Numerical study of flow through and around a circular array of cylinders

This paper describes a study of the local and global effect of an isolated group of cylinders on an incident uniform flow. Using high resolution two-dimensional computations, we analysed the flow through and around a localised circular array of cylinders, where the ratio of array diameter (DG) to cylinder diameter (D) is 21. The number of cylinders varied from NC = 7 to 133, and they were arranged in a series of concentric rings to allow even distribution within the array with an average void fraction φ = NC(D/DG)2, which varied from 0.016 to 0.30. The characteristic Reynolds number of the array was ReG = 2100. A range of diagnostic tools were applied, including the lift/drag forces on each cylinder (and the whole array), Eulerian and Lagrangian average velocity within the array, and the decay of maximum vorticity with distance downstream. To interpret the flow field, we used vorticity and the dimensionless form of the second invariant of the velocity gradient tensor. A mathematical model, based on representing the bodies as point forces, sources and dipoles, was applied to interpret the results. Three distinct flow regimes were identified. For low void fractions (φ < 0.05), the cylinders have uncoupled individual wake patterns, where the vorticity is rapidly annihilated by wake intermingling downstream and the forces are similar to that of an isolated cylinder. At intermediate void fractions (0.05 < φ < 0.15), a shear layer is generated at the shoulders of the array and the force acting on the cylinders is steady. For high void fractions (φ > 0.15), the array generates a wake in a similar way to a solid body of the same scale. For low void fraction arrays, the mathematical model provides a reasonable assessment of the forces on individual bodies within the array, the Eulerian mean velocity and the upstream velocity field. While it broadly captures the change in the rate of decay of the maximum vorticity magnitude Ωmax downstream, the magnitude is underpredicted.

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Numerical Study on the Effect of Bend Angle on Turbulent Flow through Oscillating Bend

Chemical Product and Process Modeling ◽

10.2202/1934-2659.1436 ◽

2009 ◽

Vol 4 (1) ◽

Author(s):

Elham Ameri ◽

M Nasr Esfahany

Keyword(s):

Numerical Study ◽

Bend Angle ◽

Curvature Radius ◽

Primary Flow ◽

Mean Velocity ◽

Contour Map ◽

Curved Pipes ◽

Flow Through ◽

The Mean ◽

Turbulent Air Flow

The effect of the bend angle on the unsteady developing turbulent air flow through oscillating circular-sectioned curved pipes with the various angles of 180°, 135° and 90° was investigated numerically. The bends had a diameter of 106 mm and a curvature radius ratio of 6.0 with long, straight upstream and downstream sections. Results of the mean velocity and static pressure were obtained at a Reynolds number of 31200 and at various longitudinal stations. The velocity of the primary flow was illustrated in the form of contour map and vector diagram. From the inlet plane of the three oscillating bends to the angle of 45°, the velocity fields in 180°, 90° and 135° bends are similar. The high velocity regions, however, occur near the upper and lower parts in 90° and 180° bends, respectively.

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Calculations of three-dimensional viscous flow in a multiblade centrifugal fan by modelling blade forces

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/095765003322066510 ◽

2003 ◽

Vol 217 (3) ◽

pp. 287-297 ◽

Cited By ~ 17

Author(s):

S-J Seo ◽

K-Y Kim ◽

S-H Kang

Keyword(s):

Mathematical Model ◽

Turbulent Flows ◽

Numerical Study ◽

Three Dimensional ◽

Navier Stokes ◽

Centrifugal Fan ◽

Complex Flows ◽

Flow Through ◽

Volume Method ◽

The Mathematical Model

A numerical study is presented for Reynolds-averaged Navier-Stokes analysis of three-dimensional turbulent flows in a multiblade centrifugal fan. Present work aims at development of a relatively simple analysis method for these complex flows. A mathematical model of impeller forces is obtained from the integral analysis of the flow through the impeller. A finite volume method for discretization of governing equations and a standard k-ɛ model as turbulence closure are employed. For the validation of the mathematical model, the computational results for velocity components, static pressure, and flow angles at the exit of the impeller were compared with experimental data. The comparisons show generally good agreement, especially at higher flow coefficients.

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Computational Study of the Effect of Homogeneous and Heterogeneous Bubbly Flows on Bulk Gas–Liquid Heat Transfer

Journal of Fluids Engineering ◽

10.1115/1.4047806 ◽

2020 ◽

Vol 142 (10) ◽

Author(s):

Nithin S. Panicker ◽

Alberto Passalacqua ◽

Rodney O. Fox

Keyword(s):

Heat Transfer ◽

Heat Transfer Rate ◽

Void Fraction ◽

Transfer Rate ◽

Numerical Study ◽

Computational Study ◽

Bubbly Flows ◽

Heterogeneous Flow ◽

Void Fractions ◽

Liquid Heat

Abstract A numerical investigation is performed on buoyancy-driven homogeneous and heterogeneous bubbly flows to compare the bulk gas–liquid heat transfer effectiveness for Prandtl (Pr) numbers 0.2–20 and void fractions 〈αg〉 0.3–0.5. For this purpose, transient two-fluid model simulations of bubbles rising in a stagnant pool of liquid are conducted in a rectangular box by applying periodic boundary conditions to all the sides. The temperature difference (ΔT) between gas and liquid phase is averaged over the rectangular box and monitored with respect to time, the heat transfer rate is studied based on the time at which the ΔT tends to zero. The results of numerical study show that at low Pr numbers, faster decay of ΔT is observed for homogeneous flow of bubbles indicating higher heat transfer rate in comparison with the heterogeneous flow of bubbles for the same void fraction. On the contrary, for high Pr numbers, higher heat transfer rate is observed in heterogeneous flow compared to the homogeneous. The comparison of heat transfer behavior between different void fractions for heterogeneous flow show that, for low Pr numbers higher heat transfer rate is achieved for void fraction 0.4 in comparison with void fraction 0.5. And for high Pr numbers, higher heat transfer is observed for void fraction 0.5 in comparison with void fraction 0.4.

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A MATHEMATICAL MODEL OF BLOOD FLOW IN AN INTRACRANIAL ANEURYSM: ANALYTICAL AND NUMERICAL STUDY

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519406001881 ◽

2006 ◽

Vol 06 (02) ◽

pp. 137-151 ◽

Cited By ~ 2

Author(s):

SVETOSLAV NIKOLOV ◽

STOYAN STOYTCHEV

Keyword(s):

Mathematical Model ◽

Blood Flow ◽

Numerical Study ◽

Flow Stability ◽

Wall Material ◽

Pulsatile Pressure ◽

Non Linear ◽

Flow Through ◽

Model Equations ◽

The Mathematical Model

An aneurysm is a local enlargement of the vessel lumen due to the weakening of the wall material. We propose a mathematical model of the pulsatile blood flow through the system consisting of the cerebral artery and an aneurysm. The mathematical model is based on mass and energy conservation laws. It comprises non-linear rheological properties of the aneurysm and artery, and inertial and resistant properties of the blood flow. The model equations are analyzed by the methods of non-linear dynamics and they are solved numerically. Special attention is paid to the flow stability as a function of the aneurysmal and arterial material properties, the mean and oscillating arterial pressure, and the frequency of heart pulsations. The results of the work can be summarized as follows: (i) the model equations are stable at normal physiological conditions and developed aneurysms, (ii) with decreasing of the aneurysmal compliance, the aneurysmal volume pulsations increase and a limit point of flow stability is approached, (iii) the increased amplitude of the pulsatile pressure and the heart frequency cannot lead to flow instabilities.

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