Fluid Flow and Heat Transfer Around Two Circular Cylinders in Side-by-Side Arrangement

2004 ◽  
Author(s):  
Minter Cheng
Keyword(s):  
Nusselt Number ◽  
Flow Velocity ◽  
Incompressible Flows ◽  
Temperature Fields ◽  
Circular Cylinders ◽  
Rapid Reduction ◽  
Nusselt Numbers ◽  
Gap Flow ◽  
Pitch Ratio ◽  
The Mean

Incompressible flows passing through two circular cylinders in side-by-side arrangement are investigated numerically. The calculations are carried out with pitch ratios from 1.1 to 2.0 at Reynolds number of 1000. The flow and temperature fields, flow interference, and the local and the mean Nusselt numbers are studied in this research. It is observed that for the pitch ratios in the range of 2.0 and 1.5, the emerging jet between cylinders deflects and one wide and one narrow wakes behind the cylinders are formed. The gap flow velocity increases as the pitch ratio decreases and consequently increases the mean Nusselt number of the cylinders. As the pitch ratio decreases and is less than 1.5, the jet deflection is more severe and the gap flow velocity starts to decrease slowly, which results in reducing the mean Nusselt number of the cylinders. Due to the rapid reduction of the narrow wake size, the mean Nusselt number of the cylinder with narrow wake shows an uprising tendency for the decreasing pitch ratio less than 1.2.

Simulation of the Wake of the Flow Around Two Side-By-Side Circular Cylinders at Reynolds Number 5000

2019 ◽  
Author(s):  
Anna Lyhne Jensen ◽  
Henrik Sørensen ◽  
Jakob Hærvig
Keyword(s):  
Reynolds Number ◽  
Circular Cylinders ◽  
Eddy Simulation ◽  
Gap Flow ◽  
Large Eddy ◽  
Vortex Streets ◽  
Flow Phenomena ◽  
Pitch Ratio ◽  
Pitch Distance ◽  
Stable Flow

Abstract Interaction between the wakes of two cylinders in side-by-side configuration creates interesting flow phenomena. The nature of the wake depends on the Reynolds number and the transverse pitch distance between the cylinders. The flow over two side-by-side cylinders of equal diameter is simulated in 3D at Reynolds number 5000 using Large Eddy Simulation (LES). The centre-to-centre transverse pitch ratio is varied and the flow behind the cylinders is classified into either a bi-stable flow regime with biased gap flow or a regime with parallel vortex streets. Furthermore, representative instantaneous flow fields, Strouhal number and the time varying drag coefficient C′D are presented.

Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pipe Flow ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Pitch Ratio ◽  
The Mean

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

The Influence of Coolant Unsteadiness on Impingement Heat Transfer

2014 ◽  
Author(s):  
Victor J. Zimmer ◽  
James L. Rutledge ◽  
Chris Knieriem ◽  
Shichuan Ou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Coolant Flow ◽  
Time Resolved ◽  
Average Mass ◽  
Flow Unsteadiness ◽  
Nusselt Numbers ◽  
Jet Cooling ◽  
The Mean ◽  
The Impact

Interest in impingement jet cooling and the associated convection phenomena has grown in the past few decades due in part to the desire for higher operating temperatures and reduced coolant flow in turbines. This study utilizes an array of 55 impingement jets to explore both steady and unsteady impingement flow conditions to evaluate the impact of the inherent unsteadiness present in engines compared to traditional steady experiments. Although unsteadiness occurs naturally in engines, intentional pulsation of coolant flow has also been proposed for flow control purposes, further underscoring the need for examination of the impact of pulsation on the heat transfer. Flow unsteadiness of varying amplitudes was induced at Strouhal numbers of magnitude 10−3 to 10−4. Infrared thermography was used to determine high spatial and temporal resolution Nusselt numbers. Time-resolved Nusselt number and mass flow characteristic waveforms were found to differ substantially as a function of the fluctuation amplitude relative to the mean. In some cases, transient coolant flow increases were associated with non-monotonic behavior in the time resolved Nusselt number. Although with certain configurations unsteady flow demonstrated time-averaged Nusselt numbers equivalent to steady flow with equivalent average mass flux, those with the greatest fluctuation in the amplitude of flow unsteadiness relative to the mean resulted in lower average Nusselt numbers.

