Direct numerical simulations of turbulent pipe flow up to Reτ ≈ 5200

Well-resolved direct numerical simulations (DNS) have been performed of the flow in a smooth circular pipe of radius R and axial length 10 pi R at friction Reynolds numbers up to Re-tau = 5200 using the pseudo-spectral code OPENPIPEFLOW. Various turbulence statistics are documented and compared with other DNS and experimental data in pipes as well as channels. Small but distinct differences between various datasets are identified. The friction factor lambda overshoots by 2% and undershoots by 0.6% the Prandtl friction law at low and high Re ranges, respectively. In addition,. in our results is slightly higher than in Pirozzoli et al. (J. Fluid Mech., vol. 926, 2021, A28), but matches well the experiments in Furuichi et al. (Phys. Fluids, vol. 27, issue 9, 2015, 095108). The log-law indicator function, which is nearly indistinguishable between pipe and channel up to y(+) = 250, has not yet developed a plateau farther away from the wall in the pipes even for the Re-tau = 5200 cases. The wall shear stress fluctuations and the inner peak of the axial turbulence intensity - which grow monotonically with Re-tau - are lower in the pipe than in the channel, but the difference decreases with increasing Re-tau. While the wall value is slightly lower in the channel than in the pipe at the same Re-tau, the inner peak of the pressure fluctuation shows negligible differences between them. The Reynolds number scaling of all these quantities agrees with both the logarithmic and defect-power laws if the coefficients are properly chosen. The one-dimensional spectrum of the axial velocity fluctuation exhibits a k(-1) dependence at an intermediate distance from the wall - also seen in the channel. In summary, these high-fidelity data enable us to provide better insights into the flow physics in the pipes as well as the similarity/difference among different types of wall turbulence.

Automated summary

This study conducted direct numerical simulations of flow in a smooth circular pipe and obtained various turbulence statistics. A comparison with other simulations and experiments revealed small but noticeable differences. The friction factor deviated from the Prandtl friction law at low and high Reynolds numbers. The wall shear stress fluctuations and axial turbulence intensity in the pipe were lower than in the channel, but the difference decreased with increasing Reynolds number.