OCR Text |
Show iii) multi - phase flow, iv) heat and mass transfer, v) radiation, vi) chemical kinetics. A reliable and economical model can be stated to combine judiously all the above features with particular emphasis on th~ critical rate limiting steps. The balancing of mathematical tractability and physical realism is the central problem of modelling studies. The practice of mathematical modelling of flow and heat and mass transfer characteristics of general combustor configurations has been greatly enhanced recently by considerable development in two major areas - namely, the numerical analysis of partial differential equations, and the computational representation of turbulent reacting flows. The former has allowed, for the first time, solution of the differential transport equations of convective flows without the necessity for making restrictive simplifying assumptions; the latter has provided means of embodying in the equations the effects of turbulence on the various transport processes. Numerical solution procedures now exist for flows of complexity up to and including those which exhibit variations in all spatial coordinates and these have been employed, together with turbulence models of various levels of sophistication for a variety of combustion problems. It is in this spirit that the remainder of the paper will be devoted to discussing the formulation and application of a three-dimensional, turbulent, -t~o-phase, reactive flow code developed at Avco to compute the flow field and aid in the selection of various design parameters for a toroidal vortex gas turbine combustor burning coal(1,2). A number of cases will be examined with reference to optimizing particle residence time and hence improve the expected combustion efficiency. Specific attention will be drawn to highlighting the model achievements, as well as indicate areas of potential improvement and shortcomings of the adopted numerical procedure. 2 |