Flow-Induced Forces on a Cylinder for Different Wall Confinements at High Reynolds Numbers (3.5×105)

1975 ◽  
Vol 97 (2) ◽  
pp. 110-117
Author(s):  
P. Y. Chen ◽  
P. E. Doepker
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Interference Effects ◽  
High Reynolds Numbers ◽  
Gap Flow ◽  
High Reynolds ◽  
Flow Medium ◽  
Available Information

The nearness of a cylinder to a wall has an important effect on the flow-induced forces exerted on that cylinder, particularly when the cylinder is relatively large compared to the cross section of the flow channel. This paper describes an investigation of wall interference effects that occur when crossflow-induced forces are exerted on circular cylinders with moderately large blockages (d/h = 0.2 to 0.33) at high Reynolds numbers (3.5 × 105 – 1.2 × 106). The results show that, within the range studied, the gap flow velocity is the correct flow velocity to compensate for wall interference effects. The data reported here represent the first available information on experimental cross-flow-induced forces at such high Reynolds numbers using water as a flow medium.

A Closer Investigation of the Mean Aerodynamic Forces for Two Staggered Circular Cylinders in Cross-Flow

2002 ◽  
Author(s):  
D. Sumner ◽  
M. D. Richards
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Incidence Angle ◽  
Cross Flow ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Aerodynamic Forces ◽  
Gap Flow ◽  
The Mean ◽  
Small Increments

Two circular cylinders of equal diameter in a staggered configuration, with centre-to-centre pitch ratios of P/D = 1.125 – 4.0, were tested in the subcritical Reynolds number regime, at Re = 3.0×104 – 8.0×104. The incidence angle of the cylinder configuration was varied in small increments from α = 0° – 90° and the mean aerodynamic forces were measured on both the upstream and downstream cylinders. Based on the force measurements, the behaviour of the cylinders was broadly grouped into three categories, depending on P/D. For closely spaced staggered configurations, P/D = 1.125 – 1.25, the aerodynamic forces on both the upstream and downstream cylinders varied significantly with α. Several critical incidence angles were identified for each cylinder that corresponded to local maximum, minimum, or discontinuous behaviour in the forces, which were related to shear layer reattachment and the influence of the gap flow. For moderately spaced staggered configurations, P/D = 1.5 – 2.5, shear layer reattachment and the subsequent transition to gap flow at small α were responsible for the inner lift peak, a corresponding minimum drag, and a loss of lift with increasing α, which becomes more abrupt as P/D is increased. For widely spaced staggered configurations, P/D = 3.0 – 4.0, the two cylinders undergo Ka´rma´n vortex shedding for the entire range of α. At small α, the forces on the downstream cylinder are affected by vortex impingement, and the outer lift peak replaces the inner lift peak. This outer lift peak exhibits some sensitivity to the Reynolds number.

The Convective Heat Transfer in Furcated Blood Vessels

2013 ◽  
Vol 475-476 ◽  
pp. 1599-1602
Author(s):  
Yan Zhang ◽  
Hai Wei Xie
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Element Model ◽  
Temperature Fields ◽  
Bifurcation Ratio ◽  
Single Vessel ◽  
Temperature Distributions ◽  
The Mean

A finite element model was developed to simulate the 3-D velocity and temperature distributions in a vessel system including a bifurcated blood vessel and two branches. The effect of the angel between vessels and bifurcation ratio were taken into account, and the local Nusselt number at three typical radial angels and the mean Nusselt number on a section in the branching vessel were obtained. Results show that: the flow and temperature fields were highly unlike the distributions of a single vessel; the local Nusselt number were different at different radial angels; In the entrance region of the branching vessel the mean Nusselt number on a section was larger than that in a single vessel, and there was a maximum of mean Nusselt number whose value and location varied as the different furcating angel or bifurcation ratio; the mean Nusselt number decays rapidly at a small bifurcation ratio.

