|
[Sponsors] |
how to achieve homogeneous vertical profile for turbulence |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
August 16, 2021, 14:48 |
how to achieve homogeneous vertical profile for turbulence
|
#1 |
New Member
Saugat Shrestha
Join Date: Dec 2019
Location: Thailand
Posts: 27
Rep Power: 7 |
Hello,
I am working on turbulence modeling of the Atmospheric Boundary Layer. Here I have been able to maintain a homogeneous wind velocity profile. However, I have been unable to maintain a homogeneous profile for tubrulence. I have given a manual input for the Turbulent Kinetic energy (TKE). It seems that the TKE seems to dissipate very early in the domain and doesn't travel the domain. I have attached a picture of the TKE in the along wind direction of the domain. FYI, I'm trying to implement a k-epsilon model. Can anybody please help me. I have been stuck in this problem for a long time. I will be very grateful for your help. Thank You. With best regards, Saugat |
|
August 16, 2021, 17:27 |
|
#2 |
Senior Member
Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
Rep Power: 16 |
That's probably because the inflow tke is not a solution of the homogeneous equation. If you run a flat plate simulation with periodic boundary conditions in stream wise direction you will get your homogeneous solution.
|
|
August 17, 2021, 10:27 |
|
#3 | ||
New Member
Saugat Shrestha
Join Date: Dec 2019
Location: Thailand
Posts: 27
Rep Power: 7 |
Thank You mAlletto, for the response.
The advice you gave me did work and now I am able to conserve the turbulence in my model domain. So, I gave the cyclic boundary layer inputs to the inlet and the outlet. Due to this I had to use fvOptions to give the velocity and turbulence input parameters. For the velocity I used the patchMeanVelocityForce function. However, here I could only give the a fixed value. I require to give a profile here. I tried using the fixed profile function from a CSV here but could implement it. Can you please help me give give a profile to those parameters? Your help will be really valuable in my work. Thank You. With best regards, Saugat This is for the fixed value of velocity Quote:
Quote:
|
|||
August 17, 2021, 16:19 |
|
#4 |
Senior Member
Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
Rep Power: 16 |
I didn't understand your question. Can you be more precise
|
|
August 18, 2021, 09:36 |
|
#5 |
New Member
Saugat Shrestha
Join Date: Dec 2019
Location: Thailand
Posts: 27
Rep Power: 7 |
Hello mAlletto,
I implemented the periodic boundary condition but I don't get a homogeneous solution. I have attached the profile of the TKE profile and epsilon profile. The TKE is for some reason getting attached to the top. Even in the epsilon profile, there are higher values at the top. However, for epsilon, the profile at the bottom is something that I want. FYI, I am getting a homogeneous profile for the wind speed but turbulence is a big problem for me. I am using a slip condition on the top layer. For the inlet and the outlet, I'm using cyclic boundary conditions. I have given a profile of wind speed, turbulence kinetic energy, and epsilon using the fvoption. Can you suggest a solution for this? With best regards, Saugat |
|
August 18, 2021, 18:00 |
|
#6 |
Senior Member
Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
Rep Power: 16 |
Seems like you have a source term in the middle of the domain. To achieve a homogeneous solution only a few cells in stream wise direction are required. Can you also post the velocity
|
|
August 18, 2021, 18:05 |
|
#7 |
Senior Member
Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
Rep Power: 16 |
You find a tutorial how to achieve a homogeneous solution for an atmospheric boundary layer here https://develop.openfoam.com/Develop...atmFlatTerrain
|
|
September 17, 2021, 01:11 |
|
#8 |
New Member
Saugat Shrestha
Join Date: Dec 2019
Location: Thailand
Posts: 27
Rep Power: 7 |
Sorry, mAlletto for the late response.
As request by you, I have attached the velocity profile. Thank You. |
|
January 24, 2022, 05:33 |
|
#9 |
New Member
Join Date: Jan 2019
Posts: 12
Rep Power: 7 |
Very interesting tutorial, mAlletto! I've been struggling with an ABL simulation of a complex terrain using LES and DFSEM. The velocity profile changes rapidly in streamwise direction, especially near the ground surface where I get much larger velocities compared to the reference profile.
I'm currently using pressureInletOutletVelocity at the top boundary for U. For nut at the ground surface I'm using atmNutUWallFunction. What do you suggest for the BCs at the top boundary? fixedShearStress? |
|
January 24, 2022, 05:44 |
|
#10 |
Senior Member
Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
Rep Power: 16 |
For a log profile fixedShear is ok. For a Eckman profile a slip condition is ok
|
|
Tags |
boundary layer, k-epsilon, openfoam, turbulent kinetic energy |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
3D UDF Paraboilc Velocity Profile (Can't Maintain) | Sing | FLUENT | 12 | August 7, 2017 07:25 |
problems orientating profile | Ralf Schmidt | FLUENT | 1 | March 30, 2014 11:00 |
problem with importing and exporting profile BC | Gui | CFX | 2 | July 26, 2007 09:50 |
Associating profile files for the UDS though a UDF | Bharath | FLUENT | 0 | December 1, 2006 16:58 |
Prescribed inflow velocity profile - how to? | Alan | Main CFD Forum | 10 | October 28, 2005 13:14 |