Effects of Buoyancy on the Turbulent Wake of a Horizontal Cylinder in Cross-Flow

2012 ◽  
Author(s):  
Matthieu Boirlaud ◽  
Dominique Couton ◽  
Frédéric Plourde
Keyword(s):  
Mixed Convection ◽  
Shear Layer ◽  
Thermal Wave ◽  
Thermal Field ◽  
Cross Flow ◽  
Horizontal Cylinder ◽  
Transition To Turbulence ◽  
Cylinder Surface ◽  
Convection Regime

While heat transfer around bluff-bodies have been extensively studied in natural and forced convection regime, the mixed convection regime has not still yet brought so much attention; however the latter has direct interest either in various engineering applications or for fundamental point of views. Direct Numerical Simulation was applied in this paper to study the buoyancy effects in the wake of a horizontal cylinder in cross-flow for Re∞ = 1000 and Ri = 2.77. In the framework of mixed convection regime, results mainly focus on the role of thermal field and buoyancy effects. The main visible impact in the thermal field introduction is the asymmetry in the cylinder wake. In addition, typical mushroom-like structures driven by thermal field develop along the wake. From an unsteady point of view, a thermal wave develops from the bottom of the cylinder and the latter follows the cylinder surface. As a consequence, the upper shear-layer that occurs in isotherm case is strongly disturbed because of the interaction with the thermal wave and the lower shear-layer is stretched in the flow direction. Comparisons with the isotherm case help us to better understand the role of the thermal field and the effects of buoyancy in the transition to turbulence.

A Mixed Thermal Convection Criteria for a Printed Circuit Board

2001 ◽  
Author(s):  
E. Kehoe ◽  
R. Grimes ◽  
M. Davies
Keyword(s):  
Temperature Distribution ◽  
Mixed Convection ◽  
Printed Circuit Board ◽  
Transfer Problem ◽  
Cross Flow ◽  
Electronic System ◽  
Horizontal Cylinder ◽  
Circuit Board ◽  
Printed Circuit ◽  
Wide Range

Abstract Mixed convection is a fundamentally significant heat transfer problem that occurs in a wide range of industrial and technological applications. For example, it is of great interest to thermal designers in the field of electronic cooling. Given that its occurrence is frequent, there is a necessity to understand its physics. This investigation is focused on a horizontal cylinder in cross-flow, at low Reynolds numbers of order 100–102 and high Grashof numbers of order 104 and at the Prandtl number for air. Particle image velocimetry and interferometric measurements for these cases clearly show the range of Gr/Re2 for which mixed convection occurs. Infra red temperature measurements from a printed circuit board mounted in a test electronic system at similar values of Grashof and Reynolds number are then presented which exhibit similar mixed convection phenomena. The novelty lies in using the detailed measurements from the cylinder experiments to explain the temperature distribution across the printed circuit board. To do this requires finding the correct and characteristic lengths in the similarity condition. This should therefore allow the designers of electronic systems to estimate the values of Reynolds and Grashof number for which buoyancy effects need to be considered. This in turn will enable the designer to better predict the circuit board temperature distribution and component reliability.

scholarly journals Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2746
Author(s):  
Mingjin Liu ◽  
Jiaxu Luo ◽  
Jin Chen ◽  
Xueqin Gao ◽  
Qiang Fu ◽  
...  
Keyword(s):  
Shear Layer ◽  
Crack Growth ◽  
Isotactic Polypropylene ◽  
Slow Crack Growth ◽  
Crack Growth Behavior ◽  
Polymer Science ◽  
The Past ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

scholarly journals Role of thermal field in entanglement harvesting between two accelerated Unruh-DeWitt detectors

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Dipankar Barman ◽  
Subhajit Barman ◽  
Bibhas Ranjan Majhi
Keyword(s):  
Mutual Information ◽  
Critical Point ◽  
Thermal Field ◽  
Narrow Range ◽  
Critical Value ◽  
Critical Values ◽  
Parallel Motion ◽  
Field Temperature ◽  
The Right

