Drag reduction on a square cylinder using multiple detached control cylinders

Shams-Ul-Islam,Raheela Manzoor,Umar Khan,Ghazala Nazeer,Sehrish Hassan 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.5

A two-dimensional numerical simulation for flow over a main cylinder with detached controlling cylinders placed at differentposition is performed through Lattice Boltzmann Method (LBM) to reduce fluid forces. For this study the Reynolds number (Re) isfixed at 160, while gap ratio between these cylinders are taken in the range from 0.5 to 8. The results yield in terms of vorticity, timeseriesanalysis of drag and lift coefficients, power spectra of lift coefficients and force statistics. Depending on gap spacing, flow isclassified into four different patterns, called as (i) single blender body, (ii) shear layer reattachment, (iii) fully developed flow and (iv)vortex suppression fully developed flow patterns. In comparison of all three configurations, it is examined that the maximum value ofCdmean and Strouhal number occurs for downstream configuration. Whereas, upstream and dual configuration play a vital role toreduce forces and to suppress vortex shedding. The maximum reduction found in mean drag coefficient for downstream, upstreamand for dual configuration is 8.3%, 51% and 50.8%, respectively. Whereas, the reduction in Clrms values for all three configurationsis 84.4%, 58.2% and 86.4% , respectively.

Numerical Investigation of Different Flow Regimes for Square Cylinders in Staggered Configuration

Shams Ul Islam,Ghazala Nazeer,Sehrish Hassan Shigri 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5

The present numerical investigation deals with the flow across two square cylinders placed in staggered alignment at fixed Reynolds number (Re) of 160 and varying gap spacings (g*) from 0 to 6. Numerical computations are conducted by employing the two-dimensional single-relaxation-time lattice Boltzmann method (SRT-LBM). The complex phenomena of vortex shedding are explored for different g* and outcomes are presented as vorticity snapshots, time-history analysis of drag and lift coefficients (CD and CL) and power spectra analysis of CL. Five flow patterns are observed which are named as: single bluff body flow, quasi periodic flow, chaotic flow, in-phase/anti-phase modulated flow and synchronized flow. The fluid forces are irregular for all flow pattern except for synchronized flow where lift is periodic due to synchronization of flow. It is observed that presence of an upstream cylinder in the near vicinity of downstream cylinder increases the drag at small gap spacing and vice versa.

Suppression of fluid force on flow past a square cylinder with a detached flat plate at low Reynolds number for various spacing ratios

Shams-Ul-Islam,Hamid Rahman,Waqas Sarwar Abbasi,Uzma Noreen,Aftab Khan 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.12

A numerical study for flow past a square cylinder in a two-dimensional channel with a detached flat plate is investigated in this paper. A flat plate is detached downstream in order to control the flow around and behind the square cylinder. Fluid forces acting on the squarecylinder, wake structure mechanism and vortex shedding frequency are presented systematically for different Reynolds numbers andspacing ratios. Effects of Reynolds numbers upon physical parameters are also studied. Variation of Reynolds number is from 75 to 200,based on the incoming flow velocity and width of cylinder. The lattice Boltzmann method is used for this numerical investigation. In thisstudy, we choose three different spacing ratios namely closely, moderately and widely. Numerical studies show that some physical parameterssignificantly reduced by the detached flat plate for closely spacing ratio. The results which we obtained in this investigation areauthentic in the sense that some other experimental observations by different authors can be deduced from our results.

Numerical investigation of fluid flow past a square cylinder using upstream, downstream and dual splitter plates

Shams Ul Islam,Raheela Manzoor,Zhou Chao Ying,Mohammad Mehdi Rashdi,A. Khan 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

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.

On the Effect of Reynolds Number for Flow Past Three Side-by-side Square Cylinders for Unequal Gap Spacings

Hamid Rahman,Shams-Ul-Islam,Zhou Chao Ying,Tanvir Kiyani,Suvash C. Saha 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

