Dynamic mesh unstability

Kimican · March 21, 2017, 16:28

Hi dear all,

I am simulating a gear pump with dynamic mesh. Though my settings seem good, I read very big differences in pressure contour between two following time steps. My time step size is near e-008 level. How can very big differences like this happen by this very little time step? Does it mean that analysis is still in unstable region and then will become stable? How can this be commended?

Note that, I have run the first 200-300 time steps. After reading this different pressures, I have stopped the simulation.

Thx.

Mert.

Yaju · March 21, 2017, 17:02

Hi,

The time-steps seems low. What is your base grid size and the finest refinement you are using? Can you share your log output file and solver.in file?

Kimican · March 21, 2017, 17:10

Thx for reply first

My tip gap is very very small so my tip elements have to be very small, too. Because of this, my time step is very low to avoid the negative volume issue. This makes me very slow.

Yes i can share but i could not understand what i should share exactly (log output and solver). Are theese .cas files?

Sent from my iPhone using CFD Online Forum mobile app

March 21, 2017, 16:28	Dynamic mesh unstability	#1
Kimican New Member Join Date: May 2015 Posts: 28 Rep Power: 10	Hi dear all, I am simulating a gear pump with dynamic mesh. Though my settings seem good, I read very big differences in pressure contour between two following time steps. My time step size is near e-008 level. How can very big differences like this happen by this very little time step? Does it mean that analysis is still in unstable region and then will become stable? How can this be commended? Note that, I have run the first 200-300 time steps. After reading this different pressures, I have stopped the simulation. Thx. Mert.

March 21, 2017, 17:02		#2
Yaju Member Yajuvendra Shekhawat Join Date: Mar 2017 Location: Convergent Science, Madison WI Posts: 51 Rep Power: 9	Hi, The time-steps seems low. What is your base grid size and the finest refinement you are using? Can you share your log output file and solver.in file? __________________ Yajuvendra Shekhawat Research Engineer - Applications Group CONVERGECFD

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March 21, 2017, 17:10		#3
Kimican New Member Join Date: May 2015 Posts: 28 Rep Power: 10	Thx for reply first My tip gap is very very small so my tip elements have to be very small, too. Because of this, my time step is very low to avoid the negative volume issue. This makes me very slow. Yes i can share but i could not understand what i should share exactly (log output and solver). Are theese .cas files? Sent from my iPhone using CFD Online Forum mobile app