Aerodynamics and modelling of vane-swirled flames in furnaces

Beltagui, Salah A (1974) Aerodynamics and modelling of vane-swirled flames in furnaces. PhD thesis, University of Glasgow.

Abstract

Swirl produces notable effects on flames, generally making them shorter and highly stable over a wide range of air and fuel flows. One common method of generating a swirling jet is to employ a vane swirler. In this work the aerodynamics of vane-swirled premixed town gas-air flames are investigated in two furnaces, using the same swirlers. Variables investigated include the swirler vane angle, geometry, degree of confinement, Reynolds Number and fuel/air ratio. Cold tests were also carried out for the purpose of modelling. Significant changes in the flow and the combustion patterns were produced by swirl. Strong swirl created a central recirculation zone which when well established had a maximum diameter and length of nearly fixed proportions of the furnace diameter. The jet spread rate was found to increase mainly with the swirler-vane angle and to vary slightly with combustion and confinement particularly at strong swirl. The presence of a central hub in the swirler had little effect on the flow and combustion pattern. The survey of previous work and the present results showed the need for a revised measure of swirl, This was taken as the ratio of the tangential to axial velocity momentum fluxes divided by the furnace diameter. The values of this Swirl Number obtained by integrations of the flow properties were found to be a valuable index of the flow and combustion patterns. A critical value at which the flow reversal occurs was found to be the same for all input conditions tested. The strong relation between combustion and flow patterns shows the value of isothermal model results for furnace design. For a non-swirled flame a parameter was derived on the basis of the ratio of source to shear momenta. For swirling flames, the use of the Swirl Number defined above proved to be a satisfactory modelling criterion since it has a fixed relation to the flow pattern under both cold and burning conditions. A mathematical model was developed for the prediction of the flow and combustion patterns of confined swirling flows. The results obtained for weak and medium degrees of swirl were reasonably similar to those experimentally measured. The study of the measured combustion patterns shows that swirling flames are stabilized by a mechanism of mixing between the fresh charge and the recirculated gases. These contained direct combustion products and entrained gases from the surroundings. The effective fuel/air ratio at the reaction zone versus blow-off velocity relations were obtained and found to be the same for both free and confined swirling flames. Finally some recommendations to the choice of the optimum swirl range and suggestions for further work are presented. A paper presented at the Combustion Institute European Symposium (1973) is included as an Appendix.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: R S Siliver
• Keywords: Mechanical engineering, Thermodynamics
• Date of Award: 1974
• Depositing User: Enlighten Team
• Unique ID: glathesis:1974-73298
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73298