems in Engineering

This work presents the numerical investigations performed to study the proximity effects on fluid... more This work presents the numerical investigations performed to study the proximity effects on fluid flow characteristics around three inline square cylinders using the lattice Boltzmann method. For this purpose the gap spacing (g) is systematically varied in the range 0.5 to 16 diameters of cylinder by keeping Reynolds number fixed at 200. Five different flow patterns are observed at different values of spacing: bluff body flow, gap trapped flow, irregular flow, alternate shedding, and modulated shedding. These patterns have a significant effect on flow induced forces and vortex shedding frequency. The spacing value g = 2 is found to be critical due to sudden changes in fluid flow characteristics. The flow parameters of first cylinder are found to be closer to single cylinder values but for middle and third cylinder the differences confirm the wake interference effect even at large values of spacing.

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Numerical computations are carried out to analyze the transition in flow states around two inline... more Numerical computations are carried out to analyze the transition in flow states around two inline square cylinders under the effect of Reynolds numbers (Re). For this analysis, Re is varied from 1 to 110 at a fixed spacing ratio g = 3.5. The results are presented in the form of vorticity contours, streamline graphs, temporal histories of drag and lift coefficients and power spectrum of lift coefficients. Also the physical parameters like average drag coefficient, Strouhal number and the root-mean-square values of drag and lift coefficients are presented as a function of Re. Three different states of flow are found in this study by systematically varying Re: (a) steady state, (b) quasi-unsteady state, and (c) unsteady state. The points of separation and reattachment of shear layers depend on Re. This study shows that the values of physical parameters strongly depend on flow states and change their behavior when flow mode changes from one state to another. A significant reduction in the values of flow induced forces found due to the presence of two cylinders in the flow field when compared to single cylinder values. The results of the present study are also compared with the available data of other researchers and found to be in good agreement.

Computational Particle Mechanics

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Mathematical Problems in Engineering, 2021

In this work, numerical simulations are performed in order to study the effects of aspect ratio (... more In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag forc...

In this research numerical simulations are performed, using the multi-relaxation-time lattice Bol... more In this research numerical simulations are performed, using the multi-relaxation-time lattice Boltzmann method, in the range 3 ≤ β = w[d] ≤ 30 at Re = 100, 200 and 300, where β the blockage ratio, w is the equispaced distance between centers of cylinders, d is the diameter of the cylinder and Re is the Reynolds number, respectively. Special attention is paid to the effect of the equispaced distance between centers of cylinders. Visualization of the vorticity contour visualization are presented for some simulation showing the flow dynamics and patterns for blockage effect. Results show that the drag and mean drag coefficients, and Strouhal number, in general, decrease with the increase of β for fixed Re. It is found that the decreasing rate of drag and mean drag coefficients and Strouhal number is more distinct in the range 3 ≤ β ≤ 15. We found that when β > 15, the blockage effect almost diminishes. Our results further indicate that the drag and mean drag coefficients, peak value...

A systematic study for the flow past four square cylinders in an in-line square configuration is ... more A systematic study for the flow past four square cylinders in an in-line square configuration is carried out in this paper at a Reynolds number of 150 using the Lattice Boltzmann method. The main agenda of the present study is to fully investigate the effect of gap spacing between the four cylinders on the vortex shedding mechanism and wake structure. The selected separation ratios we considered are 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 3.0, 4.0 and 6.0. Five different kinds of flow patterns are observed depending on the separation ratio: a single bluff-body pattern, shielding pattern, wiggling shielding pattern and anti-phase and in-phase vortex shedding pattern. These five different kinds of flow patterns mainly depend on the primary vortex shedding frequency and the secondary cylinder interaction frequencies. At small separation ratio the secondary frequencies play a major role and the jet flow between cylinders dominate the shielding pattern of flow. On the other hand, for intermediate and higher separation ratio the primary vortex shedding frequency dominates the flow (wiggling shielding and anti-phase and in-phase vortex shedding patterns) and the secondary frequencies almost disappear.

Journal of Mechanical Science and Technology, 2014

In this paper two-dimensional (2-D) numerical investigation of flow past four square cylinders in... more In this paper two-dimensional (2-D) numerical investigation of flow past four square cylinders in an in-line square configuration are performed using the lattice Boltzmann method. The gap spacing g=s/d is set at 1.0, 3.0 and 6.0 and Reynolds number ranging from Re=60 to 175. We observed four distinct wake patterns: (i) a steady wake pattern (Re=60 and g=1.0); (ii) a stable shielding wake pattern (80≤Re≤175 and g=1.0); (iii) a wiggling shielding wake pattern (60≤Re≤175 and g=3.0) and (iv) a vortex shedding wake pattern (60≤Re≤175 and g=6.0). At g=1.0, the Reynolds number is observed to have a strong effect on the wake patterns. It is also found that at g=1.0, the secondary cylinder interaction frequency significantly contributes for drag and lift coefficients signal. It is found that the primary vortex shedding frequency dominates the flow and the role of secondary cylinder interaction frequency almost vanish at g=6.0. It is observed that the jet between the gaps strongly influenced the wake interaction for different gap spacing and Reynolds number combination. To fully understand the wake transformations the details vorticity contour visualization, power spectra of lift coefficient signal and time signal analysis of drag and lift coefficients also presented in this paper.

