| Abstract: | The structure of the probability density of very large values of the concentration of a passive admixture is considered. The solution of this problem is of importance for modeling the emission of carbon monoxide and unburnt hydrocarbons. A theoretical model is constructed on the basis of the following ideas: (1) the dimension of the zones in which the concentration pulsations with vary large amplitudes are observed is of the order of the integral turbulence scale; (2) the probability of these zones being generated is very low. It is shown that there is a certain limiting large value of the concentration in the neighborhood of which the probability density can be described by a power function. On the basis of the theory of locally uniform turbulence it is shown that, generally speaking, if certain relationships between the unknown quantities entering into the theory are not satisfied, the probability density of very large values of the concentration depends on the Reynolds number.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 39–46, September–October, 1995. |
