Numerical investigation for flow over a square rod through a passive control method at various Reynolds numbers

2020 ◽  
Vol 98 (5) ◽  
pp. 425-432
Author(s):  
A. Ahmed ◽  
R. Manzoor ◽  
S.U. Islam ◽  
H. Rahman
Keyword(s):  
Flow Regime ◽  
Passive Control ◽  
Control Method ◽  
Sudden Change ◽  
Flow Characteristics ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Spacing Ratio ◽  
Boltzmann Method ◽  
Control Rods

This work presents a numerical simulation performed to study the effect of Reynolds number (Re = 80–200) on fluid flow over a square rod attached to two small controlling rods using the Lattice Boltzmann method. For this reason, the spacing ratio between the control rods and main rod varies systematically from g = 0.5–5. Flow has been subdivided into three flow regimes based on spacing ratios. The first flow regime is considered at a small gap (g = 0.5, 1, and 1.5), the second flow regime is obtained at a moderate gap (g = 2, 2.5, and 3), and the third flow regime is considered a at large gap (g = 4–5). Five different types of flow modes were noticed in the given flow regimes. The values Re = 200 and g = 5 were found to be critical due to a sudden change in flow characteristics. The maximum value of Cdmean is 0.869 and the largest percent reduction (65.15%) in the mean drag coefficient was found at Re = 200 and g = 2.

Numerical Simulation for Flow over Two Circular Cylinders in Micro Channel with Lattice Boltzmann Method

2014 ◽  
Vol 670-671 ◽  
pp. 747-750
Author(s):  
Zhi Jun Gong ◽  
Jiao Yang ◽  
Wen Fei Wu
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Recirculation Zone ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Micro Channel ◽  
Zone Length ◽  
Spacing Ratio ◽  
Boltzmann Method

For indepth study on flow characteristics for fluid bypass obstacles in micro-channel, the Lattice Boltzmann Method (LBM) was used to simulate fluid flow over two circular cylinders in side-by-side arrangement of a micro-channel. The velocity distribution and recirculation zone length under different Reynolds numbers (Re = 0~100) and different spacing ratio (H/D= 0~2.0) were obtained. The results show that the pattern of flow and the size of recirculation zone in the micro-channel depend on the combined effect of Re and H/D.

Flow and Energy Loss Downstream of Rectangular Sharp-Crested Weirs for Free and Submerged Flows

2021 ◽  
Author(s):  
Mahmud R. Amin ◽  
Nallamuthu Rajaratnam ◽  
David Z. Zhu
Keyword(s):  
Energy Loss ◽  
Flow Regime ◽  
Analytical Study ◽  
Flow Characteristics ◽  
Turbulent Jets ◽  
Flow Regimes ◽  
Impinging Jet ◽  
Relative Energy ◽  
Surface Flow ◽  
Upper Stage

Abstract This work presents an analytical study of the flow and energy loss immediately downstream of rectangular sharp-crested weirs for free and submerged flows, using the theory of plane turbulent jets and the analysis of some relevant studies. The flow regimes downstream of the sharp-crested weir is characterized as the impinging jet and surface flow regimes. Based on the flow characteristics and the downstream tailwater depths, each flow regime is further classified, and the relative energy loss equation is developed. It is found that significant energy loss occurs for the regime of supercritical flow and the upper stage of impinging jet flow. The energy loss for the submerged flow regime is minimal.

