The Wake Behavior Behind a Heated Cylinder in Forced and Mixed Convection Regimes

2005 ◽  
Author(s):  
H. Hu ◽  
M. M. Koochesfahani
Keyword(s):  
Mixed Convection ◽  
Flow Visualization ◽  
Vortex Shedding ◽  
Richardson Number ◽  
Temperature Fields ◽  
Molecular Tagging Velocimetry ◽  
Convection Regime ◽  
Heated Cylinder ◽  
Wake Instability ◽  
Velocity And Temperature Fields

The effect of buoyancy on the wake instability of a heated circular cylinder in a contra flow arrangement is investigated experimentally in the present study. A novel optical diagnostic technique, Molecular Tagging Velocimetry and Thermometry (MTV&T), was used for qualitative flow visualization and quantitative simultaneous measurements of velocity and temperature fields in the wake of the heated cylinder. The experiment was conducted in a water channel with the temperature and Reynolds number of the approaching flow being held constant at T∞ = 24°C and Re = ρ∞U∞D/μ∞ = 130. The temperature of the heated cylinder varied between 24°C (unheated cylinder) and 85°C, corresponding to a Richardson number (Ri) varying between zero (unheated) and unity. The heat transfer process around the heated cylinder changes from the forced convection regime to the mixed convection regime. With increasing Richardson number, significant modifications of the wake instability were revealed from both qualitative flow visualization images and quantitative simultaneous velocity and temperature fields. The effect of buoyancy on the wake instability of the heated cylinder was discussed in the terms of vortex shedding pattern, vortex shedding frequency, turbulent heat flux distribution, the wake closure length and averaged Nusselt number of the heated cylinder.

Thermal effects on the wake of a heated circular cylinder operating in mixed convection regime

2011 ◽  
Vol 685 ◽  
pp. 235-270 ◽  
Author(s):  
H. Hu ◽  
M. M. Koochesfahani
Keyword(s):  
Mixed Convection ◽  
Vortex Shedding ◽  
Thermal Effects ◽  
Richardson Number ◽  
Vortex Structures ◽  
Wake Flow ◽  
Wake Vortex ◽  
Thermally Induced ◽  
Convection Regime ◽  
Heated Cylinder

AbstractThe thermal effects on the wake flow behind a heated circular cylinder operating in the mixed convection regime were investigated experimentally in the present study. The experiments were conducted in a vertical water channel with the heated cylinder placed horizontally and the flow approaching the cylinder downwards. With such a flow arrangement, the direction of the thermally induced buoyancy force acting on the fluid surrounding the heated cylinder would be opposite to the approach flow. During the experiments, the temperature and Reynolds number of the approach flow were held constant. By adjusting the surface temperature of the heated cylinder, the corresponding Richardson number ($\mathit{Ri}= \mathit{Gr}/ {\mathit{Re}}^{2} $) was varied between 0.0 (unheated) and 1.04, resulting in a change in the heat transfer process from forced convection to mixed convection. A novel flow diagnostic technique, molecular tagging velocimetry and thermometry (MTV&T), was used for qualitative flow visualization of thermally induced flow structures and quantitative, simultaneous measurements of flow velocity and temperature distributions in the wake of the heated cylinder. With increasing temperature of the heated cylinder (i.e. Richardson number), significant modifications of the wake flow pattern and wake vortex shedding process were clearly revealed. When the Richardson number was relatively small ($\mathit{Ri}\leq 0. 31$), the vortex shedding process in the wake of the heated cylinder was found to be quite similar to that of an unheated cylinder. As the Richardson number increased to ${\ensuremath{\sim} }0. 50$, the wake vortex shedding process was found to be ‘delayed’, with the wake vortex structures beginning to shed much further downstream. As the Richardson number approached unity ($\mathit{Ri}\geq 0. 72$), instead of having ‘Kármán’ vortices shedding alternately at the two sides of the heated cylinder, concurrent shedding of smaller vortex structures was observed in the near wake of the heated cylinder. The smaller vortex structures were found to behave more like ‘Kelvin–Helmholtz’ vortices than ‘Kármán’ vortices, and adjacent small vortices would merge to form larger vortex structures further downstream. It was also found that the shedding frequency of the wake vortex structures decreased with increasing Richardson number. The wake closure length and the drag coefficient of the heated cylinder were found initially to decrease slightly when the Richardson number was relatively small ($\mathit{Ri}\lt 0. 31$), and then to increase monotonically with increasing Richardson number as the Richardson number became relatively large ($\mathit{Ri}\gt 0. 31$). The average Nusselt number ($ \overline{\mathit{Nu}} $) of the heated cylinder was found to decrease almost linearly with increasing Richardson number.

