Issue 1

JTAM, Sofia, vol. 27 Issue 1 (1997)

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

F. Durst
University of Erlangen-Nuernberg, Germany

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.

JTAM, Sofia, vol. 27 Issue 1 pp. 1 (1997)

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

J. C. F. Pereira , J. M. M. Sousa
Technical University of Lisbon, Portugal

In this paper are proposed the polynomial-harmonious motion laws with continuous 3rd and 4th transfer functions. The planer cam mechanisms are systematized in eight varieties. General equations are worked out for their synthesis, based on the envelope theory. The synthesis of the cam profile is done with a precision up to the 4-th derivative of the motion law. To achieve this, we have derived the recurrent dependencies for calculation of the n-th derivative of the cam curve.An error analysis of the motion law and its derivatives up to the 2nd have been performed. There are two approaches suggested to increase the precision of the motion laws, realized by the cam.The optimization criteria of the basic parameters of cam mechanisms are complex and refer to the Efficiency Coefficient, the distortion, the stress and the size.

JTAM, Sofia, vol. 27 Issue 1 pp. 2 (1997)

Fully Developed Gas-Solid Particles Flow in a Vertical Riser

St. Radev 1, M. Kaschiev2
1Institute of Mechanics, Bulg. Acad. Sci., Sofia
2Institute of Mathematics and Informatisc, Bulg. Acad. Sci., Sofia

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.

JTAM, Sofia, vol. 27 Issue 1 pp. 3 (1997)

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

P. Stankov
Technical University of Sofia

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.

JTAM, Sofia, vol. 27 Issue 1 pp. 4 (1997)

Current Problems in Bulgarian Combustion Technologies

N. Todoriev, V. Pavlov
Energoconsult AD, Bulgaria

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.

JTAM, Sofia, vol. 27 Issue 1 pp. 5 (1997)

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

J. L. T. Azevedo , L. M. R. Coelho , M. G. Carvalho
Technical University of Lisbon, Portugal

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.

JTAM, Sofia, vol. 27 Issue 1 pp. 6 (1997)