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Buoyancy Forces (buoyancy + force)
Selected AbstractsMixed convection in a horizontal square duct with local inner heatingHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2005Koichi Ichimiya Abstract Numerical analyses were performed for the effect of local inner heating on the mixing flow in a horizontal square duct. Three-dimensional governing equations were solved for Re = 100,Pr = 0.72, and six kinds of inner heating sizes in a duct, with insulated walls or uniform temperature walls. Local inner heating induced the local buoyancy force and produced four recirculating flows across a section in a thermally insulated duct. In a horizontal square duct with uniform wall temperature, the interaction of the buoyancy-induced flows by temperature difference between the fluid and the local inner heating, and between the fluid and the walls reduced the maximum intensity of the secondary flow. Two recirculating flows were generated in a downward region. Heat transfer was locally enhanced or depressed corresponding to the flow situation. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 160,170, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20056 [source] Direct simulation of the buoyant rise of bubbles in infinite liquid using level set methodTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Zhao Yu Abstract In this study, 3-D level set method is applied to investigate the rise of gas bubbles in infinite liquid domain due to the buoyancy force. A number of typical regimes for single bubble rising are studied, including the ellipsoidal, ellipsoidal cap, spherical cap, and skirted bubbles. The bubble shape and rise velocity predicted by the simulation are compared with the graphical correlations of Grace, Trans. Inst. Chem. Eng., 51, 116,120, (1973) and Bhaga and Weber, J. Fluid Mech., 105, 61,85, (1981). Good agreement is found between the simulation results and the correlations. These simulations cover a wide range of the parameters, including Eo, Mo, and Re, and demonstrate the capability and accuracy of level set method for simulation of bubbles under various conditions with considerable deformation. Finally, simulation results for the coalescence of two bubbles are also presented. Dans cette étude, une méthode de level set en 3-D est utilisée pour examiner la montée des bulles de gaz due à la force de flottabilité dans un domaine liquide infini. Plusieurs régimes typiques de montée d'une bulle sont étudiés, dont le régime ellipsoïdal, le chapeau ellipsoïdal, le chapeau sphérique et les ceintures de bulles. La forme des bulles et la vitesse de montée prédites par la simulation sont comparées aux corrélations graphiques de Grace, Trans. Inst. Chem. Eng., 51, 116,120, (1973), et Bhaga et Weber, J. Fluid Mech., 105, 61,85, (1981). Un bon accord est trouvé entre les résultats des simulations et les corrélations. Ces simulations couvrent un large éventail de paramètres, notamment Eo, Mo, et Re, et montrent la capacité et la précision de la méthode level set pour la simulation des bulles dans des conditions diverses avec une déformation considérable. Enfin, les résultats des simulations sont également présentés pour la coalescence de deux bulles. [source] Numerical study of influences of buoyancy and solutal Marangoni convection on flow structures in a germanium-silicon floating zoneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2005K. Lin Abstract This paper presents a numerical study of Marangoni flows in a floating zone of germanium-silicon crystals, which was performed by using a commercial finite element program FIDADTM. The numerical results point out that for fluids with a small Pr number the influence of buoyancy forces cannot be ignored in the numerical model. Furthermore, the competition between the thermocapillary (TC) and solutocapillary (SC) flows in the floating zones was qualitatively examined. If the TC flow is as strong as that in the Si-rich floating zone, the SC flow may be restricted to the bottom area near the free surface. Otherwise, the SC flow may overcome the TC flow and induce a surface transfer of species. The numerical predictions agree well with the previous experiment results. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Migration and sedimentation of spherical particles in a yield stress fluid flowing in a horizontal cylindrical pipeAICHE JOURNAL, Issue 10 2009Othmane Merkak Abstract This study looks at the dynamics of a particle suspended in a viscoplastic fluid, flowing in a horizontal circular cylindrical pipe. Inertia effects are negligible in comparison with viscous effects and plastic effects. The suspensions are highly stabilized and at rest the spheres cannot settle under gravity alone. The results of Merkak et al. (AIChE J. 2008;54:1129,1138) are extended, taking into consideration both particles of the same density or denser than the fluid and pipe-to-particle diameter ratios of 8 or 56. New migration phenomena in the sheared zone are thus evidenced when buoyancy forces are nil. In the case of particles denser than the fluid, it is shown how the spheres settle by bypassing the plug-flow zone. A map showing the stability of flowing suspensions could, thus, be drawn. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Turbulence energetics in stably stratified geophysical flows: Strong and weak mixing regimesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 633 2008S. S. Zilitinkevich Abstract Traditionally, turbulence energetics is characterised by turbulent kinetic energy (TKE) and modelled using solely the TKE budget equation. In stable stratification, TKE is generated by the velocity shear and expended through viscous dissipation and work against buoyancy forces. The effect of stratification is characterised by the ratio of the buoyancy gradient to squared shear, called the Richardson number, Ri. It is widely believed that at Ri exceeding a critical value, Ric, local shear cannot maintain turbulence, and the flow becomes laminar. We revise this concept by extending the energy analysis to turbulent potential and total energies (TPE, and TTE = TKE + TPE), consider their budget equations, and conclude that TTE is a conservative parameter maintained by shear in any stratification. Hence there is no ,energetics Ric', in contrast to the hydrodynamic-instability threshold, Ric,instability, whose typical values vary from 0.25 to 1. We demonstrate that this interval, 0.25 < Ri < 1, separates two different turbulent regimes: strong mixing and weak mixing rather than the turbulent and the laminar regimes, as the classical concept states. This explains persistent occurrence of turbulence in the free atmosphere and deep ocean at Ri , 1, clarifies the principal difference between turbulent boundary layers and free flows, and provides the basis for improving operational turbulence closure models. Copyright © 2008 Royal Meteorological Society [source] | ||||||||||