[lukedam]

Hello, I'm newbie to CFD and Fluent in particular, and I'm trying to understand how does velocity inlet and outflow boundary is defined in sst k-omega equations? I understand that sst is using F1 and F2 to define ratio between k-omega and k-epsilon for walls, but what about domain inlet and outlet parameters?

P.S. I'm trying to recreate naca validation case

[LuckyTran]

Outlets are outlets.


At inlets, you provide all the transport variables needed for the model, including turbulence model. That means you provide, velocities, temperature, pressure, k, epsilon.

[lukedam]

Originally Posted by LuckyTran

Outlets are outlets.


At inlets, you provide all the transport variables needed for the model, including turbulence model. That means you provide, velocities, temperature, pressure, k, epsilon.

I understand that we provide variables, but which part they take in these equations? https://www.afs.enea.it/project/nept.../th/node66.htm
Especially, how do we calculate velocities etc. near inlet, or do we always set the velocities in inlet to certain values that we assigned nevermind the new values after iteration?

[LuckyTran]

You have a boundary value problem. That means at interior cells you solve transport equations. At boundaries, you have boundary conditions.

The only difference between inlet types is whether you specify velocity, pressure, or mass flow. A velocity inlet means at the inlet, you directly specify the velocity at every boundary cell. That's why we call it a velocity inlet.

At any inlet, you specify all other variables. So if you have a k-epsilon turbulence model, which has a transport equation for k and a transport equation for epsilon, then you specify k and epsilon at the inlet as a boundary condition. If you have a transport equation for apples, then you specify the value of apples at the boundary. If you have a transport equation for pineapple smoothies, then you specify the value of pineapple smoothies at the boundary. If you have a k-omega model, you specify k and omega. If you have a k-omega SST model, then you specify k and omega.

Refer to the Reynolds transport theorem for what is a transport equation. Transport equations are solved in the interior. Boundary conditions are constraints imposed on the solution at boundaries.

[lukedam]

Originally Posted by LuckyTran

You have a boundary value problem. That means at interior cells you solve transport equations. At boundaries, you have boundary conditions.

The only difference between inlet types is whether you specify velocity, pressure, or mass flow. A velocity inlet means at the inlet, you directly specify the velocity at every boundary cell. That's why we call it a velocity inlet.

At any inlet, you specify all other variables. So if you have a k-epsilon turbulence model, which has a transport equation for k and a transport equation for epsilon, then you specify k and epsilon at the inlet as a boundary condition. If you have a transport equation for apples, then you specify the value of apples at the boundary. If you have a transport equation for pineapple smoothies, then you specify the value of pineapple smoothies at the boundary. If you have a k-omega model, you specify k and omega. If you have a k-omega SST model, then you specify k and omega.

Refer to the Reynolds transport theorem for what is a transport equation. Transport equations are solved in the interior. Boundary conditions are constraints imposed on the solution at boundaries.

XDDDD, Finally, good explanation on basis of apples, thank you, that's as I thought!