Secondary Currents in Wall Turbulence

Abstract

Considering the region not too close to the wall, application of the usual boundary-layer approximations to the balance equation for the turbulence kinetic energy leads to the following rule: When in a localized region the production is much greater (smaller) than the dissipation, there must be a secondary current that transports turbulence-poor fluid into (outwards) this region and turbulence-rich fluid outwards (into) the region. Depending on conditions the secondary current is either towards or away from the wall. Experiments at Delft on turbulent flow through a conduit of rectangular cross section with one of the long side walls partly corrugated showed secondary currents in the transition region from rough to smooth wall as well as in the corner regions in agreement with the above rule.