Flow Characteristics of Freely Rotating Rectangular Cylinders With Different Width to Height Ratios

2011 ◽  
Author(s):  
Y. G. Park ◽  
H. S. Yoon ◽  
M. Y. Ha
Keyword(s):  
Strouhal Number ◽  
Flow Characteristics ◽  
Periodic Oscillation ◽  
Reynolds Numbers ◽  
Immersed Boundary ◽  
Cylinder Surface ◽  
Oscillation Regime ◽  
Height Ratio ◽  
Volume Method ◽  
Rectangular Cylinders

The present study numerically investigates flow past freely rotating rectangular cylinders with different width to height ratios. The immersed boundary method (IBM) to model the rectangular cylinder based on the finite volume method is used to study a two-dimensional (2-D) laminar fluid flow for different Reynolds numbers of 50, 100, and 150 in the range of 0.2 ≤ W/H ≤ 1.0, where W/H is the width to height ratio. There are three different regimes of motion. The first one is the periodic oscillation regime. The second one is rotation with reversal of direction regime. The last one is the rotation with one direction regime. All the cases are periodic oscillation regime except the cases of Re = 100 and 150 with W/H = 1.0. For Re = 100 and 150 with W/H = 1.0, the regimes are the rotation with reversal of direction regime and the rotation with one direction regime, respectively. The Strouhal number decreases with increasing the width to height ratio for Re = 50, 100 and 150. However, for Re = 100 and 150, the Strouhal number disappears at a width to height ratio of 1.0. The present study reports the detailed information of flow structure on the cylinder surface at different width to height ratio.

Strouhal numbers of rectangular cylinders

1982 ◽  
Vol 123 ◽  
pp. 379-398 ◽  
Author(s):  
Atsushi Okajima
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Velocity Distribution ◽  
Flow Pattern ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Water Tank ◽  
Height Ratio ◽  
Rectangular Cylinders ◽  
Good Agreement

Experiments on the vortex-shedding frequencies of various rectangular cylinders were conducted in a wind tunnel and in a water tank. The results show how Strouhal number varies with a width-to-height ratio of the cylinders in the range of Reynolds number between 70 and 2 × l04. There is found to exist a certain range of Reynolds number for the cylinders with the width-to-height ratios of 2 and 3 where flow pattern abruptly changes with a sudden discontinuity in Strouhal number. The changes in flow pattern corresponding to the discontinuity of Strouhal number have been confirmed by means of measurements of velocity distribution and flow visualization. These data are compared with those of other investigators. The experimental results have been found to show a good agreement with those of numerical calculations.

Fluid Flow and Heat Transfer in an Annulus With Ribs on the Rotating Inner Cylinder Surface

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
S. Gokul ◽  
M. Deepu
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Thermal Performance ◽  
Three Dimensional ◽  
Simple Algorithm ◽  
Reynolds Numbers ◽  
Cylinder Surface ◽  
Turbulent Fluid Flow ◽  
Cylindrical Annulus ◽  
Volume Method

Abstract Numerical studies on heat transfer in Taylor-Couette-Poiseuille flow in a cylindrical annulus with ribs mounted on the rotating inner cylinder are presented. The present study focuses on two different types of ribs, namely, longitudinal ribs and helical ribs. Three-dimensional, steady, incompressible, turbulent fluid flow is solved using a semi-implicit method for pressure linked equations (SIMPLE) algorithm based finite volume method. The numerical solution method is validated using two sets of benchmark experimental data. Extensive numerical computations are carried out at various Reynolds numbers (2100 < Re < 2400) and modified Taylor numbers (30,000 < Tam < 90,000) for annulus with and without ribs. Ribs enhance the transport of heat and momentum by inducing more vorticity and turbulence in the flow. The overall performance is presented in terms of thermal performance factor (TPF), which takes in to account the heat transfer as well as pressure drop in the ribbed annulus. Helical ribs are found to offer superior thermal performance than its longitudinal counterpart.

Flow structures downstream of the horizontal cylinder laid on a plane surface

2008 ◽  
Vol 223 (2) ◽  
pp. 397-413 ◽  
Author(s):  
M Sami Akoz
Keyword(s):  
Flow Structure ◽  
Plane Surface ◽  
Water Channel ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortical Flow ◽  
Cylinder Surface ◽  
Stress Concentrations ◽  
The Stability

The complex vortical flow structure arises from the interaction between the flow and a pipeline on seabed, causing erosion scour around the pipeline, which is a threat to the stability of the structure. The viscous flow past a circular cylinder laid on a horizontal bed is analysed experimentally using the particle image velocimetry image technique to understand the vortical flow characteristics downstream of the cylinder. The experiments were conducted in a closed-loop water channel with Reynolds numbers, in the range of 1000 ≤ ReD ≤ 7000 based on the cylinder diameter. To provide a detailed evaluation of the properties of the flow structure behind the cylinder, instantaneous and time-averaged patterns of velocity vector field, corresponding vorticity contours, streamline topology, and Reynolds stress concentrations were presented. The point of the boundary layer detachment from the cylinder surface and the lengths of the primary and secondary downstream separation regions were determined as a function of Reynolds numbers. Instantaneous velocity fields clearly indicate the scour mechanism downstream of the horizontal cylinder.