Simulation of Flow Around a Cube at Moderate Reynolds Numbers Using the Lattice Boltzmann Method

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Majid Hassan Khan ◽  
Atul Sharma ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lattice Boltzmann Method ◽  
Steady Flow ◽  
Flow Regime ◽  
Lattice Boltzmann ◽  
Reynolds Numbers ◽  
Side Force ◽  
Force Coefficients ◽  
Boltzmann Method

Abstract This article reports flow behavior around a suspended cube obtained using three-dimensional (3D) lattice Boltzmann method (LBM)-based simulations. The Reynolds number (Re) range covered is from 84 to 770. Four different flow regimes are noted based on the flow structure in this range of Re: steady axisymmetric (84 ≤ Re ≤ 200), steady nonaxisymmetric (215 ≤ Re ≤ 250), unsteady nonaxisymmetric in one plane and axisymmetric in the other plane (276 ≤ Re ≤ 300), and unsteady nonaxisymmetric in streamwise orthogonal planes (339 ≤ Re ≤ 770). Recirculation length and drag coefficient follow inverse trend in the steady flow regime. The unsteady flow regime shows hairpin vortices for Re ≤ 300 and then it becomes structureless. The nature of force coefficients has been examined at various Reynolds numbers. Temporal behavior of force coefficients is presented along with phase dependence of side force coefficients. The drag coefficient decreases with increase in Reynolds number in the steady flow regime and the side force coefficients are in phase. Drag coefficients are compared with established correlations for flow around a cube and a sphere. The side force coefficients are perfectly correlated at Re = 215 and they are anticorrelated at Re = 250. At higher Reynolds numbers, side force coefficients are highly uncorrelated. This work adds to the existing understanding of flow around a cube reported earlier at low and moderate Re and extends it further to unsteady regime at higher Re.

scholarly journals Numerical Simulation of Drag Reduction on a Square Rod Detached with Two Control Rods at Various Gap Spacing via Lattice Boltzmann Method

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 475 ◽  
Author(s):  
Raheela Manzoor ◽  
Asma Khalid ◽  
Ilyas Khan ◽  
Shams-Ul-Islam ◽  
Dumitru Baleanu ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Lattice Boltzmann Method ◽  
Vortex Shedding ◽  
Lattice Boltzmann ◽  
Flow Mode ◽  
Percentage Reduction ◽  
Spacing Ratio ◽  
Boltzmann Method ◽  
Gap Spacing ◽  
Control Rods

Numerical simulations are performed to examine the effect of size of control rods (d1) and spacing ratio (g) on flow around a square rod with upstream and downstream control rods aligned in-line using the lattice Boltzmann method (LBM). The Reynolds number (Re) is fixed at Re = 160, while the spacing between the main rod and control rods is taken in the range 1 ≤ g ≤ 5 and the size of the control rod is varied between 4 and 20. Seven different types of flow mods are observed in this study at different values of g and d1. Variation in force statistics, like mean drag coefficient (Cdmean), Strouhal number (St), root mean square values of drag (Cdrms) and lift coefficients (Clrms), and percentage reduction in mean drag coefficient is discussed in detail. It was examined that vortex shedding completely suppressed at (g, d1) = (1, 12), (2, 12), and (2, 16) where steady flow mode exists. Moreover, it was found that at large gap spacing, where g = 5, the effect of control rods on the main rod vanishes. Due to this strong vortex shedding produced and as a result, maximum value of Cdmean is found at (g, d1) = (5, 8). The negative values of mean drag force are also observed at some gap spacing and size of control rods are due to the effect of thrust. Furthermore, the maximum percentage reduction in Cdmean is 121%, found at (g, d1) = (2, 20).

scholarly journals T-Shaped Control Plate Effect on Flow past a Square Cylinder at Low Reynolds Numbers

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Maryam Shahab ◽  
Shams Ul-Islam ◽  
Ghazala Nazeer
Keyword(s):  
Passive Control ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Optimum Length ◽  
Low Reynolds Numbers ◽  
Fluid Forces ◽  
Drag Forces ◽  
Control Plate ◽  
Low Reynolds

In this study, the influence of the T-shaped control plate on the fluid flow characteristics around a square cylinder for a low Reynolds numbers flow is systematically presented. The introduction of upstream attached T-shaped control plate is novel of its kind as T-shaped control plate used for the first time rather than the other passive control methods available in the literature. The Reynolds numbers (Re) are chosen to be Re = 100, 150, 200, and 250, and the T-shaped control plate of the same width with varying length is considered. A numerical investigation is performed using the single-relaxation-time lattice Boltzmann method. The numerical results reveal that there exists an optimum length of T-shaped control plate for reducing fluid forces. This optimum length was found to be 0.5 for Re = 100, 150, and 200 and 2 for Re = 250. At this optimum length, the fluctuating drag forces acting on the cylinder are reduced by 134%, 1375, 133%, and 136% for Re = 100, 150, 200, and 250, respectively. Instantaneous and time-averaged flow fields were also presented for some selected cases in order to identify the three different flow regimes around T-shaped control plate and square cylinder system.

