Hi,

the wall shear stress is the product of shear rate and dynamic viscosity.

These quantities have the following names in COMSOL (Laminar flow, single-phase - "spf" Module):

• shear rate -> spf.sr
• dynamic viscosity -> spf.mu

When you create the 2D graph with velocity colour, you can inspect the variable being plotted (in your case, spf.U, which stands for fluid velocity in laminar flow).

This graph can be duplicated (right click->duplicate) and modified, if you want to show wall shear stress.

In particular, in the Definition of the variable, please substitute spf.U with the following expression:

spf.sr*spf.mu

This creates the wall shear stress variable.

Best regards,

AP

Alessio Pricci thanks for your valuable feedback. I followed the instructions and got the image provided in attachment.

I tied to change the velocity but it appears to be a blue colored 2D object from which I expect that the shear stresses are almost zero. This should not be correct... or i am missing anything.

I will appreciate your opinions. Thanks

SWH

The maximum shear stress is near wall (approximately 35 Pa). You can also create a 1D plot about what happens near the domain inlet (if you inlet buondary condition is the "fully developed flow") and show in a graph the shear stress versus the y-coordinate (channel height, if I understand).

The fact that in the middle of the channel there is almost zero shear stress is related to the fact that probably fluid velocity in the middle of the channel is almost constant: shear rate is the local slope of the velocity profile, so if the velocity is almost constant, the corresponding shear rate is almost zero... so you have a lower (almost zero) shear stress in the middle of the channel

Alessio Pricci thanks for u comments.

Alessio Pricci few days back i sent u a message thru RG. I just wanted to know if u have received that ?