Papers by George Bergeles
The Institute of Energy's Second International Conference on Combustion & Emissions Control, 1995
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2012
ABSTRACT The turbulent flow and the pollutant dispersion in organized cubic structures simulating... more ABSTRACT The turbulent flow and the pollutant dispersion in organized cubic structures simulating an idealized building arrangement in a city is numerically investigated. The basic building arrangement under investigation is the experimental arrangement reported by Uehara et al (2000); it consists of an in line arrangement of cubic blocks having upwind a number of low rise square blocks which act as roughness elements for creating turbulent flow. The purpose of the investigation is to gain physical knowledge on the structure of the three dimensional flow and the pollutant dispersion mechanism, to compare with published two dimensional simulations and mainly to investigate the unsteady character of the flow field and its time scale characteristics.
Engineering Turbulence Modelling and Experiments 4, 1999
International Journal of Heat and Fluid Flow, 2015
The tendency of today's fuel injection systems to reach injection pressures up to 3000 bar in ord... more The tendency of today's fuel injection systems to reach injection pressures up to 3000 bar in order to meet forthcoming emission regulations may significantly increase liquid temperatures due to friction heating; this paper identifies numerically the importance of fuel pressurization, phase-change due to cavitation, wall heat transfer and needle valve motion on the fluid heating induced in high pressure Diesel fuel injectors. These parameters affect the nozzle discharge coefficient (C d ), fuel exit temperature, cavitation volume fraction and temperature distribution within the nozzle. Variable fuel properties, being a function of the local pressure and temperature are found necessary in order to simulate accurately the effects of depressurization and heating induced by friction forces. Comparison of CFD predictions against a 0-D thermodynamic model, indicates that although the mean exit temperature increase relative to the initial fuel temperature is proportional to (1 À C d 2 ) at fixed needle positions, it can significantly deviate from this value when the motion of the needle valve, controlling the opening and closing of the injection process, is taken into consideration. Increasing the inlet pressure from 2000 bar, which is the pressure utilized in today's fuel systems to 3000 bar, results to significantly increased fluid temperatures above the boiling point of the Diesel fuel components and therefore regions of potential heterogeneous fuel boiling are identified.
The paper presents a three-dimensional transient numerical model for atmospheric wind flow and in... more The paper presents a three-dimensional transient numerical model for atmospheric wind flow and industry and/or traffic pollutant dispersion over terrains having a complex topography. The model is based on a finite-volume integration of the equations governing mass, momentum, heat and pollutant transport within the earth's atmospheric boundary layer, using a collocated grid arrangement. The instability provoked by such a formulation was avoided by using a special pressure-velocity coupling. Local refinement of the grid was achieved via a domain decomposition method. The technique of "porosity" used to approximate curved three-dimensional boundaries is incorporated in the procedure thus avoiding the less accurate and more common approximation by a broken surface with segments parallel to the coordinate lines. The method was validated by simulating the flow over the Attica peninsula for which measurements of wind speed and pollutant emissions are available.
The paper presents a three-dimensional transient numerical model for atmospheric wind flow and in... more The paper presents a three-dimensional transient numerical model for atmospheric wind flow and industry and/or traffic pollutant dispersion over terrains having a complex topography. The model is based on a finite-volume integration of the equations governing mass, momentum, heat and pollutant transport within the earth's atmospheric boundary layer, using a collocated grid arrangement. The instability provoked by such a formulation was avoided by using a special pressure-velocity coupling. Local refinement of the grid was achieved via a domain decomposition method. The technique of ‘porosity’ used to approximate curved three-dimensional boundaries is incorporated in the procedure, thus avoiding the less accurate and more common approximation by a broken surface with segments parallel to the coordinate lines. The method was validated by simulating the flow over the Attica peninsula for which measurements of wind speed and pollutant emissions are available.
A plane-by-plane procedure which computes pollutant concentrations on a fine grid using the inter... more A plane-by-plane procedure which computes pollutant concentrations on a fine grid using the interpolated mass fluxes and turbulent viscosities produced on a coarse grid by a three dimensional transient code is reported. The method allows an efficient use of computer memory at the expense of slightly increased calculation time. The performance of the method has been verified by comparison with available measurements in five monitoring stations situated in the Attica peninsula, for the day 25/5/1991. The results obtained are in a mostly acceptable qualitative agreement with measurements. The procedure can be generalized to any conservation equation which is decoupled from the flow equations.
This paper describes an experimental and numerical investigation on the effects of imposed pulsat... more This paper describes an experimental and numerical investigation on the effects of imposed pulsations on the crossflow over tube arrays in the subcritical regime. Three different arrays were considered, namely inline, staggered and asymmetric with the same streamwise and transverse spacing-to-diameter ratios of 2.1 and 3.6 respectively. A laser-Doppler anemometer was employed for velocity measurements and laser-sheet visualisation was used to reveal the underlying unsteady flow patterns. Simulation of the flow was carried out by solving the Navier-Stokes equations on an orthogonal curvilinear grid and using the Smagorinsky model for scales smaller than the grid size. The timedependent simulation was performed in two dimensions in order to constrain the computational time while providing data for the entire flow field. Weaver, D.S. and Fitzpatrick, J.A. (1988) "A review of the cross-flow induced vibrations in heat exchanger tube arrays", J Fluids and Structures, 2, 73-93. Weaver, D.S., Fitzpatrick, J.A. and Elkashlan, M. (1987) "Strouhal numbers for heat-exchanger tube arrays in cross flow", J Pressure Vessel Tech, 109, 219-223.
Key words: local grid refinement; flow over complex terrain; numerical simulation A telescopic lo... more Key words: local grid refinement; flow over complex terrain; numerical simulation A telescopic local grid refinement technique is developed in order to enhance the accuracy level of wind field predictions in a subregion of a complex topography. A 3D simulation of the wind flow field over complex terrains has been carried out. The governing Navier-Stokes conservation equations of the flow field are solved numerically in a three-dimensional generalized curvilinear non-orthogonal grid, using Cartesian velocity components, following the finite volume approximation and a pressure correction method. Turbulence is simulated by a two-equation transport model. The reliability of the general flow solver is first tested by simulating the flow past a cube. The second test case simulated is the flow over the Askervein hill, with a detailed comparison of predicted and measured velocities. The third case presented concerns flow field simulation over a complete island. Comparison with measurements reveals the significance of the accurate discretization of the topography and the use of telescopic meshes on the results.
The numerous available options for the development of the Greek electric sector in combination wi... more The numerous available options for the development of the Greek electric sector in combination with the various techno-economic and political constraints make energy planning rather complex. Furthermore, as full auctioning of CO2 allowances shall be the rule from 2013 onwards for the electric sector following free allocation, even more uncertainties emerge. This work aims at investigating the main characteristics of
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Papers by George Bergeles