|
[Sponsors] |
The velocity in the inlet is not constant at all? why? |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
May 1, 2019, 04:35 |
The velocity in the inlet is not constant at all? why?
|
#1 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
Hi everyone! Thank you so much for reading this post!
1. I put the velocity at 30m/s - constant (x-drect) But when I run analysis (I use LES), in the contour of velocity, it showed some area near the bottom of INLET with velocity equal to zero (0). So, any can help me to explain this and how can to fix this situation? I will include the image in the comment! |
|
May 1, 2019, 04:44 |
|
#2 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
[QUOTE=bietchetlien1995;732371]Hi everyone! Thank you so much for reading this post!
1. I put the velocity at 30m/s - constant (x-drect) But when I run analysis (I use LES), in the contour of velocity, it showed some area near the bottom of INLET with velocity equal to zero (0). So, any can help me to explain this and how can to fix this situation? here is the picture https://www.upsieutoc.com/image/xc4BNs |
|
May 1, 2019, 11:25 |
|
#3 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,679
Rep Power: 66 |
1) You have the no-slip boundary condition on walls.
2) The figure is also rendered image and it's interpolating |
|
May 1, 2019, 21:22 |
|
#4 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
Hi Lucky! Thank you for answering.
I think the 1st reason is more suitable. But can You explain more for me. How slip or no slip effects to the constant velocity. And the wall you mentioned, are they wall of building. ? |
|
May 3, 2019, 10:56 |
|
#5 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,679
Rep Power: 66 |
The building has no slip walls obviously. But no I am talking about the boundary at the bottom upstream and downstram of the building. The 1000m before the building and 3000m or so after the building. There appears to be a wall there with the no-slip boundary condition
|
|
May 8, 2019, 04:45 |
|
#6 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
https://www.upsieutoc.com/image/xLWgRN
Can you check here, I did it. The bottom of the domain (we can say it's the ground). I set it (this wall) with no slip condition! |
|
May 8, 2019, 05:35 |
|
#7 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,400
Rep Power: 47 |
I won't click on any of these links, but here is my guess: You are displaying cell values.
These cell values are affected by the flow conditions inside the domain. E.g. by the no-slip boundary condition at the bottom. Boundary conditions are not prescribed at cell centers, but at cell faces. Switching the displayer to node values instead should give you a constant velocity for your inlet face. |
|
May 9, 2019, 03:37 |
|
#8 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
Thank you so much! , you're right! when I unstick the "node value", the velocity in the inlet came to instant. it's FEM problem I've just remember.
One more question. which one is more accurate? node or surface value (maybe it's used gauss points) |
|
May 10, 2019, 10:56 |
|
#9 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,679
Rep Power: 66 |
It's not a question of accuracy. You're just plotting things and not realizing what is being plotted and where.
Unchecking node values gives cell values which is opposite of what flotus said would happen. But nonetheless, I'm glad you're happy with your picture now. |
|
May 12, 2019, 07:43 |
|
#10 |
New Member
Michael Fily
Join Date: Feb 2019
Posts: 24
Rep Power: 7 |
actually I didn't plot the value out.
But I've realized I did totally oppositely what Flotus1 said. SO, am I right? when I uncheck it, the thing I received ARE THEY CELL VALUE? Another question, I understood that velocity will come to the inlet (plane) as a point value at every node (follow the mesh created). Won't they? Thank you so much LuckyTran! |
|
May 13, 2019, 12:18 |
|
#11 | |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,679
Rep Power: 66 |
When you uncheck node values you see the values at either the cell centers of face centers depending on which surfaces you are making the plot based on.
In FVM, you are manipulating values of cells and faces and by convention we place these at the cell centers and face centers. The nodes (the corner thingies)... never come into play directly. That's why if you make a plot and check the node values, it can look wonky because there is an interpolation/extrapolation of the actual cell/face values onto the nodal points. Quote:
The velocity is applied to the faces not the points. The points don't really matter.... until you try to make a nodal plot. |
||
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Defined inlet velocity is different with inlet velocity on CFX post | jonpewpew | CFX | 2 | November 2, 2017 16:40 |
inlet boundary condition - constant velocity profile | gfcfd | CONVERGE | 3 | November 21, 2016 09:22 |
FSI- Pipe- uniform velocity profile inlet | Absy | Main CFD Forum | 0 | April 6, 2010 03:01 |
UDF problem : inlet velocity in cyl. coord. system | Jongdae Kim | FLUENT | 0 | June 15, 2004 11:21 |
UDF paraboloid velocity inlet | Ronak Shah | FLUENT | 0 | June 4, 2003 09:44 |