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#1 |
New Member
Md. Nasimul Hoque Chowdhury
Join Date: Nov 2015
Posts: 2
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Hello Everyone,
I am trying to verify the reported wall shear stress of a model in Ansys Fluent. This two dimensional model uses standard k-e turbulent closure scheme with standard wall functions. The manual says that, it uses Launder and Spalding method. I tried to verify it with my result. However, the results do not match. Fluent results gives wall shear stress around 20.62 N/m2. If I follow the process explained in the Fluent manual, it gives me around 8.95 N/m2. Note that, If I use Log(base 10) instead of Log(base e) in the procedure, I can reproduce the same value around 20.62 N/m2. Now, I am thinking what can be the source of discrepancy. I would appreciate if anyone can suggest me regarding this issue. FYI: The velocity in the first cell is 1.111 m/s, distance from the wall is 0.0008 m and kinetic energy at the point is 0.059828 m2/s2. Note: I would like to mention that my first cell from the wall is in the log-law region. I have around 2-3 cells in the log-law region. Regards, Md Nasimul |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,728
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What's your y* for the same cell?
I don't think you're in the log region. Or maybe you can show the arithmetic to arrive at those numbers. |
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#3 |
New Member
Md. Nasimul Hoque Chowdhury
Join Date: Nov 2015
Posts: 2
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Thank You for the response. I checked my Y* value. It is 107.14. So, it is in the log-law region. One more thing, I should mention that it is an open channel flow (multi-phase) model.
Here is the actual velocity profile data. y data: 0.00E+00, 0.0008 ,0.0016 ,0.0024 ,0.0032, 0.004, 0.0048, 0.0056, 0.0064, 0.0072, 0.008, 0.0088, 0.0096, 0.0104, 0.0112, 0.012. x-velocity: 0, 1.11141, 1.30493, 1.43661, 1.53633, 1.61681, 1.68387, 1.7406, 1.78878, 1.82945, 1.86322, 1.89045, 1.91138, 1.92617, 1.93549, 1.94082. Turbulent K-E: 0.0637314, 0.0598278, 0.0543767, 0.0509705, 0.0471932, 0.0433579, 0.0395679, 0.0358986, 0.0324181, 0.0291987, 0.02632, 0.0238651, 0.0219147, 0.0205486, 0.0197962, 0.0197106. If I take yp as 0.0008 and corresponding x-velocity (up) as 1.11141 m/s, density= 998.2 kg/m3, dynamic viscosity= 0.001002, and C_mu= 0.09. y*=yp*c_mu^(0.25)*k^(0.5)*density/dynamic viscosity =107.14. ![]() taw_w becomes 8.95 N/m2. whereas Fluent gives about 20.62 N/m2. Is there something I am missing? Thank you again for looking in to the issue. |
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#4 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,728
Rep Power: 66 ![]() ![]() ![]() |
The value of k is consistent with the wall shear stress reported by Fluent.
But I also don't get agreement between velocity & y with the shear stress. How about y* reported by Fluent? Does it agree with y*~100? Also did you list the node values or cell centered values? You should be using cell centered values but it's probably not enough of a difference. You might also want to read through here as an additional reference: http://www.cfd-online.com/Wiki/Two_e...bulence_models |
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Tags |
fluent, standard wall functions, turbulence kinetic energy, wall shear stress |
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