1,720,970 research outputs found
Direct computation of aeroacoustic fields in laminar flows: Solver development and assessment of wall temperature effects on radiated sound around bluff bodies
Full text linkThis work presents results of a direct computation of acoustic fields produced by several laminar flow configurations. A solver specifically developed for compressible mass, momentum and energy equations, named caafoam, is presented. Low–storage high-order Runge-Kutta schemes were used for time integration, and an unstructured colocated finite–volume method for space discretization. A sponge-layer-type non-reflective boundary treatment was adopted to avoid spurious numerical reflections at the far-field boundaries. These techniques were chosen and tested to see if they enable a broad range of physical phenomena, with a particular emphasis on aeroacoustic problems, to be solved. The reliability, efficiency and robustness of caafoam was demonstrated by computing several benchmarks concerning far-field aerodynamic sound. After proving the direct simulation capabilities of caafoam, it was used to analyze the effect of the wall temperature conditions on the aeroacoustic sound produced by laminar flows over bluff bodies
A low-storage Runge-Kutta OpenFOAM solver for compressible low-Mach number flows: Aeroacoustic and thermo-fluid dynamic applications
No full textA robust intermittency equation formulation for transition modeling in Spalart–Allmaras simulations of airfoil flows over a wide range of Reynolds numbers
No full textThis paper introduces a new robust formulation for local correlation-based laminar-to-turbulent transition models. This mechanism is incorporated into Reynolds-Averaged Navier–Stokes equations, coupled with the Spalart–Allmaras (SA) turbulence model, considering both γ and (formula presented) transition frameworks. In this context, special attention is placed on numerical stabilization of the γ transport equation, which is identified as the root cause of instabilities observed in both γ and (formula presented)-based models. To this end, the intermittency equation is reformulated in logarithmic form and further stabilized through an energy-based limiting to bound excessively high positive values. In order to suppress unphysical pressure oscillations in the transition region, a gradient-driven artificial viscosity is also introduced. Additionally, the SA equation is augmented with strain-rate-modulated production and rotation correction terms. The presented approach has demonstrated consistent effectiveness and robustness in the simulation of flow fields around airfoils over a wide range of Reynolds numbers, making it suitable for practical aerodynamic design applications
Preliminary assessment of a two-phase direct cooling of Lithium-Ion battery pack for e-bike mobility
Full text linkElectric mobility is playing an increasingly central role in emission reduction policies to mitigate climate change effect. During the operation of electric vehicles, the batteries may be subject to high variation of the required current, which can lead to a sudden increase in the cell temperature. If this condition occurs repeatedly, there would be a reduction in battery capacity and useful life, and autonomy reduction of the electric vehicle. In the worst case, this problem can lead to the thermal runaway. Therefore, cooling of electric vehicle propulsion systems is a fundamental issue for the electric mobility development. In this article we propose an innovative cooling system using a dielectric low boiling fluid in which the batteries are directly immersed. The system was tested on an electric bicycle under real operative conditions. A special test bench was realized, consisting of a real electric bicycle, a training roller to simulate the load due to road slope and an external electric motor to simulate the pedaling of the cyclist. The results show a substantial decrease in the temperature of the cells with the proposed cooling system and there was a marked improvement in the temperature uniformity of the cells inside the battery pack
A semi-empirical correlation for the estimation of the second virial coefficients of refrigerants
No full textA new semi-empirical scaled correlation for the second virial coefficient of refrigerants, based on the corresponding states principle, is proposed. Starting from the consideration that refrigerants have different chemical structures, the considered experimental dataset, which includes 63 refrigerants and 3595 points, was split into five main subgroups: single halogenated, double halogenated, hydrocarbons, inorganics and elements. The subgroups were analyzed in detail through a factor analysis approach and the coefficients of the new equation were regressed for each group separately. When compared with the other literature models, the proposed formula is clearly simpler and easier to implement. For four of the proposed groups, the correlation adopts a minor number of constant parameters. In addition, the global RMSE is generally lower (21.4 cm3mol-1) and the proposed mathematical expression well follows the physical constraints that the second virial coefficients must satisfy, both at low and at high reduced temperatures
