ENHANCED MIXING WITH STREAMWISE VORTICITY

A quantitative description is presented of mixing augmentation mechani sms associated with embedded streamwise vortices. The specific context of interest is the flowfield downstream of convoluted (lobed) mixers, but the concepts developed apply to a range of devices that generate such vortices for enhanced mixing. Arguments are presented to illustra te the dependence of mixing augmentation on the strain field associate d with the vortices; this strain field increases both the area availab le for mixing between two streams and the local gradients in fluid pro perties which provide the driving potential for mixing. Computations a nd experiments have been carried out to assess the influence of the st reamwise vortices on both momentum interchange and mixing on a molecul ar level. Based on these investigations, scaling laws have been develo ped for the overall parametric trends of flow field structure and mixi ng rate as functions of lobe geometry, Reynolds number, stream-to-stre am velocity ratio and Mach number. (C) 1997 Elsevier Science Ltd.