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STATISTICS OF TURBULENT AND LAMINARIZING FLOW IN A CIRCULAR PIPE WITH A GRADUAL EXPANSION

Nima Moallemi
School of Engineering University of British Columbia, Okanagan campus 3333 University Way, Kelowna, BC V1V 1V7

Joshua Brinkerhoff
The University of British Columbia, Okanagan Campus, Kelowna, Canada, V1V 1V7

Аннотация

Direct numerical simulations of turbulent flow in an axisymmetric pipe with a gradual expansion have been performed for a Reynolds number of 5300 based on the inlet pipe diameter and bulk velocity in order to investigate the effect of a gradual expansion on the flow structure, with special focus on the recirculation and laminarization of the flow downstream of the expansion. An annular ribbed turbolator is used in conjunction with a periodic flow mapping approach to produce fully-developed turbulent flow conditions upstream of the gradual expansion. A turbulent free shear layer initiated at the start of the sudden expansion develops from the flow separation and then reattaches to the pipe wall downstream of the expansion. Following reattachment, the turbulent flow laminarizes as the strength and size of vortical structures gradually diminish. The laminarization process is described in terms of the evolution of the Reynolds stress tensor in the turbulent and laminarizing regions, morphometrically in terms of the evolution of coherent vortical structures, and mechanistically through analysis of the budgets of the vorticity transport equation.