[gush]

hi,

i have very simple 3d simulation: one inlet (vel in), one outlet (outflow), walls(no slip).

Rng ke with standard wall function gives very good results (compared with experimental).
but there are some papers in the literature says it is also possible with enhanced wall functions.

but it seems impossible and the whole simulation changes very much with EWT. i changed the mesh in a range from y+=0,2 to 5 but it is still exactly same.



does anyone have any idea about it? all parameters are same in both situation except "standart wall function" and "enhanced wall treatment" selection.

[gush]

anyone has an idea??
i am grateful for any comments

[AlexanderZ]

EWT usually is using with y+ 50..200

Best regards

[gush]

Originally Posted by AlexanderZ

EWT usually is using with y+ 50..200

Best regards

i have never seen such an information about EWT! it is generally said that EWT needs dense mesh where y+ is about 1.

the interesting thing in my problem is in the case of high or low y+ values SWF gives the best results. but when EWT is activated then results differ very much as seen in the first post!!

i have found more or less the same problem mentioned in another post. swf and ewt gives very different results. and he thinks that it is because wall roughness somehow

wall roughness in enhanced wall treatment

[LuckyTran]

What is this image of? Velocity mag or something?

It is odd the results are way different. You seem a sudden decay of (something) immediately after the inlet. This should have nothing to do with the wall treatment because it's not next to any walls.....

Originally Posted by gush

i have never seen such an information about EWT! it is generally said that EWT needs dense mesh where y+ is about 1.

I also have never seen any information saying EWT should be y+ 50.

[gush]

Originally Posted by LuckyTran

What is this image of? Velocity mag or something?

It is odd the results are way different. You seem a sudden decay of (something) immediately after the inlet. This should have nothing to do with the wall treatment because it's not next to any walls.....


I also have never seen any information saying EWT should be y+ 50.

this is the image of velocity contours in the mid plane!

1st image: standard wall function (coarse mesh, impossible to reach y+>30 because the velocity is too low. Re is about 630 for the inlet. results are very similar to experimental!!! )
2nd image: enhanced wall treatment (denser mesh near the wall y+=1)

nothing else is different in both simulation!

the question is, how does that sudden decay happen just with the selection of EWT (which seems wrong compared to experimental results) ?

p.s. you may say, "you got your results with SWF and it seems EWT is not suitable somehow for this specific case.". but there are many papers in the literature telling that EWT can also give good results.

[gush]

the difference disappears at higher velocities.



Has anyone any idea about it?

[Fole]

In some places it is pointed out that resolving the viscous and buffer layers is even more important than reaching an y+ value. I would play with the number of inflation layers to see what happens.

Keep us informed!

[gush]

Originally Posted by Fole

In some places it is pointed out that resolving the viscous and buffer layers is even more important than reaching an y+ value. I would play with the number of inflation layers to see what happens.

Keep us informed!

thank you very much for the advice Fole!

now i am changing the number of inflation, hope it works!

the thing is there is no direct approach for this mesh issue. it is generally so case dependent and you must find the solution (if there is one) by trying only (which takes enormous time in some unique cases). (

[gush]

Originally Posted by gush

thank you very much for the advice Fole!

now i am changing the number of inflation, hope it works!

the thing is there is no direct approach for this mesh issue. it is generally so case dependent and you must find the solution (if there is one) by trying only (which takes enormous time in some unique cases). (

different inflation numbers or any other change on the mesh did not effect the simulation results.

it seems at low velocities (Re is about 630) enhanced wall treatment is not able to give correct results while at higher velocities mentioned velocity issue is not a problem.

is there anyone here who has similar experience with EWT? or any advice is appreciated!

[Fole]

If for such low velocities the turbulence level is low, try kwSST turbulence model which behaves well for low speeds. Also, a comparison between turbulence models could give more confidence in the results.

Regards.