Modeling internal flows by an extended menter transition model

A multi-regime fluid flow model for internal flows has been applied to several pipe and duct problems. The investigated flow regimes and inter-regime transformations include fully laminar and fully turbulent, laminarization, and turbulentization. The model auto-selects both the flow regimes and the inter-regime transformations. It was employed here to study both steady and unsteady flows as well as flows in pipes and ducts of both axially unchanging cross section and axially enlarging cross section. The local nature of the flow was quantified by two related metrics. One of these is the laminarization parameter which is the ratio of the rates of turbulence production and turbulence destruction. The other is the intermittency, whose role is to dampen the rate of turbulence production at locations where the flow is not fully turbulent. Among the key results, fully developed friction factors in transition regimes, heretofore unpredicted in the literature, have been determined and presented. Heat transfer was also investigated in certain of the aforementioned fluid-flow problems. A major issue in the prediction of heat transfer coefficients in regions of flow transition is the need for a connection between the turbulent viscosity and the turbulent thermal conductivity.