## Fluids

#### Wall Skin Friction

• terjit
Subscriber

I am trying to model turbulent flow in a pipe.  I am looking at the wall skin friction and comparing it to the Blasius equation.  I am using a 2d-axisymmetric model that is 0.01905 m by 5 m long and a structured bias mesh that is smaller close to the wall.  The y+ values are in the range of 0.6 - 0.65.  Using a k-e model with enhanced wall treatments with a inlet velocity of 0.1 m/s (3791 Reynolds number) the wall skin friction is 0.0120925 vs 0.010068 from the Blasius equation, a result that is about 28% high.  When the velocity is changed to 0.2 m/s (7583 Reynolds number) the will skin friction becomes 0.0373416 vs 0.008466 from the Blasius equation, a result that is about 341% high.

So my question is why does the turbulence model not scale as the Reynolds number increases?  Is it the mesh?  I have tried a finer mesh with the same results.  Is it something with the turbulence model?  I have tried the transition SST model but the results are flipped, the 0.2 m/s is around 20% off and the 0.1 m/s is around 300% off.  Is there not a way to scale the model?

I was hoping to be able to match a friction factor to the flow that would be applied at several different flow rates to verify the model before moving on to some other tasks.

• DrAmine
Ansys Employee

Please verify first of all the reference values in Fluent. Skin friction coefficient uses the reference density and velocity.

• qamar
Subscriber
Hello Everyone, I am new to this forum. I was looking into skin friction coefficient issues. I am doing steady analysis of an airfoil using Transition SST model. I did meshing in ICEM with yplus less than 1. I am obtaining skin friction coefficient from plot-wall flux-skin friction coefficient. But the coefficient does not matches with the literature data. My lift and drag coefficients are in good match with experimental values.nWhat may be the issue with skin friction coefficient?. Am I plotting it the wright way? Kindly help accordingly. Thank you very much.n