Effect of Axis Ratio on Fluid Flow Around an Elliptic Cylinder—A Numerical Study

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
S. Kalyana Raman ◽  
K. Arul Prakash ◽  
S. Vengadesan
Keyword(s):  
Fluid Flow ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Elliptic Cylinder ◽  
Solid Boundary ◽  
Axis Ratio ◽  
Moderate Reynolds Number ◽  
Wake Formation

The bluff body simulations over canonical forms like circular and square cylinders are very well studied and the correlations for bulk parameters like mean drag coefficient and Strouhal numbers for the same are reported widely. In the case of elliptic cylinder, the literature is very sparse, especially for moderate Reynolds number (Re). Hence, in this work, a detailed study about fluid flow characteristics over an elliptic cylinder placed in a free stream is performed. Simulations are carried out for different Re ranging from 50 to 500 with axis ratio (AR) varied between 0.1 to 1.0 in steps of 0.1. Immersed boundary method is used for the solid boundary condition implementation which avoids the grid generation for each AR and a single Cartesian grid is used for all the simulations. The effect of AR for various Reynolds numbers is also focused on using the in-house code. The influence of AR is phenomenal for all the Re and the values of wake length, drag coefficient, and Strouhal number decrease with decreasing AR for a particular Re. The critical ARs, for vortex shedding and wake formation, are identified for various Re. Detailed correlations for wake length, critical ARs for vortex shedding and wake formation, mean drag coefficient and Strouhal number, in terms of AR, are reported in this work.

Numerical analysis of laminar fluid flow characteristics past an elliptic cylinder

2014 ◽  
Vol 24 (7) ◽  
pp. 1570-1594 ◽  
Author(s):  
Immanuvel Paul ◽  
K. Arul Prakash ◽  
S. Vengadesan
Keyword(s):  
Fluid Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Elliptic Cylinder ◽  
Computational Time ◽  
Percentage Error ◽  
Immersed Boundary ◽  
Axis Ratio ◽  
Content Type ◽  
Functional Relationships

Purpose – The purpose of this paper is to study the effects of Angle of Attack (AOA), Axis Ratio (AR) and Reynolds number (Re) on unsteady laminar flow over a stationary elliptic cylinder. Design/methodology/approach – The governing equations of fluid flow over the elliptic cylinder are solved numerically on a Cartesian grid using Projection method based Immersed Boundary technique. This numerical method is validated with the results available in open literature. This scheme eliminates the requirement of generating a new computational mesh upon varying any geometrical parameter such as AR or AOA, and thus reduces the computational time and cost. Findings – Different vortex shedding patterns behind the elliptic cylinder are identified and classified using time averaged centerline streamwise velocity profile, instantaneous vorticity contours and instantaneous streamline patterns. A parameter space graph is constructed in order to reveal the dependence of AR, AOA and Re on vortex shedding. Integral parameters of flow such as mean drag, mean lift coefficients and Strouhal number are calculated and the effect of AR, AOA and Re on them is studied using various pressure and streamline contours. Functional relationships of each of integral parameters with respect to AR, AOA and Re are proposed with minimum percentage error. Practical implications – The results obtained can be used to explain the characteristics of flow patterns behind slender to bluff elliptical cylinders which found applications in insect flight modeling, heat exchangers and energy conservation systems. The proposed functional relationships may be very useful for the practicing engineers in those fields. Originality/value – The results presented in this paper are important for the researchers in the area of bluff body flow. The dependence of AOA on vortex shedding and flow parameters was never reported in the literature. These results are original, new and important.

Flow Around an Elliptic Cylinder in the Critical Reynolds Number Regime

1987 ◽  
Vol 109 (2) ◽  
pp. 149-155 ◽  
Author(s):  
T. Ota ◽  
H. Nishiyama ◽  
Y. Taoka
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Critical Reynolds Number ◽  
Separation Bubble ◽  
Leading Edge ◽  
Elliptic Cylinder ◽  
Reynold Number ◽  
Major Axis ◽  
Cylinder Surface ◽  
Axis Ratio

