Learning Forum

[Momen_Amer]

I am trying to model flow in a rotary lobe pump. I want to look at the maximum shear stress in the flow domain and I don't fully understand what is the difference between the Wall shear and the turbulence shear.nThe maximum wall shear that I get is higher than the maximum shear I calculate from the maximum turbulence eddy dissipation. I am wondering if these are two different kinds of shear? and how much I can trust the wall shear calculation? currently I am setting 10 inflation layers at my wall.n

[Karthik R]

Hi,nTurbulent shear stress is a term you will come across generally in Turbulence modeling, especially when dealing with Reynolds averaging of the NS equation. When dealing with turbulence, the shear stress term in the momentum equation can be written as the sum of laminar and turbulent components. The turbulent shear stress is also commonly referred to as the Reynolds tensor. Please see the lesson on Governing Equations of Turbulent Flows in our Basics of Turbulent Flows course (part of the Ansys Innovation Courses - AICs). Here is the link.nKarthikn

[Momen_Amer]

Hi Kremella, nThanks for the link, it is very helpful. What I still don't fully understand is the maximum wall shear doesn't correspond to a maximum turbulence eddy dissipation. The maximum eddy dissipation in the core of the domain would correspond to ~150 Pa while the wall shear is 450 Pa. the max turbulence eddy dissipation at the wall is 10,000 m2s-3 and 24,000 in the fluid domain. Is the wall shear a different kind of shear than the turbulent shear that can be calculated in the fluid core? it makes sense in my simulation for the maximum shear to happen at the walls since I am having a very tiny clearance between the pump lobes and walls with highest velocity there, but as I am looking for the maximum shear in the system, which one should I be looking at?n