Flow patterns and aerodynamic characteristics behind three side-by-side square cylinders has been found depending upon theunequal gap spacing (g1= s1/d and g2= s2/d) between the three cylinders and the Reynolds number (Re) using the Lattice Boltzmannmethod. The effect of Reynolds numbers on the flow behind three cylinders are numerically studied for 75 ≤ Re ≤ 175 and chosenunequal gap spacings such as (g1, g2) = (1.5, 1), (3, 4) and (7, 6). We also investigate the effect of g2 while keeping g1 fixed forRe = 150. It is found that a Reynolds number have a strong effect on the flow at small unequal gap spacing (g1, g2) = (1.5, 1.0). It isalso found that the secondary cylinder interaction frequency significantly contributes for unequal gap spacing for all chosen Reynoldsnumbers. It is observed that at intermediate unequal gap spacing (g1, g2) = (3, 4) the primary vortex shedding frequency plays a majorrole and the effect of secondary cylinder interaction frequencies almost disappear. Some vortices merge near the exit and as a resultsmall modulation found in drag and lift coefficients. This means that with the increase in the Reynolds numbers and unequal gapspacing shows weakens wakes interaction between the cylinders. At large unequal gap spacing (g1, g2) = (7, 6) the flow is fullyperiodic and no small modulation found in drag and lift coefficients signals. It is found that the jet flows for unequal gap spacingstrongly influenced the wake interaction by varying the Reynolds number. These unequal gap spacing separate wake patterns fordifferent Reynolds numbers: flip-flopping, in-phase and anti-phase modulation synchronized, in-phase and anti-phase synchronized. It is also observed that in case of equal gap spacing between the cylinders the effect of gap spacing is stronger than the Reynoldsnumber. On the other hand, in case of unequal gap spacing between the cylinders the wake patterns strongly depends on both unequalgap spacing and Reynolds number. The vorticity contour visualization, time history analysis of drag and lift coefficients, powerspectrum analysis of lift coefficient and force statistics are systematically discussed for all chosen unequal gap spacings and Reynoldsnumbers to fully understand this valuable and practical problem.

Variation of wake patterns and force coefficients of the flow past square bodies aligned inline

Raheela Manzoor,Shams-Ul-Islam,Waqas Sarwar Abbasi,Sajida Parveen 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.4

In this numerical study, the variation of wake patterns and force coefficients of the flow past four square bodies aligned inline are investigated. A two-dimensional numerical code is developed using the Lattice Boltzmann method (LBM) for this study. The code is first validated for the flow past a single and two tandem square cylinders. The results are compared to those available in literature and found to be in good agreement. After validation the calculations are further performed to investigate the effect of gap spacing (g) for the flow past four inline square cylinders at two different Reynolds numbers (Re) 100 and 200. The gap spacing is chosen in the range 0.25 ≤ g ≤ 7. Six different flow patterns: Single slender body, alternate reattachment, quasi steady reattachment, intermittent shedding, chaotic flow and periodic flow are found in this study with successive increment in spacing. It is found that some flow patterns existing at Re = 100 do not exist at Re = 200. The generated vortices at Re = 200 are much stronger as compared to those at Re = 100. The spacing value g = 3 is found to be critical at Re = 100 while at Re = 200 the spacing value g = 2 is critical due to abrupt changes in flow characteristics. At some spacing values the downstream cylinders have higher values of average drag coefficients as compared to upstream ones. In general the upstream cylinder (c1) have higher drag forces at Re = 200 than at Re = 100. The root mean square values of lift coefficient are found to be greater than the corresponding root mean square values of drag coefficient.

Effect of Reynolds numbers on flow past four square cylinders in an in-line square configuration for different gap spacings

Waqas Sarwar Abbasi,Shams-Ul-Islam,Suvash C. Saha,Yuan Tong Gu,Zhou Chao Ying 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.2

In this paper two-dimensional (2-D) numerical investigation of flow past four square cylinders in an in-line square configuration areperformed using the lattice Boltzmann method. The gap spacing g = s/d is set at 1, 3 and 6 and Reynolds number ranging from Re = 60 to175. We observed four distinct wake patterns: (i) a steady wake pattern (Re = 60 and g = 1); (ii) a stable shielding wake pattern (80 ≤ Re≤ 175 and g = 1); (iii) a wiggling shielding wake pattern (60 ≤ Re ≤ 175 and g = 3) and (iv) a vortex shedding wake pattern (60 ≤ Re ≤175 and g = 6). At g = 1, the Reynolds number is observed to have a strong effect on the wake patterns. It is also found that at g = 1, thesecondary cylinder interaction frequency significantly contributes for drag and lift coefficients signal. It is found that the primary vortexshedding frequency dominates the flow and the role of secondary cylinder interaction frequency almost vanish at g = 6. It is observed thatthe jet between the gaps strongly influenced the wake interaction for different gap spacing and Reynolds number combination. To fullyunderstand the wake transformations the details vorticity contour visualization, power spectra of lift coefficient signal and time signalanalysis of drag and lift coefficients also presented in this paper.