Numerical Simulation on the Scalar Transport in Rotating Channel Turbulence

Passive scalar transport in channel turbulence with spanwise rotation is of relevance to many engineering applications. A systematical study on this problem was conducted based on direct numerical simulations. The Reynolds number defined by wall-friction velocity was fixed at 180, and the influences of the Schmidt and rotation numbers were investigated. Results reveal that even a weak rotation can have strong effects on the dominant flow structures: streamwise long streaks appear in scalar field at the unstable side due to the development of large scale streamwise rolls in the momentum field. With strong rotation, there exists a well mixed turbulent region at the unstable side, and a conductive region with near laminar flow at the stable side. The mean scalar profiles are linear in both the turbulent and conductive regions with different slopes. When the Schmidt number is smaller than unity, both the scalar fluctuation and convective transport in the turbulent region show nonmonotonic variations with rotation number, while they monotonically decrease for Schmidt number equal to or larger than unity. Therefore, for Schmidt number smaller than unity, the total flux first increases and then decreases as the rotation becomes faster. But the total flux decreases with the rotation speed when the Schmidt number is equal to or larger than unity, and it decreases fastest at small rotation speeds.