Reynolds number effects in DNS of pipe flow and comparison with channels and boundary layers

Direct numerical simulations of turbulent pipe flow were performed at four Reynolds numbers: Re τ = 180 , 500 , 1002 and 2003 . Beyond Re τ = 1000 viscous scaling holds near the wall for the mean velocity, Reynolds shear stress and wall-normal velocity variance. Streamwise and spanwise velocity variances do not exhibit inner (viscous) scaling due to increasing large-scale energy contributions. A comparison with channel and boundary layer DNS data shows negligible statistical differences between pipes and channels, whereas the transverse velocities for pipes/channels are significantly different when compared with boundary layers. A further comparison displays that the boundary layer pressure fluctuations is greater than pipes/channels. In addition, is it shown that the higher pressure fluctuations in the boundary layer is not the sole mechanism responsible for a stronger wake region in the flow.