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Show 1 Introduction In this paper we describe the behavior of coal particles injected into hot combustion atmospheres in turbulent flow using Direct Numerical Solution (DNS) to describe the flow. According to Montgomery [8], DNS was first used in combustion in 1986 for prediction of behavior of gas flames. It has not yet been used for particle flames, however, so far as we know. We have found no citation of its use in the most complete recent (1993) listing [12] of 14 different programs for multidimensional modelling of pulverized coal (entrained particle) flames. In this context, this investigation is, therefore, designed as a first step in computer simulation of complete pulverized coal flames, using DNS for the turbulent flow in place of commonly used alternatives, as in the reference [12] listings, such as k-€ and similar modelling and simulation procedures. Modeling of pulverized coal flames has a long history, starting in the 1950s, using analog computers, with a switch to digital in the 1960s, notably in the CE "Slice Model" developed by Bueters and associates [2] but with the flow field averaged in a way that excluded turbulence explicitly. Attempts through the 1970s and after to explicitly include turbulence grew out of those early models; however, with the computing limitations imposed by the machines at that time, turbulence could be included using only the modelling and simulation techniques of the k-€ or Reynolds stress and similar types. DNS was known as a theoretical possibility, but it was not seen as a practicable procedure until the technical development of parallel computing from the 1980s onward enabled handling the quantity of computations involved. The limitations of k-€ and similar modelling methods, nevertheless, have long been recognized. Notably, it was necessary to characterize the complete flow field with a single turbulence characteristic, which was often acceptable in isothermal flow. In non-isothermal flow, as in flames, however, changes in flow characteristics (conveniently defined by local . Reynolds number) can be too great for a single-number flow characterization. Flow is highly turbulent in any entering jet, with Reynolds numbers typically in the region of 106 ; but 1 |
