Mesh independence for a baffled 2D mixing tank

Joe walker1 · May 1, 2023, 08:32

Hi,
I'm trying to perform a mesh independence study for a 2D mixing tank which uses a sliding mesh. Also, the case is transient.
I am measuring velocities, dissipation rates and RMS velocities near the baffles on the outside of the tank. The velocities and dissipation rates converge to a constant value, whereas the RMS values are still rising. As I understand, the RMS is supposed to take longer.
My question is, is this an indication the mesh isn't refined enough, or is it that the simulation time is too short? Or could it be an issue with the timestep I have used.
The case I'm currently testing is a 100mm diameter turbine, inside of a 300mm tank, at 250rpm. The mesh has ~73,000 elements. The calculation conditions are 600 time steps and 0.02s per.
The simulations take very long so I was hoping to get advice on here before I waste time changing the wrong thing about the simulation.

Any help is greatly appreciated, as this is very important.

Joe walker1 · May 3, 2023, 08:12

Disregard this post, realised the sim time was too low to reach a steady state.

May 1, 2023, 08:32	Mesh independence for a baffled 2D mixing tank	#1
Joe walker1 New Member Joe walker Join Date: Apr 2023 Posts: 14 Rep Power: 3	Hi, I'm trying to perform a mesh independence study for a 2D mixing tank which uses a sliding mesh. Also, the case is transient. I am measuring velocities, dissipation rates and RMS velocities near the baffles on the outside of the tank. The velocities and dissipation rates converge to a constant value, whereas the RMS values are still rising. As I understand, the RMS is supposed to take longer. My question is, is this an indication the mesh isn't refined enough, or is it that the simulation time is too short? Or could it be an issue with the timestep I have used. The case I'm currently testing is a 100mm diameter turbine, inside of a 300mm tank, at 250rpm. The mesh has ~73,000 elements. The calculation conditions are 600 time steps and 0.02s per. The simulations take very long so I was hoping to get advice on here before I waste time changing the wrong thing about the simulation. Any help is greatly appreciated, as this is very important.

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May 3, 2023, 08:12		#2
Joe walker1 New Member Joe walker Join Date: Apr 2023 Posts: 14 Rep Power: 3	Disregard this post, realised the sim time was too low to reach a steady state.