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THE EFFECT OF DYNAMICS AND THERMAL PREHISTORY ON TURBULENT SEPARATED FLOW AT ABRUPT TUBE EXPANSION

DOI: 10.1615/ICHMT.2012.CHT-12.1010
pages 1687-1700

Tatyana V. Bogatko
Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, 1 Acad. Lavrent'ev Ave., Novosibirsk, 630090, Russia

Viktor I. Terekhov
Kutateladze Institute of Thermophysics, Laboratory of Thermal and Gas Dynamics, Russian Academy of Sciences, Siberian Branch, 630090,1, Acad. Lavrent'ev Avenue, Novosibirsk, Russia; Novosibirsk State Technical University, K. Markx av., 20, Novosibirsk, 630073, Russia

Abstract

Results of a numerical investigation on the effect of aerodynamics and heat boundary layer thickness in front of an abrupt expansion of a round tube on turbulent transfer in the zone of flow separation, attachment and relaxation are presented. Studying this problem is very important for understanding the physics heat and mass transfer processes in separated flows. Before separation, the flow was hydrodynamically stable and the heat layer in front of the expansion could change its thickness in maximally possible limits: from zero to half of a tube diameter. In the other case, the thickness of an aerodynamic layer could change and the thermal layer before separation was absent.
The Reynolds number varied from 6.7·103 to 1.33·105. Expansion ratio of the tube is constant ER = (D2/D1)2 =1.78. The RANS method, comprising the Fluent 6.2 software, was used for numerical calculations. According to the experience of this package application for calculation of separated flows, the model of shear stress transfer (k−ω SST) gives the best coincidence with experimental data because its description of transfer features in the flows with recirculation is the most adequate.
It was found out that the growth of dynamics and heat layer thickness led to reduction of heat transfer intensity in the separation area and moving away of the coordinate of maximal heat transfer from the place of tube expansion. Generalizing dependence for the maximal Nusselt number is given for variation of the heat layer thickness. Comparison with experimental data have proved the main behavior tendencies of heat and mass transfer processes in separation flows behind a back-facing step with different dynamics and thermal prehistory.

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