TURBULENT TRANSITION AND MAINTENANCE OF TURBULENCE - IMPLICATION TO HEAT-TRANSFER AUGMENTATION

In this communication we present formulation of a criterion for (turbu lent) transition for wall bounded flows. In addition, we discuss the i mplication of the findings to heat transfer augmentation. The Presenta tion has three parts. First, we argue that transition to turbulence sh ould be interpreted solely in the context of the system's capacity to maintain turbulent motions. Second, we propose a model that links main tenance of turbulence to the intermittent transfer of vorticity from t he wall region (the demarcation of transition follows directly from th e model: it is simply a limiting case of the conditions for maintenanc e). Third, we apply the findings to estimate heat transfer in the tran sition region. Experimental results show a good agreement with the pro posed criterion; they show a strong cause-effect coherency between vor ticity production and the system capacity to maintain turbulence (a co rrespondence implied by the proposed model). It was also found that th e heat transfer coefficient in the transition region is significantly increased when the transition Reynolds number is lowered through deplo yment of suitable augmentation schemes.