Enhanced heat transfer under the influence of coherent structure induced by arc vortex generator in square pipe flows

Abstract

Experiments and numerical simulations were both performed to investigate coherent structures and heat transfer process in a square pipe turbulent flows induced by arc vortex generator. The velocity fields of induced turbulent flow was obtained by planar particle image velocimetry. The analysis of velocity profiles revealed the co-existence of various coherent structures. Turbulent fluctuation quantities, such as turbulent intensities, Reynolds stress, etc. exhibited the different behaviors of fluid motions introduced by arc vortex generator. Probability density function of swirling strength showed the complication of the vortex-rotating. Heat transfer process was simulated using large eddy simulation. The results of Nusselt number achieved the maximal improvement 57% with the use of arc vortex generator. The distribution of Nusselt number was in good agreement with the distribution of coherent structures, especially hairpin vortices and subsequent secondary coherent structures, which highlighted the influence of coherent structures by arc vortex generator on heat transfer enhancement.