Abstract We investigate the effects of field temperature T(f) on the entanglement harvesting between two uniformly accelerated detectors. For their parallel motion, the thermal nature of fields does not produce any entanglement, and therefore, the outcome is the same as the non-thermal situation. On the contrary, T(f) affects entanglement harvesting when the detectors are in anti-parallel motion, i.e., when detectors A and B are in the right and left Rindler wedges, respectively. While for T(f) = 0 entanglement harvesting is possible for all values of A’s acceleration aA, in the presence of temperature, it is possible only within a narrow range of aA. In (1 + 1) dimensions, the range starts from specific values and extends to infinity, and as we increase T(f), the minimum required value of aA for entanglement harvesting increases. Moreover, above a critical value aA = ac harvesting increases as we increase T(f), which is just opposite to the accelerations below it. There are several critical values in (1 + 3) dimensions when they are in different accelerations. Contrary to the single range in (1 + 1) dimensions, here harvesting is possible within several discrete ranges of aA. Interestingly, for equal accelerations, one has a single critical point, with nature quite similar to (1 + 1) dimensional results. We also discuss the dependence of mutual information among these detectors on aA and T(f).

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.

Flow Reversal in Opposing Mixed Convection Flow in Inclined Pipes

1989 ◽  
Vol 111 (1) ◽  
pp. 114-120 ◽  
Author(s):  
A. S. Lavine ◽  
M. Y. Kim ◽  
C. N. Shores
Keyword(s):  
Mixed Convection ◽  
Tilt Angle ◽  
Maximum Flow ◽  
Flow Reversal ◽  
Transition To Turbulence ◽  
Convection Flow ◽  
Periodic Behavior ◽  
Tube Cross Section ◽  
High Reynolds ◽  
Inclined Pipe

An experimental investigation of opposing mixed convection in an inclined pipe has been conducted. Dye injection reveals the existence of flow reversal regions. There is an optimal tilt angle that yields maximum flow reversal length. Flow reversals are seen to cause early transition to turbulence. Temperature profiles are measured across the tube cross section near the entrance to the heated section, and show the effect of tube inclination. Temperature measurements exhibit periodic behavior in the flow reversal region under some conditions, generally characterized by low tilt angle and moderate to high Reynolds and Grashof numbers. Flow visualization indicates that this periodic behavior is due to the intermittent breakdown of the flow reversal region.

Study of the Mixed Convection in a Horizontal Channel Heated from below

2015 ◽  
Vol 789-790 ◽  
pp. 398-402
Author(s):  
N. Mahfoud Sahraoui ◽  
Samir Houat ◽  
Nawal Saidi
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Lattice Boltzmann ◽  
Thermal Field ◽  
Lattice Boltzmann Model ◽  
Horizontal Channel ◽  
Comparison Of The Results ◽  
Stretching Ratio ◽  
Boltzmann Model

In this work, a contribution to the modeling and numerical simulation of mixed convection in a horizontal channel heated from below is presented. The lattice Boltzmann model with double thermal populations (TLBM) is used with the D2Q9 model for the dynamic field and D2Q5 for the thermal field. A comparison of the results obtained by the lattice Boltzmann model with those of the literature is presented for an area stretching ratio B = H / L = 20, a Reynolds number Re = 10, Rayleigh Ra = 104 and Peclet number Pe = 20/3. The streamlines and isotherms are presented for different periods of flow.

Mixing in Symmetric Holmboe Waves

2007 ◽  
Vol 37 (6) ◽  
pp. 1566-1583 ◽  
Author(s):  
W. D. Smyth ◽  
J. R. Carpenter ◽  
G. A. Lawrence
Keyword(s):  
Shear Layer ◽  
Effective Viscosity ◽  
Laboratory Experiments ◽  
Density Difference ◽  
Transition To Turbulence ◽  
Mixing Efficiency ◽  
Effective Diffusivities ◽  
Key Parameter

Abstract Direct simulations are used to study turbulence and mixing in Holmboe waves. Previous results showing that mixing in Holmboe waves is comparable to that found in the better-known Kelvin–Helmholtz (KH) billows are extended to cover a range of stratification levels. Mixing efficiency is discussed in detail, as are effective diffusivities of buoyancy and momentum. Entrainment rates are compared with results from laboratory experiments. The results suggest that the ratio of the thicknesses of the shear layer and the stratified layer is a key parameter controlling mixing. With that ratio held constant, KH billows mix more rapidly than do Holmboe waves. Among Holmboe waves, mixing increases with increasing density difference, despite the fact that the transition to turbulence is delayed or prevented entirely by the stratification. Results are summarized in parameterizations of the effective viscosity and diffusivity of Holmboe waves.

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