DNS-based thermal second-moment closure for buoyant convection at vertical walls

摘要

Direct numerical simulations (DNS) of natural convection in a vertical channel by Versteegh & Nieuwstadt (1998) are used for assessing the budget of the turbulent heat flux and the temperature variance and for modelling the transport equations governing these two properties. The analysis is confined to a simple fully developed situation in which the gravitational vector, as the sole driving force, is perpendicular to the only non-zero component of the mean temperature gradient. Despite its simplicity, the flow displays many interesting features and represents a generic case of the interaction of buoyancy-driven turbulent temperature and velocity fields. The paper discusses the near-wall variation of the second moments and their budgets, as well as possible scaling of turbulent heat flux and temperature variance both in the near-wall region and away from the wall. Various proposals for the Reynolds-averaged modelling are analyzed and new models are proposed for these two transport equations using the term-by-term approach.