Abstract
The eddy viscosity and the representative mixing time and length, which are the most indispensable basic informations in studying turbulent mixing phenomena, are investigated theoretically and experimentally.
The new eddy viscosity is defined as the product of kinematic viscosity and coefficient which relates the turbulence energy dissipation through fluctuating motion with that through mean motion. The turbulent flow field being looked upon as the flow field in which the turbulent elements move transverse to the mean flow, new representative mixing time and length are proposed. The representative mixing time is applied to relate the above eddy viscosity with the mean velocity gradient. Being different from the conventional eddy viscosity, the newly defined eddy viscosity is determined uniquely on the notice point if there is only one mean velocity gradient to any direction at that point.
In the transitional region from laminar to turbulent flow of liquid in a circular pipe, experimental values of the newly defined eddy viscosity and the representative mixing length are obtained by measuring the liquid velocity fluctuations by an electro-chemical technique based on an electro-chemical reaction controlled by diffusional mass transfer rate.
