How to increase wall shear stress?

- January 11, 2019 at 10:22 am
  
  shaheen wahab
  Subscriber
  
  Hello,
  
  Is there any way to increase the Wall shear stress at the bottom? It is too low and thereby the sediments move too slow (undesirable).
  
  I have used Roughness height of 200 micrometers and a Roughness constant of 0.5.
  
  I use "water-liquid" in the Cell zone condition and for the Reference values, I set Density = 998.2 kg/m3 and Viscosity = 0.001003 kg/m-s
  
  What could be done to increase the Wall shear stress? I read in the manual about Reference values but couldn't find anything that might help. Do you think changing the "Compute from" in Reference values would help or something as such?
  
  I would be very grateful if anyone could help me in this regard.
  
  Thank you
  
  With regards
  
  Shaheen Wahab
- January 11, 2019 at 10:34 am
  
  DrAmine
  Ansys Employee
  
  What do you mean with increasing wall shear? Artificially? What is the reality? What are you modeling? Are you talking about skin friction ( which is based on reference values)
  
  Wall shear stress for turbulent Flows is based on wall function. For laminar flows on the molecular viscosity and velocity gradient in the live wall cell.
- January 11, 2019 at 11:37 am
  
  shaheen wahab
  Subscriber
  
  Dear Amine,
  
  Thank you for your reply.
  
  No, I want the Wall shear stress to be increased in the results itself. So, I wanted to know if there is any way (input conditions such as Roughness height, Roughness const. etc.) so that the Wall shear stress at the bottom increases.
  
  I have increased the Roughness height from 200 Micrometers to 2 mm at the bottom.
  
  I have a rectangular channel with water. The Wall shear stress will move the sediments. In my results, the Wall shear stress is so slow that the sediments move too slow. So I wanted to know if I can increase the Wall shear stress so that the sediments move faster.
  
  No, I am not talking about skin friction I have issues with Wall shear stress (Bed shear stress in the channel bottom)
  
  Thank you
  
  With regards
  
  Shaheen
- January 11, 2019 at 11:59 am
  
  Rob
  Forum Moderator
  
  The wall shear stress is a result of the flow field, so the solution to sedimentation is (usually) to increase the flow rate.
  
  Can you sketch out what you're trying to model (and learn) as I think Amine & I are missing something by not knowing what you're trying to model.