Fluid flow and mixing in a channel with dual bluff bodies

Placing bluff bodies in a mixing channel is an important technique to enhance mixing. This paper numerically investigates the effects of transversal spacing and axial spacing of two bluff bodies on the outlet mixing efficiency (M-out), the pressure loss (Delta P), and the combined performance parameter eta (the ratio of M-out to dimensionless Delta P) of fluid flow within mixing channels with dual bluff bodies having three cross-sectional shapes of circle, square, and sector with Reynolds numbers based on bluff body dimension Re-d = 20, 60, and 100. The study reveals that, at Re-d = 20, altering the spacing between the two bluff bodies in the mixing channel does not improve mixing but instead increases Delta P, leading to a decrease in eta. At Re-d = 60 and 100, changing the transversal spacing and axial spacing in a certain range can effectively enhance mixing and improve the combined performance. There exists an optimal transversal spacing to maximize M-out and eta. Furthermore, the mixing channel with sector-shaped dual bluff bodies exhibits the highest M-out and eta among the three kinds of cross-sectional shapes. When Re-d = 60 and 100, eta of the mixing channel with sector-shaped dual bluff bodies increases by 212% and 270% by the transversal offsetting compared to the case with zero transversal spacing and increases by 489% and 331% by the axial offsetting compared to the case with an axial spacing of 2 times the bluff body dimension. The present findings hold significant implications for the design optimization and performance improvement of mixers.