CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Irregular near wall velocity profile

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By AlexanderZ

LinkBack Thread Tools Search this Thread Display Modes
Old   October 20, 2021, 14:41
Question Irregular near wall velocity profile
New Member
Mohammad Shafiee
Join Date: Apr 2021
Posts: 22
Rep Power: 5
Mohammad74 is on a distinguished road

I'm trying to simulate an array of 3*3 cubes using k-w sst turbulence model in Ansys Fluent. I've used gambit to generate a fully structured hexahedral mesh and with relatively fine mesh near the walls for boundary layer simulation. As for boundary conditions, I defined inlet boundary as velocity inlet with custom velocity profile and 10% turbulence intensity, outlet boundary as pressure outlet and side walls as symmetric. I posted pictures of the mesh below:


After the simulation, I compared the velocity magnitude along a vertical line located at the middle of the top of central cube with the data I obtained from a journal article. I posted the plot of this comparison below:


As can be seen by the picture, my velocity values in vicinity of the wall is underpredicted by a relatively large margin. What is the problem here? What am I missing?
I'm struggling to find the reason since my domain dimensions are larger and my cell counts are higher than that of the article I mentioned earlier.

Any helps/suggestions would be much appreciated.
Mohammad74 is offline   Reply With Quote

Old   November 27, 2021, 12:23
New Member
Mohammad Shafiee
Join Date: Apr 2021
Posts: 22
Rep Power: 5
Mohammad74 is on a distinguished road
Hello again,

So I've been struggling with this problem for over a month now, and wasn't able to solve it. I've tried different mesh resolutions with different strategies and non of them worked. In my latest attempt, I simplified my domain by using an array of 1 building in the span wise direction and 3 buildings in the stream wise direction and used symmetric BC on side walls to account for the removed 6 buildings. Also wall y+ values accross building walls is around 1,here's my mesh::


But still I'm having trouble validating my results near the 2nd building wall. I've noticed the separation zone above the 1st building is extended all over to the 2nd building!? Which gives me wrong results. I'm posting pictures of the velocity contour and velocity profile at the point I'm having problem with:


Any Ideas why this is happening?
Mohammad74 is offline   Reply With Quote

Old   November 28, 2021, 20:56
Senior Member
Join Date: Apr 2013
Posts: 1,988
Rep Power: 30
AlexanderZ will become famous soon enoughAlexanderZ will become famous soon enough
for me it seems, that this separation zone should be bigger, isn't it?

you may try to play with inlet BC, of example turbulence intensity, and the other one, don't remember the name

you may try to use other turbulence model.

other idea is to extend zone with refined mesh higher above "buildings" as that separation zone from the first building could interact with course mesh and could be influence by course mesh. Its hard to say from pictures is it the case or not.

the last "expensive" approach is to simulate this in transient with relatively small timestep.
Mohammad74 likes this.
best regards

press LIKE if this message was helpful
AlexanderZ is offline   Reply With Quote


boundary layer, building aerodynamics, validation, velocity calculation

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
How does FLUENT caculate velocity profile at wall when shear is specified? Faizan89 FLUENT 2 June 5, 2021 12:04
How to define velocity profile to wall of circle Tufan Tuna Fluent UDF and Scheme Programming 2 April 23, 2021 10:37
Import .csv - velocity profile - error eSKa CFX 9 April 3, 2021 13:38
How to plot near cylinder (wall) velocity profile in ParaView? Derek2580 OpenFOAM Running, Solving & CFD 1 March 22, 2018 00:45
Patch fully developed velocity and turbulence profile over full domain Teumde FLUENT 2 June 29, 2015 13:47

All times are GMT -4. The time now is 08:01.