High-speed turbulent gas jets: an LES investigation of Mach and Reynolds number effects on the velocity decay and spreading rate

AbstractThe aim of this work is the investigation of Mach and Reynolds numbers effects on the behaviour of turbulent gas jets in order to gain new insights into the fluid dynamic process of turbulent jet mixing and spreading. An in-house solver (Flow-Large Eddy and Direct Simulation, FLEDS) of the Favre-filtered Navier Stokes equations has been used. Compressibility has been analyzed by considering gas jets with Mach number equal to 0.8, 1.4, 2.0 and 2.6, and Re equal to 10,000. As concerns the influence of Re on gas jets, four cases have been investigated, i.e. $$\mathrm{Re} = 2500$$ Re = 2500 , 5000, 10,000 and 20,000, with Mach number equal to 1.4. The results show that, in accordance with previous experimental and numerical studies, the potential core length increases with Mach number. As regards the velocity decay and the spreading rate downstream of the potential core, compressibility effects are not relevant except for the jet with Mach number of 2.6. The normalized turbulent kinetic energy along the centerline as a function of the normalized streamwise distance shows a similar peak at the end of the potential core for all jets, except for the case with Mach number of 2.6. By increasing Re, the length of the potential core decreases up to the same value for all Re higher than 10,000. In the region downstream of the potential core, the velocity decay decreases as Re number increases from 10,000 to 20,000, whereas, for lower values of Re, the influence is almost negligible

Numerical Simulation of Energy Systems to Control Environment Microclimate

The aim of the present work is the development of a predictive mathematical model for the analysis and optimization of energy systems used to control the environment microclimate in industrial plants. This model provides not only the evaluation of the optimal configuration on the basis of different process parameters in the existing environments, but also the analysis and the prediction of the energy consumption of a plant during the design phase. The model describes the thermodynamics of conditioning processes and allows the evaluation of the influence of design variables and of hourly averaged weather conditions on energy consumption. The model is developed both in TRNSYS-17 and C ++ programming language such that it can also be used under MATLAB computing environment. The results obtained with the two models are compared under different climatic conditions in terms of heating/cooling and humidification/dehumidification energy consumption, thus assessing the accuracy of both models. The results obtained by using different set-point conditions under different climatic zones are also presented

Dynamic Modeling and Simulation of Buildings Energy Performance Based on Different Climatic Conditions

The aim of this work is the analysis, under dynamic conditions, of the energy performance of buildings based on different climatic conditions. Two school buildings, Liceo Classico “E. Duni” and Liceo Scientifico “D. Alighieri”, located in Matera, Italy, are considered. Furthermore, a strategy to improve the energy performance of the two school buildings is proposed by the installation of a co-trigeneration plant integrated with a solar plant. Such a plant is equipped with an absorption chiller to produce chilled fluid. The analysis under dynamic conditions has been performed by using a well-known simulation software, TRNSYS 17, and the results have been compared with those obtained under stationary conditions by employing a numerical solver, MC-11300, which is certified by the Italian Thermotechnical Committee. At first, the results obtained by considering the dynamic and stationary states and the experimental data measured in situ are compared by considering the actual buildings plants. Then, the energy performance of the two buildings is computed by considering three different climatic zones of Italy. Finally, a discussion of the advantages of the proposed requalification solution, which employs the trigeneration plant, is given

influence of piston shape and injector geometry on combustion and emission characteristics of syngas in direct injection spark ignition engine

Abstract This paper presents a numerical study of the influence of piston shape and injector geometry on combustion and emissions characteristics of a direct-injection spark-ignition engine fueled by syngas (50% by volume of hydrogen, 50% by volume of carbon monoxide) under low/medium load conditions. Three different piston cup geometries namely: High-clearance Combustion Cup (HCC), Low-clearance Combustion Cup (LCC) and Omega Combustion Cup (OCC) have been considered with a compression ratio of 14. An axial full-cone gas jet injector has been considered together with a hollow-cone gas jet injector with several included half-angles, i.e. 30°, 45°, 52.5° and 60°. Computational fluid dynamics modelling has been performed to simulate the combustion process. The results indicate that, in terms of performance, OCC shape is favorable, even if OCC generates relatively higher NOx than the other two configurations. A further analysis has been performed by simulating an engine with OCC piston shape and an included half-angle of injection of 30°, by varying the Start Of Injection (SOI). The results show that the flame propagation velocity reduces as the SOI advances, since the fuel distribution becomes more homogeneous approaching to a premixed case. However, the flame speed reduction is partially balanced by the disappearance of very lean regions thanks to fuel convection and diffusion

Quasi-Conservative Lambda Formulation

The numerical simulation of inviscid transonic flows by means of a "modified lambda formulation" takes into account the shock transition from supersonic to subsonic flow conditions, thus allowing the coupling of the supersonic region with the shocked subsonic one and, as a consequence, the upstream movement of the shock. The present methodology is applied to one- and two-dimensional transonic flows. Although the two-dimensional flow calculations involve Cartesian coordinates and are limited to the thin-airfoil approximation, the method can be generalized to arbitrary two- and three-dimensional flow cases. In all of the computed cases, the shock is found to have appropriate strength and position for steady flow conditions and to move upstream properly when a change in the downstream pressure warrants it

Chapter 5 - A comprehensive perspective on a promising fuel for thermal engines: Syngas and its surrogates

Syngas can be considered a promising fuel leading to a drastic reduction of greenhouse gas emissions in its life cycle. Given the strong demand for energy and the need to resort to energy systems, in general, and to thermal engines, in particular, that are sustainable in terms of polluting emissions, the use of innovative fuels, such as syngas, becomes essential. This work intends to present syngas as one of the possible candidates for advanced thermal engines. Specifically, this work investigates the energy capability of syngas in industrial applications based on the use of internal combustion engines. A brief overview on the production of syngas is given, followed by an analysis of the different applications of this fuel in thermal engines. Dual-fuel compression ignition, homogeneous charge and direct injection spark ignition engines are analyzed from performance and emissions perspectives, following both experimental and numerical approaches. The performance and emissions of these engines are compared with those of engines running on conventional fuels and the main differences are highlighted. One of the main conclusions is that the combustion characteristics of syngas are strongly dependent on its component species, which influence the low density, the laminar flame speed and the wide flammability range

Drop Interactions in Transient Flows with Applications to Liquid Sprays

The behavior of isolated drops, and binary and ternary systems of drops moving in tandem, in decelerating flows are numerically studied employing a finite-volume interface-tracking numerical scheme and a lattice-Boltzmann method for two-phase flows. The influence of Weber and Ohnesorge numbers, separation distance between drops, and drop size-ratio on the transient deformation and breakup of the drops are discussed. Drag coefficients for the drops are also reported. It is shown that in binary drops, the trailing drop decelerates slower than the leading one and breaks up slower. Both drops decelerate slower than the isolated drop. In the case of ternary drops, the three drops decelerate slower than the isolated one. The leading drop breaks up fastest followed by the middle one. The drag coefficients are transient and vary significantly from those of spheres in transient flows as a result of drop deformation