Non zero radial velocity in axisymmetric problem

Llume · June 23, 2015, 07:53

Hi all,
I'm currently working on a simulation of an axisymmetric synthetic jet, I'm using a 2D axisymmetric solver, I've set the x-axis as my axis, axis boundary condition, I've checked the mesh and there are no points below the x-axis and the minimum y value is 0. Despite the fact that the problem should be axisymmetric and I've set in this way my boundaries i still get non zero values for the radial velocity and of the normal gradients of the velocities on the axis.

I'm not simulating the cavity and the non zero values appear in the part of the axis inside the nozzle, they get as high as 0.01 m/s and for the most are around 0.001m/s while the maximum inlet velocity is equal to 0.31 m/s.

Has anyone any idea on why this is happening and how could i fix and force the axisymmetric condition?

Llume · June 23, 2015, 12:27

I've tried to make a much finer mesh near the axis (as fine as the one I need near the wall to get acceptable values of Y+) and now the values of the radial velocity seems to be much lower ~10^-6. Is this an expected behaviour?

tatiana33 · November 8, 2018, 17:15

Hello Llume,

Could you solve this problem?
I am having a similar issue with an axisymmetric 2-D pipe mode.
But this time, the radial velocity is extremely unstable at the upper wall of the pipeline.
Hope you could give me some ideas on how to solve this.
By the way, I already made sure to capture the boundary layer with a fine mesh and I am currently working with 10^-7s as time step.

Thanks for any help,

Tatiana

June 23, 2015, 07:53	Non zero radial velocity in axisymmetric problem	#1
Llume New Member Join Date: Jun 2015 Posts: 7 Rep Power: 10	Hi all, I'm currently working on a simulation of an axisymmetric synthetic jet, I'm using a 2D axisymmetric solver, I've set the x-axis as my axis, axis boundary condition, I've checked the mesh and there are no points below the x-axis and the minimum y value is 0. Despite the fact that the problem should be axisymmetric and I've set in this way my boundaries i still get non zero values for the radial velocity and of the normal gradients of the velocities on the axis. I'm not simulating the cavity and the non zero values appear in the part of the axis inside the nozzle, they get as high as 0.01 m/s and for the most are around 0.001m/s while the maximum inlet velocity is equal to 0.31 m/s. Has anyone any idea on why this is happening and how could i fix and force the axisymmetric condition?

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June 23, 2015, 12:27		#2
Llume New Member Join Date: Jun 2015 Posts: 7 Rep Power: 10	I've tried to make a much finer mesh near the axis (as fine as the one I need near the wall to get acceptable values of Y+) and now the values of the radial velocity seems to be much lower ~10^-6. Is this an expected behaviour?

November 8, 2018, 17:15		#3
tatiana33 New Member Tatiana Flechas Join Date: Sep 2017 Posts: 10 Rep Power: 8	Hello Llume, Could you solve this problem? I am having a similar issue with an axisymmetric 2-D pipe mode. But this time, the radial velocity is extremely unstable at the upper wall of the pipeline. Hope you could give me some ideas on how to solve this. By the way, I already made sure to capture the boundary layer with a fine mesh and I am currently working with 10^-7s as time step. Thanks for any help, Tatiana