Mathematical Problems in Engineering

This article is concerned with the numerical analysis of reduction of fluid forces (drag and lift... more This article is concerned with the numerical analysis of reduction of fluid forces (drag and lift) and suppression of vortex shedding around two side-by-side square cylinders using the lattice Boltzmann method. For this purpose, a passive flow control methodology is adopted in which a flat plate (termed as the control plate) is placed at the upstream position of cylinders. The gap ratio ( g ) between the cylinders and the plate is varied from 0 to 4 while the height of the control plate is varied from 0.2 to 0.8 at fixed Reynolds number of 150. Different flow patterns are found in this study depending on the gap ratios and different heights of the control plate. These flow patterns are single bluff body flow, flip-flopping flow, and antiphase vortex shedding flow patterns. The narrow gap ratio ( g = 0.5) is found to have more impact in terms of force reduction and flow control as compared to larger gap ratios. This article also shows that the fluid flow parameters such as the mean ...

International Journal of Modern Physics C, 2020

World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, 2014

Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-... more Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann method at Reynolds number 150. The effects of upstream locations, downstream locations and blockage are investigated systematically. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The results had shown that the upstream, downstream and height of the computational domain are at least 7.5, 37.5 and 12 diameters of the cylinder, respectively. Keywords—Grid independence, Multi-relaxation-time lattice Boltzmann method, Physical quantities, Square cylinder, Vorticity c...

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Numerical investigation of flow around a square cylinder are presented using the multi-relaxation... more Numerical investigation of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann methods at different Reynolds numbers. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations, streamlines and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The Reynolds numbers affected the physical quantities. Keywords—Code validation, Force statistics, Multi-relaxationtime lattice Boltzmann method, Reynolds numbers, Square cylinder.

I Waqas Sarwar Abbasi, CIIT/SP13-PMT-003/ISB, hereby declare that I have produced the work presen... more I Waqas Sarwar Abbasi, CIIT/SP13-PMT-003/ISB, hereby declare that I have produced the work presented in this thesis, during the scheduled period of study. I also declare that I have not taken any material from any source except referred to wherever due that amount of plagiarism is within acceptable range. If a violation of HEC rules on research has occurred in this thesis, I shall be liable to punishable action under the plagiarism rules of the HEC.

Arabian Journal for Science and Engineering, 2021

Numerical investigations are carried out for the flow around two inline square cylinders with a f... more Numerical investigations are carried out for the flow around two inline square cylinders with a flat plate, placed in the wake, using the lattice Boltzmann method. Main emphasis of this work is to find the optimum values of the gap ratio ( L / d ) between cylinders and plate for maximum vortex shedding control and suppression of flow induced forces. The gap ratio between both cylinders as well as between second cylinder and plate is varied in the range 0.5 to 10 by fixing Reynolds number at 150. Three different flow structures are observed by systematically increasing the gap ratio: solo body ( L / d = 0.5), reattachment flow (1 ≤ L / d < 4) and binary vortex flow (4 ≤ L / d ≤ 10). Comparison of results with the case of two inline square cylinders without control plate shows that the fluctuating lift for both cylinders is completely suppressed in the range 0.5 < L / d ≤ 2, resulting in a steady flow pattern due to comprehensive vortex shedding control. Furthermore, the ...

Mathematical Problems in Engineering

The present work is concerned with a comprehensive analysis of hydrodynamic forces, under MHD and... more The present work is concerned with a comprehensive analysis of hydrodynamic forces, under MHD and forced convection thermal flow over a heated cylinder in presence of insulated plates installed at walls. The magnetic field is imposed in the transverse direction of flow. The Galerkin finite element (GFE) scheme has been used to discretize the two-dimensional system of nonlinear partial different equations. The study is executed for the varying range of flow behavior index n from 0.4 to 1.6, Hartmann number Ha from 0 to 100, Reynolds number Re from 10 to 50, Grashof number Gr from 1 to 10, thickness ratio e from 0.5 to 1.0, and Prandtl number Pr from 1 to 10, respectively. A coarse hybrid computational grid is developed, and further refinement is carried out for obtaining the highly accurate solution. The optimum case selection is based on flow patterns, drag and lift coefficients, and pressure drop reduction against cylinder thickness ratios and average Nusselt numbers. Drag coeffici...

