## Fluids

#### Uncertainties with the Near-Wall Region

• trippleD
Subscriber

Hello,

i have a question about the near-wall region.

As you can see on the picture, the inner layer consits of three layers:

• viscous sublayer

• buffer layer

• fully turbulent region

In the documentation, you can find the follwing explanation:

Numerous experiments have shown that the near-wall region can be largely subdivided into three layers. In the innermost layer, called the “viscous sublayer”, the flow is almost laminar, and the (molecular) viscosity plays a dominant role in momentum and heat or mass transfer. In the outer layer, called the fully-turbulent layer, turbulence plays a major role. Finally, there is an interim region between the viscous sublayer and the fully turbulent layer where the effects of molecular viscosity and turbulence are equally important.

The explanation isn't clear for me. Is the outer layer, mentioned in te explanation that one that ist named the same as in the picture? The rigth layer of ther inner layer is fully turbulent as well. So is the outer layer and the right layer of the inner layer one layer (the same) or different? Which layer does the explanation mean exactly?

trippled

• DrAmine
Ansys Employee

Yes the outer layer mentioned is the log-law region. Viscous+buffer layer+log-law layer constitute less than 0.15-0.2 of the whole boundary layer.  The right layer called fully turbulent layer or velocity defect layer (for modeling requires some wake functions).

• trippleD
Subscriber

Yes the outer layer mentioned is the log-law region. Viscous+buffer layer+log-law layer constitute less than 0.15-0.2 of the whole boundary layer.  The right layer called fully turbulent layer or velocity defect layer (for modeling requires some wake functions).

I'm sorry but it is still not clear for me

1: viscous sublayer

2: buffer layer

3: log-law region

4: outer region

So which layer is mentioned in the documentation

Numerous experiments have shown that the near-wall region can be largely subdivided into three layers. In the innermost layer, called the “viscous sublayer”, the flow is almost laminar, and the (molecular) viscosity plays a dominant role in momentum and heat or mass transfer. In the outer layer, called the fully-turbulent layer, turbulence plays a major role. Finally, there is an interim region between the viscous sublayer and the fully turbulent layer where the effects of molecular viscosity and turbulence are equally important.

Sorry for double asking but thanks a lot

• DrAmine
Ansys Employee

log-law layer.

• trippleD
Subscriber

The vleocity u, is it the absolut velocity or the velocity in a special direction?