|
[Sponsors] |
I have problem in expression in specified shear of boundary condition |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
May 15, 2020, 07:13 |
I have problem in expression in specified shear of boundary condition
|
#1 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
hello
i'm doing graduation project but i got a problem when i try to input the formula sheart stress = dynamic viscosity * dvelocity/dy on the expression of boundary condition, the message on the image keeps coming up. i also attach the image, please answer the question~ |
|
May 15, 2020, 07:20 |
Scalar and Vector
|
#2 |
Senior Member
|
You are trying to use an expression that returns a vector for a field that is a scalar. Since you are providing value for the component, expression should return a component and not the whole vector.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
May 15, 2020, 08:56 |
how can i make it scalar?
|
#3 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
thank you very much for the answer
but i still have the problem I also thought the same way and i tried to make it absolute value but another message comes up. i guess dVelocitydy is the vector how can i make it scalar? i attach the image... |
|
May 15, 2020, 09:02 |
Vector
|
#4 |
Senior Member
|
Yes, dvelocity/dy is a vector because velocity is a vector. You have to use velocity component, say, xvelocity or velocity-x, whichever is correct format.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
May 15, 2020, 09:56 |
thank you
|
#5 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
thank you for the answer
but i don't know if i can change the component i can only select the component of pascal i will try to find if i have another measure to solve it. one more question though, is it right that if specified shear is zero wall doesn't affect the velocity of fluid? |
|
May 15, 2020, 10:01 |
Clarity
|
#6 |
Senior Member
|
Your query is not very clear to me. Whether you use velocity vector or scalar, result is always in Pa. A value of 0 implies slip boundary condition; it is different from what you are trying to apply now. You should use the condition that is appropriate for your case.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
May 15, 2020, 10:13 |
what im trying to do
|
#7 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
yes what you're saying is right
once i simulated with zero shear stress on the wall the streamline seemed like the wall doesn't affect the velocity of the fluid. in real situation fluid gradually loses its speed. so i thought it isn't realistic. so i though shear stress would make it realistic, but putting in the expression, i have problem as the images i attached before. if result comes to pascal from both vector and scalar, why there's an error? i can't understand... |
|
May 15, 2020, 10:18 |
Expression
|
#8 |
Senior Member
|
Why do you want to apply an expression? Just select no-slip condition.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
May 15, 2020, 10:25 |
no slip condition
|
#9 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
in no silip condition stream line stops right at the wall
but in my project, i'm trying to improve the flow of fluid in smoking booth so stream line matters.. |
|
May 15, 2020, 10:32 |
Wall
|
#10 |
Senior Member
|
Walls are walls; they are supposed to stop the flow. If you want a slip, then you have to find out how much slip should be there.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
May 15, 2020, 10:56 |
no slip
|
#11 |
Member
kim jihyun
Join Date: May 2020
Posts: 31
Rep Power: 5 |
now i think no slip condition is right
i just simulated again with no slip condition and found out that fluid near the wall doesn't stop. the simulation that i did the other day stopped all the fluid soonner because every stream line was on the wall almost right after it's come out from the inlet ( the shape was different from now). thank you |
|
May 15, 2020, 12:56 |
Streamlines
|
#12 |
Senior Member
|
Those are not streamlines, but pathlines. And whether those stop due to wall or not depends on number of steps used for pathline calculation. Default is 500. Use higher value, such as, 20000 or higher, until most of the pathlines have reached outlet.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Wind turbine simulation | Saturn | CFX | 58 | July 3, 2020 01:13 |
Speed problem of periodic boundary condition imposed on pitching airfoil. | TG777 | OpenFOAM Running, Solving & CFD | 1 | March 20, 2020 16:33 |
Error - Solar absorber - Solar Thermal Radiation | MichaelK | CFX | 12 | September 1, 2016 05:15 |
Wall Shear in Expression as boundary condition | w.andreao | CFX | 2 | May 11, 2016 19:53 |
Low Mixing time Problem | Mavier | CFX | 5 | April 29, 2013 00:00 |