On the role of secondary motions in turbulent square duct flow

Abstract

We use a direct numerical simulations (DNS) database for turbulent flow in a square duct up to bulk Reynolds number $\Rey_b=40000$, to quantitatively analyze the role of secondary motions on the mean flow structure. For that purpose we derive a generalized form of the identity of Fukagata, Iwamoto and Kasagi (FIK), which allows to quantify the effect of cross-stream convection on the mean streamwise velocity, wall shear stress and bulk friction coefficient. Secondary motions are found to contribute for about $6\%$ of total friction, and to act as a self-regulating mechanism of turbulence whereby wall shear stress nonuniformities induced by corners are equalized, and universality of the wall-normal velocity profiles is established. We also carry out numerical experiments whereby the secondary motions are artificially suppressed, in which case their equalizing role is partially taken by the turbulent stresses.

References in corpus (1)

• Turbulence and secondary motions in square duct flow

Cited by in corpus (4)

• Direct numerical simulation of forced thermal convection in square ducts up to $R{e}_{\tau }\approx 2000$
• Integral relations for the skin-friction coefficient of canonical flows
• Small-scale resolving simulations of the turbulent mixing in confined planar jets using one-dimensional turbulence
• Investigation of unsteady secondary flows and large-scale turbulence in heterogeneous turbulent boundary layers