Koji Fukudome

Low Reynolds number effects on rotating turbulent Poiseuille flow

Direct numerical simulations with a spectral method are performed to study the effects of spanwise rotation on a turbulent Poiseuille flow at very low Reynolds number. At this Reynolds number, the region of zero absolute vorticity, typically observed in the mean velocity profile of rotating Poiseuille flow, disappears in the channel center, and the mean velocity gradient becomes opposite to that of zero absolute vorticity. When zero absolute vorticity disappears, very long low-speed streaks, accompanied by the vortices aligned in the streamwise direction like a chain, dominate the flow, in which the transfer of turbulent kinetic energy into the vicinity of the wall and small-scale streamwise vortices disappear there. However, low-speed fluids are pumped up from the near-wall region, and trapped into the channel center by the larger-scale chain vortices away from the wall, which decreases the mean velocity in the channel center and shifts its peak location toward the wall.

The Effect of Spanwise System Rotation on Turbulent Poiseuille Flow at Very-Low-Reynolds Number

Direct numerical simulations (DNSs) with a spectral method are performed with large and small computational domains to study the effects of spanwise rotation on a turbulent Poiseuille flow at the very low-Reynolds numbers. In the case without system rotation, quasi-laminar and turbulent states appear side by side in the same computational domain, which is coined as laminar-turbulence pattern. However, in the case with system rotation, the pattern disappears and flow is dominated by quasi-laminar region including very long low-speed streaks coiled by chain-like vortical structures. Increasing the Reynolds number can not generate the laminar-turbulence pattern as long as system rotation is imposed.