Numerical Study of Mixed Convection around a Heated Circular Cylinder

2016 ◽  
Vol 836 ◽  
pp. 85-89
Author(s):  
Vivien S. Djanali ◽  
Ahmad Nurdian Syah ◽  
Syaiful Rizal
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Mixed Convection ◽  
Buoyancy Force ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Main Flow ◽  
Heat Transfer Characteristics ◽  
Convection Regime ◽  
Heated Cylinder

Wake and heat transfer characteristics around a heated circular cylinder were studied numerically in this paper. Heat transfer from a heated cylinder to the freestream flow was in mixed convection regime, with the free convection-bouyancy driven flow in opposite direction to the forced convection-main flow. Numerical simulations were performed for three Reynolds numbers of 100, 135 and 200, with the Richardson (Ri = Gr/Re2) numbers varied from 0 to 1. Results showed that buoyancy force significantly altered wake formation behind the heated cylinder, further resulted in increasing drag and decreasing Nusselt number.

Study of the Flow Around a Heated Cylinder in Mixed Convection Regime

2019 ◽  
pp. 277-283
Author(s):  
S. Rolfo ◽  
K. Kopsidas ◽  
S. A. Rahman ◽  
C. Moulinec ◽  
D. R. Emerson
Keyword(s):  
Mixed Convection ◽  
Convection Regime ◽  
Heated Cylinder

scholarly journals Experimental Measurement of Vortex Ring Screen Interaction Using Flow Visualization and Molecular Tagging Velocimetry

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
John T. Hrynuk ◽  
Colin M. Stutz ◽  
Doug G. Bohl
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Laser Induced Fluorescence ◽  
Wire Mesh ◽  
Vortex Rings ◽  
Thin Wire ◽  
Molecular Tagging Velocimetry ◽  
Molecular Tagging

The interaction of vortex rings with thin wire mesh screens is investigated using laser-induced fluorescence (LIF) and molecular tagging velocimetry (MTV). The existence of vortex shedding from individual wires of the porous screens, suggested by prior works, is shown and compared to flow visualization results. A range of interaction Reynolds numbers and screen porosities are studied to determine the conditions affecting the interaction. Transmitted vortex (TV) ring formation is shown to be a function of vortex shedding and the shedding Reynolds number, but not a function of porosity. Screen porosity is shown to affect the TV convective speed but did not impact the formation behaviors. Three major flow regimes existed for the interaction: TV formation with no vortex shedding, TV formation with visible vortex shedding, and no downstream formation with strong shed vortices.

U-RANS Simulation of Mixed-Convection Around a Finite Wall-Mounted Heated Cylinder Cooled by Cross-Flow

2008 ◽  
Author(s):  
Y. Lecocq ◽  
S. Bournaud ◽  
R. Manceau ◽  
B. Duret ◽  
L. Brizzi
Keyword(s):  
Experimental Data ◽  
Mixed Convection ◽  
Cross Flow ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Inertia Force ◽  
Convection Flow ◽  
Test Cases ◽  
Heated Cylinder ◽  
Flow Circulation

VALIDA experiments [1] were carried out within the framework of radioactive waste management to improve the understanding of mixed-convection flow and more particularly the interaction between a global cross-flow circulation and local natural convection effects around a vertical heated cylinder. The VALIDA loop implements a cylinder of 3.1 height to diameter ratio, mounted vertically in an insulated tunnel and cooled by a cross-flow air circulation. The air flow and the temperature fields on the cylinder and in the plume behind it have been numerically studied using Unsteady Reynolds Average Navier Stokes simulation (U-RANS) and compared to experimental data. The purpose of this paper is to present the results of a k-ω SST model on several test cases. The numerical tools used herein are Code_Saturne, EDF finite volume CFD code [2], and Syrthes, EDF finite element code for solid temperatures [9]. For the studied test-cases, Reynolds and Grashof numbers are characteristic of a sub-critical flow regime with laminar boundary layers around the cylinder and a turbulent wake. From the transient downstream air calculations, the plume behind the cylinder and its wall temperatures are analysed and compared to experimental data. The flow pattern strongly depends on the ratio of the buoyancy to the inertia force. Results show satisfactory qualitative and quantitative behaviour.

