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  • A High Resolution Pressure-Based Method for Compressible Fluid Flow
  • Abstract A pressure-based Euler scheme, based on a collocated grid arrangement is described. The newly developed algorithm has two new prominent features: (i) the use of normalized variables to bound the convective fluxes and (ii) the use of a high-resolution scheme in calculating interface density values to enhance the shock-capturing property of the algorithm. The algorithm is first tested for flows at different Mach numbers ranging from subsonic to supersonic on a bump in a channel geometry; then the results are compared with the corresponding ones obtained without the bounded scheme in the correction step. The output is also compared with…
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  • Numerical Study of Low Frequency G-jitter Effect on Thermal Diffusion
  • Abstract Convection has a major impact on diffusion in fluid mixtures either on the Earth or in the microgravity condition. G-jitters, as the primary source that induces the vibrational convection in space laboratories, should be studied thoroughly in order to improve the diffusion-dominated fluid science experiments. In this paper we consider the effect of g-jitters on thermal diffusion. The mixture water-isopropanol (90:10 wt%) bounded in a cubic cell is simulated with a lateral heating and various vibration conditions. The fluid flow, concentration and temperature distributions are thoroughly analyzed for different g-jitter scenarios. It is shown that the overall effect of vibrations…
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  • Thermal Communication between Two Vertical Systems of Free and Forced Convection via Heat Conduction across a Separating Wall
  • Abstract This work deals with the problem of thermal interaction between two fluid media at two different bulk temperatures and separated by a vertical plate. The problem is analyzed by taking into account the heat conduction across the separating plate. The flow configuration considered is one in which the two vertical boundary layers of free and forced convection developed on plate sides are in parallel flow. The dimensionless parameters governing the thermal interaction mechanisms are analytically deduced. The obtained results are presented in graphs to demonstrate the heat transfer characteristics of investigated phenomenon. The work reports a means to estimate the…
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  • On the Stability of the Hadley Flow under the Action of an Acoustic Wave
  • Abstract The effects of an acoustic wave on the instabilities occurring in a lateral differentially heated cavity are investigated numerically. Linear stability results show that the acoustic wave affects significantly the instability characteristics of such a Hadley flow. Indeed, the sound field is found to stabilize both two dimensional transverse stationary and three dimensional longitudinal oscillatory instabilities which are the most critical modes affecting the buoyant convection in the fluid layer. Nevertheless, when stabilized by an acoustic wave, the 2D modes turn from stationary to oscillatory, with the known consequences of such a change on mass and heat transfer, especially in…
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  • On the Dynamic Capillary Effects in the Wetting and evaporation process of Binary Droplets
  • Abstract In this paper the experimental results on the wetting behaviour of volatile binary sessile drops are reported. The evaporation rate is varied through the control of the ambient total pressure. The dynamic wetting contact angle of an evaporating Water-Ethanol drop is investigated at various sub-atmospheric pressures. The wetting properties (contact angle, shape and volume) are monitored in time using a drop shape analysis instrument. The results show that the evaporation of the binary droplet takes place in two stages: the first stage where the wetting behaviour is very similar to the pure ethanol case and a second stage where the…
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  • A Model for Electromagnetic Control of Buoyancy Driven Convection in Glass Melts
  • Abstract Buoyancy driven motion of a highly viscous electrically conducting fluid under the influence of Lorentz forces is investigated theoretically and experimentally. This problem is relevant to the processing of glass, where it is of considerable interest to know whether electromagnetic forces can effectively improve mixing and help to avoid undesired flow patterns in glass melting furnaces. Two highly simplified models are proposed in which the fluid is assumed to be confined in a circular loop containing several localized resistive heating, convective cooling, and electromagnetic forcing elements. The first model is used to derive the scaling laws of the mean velocity…
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  • Fluid Dynamics of a Micro-Bioreactor for Tissue Engineering
  • Abstract A numerical model is developed for the investigation of flow field and mass transport in a micro-bioreactor, of working volume below 5 ml, in which medium mixing is generated by a magnetic stirrer-rod rotating on the bottom. The flow-field results show that a recirculation region exists above the stirrer rod and rotates with it; the related fluid mixing is characterized by a circulation coefficient of up to 0.2 which is about five times smaller than that of a one-litre stirred-tank bioreactor. The oxygen transfer coefficient is less than 5 h-1 which is two orders smaller than that of a 10-litre…
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  • Coalescence and Non-coalescence Phenomena in Multi-material Problems and Dispersed Multiphase Flows: Part 2, A Critical Review of CFD Approaches
  • Abstract The physical properties of many emulsions and metal alloys strongly depend on the multiphase morphology which is controlled to a great degree by particle-particle interaction during the related processing. In the present article significant effort is devoted to illustrate the philosophy of modeling for these phenomena and some insights into the physics. Within such a context working numerical techniques that have enjoyed a widespread use over recent years are presented and/or reviewed. Finally a focused and critical comparison of these possible approaches is reported illustrating advantages and disadvantages, strengths and weaknesses, past history and future directions.
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  • Coalescence and Non-coalescence Phenomena in Multi-material Problems and Dispersed Multiphase Flows: Part 1, A Critical Review of Theories
  • Abstract The manuscript deals with a presentation of the most reliable theories introduced over the years to model particle coalescence and non-coalescence phenomena at both macroscopic and microscopic length scales (including historical developments and very recent contributions) and moves through other macrophysical mechanisms that can cause spatial separation of the fluid phases (liquid-liquid or liquid-gas) in multi-material problems, while providing a rigorous theoretical framework for deeper understanding of how drop (or bubble) migration due to gravity and/or Marangoni effects can interact cooperatively with coalescence to significantly affect the multiphase pattern formation, its evolutionary progress as well as the final quality of…
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