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Geert Brethouwer
Linne FLOW Centre, KTH Mechanics Royal Institute of Technology 100 44 Stockholm, Sweden

Phillipp Schlatter
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden

Arne V. Johansson
Linne FLOW Centre, Dept. of Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden


Direct numerical simulations of fully developed turbulent channel flow including a passive scalar rotating about the spanwise axis have been performed. The mean bulk Reynolds number, Reb = Ubh/ν ≥ 20000, where Ub is the bulk mean velocity and h the channel half width, is higher than in previous simulations and the rotation rate covers a wide range. At moderate rotation rates, turbulence on the stable channel side is significantly less damped than in DNS at lower Reb. At high rotation rates we observe re-occurring, quasi-periodic instabilities on the stable channel side. Between these events the turbulence is weak, but during the instability events the wall shear stress and turbulence intensity are much stronger. The instabilities are caused by structures resembling Tollmien-Schlichting (TS) waves that at some instant rapidly grow, then become unstable and finally break down into intense turbulence. After some time the TS waves form again and the process repeats itself in a periodic-like manner.
Mean scalar profiles are also strongly affected by rotation and large scalar fluctuations are found on the border of the stable and unstable channel side. The turbulent Prandtl/Schmidt number of the scalar is much less than unity if there is rotation. Predicting scalar transport in rotating channel flow will therefore pose a challenge to turbulence models.