5,050 research outputs found
Effect of Temperature Dependent Fluid Properties on Heat Transfer in Turbulent Mixed Convection
No full textSupplemental_Material_Mesh_Study_Revision_V1.0 – Supplemental material for Validation of numerically simulated ventricular flow patterns during left ventricular assist device support
No full textSupplemental material, Supplemental_Material_Mesh_Study_Revision_V1.0 for Validation of numerically simulated ventricular flow patterns during left ventricular assist device support by Mojgan Ghodrati, Thananya Khienwad, Alexander Maurer, Francesco Moscato, Francesco Zonta, Heinrich Schima and Philipp Aigner in The International Journal of Artificial Organs</p
Influence of anisotropic permeability on convection in porous media: Implications for geological Co2 sequestration
No full textSolute convection in porous media at high Rayleigh-Darcy numbers has important fundamental features and may also bear implications for geological CO2 sequestration processes. With the aid of direct numerical simulations, we examine the role of anisotropic permeability on the distribution of solutal concentration in fluid saturated porous medium. Our computational analyses span over few decades of Rayleigh-Darcy number and confirm the linear scaling of Nusselt number that was previously found in the literature. In addition, we find that anisotropic permeability gamma < 1, i.e., with vertical permeability smaller than horizontal permeability, effectively increases the Nusselt number compared with isotropic conditions. We link this seemingly counterintuitive effect with the occurring modifications to the flow topology in the anisotropic conditions. Finally, we use our data computed for the two-sided configuration (i.e., Dirichlet conditions on upper and lower boundaries) to examine the time evolution of solutal dynamics in the one-sided configuration, and we demonstrate that the finite-time (short-term) amount of CO2 that can be dissolved in anisotropic sedimentary rocks is much larger than in isotropic rocks. Published by AIP Publishing
Turbulent drag reduction in water-lubricated channel flow of highly viscous oil
No full textWe study the problem of drag reduction (DR) in a lubricated conduit, in which a thin layer of low-viscosity (e.g., water) fluid is injected in the near-wall region and facilitates the transport of a core of high-viscosity fluid (e.g., oil). In the present investigation, the flow instance is a channel flow, and consequently we have one thin layer of low-viscosity fluid lubricating each wall. We run direct numerical simulations of this flow instance, respecting the protocol of the constant power input approach. This approach prescribes that the flow rate is adjusted according to current pressure gradient, so to keep constant the power in- jected into the flow, it mimics closely real transport pipelines. A phase-field method is used to describe the dynamics of the liquid-liquid interface. As this technique is tailored toward the transport of very viscous fluids like oils, we study the drag reduction performance of the system by keeping fixed the lubricating fluid properties (e.g., water) and by considering two different types of oil characterized by different viscosities, 10 and 100 times more viscous than water, respectively. As in real instances the presence of impurities and surfactants— which act by locally reducing the local value of the surface tension—is inevitable, we consider, for each type of transported oil, a clean and a surfactant-laden interface. For all four tested configurations, we unambiguously show that significant DR can be achieved. Reportedly, compared to the single-phase case, we observe a reduction of the mean pressure gradient down to px/px,sp = 0.25 for the largest viscosity oil. By analyzing the features of turbulence in the lubricating layer, and the close interaction with the perturbations induced by the oil-water interface deformation, we elucidate the physical mechanisms leading to DR and we underline the effects of viscosity ratios and of surfactants
Influence of thermal stratification on the surfacing and clustering of floaters in free surface turbulence
No full textDecay of gravity-capillary waves in air/water sheared turbulence
No full textDirect Numerical Simulation (DNS) is used to analyze the wave-decay process in a countercurrent air/water turbulent flow. Three dimensionless numbers describe the problem: the Reynolds number Reτ (which measures the importance of inertia compared to viscosity), the Weber number We (which measures the importance of inertia compared to surface tension) and the Froude number Fr (which measures the importance of inertia compared to gravity). We keep Reτ constant and we vary We and Fr. Regardless of the values of the physical parameters, we observe an initial exponential decay followed by the achievement of a new statistically stationary condition. The parameters characterizing this exponential decay do depend on the specific values of Re, Fr and We. Wavenumber spectra computed at different time instants during the wave decay process reveal that the spectral properties of waves change in time: starting from a condition characterized by the predominance of low-wavenumber waves, we observe a “blue shift” of the energy spectra towards higher wavenumbers, indicating the emergence of a strong capillary behavior. At the new asymptotic steady state condition, wave energy spectra are in fair agreement with the predictions given by the Wave Turbulence Theory. We also characterize the statistical behavior of the interface deformation to highlight the interplay between gravity and surface tension in determining the interface structure. © 2016 Elsevier Inc
Direct numerical simulation of turbulent heat transfer modulation in micro-dispersed channel flow
No full textsj-pdf-1-jao-10.1177_03913988211056018 – Supplemental material for Effects of the atrium on intraventricular flow patterns during mechanical circulatory support
No full textSupplemental material, sj-pdf-1-jao-10.1177_03913988211056018 for Effects of the atrium on intraventricular flow patterns during mechanical circulatory support by Mojgan Ghodrati, Thomas Schlöglhofer, Alexander Maurer, Thananya Khienwad, Daniel Zimpfer, Dietrich Beitzke, Francesco Zonta, Francesco Moscato, Heinrich Schima and Philipp Aigner in The International Journal of Artificial Organs</p
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