AIP Advances

Low-Reynolds-number flow around a wall-mounted square cylinder: Flow structures and onset of vort... more Low-Reynolds-number flow around a wall-mounted square cylinder: Flow structures and onset of vortex shedding

Journal of the Brazilian Society of Mechanical Sciences and Engineering

The present study investigates the wake interference effects for flow around two tandem cylinders... more The present study investigates the wake interference effects for flow around two tandem cylinders under the effect of gap spacing ranging from 0.5 to 10. The flow Reynolds number is fixed at 150, and lattice Boltzmann method is used as a numerical tool for this study. The results show that three different regimes exist depending on gap spacing and flow structure mechanism around cylinders: single cylinder body regime, reattachment regime and co-shedding regime. The results also show that in a particular regime multiple flow patterns may coexist and affect the behavior of fluid forces. This study reveals that there exists a critical value of spacing which alters the fluid flow characteristics abruptly. The drag coefficient of second cylinder is negative until critical spacing and becomes positive after that. It is found that when spacing crosses the critical value, both cylinders start shedding vortices and the drag coefficient oscillates. The wake interference effect is found to be dominant at small spacing values which weakens with increment in spacing between cylinders.

Iranian Journal of Science and Technology, Transactions of Mechanical Engineering

In this paper, numerical simulations are carried out for a laminar, incompressible and Newtonian ... more In this paper, numerical simulations are carried out for a laminar, incompressible and Newtonian fluid flow past three square cylinders in triangular arrangement using the lattice Boltzmann method. Two different arrangements are considered for the present study: In arrangement-I, a square cylinder is placed at the front side of two side-by-side square cylinders and in arrangement-II, a square cylinder is placed at the rear side of two side-by-side square cylinders. The Reynolds number ( Re ) is fixed at 150, and gap ratio ( g ) is varied from 0.5 to 7. It is found that both the arrangements and gap ratios affect the flow characteristics significantly. Four flow patterns are observed for each arrangement, corresponding to different values of g . The numerical results show that in arrangement-I, the downstream two side-by-side cylinders experience larger drag than the upstream single cylinder, while in arrangement-II, the upstream two side-by-side cylinders experience smaller drag than the downstream single cylinder for all g , except at g = 0.5, where the trend reverses. The results also show that with increment in g , the mean drag coefficient of all three cylinders approaches single cylinder mean drag coefficient for both arrangements. In addition, it is also observed that by increasing g the effect of a square cylinder, placed either at upstream position or downstream position of two side-by-side square cylinders, on the force coefficients of these side-by-side square cylinders almost vanishes. As a result, these force coefficients approach two side-by-side cylinders data without an upstream/downstream cylinder.

Mathematical Problems in Engineering

This work presents the numerical investigations performed to study the proximity effects on fluid... more This work presents the numerical investigations performed to study the proximity effects on fluid flow characteristics around three inline square cylinders using the lattice Boltzmann method. For this purpose the gap spacing (g) is systematically varied in the range 0.5 to 16 diameters of cylinder by keeping Reynolds number fixed at 200. Five different flow patterns are observed at different values of spacing: bluff body flow, gap trapped flow, irregular flow, alternate shedding, and modulated shedding. These patterns have a significant effect on flow induced forces and vortex shedding frequency. The spacing value g = 2 is found to be critical due to sudden changes in fluid flow characteristics. The flow parameters of first cylinder are found to be closer to single cylinder values but for middle and third cylinder the differences confirm the wake interference effect even at large values of spacing.

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Numerical computations are carried out to analyze the transition in flow states around two inline... more Numerical computations are carried out to analyze the transition in flow states around two inline square cylinders under the effect of Reynolds numbers (Re). For this analysis, Re is varied from 1 to 110 at a fixed spacing ratio g = 3.5. The results are presented in the form of vorticity contours, streamline graphs, temporal histories of drag and lift coefficients and power spectrum of lift coefficients. Also the physical parameters like average drag coefficient, Strouhal number and the root-mean-square values of drag and lift coefficients are presented as a function of Re. Three different states of flow are found in this study by systematically varying Re: (a) steady state, (b) quasi-unsteady state, and (c) unsteady state. The points of separation and reattachment of shear layers depend on Re. This study shows that the values of physical parameters strongly depend on flow states and change their behavior when flow mode changes from one state to another. A significant reduction in the values of flow induced forces found due to the presence of two cylinders in the flow field when compared to single cylinder values. The results of the present study are also compared with the available data of other researchers and found to be in good agreement.