JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 27 Number 1 1997
                                                                    CONTENTS

FLUID

MECHANICS

F. Durst

University of Erlangen-Nuernberg, Germany

High-Performance Scientific Computing and its Application in Solving Engineering Problems

The discipline called High-Performance Scientific Computing can provide support to engineering developments through results obtained by numerical simulations. This is most clearly perceptible in the field of numerical fluid mechanics, where program developments are under way to compute fluid flows with complex boundaries and involving heat and mass transfer. The present paper summarizes the computer program developments at the Institute of Fluid Mechanics at the University of Erlangen-Nuernberg and shows that two- and three-dimensional computer programs are available to compute steady and unsteady fluid flows of compressible and incompressible media. Multi-grid solution algorithms are incorporated into the programs and speed up the solution considerably. All programs are parallelized and can be run on computers of different parallel architectures.


J. C. F. Pereira
J. M. M. Sousa

Technical University of Lisbon, Portugal

Coherent Sructures in the Flow over a Cavity: Experiments and Computations

This paper presents the results of experimental and numerical investigations on the formation of organized motions in the flow over cavity-type geometries. It is shown that stability analysis can predict the occurrence of coherent, traveling vortices within the impingement length of the cavity. This is associated to instability of the separated shear layer. At Re = 3360, Kelvin-Helmholtz vortices can be experimentally observed to travel and impinge on the trailing-edge of the cavity. Appropriate numerical simulations have shown to be able of predicting this behaviour, further disclosing the complex coupling between shear layer instability and recirculating flow field dynamics. At Re = 63.600, the presence of organized, turbulent structures persists. Thus, the use of large-eddy numerical simulations for high Reynolds number flow over a cavity has proved superior performance over classical k-\eps modelling, from both statistical and topological viewpoints.


St. Radev
M. Kaschiev

Institute of Mechanics, Bulg. Ac. Sci., Sofia
Institute of Mathematisc and Informatisc, Bulg. Ac. Sci., Sofia

Fully Developed Gas-Solid Particles Flow in a Vertical Riser

The aim of the present paper is to perform a numerical algorithm for the simulation of the flow of gas-particle mixture in Circulating Fluidized Bed riser in the zone where the flow is fully developed. In this zone the equations of motion could be reduced to one-dimensional form. An algorithm for solving the one-dimentional equations of motion is proposed based on the Continuous Analogue of the classical Newton Method (CANM). The corresponding results and related comparisons as well as a discussion are presented.


P. Stankov

Technical University of Sofia

Computer Simulation of 3D Complex Turbulent Flows: Real Needs, Possibilities and Perspectives

The paper presents a review of the state of the art of computer modelling of 3D complex turbulent flows in heat and mass transfer processes, the real needs for such modelling, the possibilities for the flows to be predicted numerically as well as the perspectives for the future development of this technique. The discussion is based on the particular example of combustion processes in industrial furnaces as a typical case of a 3D flow process. The real needs for mathematical modelling of combustion processes aiming to improve the practical predictions and design are evaluated on the basis of a comparison with other methods for investigation and modelling of such processes. The discussion and conclusions are supported by particular numerical predictions of the PTVM 100-type industrial furnace operating in a power plant in Sofia. On this basis is drawn the main conclusion: computer simulation of complex 3D turbulent flows in practical heat and mass transfer processes is the best, if not the only tool for engineering predictions and design.


N. Todoriev
V. Pavlov
Energoconsult AD, Bulgaria

Current Problems In Bulgarian Combustion Technologies
The paper discusses some of the problems arising in the combustion technologies used in Bulgarian power industry. The discussion concerns mainly the prevailing organic substances used as energy resources in Bulgaria and the choice of most appropriate combustion technology. Technologies both for pulverized - coal burning of high ballast lignites and for pulverized - coal burning of local coal mixtures having different characteristics are examined. The problem of limiting NOx is also discussed.


J. L. T. Azevedo
L. M. R. Coelho
M. G. Carvalho

Technical University of Lisbon, Portugal

Numerical Modelling of In-Fur- nace NOx Reduction Technologies for Pulverised Coal Combustion

The reduction of NOx emissions from pulverised coal fired boilers may be performed either by post-combustion flue gas treatment or by modifications in the combustion process which is in general more economical. The techniques to reduce NOx emissions within the boiler furnace consist on the promotion of air and/or fuel staging either close to the burner (using low NOx burners) or at the boiler level. For boilers without overfire air ports, air staging may be performed using burners out of service. Further NOx reduction is achieved in the reburning technology using fuel staging followed by overfire air to complete combustion. The paper presents results of the application of a comprehensive numerical model developed at IST to study the influence of using different NOx abatement technologies, namely the use of burners out of service for air staging and the implementation of reburning technology on the performance of industrial boilers.


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