ABSTRACT
This chapter discusses theoretical descriptions of turbulent diffusion flames and of turbulent premixed flames and provides some background information on theories of turbulent combustion. The most fundamental question in turbulent combustion concerns the applicability of a continuum description. There are particular problems in turbulent combustion, such as the homogeneous thermal explosion of turbulent hydrogen-oxygen mixtures, in which these kinetic-theory effects have been found to be significant, for example, in reducing explosion times appreciably. The cascade concepts may be applied to intensities of scalar fields as well as to the turbulent kinetic energy. The chapter argues that disparate length scales and time scales exist for turbulent flows. In the face of the difficulties imposed by the chemistry in turbulent-combustion problems, a rational philosophy is to attempt to reduce the problem to one involving a nonreacting turbulent flow. Coupling functions play a central role in reducing problems of turbulent diffusion flames to problems of nonreacting turbulent flows.