Study of unsteady separated fluid flows using a multi-block lattice Boltzmann method

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Eslam Ezzatneshan
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Fluid Flows ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Near Wake ◽  
Content Type ◽  
Boltzmann Method

Purpose Numerical simulations are performed for studying the vorticity dynamics of a dipole colliding with the wall in a bounded flow and the wake structure and separated flow properties past a circular cylinder at the values of Reynolds numbers. Design/methodology/approach The near wake statistics of separated fluid flows are investigated by using the lattice Boltzmann method (LBM) in a two-dimensional framework. A multi-block technique is applied to accurately resolve the flow characteristics by the grid refinement near the wall and preserve the stability of the numerical solution at relatively high Reynolds numbers. Findings The results show that the rolling-up of the boundary layer occurs due to the shear-layer instabilities near the surface which causes a boundary layer detachment from the wall and consequently leads to the formation of small-scale vortices. These shear-layer vortices shed at higher frequencies than the large-scale Strouhal vortices which result in small-scale high-frequency fluctuations in the velocity field in the very near wake. The present study also demonstrates that the efficiency of the multi-block LBM used for predicting the statistical features of flow problems is comparable with the solvers based on the Navier-Stokes equations. Practical implications Studying the separated flow characteristics in aerospace applications. Originality/value Applying a multi-block lattice Boltzmann method (LBM) for simulation of separated fluid flows at high-Reynolds numbers. Studying of the near wake statistics of unsteady separated fluid flows using the multi-block LBM. Comparison of flow characteristics obtained based on the LBM with those of reported based on the Navier-Stokes equations.

Numerical Analysis of Combustion Instability and Its Suppression in Gas Turbine Combustor With Swirlers Modeled on EV Premix Burners

2005 ◽  
Author(s):  
Chae Hoon Sohn ◽  
Han Chang Cho
Keyword(s):  
Numerical Analysis ◽  
Gas Turbine ◽  
Passive Control ◽  
Acoustic Analysis ◽  
Control Method ◽  
Flow Characteristics ◽  
Pressure Oscillation ◽  
Scaling Analysis ◽  
Gas Turbine Combustor ◽  
Air Mixing

Pressure oscillation in an industrial gas-turbine combustor is numerically investigated based on thermo-acoustic instability. The combustor has 37 EV premix burners through which methane and air are mixed and then injected into the chamber. First, acoustic eigenmodes and frequencies of the chamber are examined by adopting linear acoustic analysis. Next, combustion instabilities are simulated. In simulating instabilities, first, steady fuel/air mixing and flow characteristics established by the burner are investigated by numerical analysis with single burner. And then, based on the calculated flow data, the burners are modeled numerically via equivalent swirlers, which facilitates the numerical analysis with the whole combustion system including the chamber and numerous burners. Finally, reactive flow fields within the chamber are investigated numerically by unsteady analysis and thereby spontaneous instability is simulated. Based on the numerical results, scaling analysis is conducted to find out the instability mechanism in the combustor and a passive control method to suppress the instability is proposed and verified numerically.