Forced Convection in a Square Cavity With Inlet and Outlet Ports

2004 ◽  
Author(s):  
S. M. Saeidi ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Forced Convection ◽  
Computational Study ◽  
Temperature Fields ◽  
Primary Vortex ◽  
Square Cavity ◽  
Outlet Port ◽  
Nusselt Numbers ◽  
The Right

A finite-volume-based computational study of steady laminar forced convection inside a square cavity with inlet and outlet ports is presented. Given a fixed position of the inlet port, the location of outlet port is varied along the four walls of the cavity. The widths of the ports are equal to 5, 15 and 25 percent of the side. By positioning the outlet ports at 9 locations on the walls for Re = 10, 40, 100 and 500 and Pr = 5, a total of 101 cases were studied. For high Re and with the shortest distance between the inlet and outlet ports along the top wall, a primary CW rotating vortex that covers about 70 to 80 percent of the cavity is observed. Similar cases with smaller Re exhibit identical flow patterns but with weaker vortices as Re is lowered. As the outlet ports is lowered along the right wall, the CW primary vortex diminishes its strength; however a CCW vortex that is present next to the top right corner covers a greater portion of the cavity. With the outlet port moving left along the bottom wall, the CW primary vortex is weakened further and the CCW vortex occupies nearly the right half of the cavity. The temperature fields are directly related to the presence of the multiple vortices in the cavity. Regions of high temperature gradient are consistently observed at the interface of the throughflow and next to the solid walls on both sides of the outlet port. Local Nusselt numbers are low at 3 corners when no outlet port is present in their vicinity, whereas intense heat transfer rate is observed on the two sides of the outlet port. Between these minima and maxima, the local Nusselt number can vary drastically depending on the flow and temperature fields. By placing the outlet port with one end at the 3 corners, maximum total Nusselt number of the cavity can be achieved. Minimum total heat transfer of the cavity is achieved with the outlet port located at the middle of the walls.

scholarly journals Numerical Analysis of the Improving Thermal Energy Efficiency of Taylor-couette Flow

2021 ◽  
Vol 15 ◽  
pp. 236-247
Author(s):  
Khaoula Ben Abdelmlek ◽  
Fayçal Ben Nejma
Keyword(s):  
Energy Efficiency ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Rotation Velocity ◽  
Radius Ratio ◽  
Nusselt Numbers ◽  
Cylindrical Annulus ◽  
The Mean ◽  
Rayleigh Numbers

This paper deals with adimensionnal analysis of natural convection in a horizontal cylindrical annulus. The inner cylinder is isothermally heated and rotates with an angular velocity Ω, however the outer one is kept cold and motionless. The gap between cylinders is defined by an adimensional radius ratio f. The numerical study was carried out using COMSOL Multiphysics. The effects of Rayleigh number ranging from 102 to 106, radius ratio and rotation velocity on the flow pattern and the thermal behavior in the annulus are then elaborated. Particular attention is paid to the effect of different parameters on the local Nusselt numbers on the inner and outer cylinders, the mean Nusselt number and the energy efficiency of the process. Results show that the mean Nusselt number increases with the increase of Rayleigh number. However, it decreases with the increase of the radius ratio f because of the narrowing of the annulus. The results prove also that the heat transfer rate drops with the rise of rotation velocity. Finally, it was found that the energy efficiency achieved its maximum for lower Rayleigh numbers Ra=103, and lower rotation velocities.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

Experimental Study on Hydraulic Roughness of Submerged Grass in Ecological Riverbank

2013 ◽  
Vol 838-841 ◽  
pp. 1743-1748
Author(s):  
Dian Guang Ma ◽  
Chun Xin Zhong ◽  
Wu Ning ◽  
Qing Ye ◽  
Sheng Zhu
Keyword(s):  
Flow Velocity ◽  
Roughness Coefficient ◽  
Theoretic Analysis ◽  
Mean Flow ◽  
Normal Range ◽  
Obvious Effect ◽  
Hydraulic Roughness ◽  
Natural Turf ◽  
Scouring Process ◽  
The Mean

A model experiment about the hydraulic roughness of natural turf used in riverbank was carried out in flume. To examine the rationality of experimental design, the hydraulic roughness coefficient of plexiglass-flume was tested firstly. The result was 0.0085, which is quite normal. Then the tested hydraulic roughness caused by vegetation ranges from 0.020 to 0.090 for the chosen plants, which is also acceptable. Furthermore, the tested incipient velocities of krasnozem, and paddysoil had the range of 0.55~0.65m·s-1 and 1.0~1.1m·s-1, respectively. All these experimental results are in normal range, which means that the design of this experimental is rational. Experimental research illustrate that, the roughness coefficient of plant reduces with the increasing of flow velocity. When the mean flow velocity is over 3m·s-1, Mannings n values vary between 0.025 and 0.035. This phenomenon is accord with the theoretic analysis. During the scouring process, not only the flow velocity, but also the flow duration has an obvious effect on the coarseness of vegetative bed.

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