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.

Numerical Investigation of 3-D Turbulent Flow in Orifice Plate within a Pipe

2015 ◽  
Vol 761 ◽  
pp. 27-31
Author(s):  
Mohamed Abed Alabas Siba ◽  
Wan Mohd Faizal Wan Mahmood ◽  
Mohd Zaki Nuawi ◽  
Rasidi Rasani
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Finite Volume ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Orifice Plate ◽  
Navier Stokes ◽  
Volume Method

A numerical study of the turbulent flow in an orifice plate within a pipe is carried out by utilizing the Navier-Stokes (N-S) equations. The governing equations are solved using primitive variables with a finite volume method (FVM) and simulated using the finite volume based commercial CFD code ANSYS. The study investigates the influences of Reynolds numbers (Re = 5000, 10000, and 15000) and aspect ratio (β = 0.2, 0.3, and 0.5), on the flow characteristics, i.e. the velocity profile, the differential pressure, and the vorticity, and on the mechanical properties, i.e. the strain, the stress, and the total deformation of the flow around and beyond the orifice. It is found that as the Reynolds number increases, the flow velocity and the pressure increase. The vorticity images show a slightly different behavior. As the Reynolds number has its own effect on the results, it is also found that the aspect ratio affects the results more significantly. The flow patterns are presented for unsteady flow throughout the orifice plate at different values of the Reynolds number.

scholarly journals Quasi-Periodic Oscillating Flows in a Channel with a Suddenly Expanded Section

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1403 ◽  
Author(s):  
Masuda ◽  
Tagawa
Keyword(s):  
Oscillatory Flow ◽  
Harmonic Component ◽  
Periodic Oscillation ◽  
Reynolds Numbers ◽  
Flat Plates ◽  
Downstream Region ◽  
Harmonic Components ◽  
Pass Through ◽  
High Reynolds ◽  
Volume Method

In this study, two-dimensional numerical simulation was carried out for an oscillatory flow between parallel flat plates having a suddenly expanded section. Governing equations were discretized with the second-order accuracy by a finite volume method on an unequal interval mesh system resolving finer near walls and corners to obtain the characteristics of the oscillatory flow accurately. Amplitude spectrums of a velocity component were obtained to investigate the periodic characteristics of the oscillatory flow. At low Reynolds numbers, the flow is periodic because the spectrum mostly consists of harmonic components, and then at high Reynolds numbers, it transits to a quasi-periodic flow mixed with non-harmonic components. In conjunction with the periodic oscillation of a main flow, separation vortices that are not uniform in size are generated from the corner of a sudden contraction part and pass through a downstream region coming into contact with the wall. The number of the vortices decreases rapidly after they are generated, but the vortices are generated again in the downstream region. In order to specify where aperiodicity is generated, the turbulent kinetic energy is introduced, and it is decomposed into the harmonic and non-harmonic components. The peaks of the non-harmonic component are generated in the region of the expanded section.

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.

scholarly journals Oscillations in cylinder wakes at Mach 4

2015 ◽  
Vol 785 ◽  
Author(s):  
B. E. Schmidt ◽  
J. E. Shepherd
Keyword(s):  
Reynolds Number ◽  
Supersonic Flow ◽  
Strouhal Number ◽  
Subsonic Flow ◽  
Reynolds Numbers ◽  
Acoustic Signals ◽  
Cylinder Surface ◽  
Periodic Oscillations ◽  
Number Range ◽  
Subsonic Region

The wake behind a circular cylinder in Mach 4 flow is examined experimentally in the Reynolds number range $2\times 10^{4}$ to $5\times 10^{5}$. Periodic oscillations of the sliplines in the wake are observed. The Strouhal number of the oscillations based on the diameter of the cylinder is found to increase monotonically from 0.30 to 0.50 with increasing Reynolds number. If the Strouhal number is formed using the length of the sliplines, however, it has a constant value of approximately 0.48 for all Reynolds numbers studied. This scaling indicates that the oscillations in supersonic flow are likely driven by acoustic signals propagating back and forth through the subsonic region between the separation points on the cylinder and the neck where the sliplines converge, unlike in subsonic flow where oscillations are caused by vortices shed from the cylinder surface.

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

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