Why would it be different from non-moving walls?

To me its feasible there is a line of code saying something like "if at wall V = 0" which would then cause an issue with a moving wall But that doesn't sounds like best practice for this exact reason

Which BC are you talking about?

a simple fixedValue does the job...

Thanks guys 🙂 I don't know how to answer your question, so can I ask why would it not be different from a non-moving wall?

does a wall produce TKE

?

Well I suppose not 🙂

Thanks again both!

Does your answer change if the wall moves? (Imagine yourself moving w/ the wall, at same speed, if it makes things easier)

So the main point here is the no-slip condition?

No, the main point is the definition of TKE. TKE = 0.5*(u')^2, where u' refers to velocity increments/fluctuations. Since we are not at the statistical mechanics side of things, the wall's constituent "particles" dont vibrate hence no fluctuations ergo k = 0

That makes a lot of sense!

Even in the kinetic theory side of things, the transfer of momentum via collisions between the wall and the fluid is exceedingly small due to the fact that one is a solid...

Great 🙂 this helps a lot. Thanks slopez!

Since you're so helpful, could I ask what the boundary condition at the top would be if the lid is only covering a part of the top surface?

Something like this, where the lid is the colorful part and the sides are free surfaces

It's a step ahead so I haven't thought about it yet, but since we're on the topic 🙂

(So this would be a 3D cavity and that is the view from above)

Not sure what you mean by if the lid is only covering part of the surface That to me implies that you have a container open to the air which would then become a multiphase problem

Sorry, just saw this 🙂 and I'm only looking at the liquid in the container. The free surface should just be a different set of boundary conditions on that part of the top boundary

And the height of the liquid in the container is kept constant

What do you mean by free surface but constant liquid height

Hey! So the velocity at that part of the surface is (u, v, 0). I'm imposing that as a boundary condition

that would be a slip wall

The z component is 0 throughout the top surface actually

Right! Yes :) free slip basically

This is different from what you described earlier!! You are not describing well your process here. What is driving your flow? It seems a temperature gradient is driving your flow. A "free-surface" is very different from "free-slip" which is very different from a "moving wall"

Sorry about that @slopezcastano So it's a moving lid with a temperature gradient