Numerical Investigation of “Frog-Leap” Mechanisms of Three Particles Aligned Moving in an Inclined Channel Flow

2015 ◽  
Vol 7 (2) ◽  
pp. 207-228 ◽  
Author(s):  
Xiao-Dong Niu ◽  
Ping Hu ◽  
Xing-Wei Zhang ◽  
Hui Meng ◽  
Hiroshi Yamaguchi ◽  
...  
Keyword(s):  
Channel Flow ◽  
Particle Surface ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Immersed Boundary ◽  
Inclined Channel ◽  
Channel Boundary ◽  
Boltzmann Method ◽  
Recent Experimental Work ◽  
Present Simulation

AbstractIntrigued by our recent experimental work (H. Yamaguchi and X. D. Niu, J. Fluids Eng., 133 (2011), 041302), the present study numerically investigate the flow-structure interactions (FSI) of three rigid circular particles aligned moving in an inclined channel flow at intermediate Reynolds numbers by using a momentum-exchanged immersed boundary-lattice Boltzmann method. A ”frog-leap” phenomenon observed in the experiment is successfully captured by the present simulation and flow characteristics and underlying FSI mechanisms of it are explored by examining the effects of the channel inclined angles and Reynolds numbers. It is found that the asymmetric difference of the vorticity distributions on the particle surface is the main cause of the “frog-leap” when particle moves in the boundary layer near the lower channel boundary.

scholarly journals Numerical Study on Flow around Four Square-Arranged Cylinders at Low Reynolds Numbers

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Yang-yang Gao ◽  
Chang-shan Yin ◽  
Hao-qiang Zhang ◽  
Kang Yang ◽  
Xi-zeng Zhao ◽  
...  
Keyword(s):  
Vortex Shedding ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Low Reynolds Numbers ◽  
Force Coefficients ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Four Square

In this paper, numerical simulations of flow past four square-arranged cylinders are carried out at different spacing ratios (1.5≤L/D≤5.0; L is the center to center distance; D is the cylinder diameter) and Reynolds numbers (100≤Re≤1000). The effects of spacing ratio and Reynolds number on the wake flow characteristics are investigated, such as the instantaneous vorticity contours, force coefficients, and vortex shedding frequencies. The results show that the flow characteristics behind the four-cylinder cases are significantly affected by the spacing ratios and Reynolds numbers. At the same spacing ratio, the transformation of flow pattern is advanced quickly with increasing of Reynolds numbers, the values of force coefficients are correspondingly fluctuated with large amplitude, and the vortex shedding frequency is increased significantly with Re.

Flow features of three side-by-side rectangular cylinders under the effect of aspect ratios and Reynolds numbers

2020 ◽  
pp. 2150034
Author(s):  
Hamid Rahman ◽  
Waqas Sarwar Abbasi ◽  
Shams-ul-Islam ◽  
Raees Khan ◽  
Muhammad Uzair Khan
Keyword(s):  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Physical Parameters ◽  
Drag And Lift Coefficients ◽  
Fluid Forces ◽  
Aspect Ratios ◽  
Flow Features ◽  
Drag And Lift ◽  
Boltzmann Method ◽  
Rectangular Cylinders

This study focuses on the characteristics of flow past three side-by-side rectangular cylinders under the effect of aspect ratios (AR) and Reynolds numbers (Re) at two different gap ratios ([Formula: see text]) using the lattice Boltzmann method. For this purpose, AR is varied in the range of 0.25–4, the Re values are 100, 140 and 180 and the two different values of [Formula: see text] taken into account are [Formula: see text] and 3. The results are presented in the form of vorticity contours, temporal histories of drag and lift coefficients and power spectrum of lift coefficients. Also, the variation of physical parameters like mean drag coefficient, Strouhal number and the root-mean-square values of drag and lift coefficients with Re and AR is presented for [Formula: see text] and 3. The current numerical computations yield that for both gap ratios and all Re, there exist four different flow regimes depending on AR: (a) steady flow, (b) modulated flow, (c) symmetric flow and (d) periodic flow. At narrow gap ratios, the jet flow emerging within the gaps of cylinders altered the flow structures and fluid forces abruptly. The aspect ratio is found to have more influence on the flow characteristics of cylinders as compared to the Reynolds numbers at large gap ratios.

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