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# Article

## Direct numerical simulations of variable-aspect-ratio turbulent duct flows at low to moderate reynolds numbers

Authors: Vinuesa, R., Noorani , A. N., Lozano-Dur´an, A.L.D., El Khoury, G.E.K., Schlatter, P., Fischer, P F, Nagib, H.M. Conference Published 8th International Symposium on Turbulence and Shear Flow Phenomena (TSFP-8) 2013

### Abstract

Three-dimensional effects in turbulent duct flows, i.e., side-wall boundary layers and secondary motions, are studied by means of direct numerical simulations (DNS). The spectral element code Nek5000 is used to compute turbulent duct flows with aspect ratios 1 to 7 (at $Re_{b,c}=2800$, $Re_{\tau} \simeq 180$) and 1 (at $Re_{b,c}=5600$, $Re_{\tau} \simeq 330$) in streamwise-periodic boxes of length $25h$. The total number of grid points ranges from 28 to 145 million, and the fluid kinematic viscosity $\nu$ was adjusted iteratively in order to keep the same bulk Reynolds number at the centerplane with changing aspect ratio. Spanwise variations in wall shear, mean-flow profiles and turbulence statistics are analyzed with aspect ratio, and also compared with the 2D channel. These computations show good agreement with experimental measurements carried out at IIT in parallel, and reinforces one important conclusion: the conditions obtained in the core region of a high-aspect-ratio duct cannot exactly be reproduced by spanwise-periodic DNSs of turbulent channel flows.