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

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.

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.

COMPARISON OF LES WITH DSM, k-ε AND EXPERIMENTS FORTURBULENT VORTEX SHEDDING FLOW PAST 2D SQUARE CYLINDER

1994 ◽  
Vol 59 (459) ◽  
pp. 49-56 ◽  
Author(s):  
Shigehiro SAKAMOTO ◽  
Akashi MOCHIDA ◽  
Shuzo MURAKAMI ◽  
Wolfgang RODI
Keyword(s):  
Vortex Shedding ◽  
Square Cylinder ◽  
Flow Past

An experimental assessment of the evaporation correlations for natural, forced and combined convection regimes

2011 ◽  
Vol 226 (1) ◽  
pp. 145-153 ◽  
Author(s):  
A Jodat ◽  
M Moghiman
Keyword(s):  
Mixed Convection ◽  
Forced Convection ◽  
Evaporation Rate ◽  
Density Variation ◽  
Convection Regime ◽  
Combined Convection ◽  
Wide Range ◽  
The Difference ◽  
Rate Of Evaporation ◽  
Evaporation Models

In the present study, the applicability of widely used evaporation models (Dalton approach-based correlations) is experimentally investigated for natural, forced, and combined convection regimes. A series of experimental measurements are carried out over a wide range of water temperatures and air velocities for 0.01 ≤ Gr/Re2 ≤ 100 in a heated rectangular pool. The investigations show that the evaporation rate strongly depends on the convection regime's Gr/ Re2 value. The results show that the evaporation rate increases with the difference in vapour pressures over both forced convection (0.01 ≤ Gr/Re2 ≤ 0.1) and turbulent mixed convection regimes (0.15 ≤ Gr/Re2 ≤ 25). However, the escalation rate of evaporation decreases with Gr/ Re2 in the forced convection regime whereas in the turbulent mixed convection it increases. In addition, over the range of the free convection regime ( Gr/Re2 ≥ 25), the evaporation rate is affected not only by the vapour pressure difference but also by the density variation. A dimensionless correlation using the experimental data of all convection regimes (0.01 ≤ Gr/Re2 ≤ 100) is proposed to cover different water surface geometries and airflow conditions.

Buoyancy Effect on Heat Transfer in 5×5 Rod Bundles

2017 ◽  
Author(s):  
Da Liu ◽  
Fujun Gan ◽  
Chaozhu Zhang ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Buoyancy Force ◽  
Reynold Number ◽  
Low Flow ◽  
Buoyancy Effect ◽  
Rod Bundles ◽  
Convection Regime ◽  
Dc Power

Experiments of heat transfer at low flow rate are performed in a 5×5 square arrayed rod bundles. The diameter of the rod is 10mm with a pitch of 13.3mm, length of the test section is about 3 meters. Inlet Reynold number ranges from 2000 to 30000, Bo * ranges from 4×10−6 to 5×10−3. The rods are heated using a DC power, the heat flux ranges from 30 to 300 kW/m2. The experiment is aimed to investigate the buoyancy effect of mixed convection in rod bundles. The experimental data shows that similar with mixed convection in circular channels, buoyancy force has great effect on heat transfer at mixed convection regime in rod bundles. But the buoyancy effect appears at higher Bo* conditions. The spacer effect have also been investigated at both turbulent forced convection regime and mixed convection regime. The reconstruction of heat transfer downstream of spacers is different at different flow regimes, a reasonable explanation was provided.

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