what is mean of your t?
it is time ? |
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When then yield stress is above the limit on the wall, there is a wall slip velocity given by where is the dynamic viscosity and is the friction coefficient. (I have omitted in my previous message ) So what do you think about the boundary condition ? |
Wall Motion Based on Velocity Components
For problems that include linear or non-linear translational motion of the wall boundary you can enable the Components option and specify the X-Velocity, Y-Velocity, and Z-Velocity of the wall. You can define non-linear translational motion using a boundary profile or a user-defined function for the X-Velocity, Y-Velocity, and/or Z-Velocity of the wall I think this condition is that you want. |
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see below for the message.
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Here is my code below. If I understand well I have to put two component udf: wall_shear_x and wall_velocity_x. Code:
#define Cf 1 /* friction coefficient */ and I check specified shear and I put udf wall_shear_x in X-VELOCITY. Is it right ? I will test tomorrow but I wonder if I follow exactly the wall-slip model below with this boundary condition : if if where is the dynamic viscosity and is the friction coefficient. and with where is the stress tensor and is the strain tensor. What do you think about that ? Is the boundary condition appropriate to the model ?? Thank for your answer... |
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In other words, you calculate wall shear for each individual cell next to the walls and then integrate/add to get the total force, and then use that total wall shear to compare to your slipping wall criteria. Put in other words, you cannot change the wall-slip velocity locally for each cell since the entire wall must have the same slip velocity. Also, is it necessary to calculate TAUxy? Fluent should already have a variable called x-wall-shear or something that you should be able to access directly and not calculate through UDF. I am not the best at UDF so I wanted to ask you to make sure. |
I don't find anywhere how to access directly the wall shear stress.
So, in my case I have to calculate the element of the strain tensor in each cell to calculate the wall shear stress and to be able to compare this value with the limit stress . This comparison has to be made in each cell to know if there is a wall slip or not. My real purpose is to have a numerical wall slip model for non newtonian flow. That's why I have to calculate in each cell. With a newtonian flow it's not very usefull to make a loop on each cell. You say that it's impossible to have different slip velocity for each cell with a wall motion boundary condition (?). So how can I make this model ? Thank you. |
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The steady flow, the wall shear stress is again stored in a simple variable wall-shear-x y and z. Since it can be outputted to file / printed to screen, that variable should be accessible. Anyway, you can calculate if you really want to spend that effort. |
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