Numerical investigation of parallel plane jets at low Reynolds number

•Low Reynolds number parallel plane jet is studied using lattice Boltzmann method.•In converging region, steady and periodically unsteady flow states are demonstrated.•The periodically unsteady flow state is found to have faster mean maximum streamwise velocity decay in converging region.•This study provides some flow physics to control mixing based on parallel jets.

Two parallel plane jets with various jet spacing between two jet centerlines, defined as s, are numerically simulated using lattice Boltzmann method. The Reynolds number based on jet-exit-width d is set to be Re=56 and the jet spacing is set to be less than or equal 8 times the jet-exit-width. Generally, there exist three distinct regions, a converging region, a merging region and a combined region. When the jet spacing is in the range of s∕d<7, the flow field displays periodic oscillation in the combined region, while it remains steady in the converging region with two counter-rotating vortices. When 7≤s∕d≤8, the whole flow field reveals periodic vortex shedding, even in the converging region close to the nozzle plate, and the non-dimensional periodic oscillation frequency (Strouhal number) is nearly one order of magnitude larger than that in the cases of s∕d<7, indicating the scale of the oscillation for 7≤s∕d≤8 is smaller than that of s∕d<7.