Flow around an elliptic cylinder of axis ratio 1:3 has been investigated experimentally in the critical Reynolds number regime on the basis of mean static pressure measurements along the cylinder surface and of hot-wire velocity measurements in the near wake. The critical Reynold number has been found to vary with the angle of attack α and attains a minimum around α = 5 to 10 deg. At the critical Reynolds number, the drag, lift, and moment coefficients change discontinuously, and the Strouhal number based on the upstream uniform flow velocity and the major axis length of the cylinder reaches a maximum of about 1.0 to 1.5 depending on α. It is found, however, that the universal Strouhal number based on the velocity along the separated shear layer and the wake width is nearly equal to 0.19, on average, even in the critical Reynolds number regime. The pressure distribution along with the surface oil flow pattern revealed the existence of a small separation bubble near the leading edge accompanying a turbulent boundary layer.

A Numerical Simulation of Vortex Induced Vibration on a Elastically Supported Circular Rigid Cylinder at Moderate Reynolds Numbers

2008 ◽  
Author(s):  
Jean-Franc¸ois Sigrist ◽  
Cyrille Allery ◽  
Claudine Beghein
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Circular Cylinder ◽  
Finite Volume ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Forced Oscillations ◽  
Vortex Induced Vibration ◽  
Elastically Supported

The present paper is the sequel of a previously published study which is concerned with the numerical simulation of vortex-induced-vibration (VIV) on an elastically supported rigid circular cylinder in a fluid cross-flow (A. Placzek, J.F. Sigrist, A. Hamdouni; Numerical Simulation of Vortex Shedding Past a Circular Cylinder at Low Reynolds Number with Finite Volume Technique. Part I: Forced Oscillations, Part II: Flow Induced Vibrations; Pressure Vessel and Piping, San Antonio, 22–26 July 2007). Such a problem has been thoroughly studied over the past years, both from the experimental and numerical points of view, because of its theoretical and practical interest in the understanding on flow-induced vibration problems. In this context, the present paper aims at exposing a numerical study based on a fully coupled fluid-structure simulation. The numerical technique is based on a finite volume discretisation of the fluid flow equations together with i) a re-meshing algorithm to account for the cylinder motion ii) a projection subroutine to compute the forces induced by the fluid on the cylinder and iii) a coupling procedure to describe the energy exchanges between the fluid flow and solid motion. The study is restricted to moderate Reynolds numbers (Re∼2.000–10.000) and is performed with an industrial CFD code. Numerical results are compared with existing literature on the subject, both in terms of cylinder amplitude motion and fluid vortex shedding modes. Ongoing numerical studies with different numerical techniques, such as ROM (Reduced Order Models)-based methods, will complete the approach and will be published in next PVP conference. These numerical simulations are proposed for code validation purposes prior to industrial applications in tube bundle configuration.

Numerical study of fluid flow past a rotating elliptic cylinder

2017 ◽  
Vol 68 ◽  
pp. 15-31 ◽  
Author(s):  
Sandeep N. Naik ◽  
S. Vengadesan ◽  
K. Arul Prakash
Keyword(s):  
Fluid Flow ◽  
Numerical Study ◽  
Elliptic Cylinder ◽  
Flow Past

Fluid dynamics around three cylinders in presence of small control cylinders

2020 ◽  
Vol 98 (11) ◽  
pp. 1060-1076
Author(s):  
Ali Ahmed ◽  
Shams-ul Islam ◽  
Chao Ying Zhou ◽  
Raheela Manzoor
Keyword(s):  
Drag Coefficient ◽  
Flow Regime ◽  
Strouhal Number ◽  
Numerical Study ◽  
Critical Flow ◽  
Square Cylinders ◽  
Tandem Square Cylinders ◽  
Critical Flow Regime ◽  
Force Reduction ◽  
Control Cylinder

