Low Reynolds number turbulent swirling pipe flows

Abstract

A direct numerical simulation of a swirling pipe flow is performed to investigate the effects of swirl on turbulence statistics. The swirling motion is imposed via a constant azimuthal body force coupled with a body force in the axial direction that drives the flow. The friction Reynolds number Ret ≈ 170 with a pipe length of 8pd (where d is the pipe radius). The simulations are performed at two swirl numbers S = 0.01 and 0.13. At the lower swirl number, the mean statistics appear to collapse well with non-swirling pipe flows. At the higher swirl number, the axial, radial and azimuthal turbulence intensities show a higher value in the outer region, whereas the axial turbulence intensity decreases closer to the wall. The higher swirl number simulation shows that there is an increase in drag, possibly due to the swirl imposing an increase in axial flow resistance. This is accompanied by an increase in the inertial region with increased swirl. We also show that similar to the total axial stress, the total azimuthal stress when normalised by the azimuthal friction velocity follows decreases linearly from wall to the pipe centerline