1,722,789 research outputs found
Comparison of Semi Empirical Correlations and a Navier-Stokes Method for the Overall Performance Assessment of Turbine Cascades
No full textSviluppo di un codice CFD per la previsione delle prestazioni di profili aerodinamici per turbomacchine assial
A CFD model for real gas flows
No full textNumerical solutions of Navier-Stokes equations are nowadays widely used for several industrial applications in different fields (aerodynamic, propulsion, naval, combustion, etc..), but the solution methods still require significant improvements especially in two aspects: turbulence modeling and fluid modeling. The paper describes in some detail a real fluid model based on Redlich-Kwong-Aungier equation of state and its implementation into a Navier-Stokes solver developed by the authors for turbomachinery flows analysis
A navier-stokes based strategy for the aerodynamic optimisation of a turbine cascade using a genetic algorithm
No full textThe problem of turbine cascade design is considered using automatic optimisation strategies. After the profile parameterisation, two different models are considered to simulate the cascade performances: experimental correlations and a Navier-Stokes code. Interesting considerations on the optimisation algorithm can be drawn using correlations because the evaluation of the fitness is almost instantaneous. By fixing certain of the design constraints two optimised configurations are obtained using simplified correlating function or the viscous flow solver. The optimised configurations are then investigated with an accurate viscous flow computation in order to have a deeper insight into the flowfield. Copyright © 2001 by ASME
Degradation of Cd-yellow Paints: ab initio Study of the adsorption of oxygen and water on {10.0} CdS surface
No full textThe cadmium yellow paints (CdS) used in impressionist and modernist paintings in early 1900s are undergoing several deterioration processes including whitening and discoloration. A relevant effect produced at the surface of the paintings is the growth of discolored crusts formed mainly by white globular hydrated cadmium sulfate (CdSO4*nH2O) and cadmium carbonate (CdCO3). Recent studies [1,2] ascribe to an initial photo-oxidation process of CdS the input for the formation of such whitish compounds.
In order to understand the oxidation and hydration mechanisms, at atomic level, of these whitish globules, we present the early stages of a theoretical study on the interaction between the hexagonal (10-10) surface of CdS and O2 and H2O molecules to simulate the combined effects of exposure to air and humidity. More specifically, we determined the favorite adsorption sites and calculated the adsorption energies of the different molecules on top of the surface. The details of the electronic structure of the interactions are given via the bonding charge analysis along with a thorough description of the geometry
A hierarchical optimisation approach for automatic turbomachinery blade design
No full textThe problem of turbine cascade design is considered using automatic optimisation strategies. Genetic algorithms (GA) have proved, in previous applications, to be able to deal with optimisation problems with many independent variables and to be extremely easy to use into a general computational system. On the other hand GA require a high number of fitness evaluation in order to get the best individual and this aspect is particularly negative when the fitness is obtained from Navier-Stokes computations. In the paper an optimisation strategy to reduce the overall computational time is proposed. It consists of an alternate use of fine and coarse grids for the evaluation of the profile loss with a Navier-Stokes solver developed by the authors. © 2001 by the American Institute of Aeronautics and Astronautics, Inc
Surface structure and core-level shifts in lead chalcogenide (001) surfaces
No full textWe study the geometrical structure, the relaxation, and the surface core-level shifts of PbS and PbTe (001) surfaces via ab initio pseudopotential. calculations. In both systems, an oscillatory relaxation of the surface-layer separations is predicted and this feature is expected to be present in other polarizable ionic rocksalt compounds. In agreement with experiment, PbTe displays a large surface rumpling that is absent in PbS. Reasons far these similarities and differences are addressed. Our results compare well with most available experimental data. Partial disagreement with a recent x-ray standing wave investigation in PbS is discussed. Core-level shifts in PbS are very small and ate not sensitive to surface relaxation. Therefore, they are not a useful tool to investigate surface geometry in these compounds
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
Computational Analysis of the Unsteady Wind Turbine Wake Evolution
No full textIn this paper a model to calculate the wake birth and development behind a straight bladed vertical axis wind turbine is presented and applied to a specific example. The performances of the turbine are calculated by means of a vortex model while the wake development is predicted by making use of a finite volume viscous solver. By combining these two different approaches the wake development for different operating conditions has been calculated. The inherently unsteady wake production for this kind of wind turbine, which gives rise to a cyclic evolution of the speed deficit, can be modeled through the free wake vortex model. Therefore the present integrated model allows capturing the details of the flow field as the final calculation shown demonstrates
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