%0 Journal Article
%T Direct Numerical Simulation of Twin Swirling Flow Jets: Effect of Vortex-Vortex Interaction on Turbulence Modification
%A Wenkai Xu
%A Nan Gui
%A Liang Ge
%A Jie Yan
%J Journal of Computational Engineering
%D 2014
%R 10.1155/2014/313201
%X A direct numerical simulation (DNS) was carried out to study twin swirling jets which are issued from two parallel nozzles at a Reynolds number of and three swirl levels of , 1.08, and 1.42, respectively. The basic structures of vortex-vortex interaction and temporal evolution are illustrated. The characteristics of axial variation of turbulent fluctuation velocities, in both the near and far field, in comparison to a single swirling jet, are shown to explore the effects of vortex-vortex interaction on turbulence modifications. Moreover, the second order turbulent fluctuations are also shown, by which the modification of turbulence associated with the coherent or correlated turbulent fluctuation and turbulent kinetic energy transport characteristics are clearly indicated. It is found that the twin swirling flow has a fairly strong localized vortex-vortex interaction between a pair of inversely rotated vortices. The location and strength of interaction depend on swirl level greatly. The modification of vortex takes place by transforming large-scale vortices into complex small ones, whereas the modulation of turbulent kinetic energy is continuously augmented by strong vortex modification. 1. Introduction Swirling flows exist in many engineering applications, such as gas turbine combustors, internal combustion engines, cyclone separators, and industrial burners. It is proven as an effective mixing enhancement approach. Swirling flows are extensively studied in many aspects, such as vortex breakdown [1], instability [2], and recirculation zones [3]. Theoretical and experimental approaches are two important tools to research swirling flow. Most early theories were developed to characterize the conditions of vortex breakdown and predict its location and criterion. Recent theoretical studies tried to describe the whole process and predict the internal structure. Although lots of theories have been proposed, none of them agreed well with all features of breakdown [4]. Therefore, many experiments were conducted to investigate swirling flows in detail. For example, Zohir [5] studied heat transfer characteristics and pressure drop for turbulent airflow with propeller swirl generator. It indicated that inserting the propeller downstream provides considerable improvement of heat transfer rate higher than inserting the propeller upstream. Xie et al. [6] investigated the effect of rotational acceleration on flow and heat transfer in swirl microchannels. They showed complicated flow and heat transfer characteristics at different acceleration directions, and the
%U http://www.hindawi.com/journals/jcengi/2014/313201/