scholarly journals Magnetohydrodynamic mixed convection in a nanofluid filled tubular enclosure

2020 ◽  
Vol 4 (1) ◽  
pp. 19-24
Author(s):  
Mohammad Mokaddes Ali
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Temperature Fields ◽  
Convection Flow ◽  
Governing Equations ◽  
Convection Regime ◽  
Special Cases ◽  
Flow Domain

Mixed convection flow in a tubular enclosure filled with nanofluid in the presence of a magnetic field is numerically investigated in the present study. The bottom and top curved wall of the enclosure are respectively kept isothermally hot and cool while the remaining walls are insulated. The governing equations are formulated based on Boussinesq assumptions and solved with finite element method. The computation is carried out for mixed convection regime (0.1 ≤ Ri ≤ 10) and also natural convection regime (10 < Ri ≤ 100) with fixed values of remaining parameters. A detailed parametric discussion is presented for the physical properties of flow and temperature distributions in terms of streamlines, isotherms, average heat transfer rate within the flow domain. The results show that the flow and temperature fields affected by varying of pertinent parameters. Moreover, heat transfer rate is increased by 139.50% with the increase in Richardson number from 0.1 to 100. The increasing rate of heat transfer due to Ri is respectively decreased by 58.11% with varying of Ha from 0 to 60 and increased by 23.97% with the addition of nanoparticles up to 3%. Comparison is performed against the previously published results on the basis of special cases and found to be in excellent agreement.

Vortex shedding suppression of vibrating square cylinder in mixed convection regime

2021 ◽  
Vol 33 (12) ◽  
pp. 123610
Author(s):  
Mohammad Athar Khan ◽  
Syed Fahad Anwer ◽  
Saleem Anwar Khan ◽  
Nadeem Hasan
Keyword(s):  
Mixed Convection ◽  
Vortex Shedding ◽  
Square Cylinder ◽  
Convection Regime

Paper 40: Superimposed Laminar Forced and Free Convection between Vertical Parallel Plates when One Plate is Uniformly Heated and the Other is Thermally Insulated

1967 ◽  
Vol 182 (8) ◽  
pp. 374-381 ◽  
Author(s):  
T. L. S. Rao ◽  
W. D. Morris
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pipe Flow ◽  
The Other ◽  
Temperature Fields ◽  
Parallel Plates ◽  
Upward Flow ◽  
Vertical Pipe ◽  
Convection Regime ◽  
Velocity And Temperature Fields

Laminar flow between two vertical parallel plates, with one of the plates uniformly heated and the other thermally insulated, has been studied theoretically for the case where gravitational buoyancy modifies an otherwise forced convection regime. Velocity and temperature fields for two conditions of flow—heated upward flow and cooled upward flow—have been derived. From these results heat transfer and pressure drop data have been calculated and similar tendencies to those which occur in uniformly heated vertical pipe flow were found.

Mixed Convection in Non-Newtonian Fluids Along a Horizontal Plate in a Porous Medium

1997 ◽  
Vol 119 (1) ◽  
pp. 34-37 ◽  
Author(s):  
M. Kumari ◽  
Rama Subba Retty Gorla ◽  
L. Byrd
Keyword(s):  
Heat Flux ◽  
Porous Medium ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Power Law ◽  
Viscosity Index ◽  
Temperature Fields ◽  
Horizontal Plate ◽  
Velocity And Temperature Fields ◽  
Variable Wall

The problem of mixed convection from horizontal surfaces in a porous medium saturated with a power-law-type non-Newtonian fluid is investigated. The transformed conservation laws are solved numerically for the case of variable wall heat flux conditions. Results for the details of the velocity and temperature fields as well as the Nusselt number have been presented. The viscosity index ranged from 0.5–1.5.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

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