A numerical study is performed to analyze the effect of small control cylinders on fluid force reduction and vortex shedding suppression on the flow past three inline square cylinders using the lattice Boltzmann method. The Reynolds number Re = 160 is fixed while the spacing between the cylinders is taken in the range of 1.0D ≤ g* ≤ 5.0D (where D is the size of the main cylinder) and the control cylinder size is varied from 0.1D to 0.5D. To systematically understand the effect of control cylinders on the forces, a detailed analysis of Strouhal number (St), mean drag coefficient (CDmean), and root mean square values of the drag and lift coefficients is presented in this paper. In this study, it is observed that the average mean drag coefficient (CDmeanaverage) and Strouhal number reached either maximum or minimum values at different values of separation ratio (g*) and small control cylinder size (d). It is found that at (g*, d) = (5.0, 0.0) and (1.0, 0.5), the average CDmean attains its maximum (CDmeanaverage = 0.7813) and minimum (CDmean = 0.0988) values. Furthermore, at (g*, d) = (5.0, 0.3) and (2.0, 0.0) the average St attains its maximum (St = 0.1780) and minimum (St = 0.041) values. It is found that the flow regimes completely change in the presence of control cylinders. In particular, at g* = 4.0 there is a critical flow regime when the size of the control cylinder changes from 0.1 to 0.5. The sudden jump in the mean drag coefficient and Strouhal number for the middle cylinder with their maximum and minimum values also confirms the critical flow regime. The effect of control cylinders within tandem square cylinders has not been studied before.

A Numerical Study of Geometrical Effects on the Strouhal Number of a Circular Cylinder

2008 ◽  
Author(s):  
Farzan Kazemifar ◽  
Mehdi Molai ◽  
Bahar Firoozabadi ◽  
Goodarz Ahmadi
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Circular Cylinders ◽  
Percentage Reduction ◽  
Blade Angle ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Geometrical Effects

In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α = 0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d = 0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α = 0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was increased from zero to 90°, the percentage reduction in Strouhal number decreased; however, as the blade angle was further increased from 90° to 150°, the percentage reduction in Strouhal number increased. Although the modifications studied here decrease the vortex shedding frequency they make the vortices shed from the cylinder farther and stronger hence increasing the magnitude of the fluctuating forces.

An Experimental Investigation of Aspect Ratio and Incidence Angle Effects for the Flow Around Surface-Mounted Finite-Height Square Prisms

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
J. F. McClean ◽  
D. Sumner
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Incidence Angle ◽  
Lift Coefficient ◽  
Ground Plane ◽  
Aspect Ratios ◽  
Square Prism ◽  
The Mean

The flow around a surface-mounted finite-height square prism was investigated using a low-speed wind tunnel. The experiments were conducted at a Reynolds number of Re = 7.3 × 104 for prism aspect ratios of AR = 3, 5, 7, 9, and 11 and incidence angles from α = 0 deg to 45 deg. The thickness of the boundary layer on the ground plane relative to the side length was δ/D = 1.5. Measurements of the vortex shedding frequency were made with a single-component hot-wire probe, and measurements of the mean drag and lift forces were obtained with a force balance. For all aspect ratios and incidence angles, the mean drag coefficient and Strouhal number were lower than those of an infinite prism, while the mean lift coefficient was of nearly similar magnitude. As the aspect ratio was increased from AR = 3 to 11, the force coefficients and Strouhal number slowly approached the infinite-square-prism data. The mean drag coefficient and Strouhal number for the finite prism were less sensitive to changes in incidence angle compared to the infinite square prism. The critical incidence angle, corresponding to minimum mean drag coefficient, minimum (most negative) mean lift coefficient, and maximum Strouhal number, shifted to a higher incidence angle compared to the infinite square prism, with values ranging from αcritical = 15 deg to 18 deg; this shift was greatest for the prisms of higher aspect ratio. The behavior of the force coefficients and Strouhal number for the prism of AR = 3 was distinct from the other prisms (with lower values of mean drag coefficient and mean lift coefficient magnitude, and a different Strouhal number trend), suggesting the critical aspect ratio was between AR = 5 and AR = 3 in these experiments. In the wall-normal direction, the power spectra for AR = 11 and 9 tended to have weaker and/or more broad-banded vortex shedding peaks near the ground plane and near the free end at α = 0 deg and 15 deg. For AR = 7 to 3, well-defined vortex shedding peaks were detected along the entire height of the prisms. For AR = 11 and 9, at α = 30 deg and 45 deg, vortex shedding peaks were absent in the power spectra in the upper part of the wake.