A Multi-Scale Approach for Modelling Airborne Transport of Mucosalivary Fluid
No full textCOVID-19 pandemic promoted a lot of research activities in relation to mucosalivary fluid airborne transport. Indeed, infection mechanisms are the result of mucosalivary fluid droplets exchange and the knowledge in this area is still largely inadequate. One of the main challenges concerns the modelling of mucosalivary fluid complex nature. Specifically, this is a key element to predict small diameters dry nuclei formation which are highly relevant from the transmission risk point of view. For this reason, in this paper we present and discuss the development of a new multi-scale modelling technique which incorporates the Population Balance Equation into a standard particle-source-in-cell method. Thus, the effectiveness of the aforementioned technique in droplet nuclei generation modelling is showed and discussed. Also the impact of velocity boundary conditions at the mouth print is assessed as well as the effect of the correlations for mass transfer showing that their neglect causes an underestimation in distance reached by the droplets
Numerical modeling of skin tumors subjected to gold nanoparticle assisted laser-induced thermal therapy
Full text linkGold nanoparticle (GNP) laser-induced thermal therapy (LITT) for cancer tumor treatment, is a promising therapeutic procedure. It combines the laser deep penetration when operating in near-infrared band and the contrast agent high absorption at the considered wavelengths. Nevertheless, the treatment success is highly sensitive to the nanoparticles spatial/temporal distribution. Therefore, in this work we investigate the LITT effectiveness under conditions of non-uniform GNPs arrangement. In particular, the impact of gold nanoparticles diffusion mass transfer for different waiting periods between the GNPs injection and the treatment start was assessed. Moreover, the inoculated contrast agent concentration effect on the thermal therapy was also evaluated. Therefore, a numerical solver relying on foam-extend v.5.0 library was developed for modeling: (i) realistic intra-tumor injection. (ii) GNPs diffusion in the target area. (iii) thermal effects on skin tumors by means of LITT. It was found that a waiting period of about 24 h between the contrast agent inoculation and the treatment start is recommended. Lastly, injected GNPs concentration has to be also accurately calibrated to guarantee LITT success
Preliminary analysis of a novel battery thermal management system based on a low boiling dielectric fluid
No full textIn this paper a novel battery thermal management system was experimentally studied. The batteries are submerged in a low boiling dielectric fluid with the aim to reduce the batteries surface temperature when subjected to high charge or discharge currents. The fluid change of phase allows to create a thermal buffer in case of instantaneous peak of absorbed current. This innovative system was studied on a battery pack composed of 3 cells in series and 3 cells in parallel connection for several discharge currents. For the sake of comparison, two battery packs of same dimensions were investigated: one submerged in the dielectric fluid and the second without the fluid. The cells potential and surface temperature were measured during discharges. Moreover, also the fluid temperature was evaluated in the external region. The results show a significant improvement of the thermal management since the increase of temperature is very restricted. This effect is even more evident when the fluid reaches the boiling point
Eulerian-Lagrangian modeling of cough droplets irradiated by ultraviolet-C light in relation to SARS-CoV-2 transmission
Full text linkIt is well known that several viruses, as well as SARS-CoV-2, can be transmitted through airborne diffusion of saliva micro-droplets. For this reason, many research groups have devoted their efforts in order to gain new insight into the transport of fluids and particles originated from human respiratory tracts. This paper aims to provide a contribution to the numerical modeling of saliva droplets' diffusion produced by coughing. It is worth noting that droplets' diameters of interest in this work are such that represent typical emission during a cough. Aerosolization effects are neglected since emitted droplets' diameters are greater than 10 μm. In particular, the well-known problem around the safety distance to be held for avoiding virus transmission in the absence of external wind is further investigated. Thus, new indices capable of evaluating the contamination risk are introduced, and the possibility to inactivate virus particles by means of an external ultraviolet-C (UV-C) radiation source is studied. For this purpose, a new model which takes into account biological inactivation deriving from UV-C exposure in an Eulerian-Lagrangian framework is presented
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