Lagrangian and Eulerian time scales were obtained from the direct numerical simulation of turbulent channel flow at two Reynolds numbers based on the friction velocity and channel half-height,Reτ=80,100.The Lagrangian integral time scales and time microscales were compared to their Eulerian equivalents.It is found that the ratio of Lagrangian to Eulerian integral time scales is given by TiL/TiE=1+0.1y+ for y+≤10,and that the ratios between the Lagrangian to the Eulerian time microscales are almost the same irrespective of the components.Those increase with y+ are approximated by TiL/TiE≈ 2.75-1.75 exp "-yα+ ".These results also show that these expressions are independent of the Reynolds number.
This is a study on the mass transport of a solute or contaminant in oscillating flows through a circular tube with a reactive wall layer.The reaction consists of a reversible component due to phase exchange between the flowing fluid and the wall layer,and an irreversible component due to absorption into the wall.The short-time dispersion characteristics are numerically investigated,incorporating the coupling effects between the flow oscillation,sorption kinetics,and retardation due to phase partitioning.The effects of various dimensionless parameters e.g.,Da(the Damk&o&h lernumber),α(phase partitioning number),Γ(dimensionless absorption number),and δ(dimensionless Stokes boundary layer number) on dispersion are discussed.In particular,it is found that there exist trinal peaks of the breakthrough curves in some cases.
