Learning Forum

[xing]

[Karthik Remella]

Hello If this is a 2D problem, could you not use the y-velocity on that boundary?
Karthik

[DrAmine]

Expression : density×velocity vector×face area vector

[xing]

Yes, it is a 2D problem, but the surface where we want to plot the normal velocity is not a perfectly straight line as you can see in the image. Therefore, y-velocity would not be a normal velocity. The non-straight surface is making the flux go inside and out of the top (Pressure inlet) boundary as seen in the flow lines. Also, we have a curved boundary near the center where we also need the normal velocity.
Also please let us know how to plot mass flux across the same boundary.The mass flux = rho*v_n (v_n: normal velocity). We want to plot this normal velocity at the top boundary.

[DrAmine]

You can create a custom vector with the mass flux expression. You can create a custom field function or Expression with rho*v_n and use it as additional variable for plotting, contour plots, etc..

[xing]

[DrAmine]

You can create your own Custom Field Function or Expression with that formula to get mass flux calculated and use that either as contour plot or to create a vector.

[xing]

How to get x and y-components of "grid unit normal vectors" so that we can use in the formula to find normal velocity?
Once you find new function using "Custom field Function Calculator", how to display in contours and vectors? I did not find this new function appear on vectors and contours.

[Rob]

Custom Field Functions can be displayed once they're created: look in the Fluent Post-processing. If you're looking for the velocity normal to a boundary (as opposed to x, y or z component) you may need to do a little trigonometry.

[xing]

[Rob]

Can you post an image showing exactly where the boundaries are? If you have a periodic flow, how can you also have an inlet but no outlet?

[xing]

Bob: We applied pressure inlet on the top boundary, periodic boundary conditions on the left and right boundary, and then no-slip wall on the bottom boundary, as shown below. Note that, pressure inlet also allows the flow to go out of the domain and the same for the periodic boundary on the right. Our question was on the discrepancy between the mass flow rates calculated using two approaches. To save time, could you please have a zoom meeting with my Ph.D. student Bishal (bhat7152@vandals.uidaho.edu)?

[Rob]

Can you alter the model to meet the requirements https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v212/en/flu_ug/flu_ug_sec_periodic_overview.html for periodic boundaries and repeat the calculation?