Eddy Viscosity Eddy viscosity is a dimensionless quantity that characterizes the local behavior of turbulent flows. It measures the ability of a fluid to re...
Eddy Viscosity
Eddy viscosity is a dimensionless quantity that characterizes the local behavior of turbulent flows. It measures the ability of a fluid to respond to small-scale disturbances or eddies in the flow, resulting in non-local flow characteristics.
Eddy viscosity is a complex function of frequency, turbulent intensity, and flow geometry. At low frequencies, eddy viscosity is typically low, as eddies are able to dissipate rapidly due to the dominant role of viscosity in molecular transport. As frequency increases, the eddy viscosity initially increases due to the increased ability of eddies to propagate and evolve. However, at even higher frequencies, eddy viscosity typically reaches a maximum value and then decreases as the flow becomes more laminar.
Eddy viscosity can be expressed in different units, such as:
m²/s (for laminar flows)
µm²/s (for turbulent flows)
Examples:
In turbulent pipe flow, the eddy viscosity can be much higher than in laminar pipe flow due to the larger size and presence of multiple scales of eddies.
Eddy viscosity is typically lower in high-Reynolds-number flows due to the dominance of molecular transport over turbulent transport.
In turbulent boundary layers, eddy viscosity can play a significant role in determining the wall shear stress and heat transfer