1,721,008 research outputs found
Prove in Galleria del Vento sugli effetti di un di Aerofreno sul Piano di Coda Verticale
No full textReport of Depart. of Aerospace Eng. of Pisa, DDIA 2005-3, Jan. 2005
Analisi Della Soluzione Numerica Di Flussi Interni Su Vetture ad Alte Prestazioni
No full textReport of Depart. of Aerospace Eng. of Pisa, DDIA 2003-15, Sept. 2003
Caratterizzazione in Galleria del Vento del Flusso Aerodinamico Prodotto da Diversi Tipi di Aerofreno
No full textReport of Depart. of Aerospace Eng. of Pisa, DDIA 2002-4, Feb. 2002
Stochastic sensitivity analysis of numerical simulations of injector internal flows to cavitation modeling parameters
No full textA stochastic analysis of the cavitation model parameter sensitivity is carried out for internal flows relevant to injector configurations. Stochastic methodologies, namely generalized polynomial chaos and stochastic collocation, are used to obtain continuous response surfaces of the quantities of interest in the parameter space starting from a limited number of simulations. Cavitation is modeled through a transport equation for the void fraction closed by the Schnerr-Sauer relation, containing four free parameters. As for turbulence, the URANS equations are considered, together with two different closure models. The sensitivity to the cavitation model parameters is investigated, first, for a throttle geometry, for which experimental and LES data are available. First, two out of the four parameters are identified as the most important through a preliminary analysis based on 2D simulations, namely the vaporization and condensation factors. Then, the sensitivity of 3D simulation results to the previously identified most important parameters is investigated. The stochastic range of variability of the results contains the reference data. Thus, a parameter optimization is carried out in order to obtain the values giving the best agreement with the LES data. It is then shown that the cavitation parameter sensitivity is practically independent of the working fluid. Finally, it is shown that the calibrated cavitation model can be successfully applied to a different configuration, characterized by the hydraulic flip phenomenon, namely a 3-phase case in which liquid N-heptane flows from an inlet reservoir through a circular channel in an outlet reservoir where air is present
Enhanced energy dissipation through 3D printed bottom geometry in Tuned Sloshing Dampers
No full textThis paper presents an experimental investigation about the dissipation properties of Tuned Sloshing Dampers (TSDs) characterized by different bottom geometries. An experimental campaign on sloped and rounded shaped TSDs is carried out considering a uni-directional harmonic base motion, by varying the water level and the excitation characteristics, i.e. amplitude and frequency. Results are compared with those obtained on a rectangular flat bottom TSD and benchmarked against a classic Tuned Mass Damper (TMD). The present study demonstrates that a TSD with a suitably modified bottom shape can significantly outperform a traditional flat-bottom TSD in terms of maximum amount of dissipated energy and robustness against frequency mistuning
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Stochastic calibration of cavitation model parameters for simulations of 3-phase injector internal flows
No full textThe work focuses on the calibration of cavitation model parameters for the numerical simulation of three-phase injector flows. Cavitation is modeled through a transport equation for the void fraction closed by the Schnerr-Sauer relation. The vaporization and condensation factors contained in this model are considered for calibration against experimental data available for a test-case characterized by fuel injection in a reservoir filled of air through an axisymmetric channel. In spite of the simplified geometry, this flow configuration is representative of a real injector and contains most of the complex physical phenomena which may be encountered in injector flows, as turbulence, cavitation and hydraulic flip, i.e. a back flow of air from outside the injector along the whole length of the channel replacing the cavitating regions. Since a direct calibration would imply huge computational costs, not affordable in practical applications, response surfaces of the quantities of interest are built through generalized Polynomial Chaos. These response surfaces, which can be obtained starting from only a few deterministic simulations, have been then used to carry out the parameter calibration. The quantities of interest taken into consideration are the critical cavitation point (CCP), i.e. the value of the outlet pressure at which the flow inside the injector can be considered choked (for a fixed inlet pressure), and the mass-flow-rate (MFR) at the CCP. To further reduce the computational costs, calibration is carried out by using axisymmetric simulations. It has been then checked that the obtained cavitation model gives accurate results also in three-dimensional simulations of the actual geometry. Moreover, this set-up has been applied to two different complex one-hole injector geometries, i.e. a sector of real injector geometries, and the results have been compared against available experimental data. The calibrated cavitation model set-up appears to be robust, giving good predictions also in conditions significantly different from those in which it has been obtained
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