Stochastic models for large-scale turbulence

Abstract

The closure problems related to the use of RANS equations pointed out in section 4.6 may be overcome by the construction of stochastic turbulence models. This approach will be addressed here with regard to both velocity and scalar models. In particular, this is done by generalizing (in analogy to the derivation of the fluid dynamic equations in chapter 4) the equations for the equilibrium dynamics of relevant variables derived in Appendix 3A. The most essential assumption related to stochastic models presented in this chapter is the consideration of large-scale fluctuations around ensemble means (see the discussion of averaging procedures in Appendix 1A). The alternative modeling of small-scale turbulence will be addressed in chapter 6.