The Effect of Boat-Tailing on the Flow Round a Two-Dimensional Blunt-Based Aerofoil at Zero Incidence

1967 ◽  
Vol 71 (684) ◽  
pp. 854-858 ◽  
Author(s):  
D. J. Maull ◽  
B. J. Hoole
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Pressure Distribution ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Base Pressure ◽  
Two Dimensional ◽  
Flow Round ◽  
Low Speeds

SummarySome experiments on the effect of boat-tailing on the pressure distribution round blunt-based aerofoils are described. The experiments were carried out at low speeds at a Reynolds number of 1.5 X 105. The wake was investigated with attention being paid to the vortex shedding, and to the distance downstream of the base where vortices form.It is shown that the theory due to Nash predicts the effect of boat-tailing on base pressure quite well and that a correlation of drag coefficient, Strouhal number and base pressure proposed by Bearman applies to the models tested here.

Steady and Unsteady Laminar Flow Past an Equilateral Triangular Cylinder for Two Different Orientations

2007 ◽  
Author(s):  
Zakir Faruquee ◽  
Temitope V. Olatunji
Keyword(s):  
Fluid Flow ◽  
Laminar Flow ◽  
Drag Coefficient ◽  
Incompressible Flow ◽  
Vortex Shedding ◽  
Equilateral Triangle ◽  
Downstream Side ◽  
Flow Past

Unconfined fluid flow past an equilateral triangle was numerically studied for laminar incompressible flow. Two configurations of the cylinder were studied. In the first configuration; a vertex was placed upstream and a side was placed in the downstream position normal to the flow, while in the second configuration; the orientation of the triangle was reversed, i.e. the side normal to the flow was placed upstream and a vertex was placed at the downstream. Both steady and unsteady simulations were performed at 30 ≤ Re ≤ 150. The results clearly show that the orientation of the triangle with the vertex at the downstream side stabilized the flow and delayed the onset of vortex shedding. Significant differences of drag coefficient, wake length, and velocity distributions were found between the two orientations of the equilateral triangle.

Aerodynamic Forces and Vortex Shedding for Surface-Mounted Finite Square Prisms and the Effects of Aspect Ratio and Incidence Angle

2012 ◽  
Author(s):  
John F. McClean ◽  
David Sumner
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Incidence Angle ◽  
Lift Coefficient ◽  
Ground Plane ◽  
Aspect Ratios ◽  
Square Prism ◽  
The Mean

The flow around a surface-mounted square prism of finite height was investigated experimentally using a low-speed wind tunnel. Of interest were the effects of aspect ratio and incidence angle on the mean aerodynamic forces and vortex shedding. Compared to the case of the “infinite” (or two-dimensional) square prism, the flow around the finite square prism has not been extensively studied. The experiments were conducted at a Reynolds number of Re = 7.2 × 104 for aspect ratios of AR = 3, 5, 7, 9, and 11 and incidence angles of α = 0°, 15°, 30° and 45°. The thickness of the boundary layer on the ground plane relative to the side length was δ/D = 1.5. Measurements of the vortex shedding frequency were made with a single-component hot-wire probe in the wake, and measurements of the mean drag and lift forces were obtained with a force balance. For all aspect ratios and incidence angles, the Strouhal number and the mean drag coefficient were lower than those of an infinite prism, while the mean lift coefficient was of nearly similar magnitude. As the aspect ratio was increased from AR = 3 to 11, the force coefficients and Strouhal number slowly approached the infinite-square-prism data. The behaviours of the mean drag coefficient and Strouhal number with incidence angle were less sensitive compared to the case of the infinite square prism, although a minimum mean drag coefficient, minimum (most negative) mean lift coefficient, and maximum Strouhal number were found at α = 15°. The reduced sensitivity to incidence angle is attributed to the complex three-dimensional flow over the free end of the prism and the downwash flow that enters the near wake. The behaviour of the force coefficients and Strouhal number for the prism of AR = 3 was distinct from the other prisms (with lower values of drag coefficient and lift coefficient magnitude, and a different Strouhal number trend), suggesting the critical aspect ratio was between AR = 5 and AR = 3 in these experiments. In the wall-normal direction, the power spectra for AR = 11 and 9 tended to have weaker and/or more broad-banded vortex shedding peaks near the ground plane and near the free end at α = 0° and 15°. For AR = 7 to 3, well-defined vortex shedding peaks were detected along the entire height of the prisms. For AR = 11 and 9, at α = 30° and 45°, vortex shedding peaks were absent in the power spectra in the upper part of the wake.

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