steady in cylinder simulations: having problems with the mesh and simulation settings

shaoyikai813 · August 22, 2015, 05:56

Hello everyone,
I am doing inlet port design as my uni project with star ccm+. I am having problems now but my supervisor is away.

First of all I am planning to simulat two engine speed, 4500rpm and 14500rpm.
There is not a option of velocity outlet. How can I simulate different engine speed? Currently, I am having pressure outlet with negtaive number which makes outlet avg velocity around the piston mean velocity at that engine speed. Is it right way to do?

Secondly, I have mesh error when I use corse mesh such as 3mm base mesh. As picture shows below:

It is fine if I use fine mesh like 1mm. It getting worse as base mesh getting bigger. I created the geometry in Solidoworks and input into ccm with STEP file.

The last is the simulations are not converging with any of mesh size. The polt of outlet mass flow showing wave.

The model I used:

Thank you in advance.

shaoyikai813 · August 24, 2015, 08:12

All good now. Solved mesh error with decrease min gap between two parts to 0.5mm. And results became stable as well.

fluid23 · August 24, 2015, 11:53

FYI, I think you can specify a velocity outlet by giving a negative value. I know this can be done with a mass flow inlet as an outlet, I would assume that it would work for velocity as well.

shaoyikai813 · August 25, 2015, 03:47

Quote:

Originally Posted by MBdonCFD

FYI, I think you can specify a velocity outlet by giving a negative value. I know this can be done with a mass flow inlet as an outlet, I would assume that it would work for velocity as well.

Two inlets? Ok. I will try

shaoyikai813 · August 25, 2015, 04:47

Quote:

Originally Posted by MBdonCFD

FYI, I think you can specify a velocity outlet by giving a negative value. I know this can be done with a mass flow inlet as an outlet, I would assume that it would work for velocity as well.

Two inlets? Ok. I will try

fluid23 · August 25, 2015, 08:45

I wouldn't do 2 inlets. You can have one downstream or one upstream. The opposing inlet/outlet should be either a pressure outlet or stagnation inlet. Chances are you will have some convergence issues if you try to use a velocity inlet/outlet arrangement.

shaoyikai813 · August 25, 2015, 08:49

Quote:

Originally Posted by MBdonCFD

I wouldn't do 2 inlets. You can have one downstream or one upstream. The opposing inlet/outlet should be either a pressure outlet or stagnation inlet. Chances are you will have some convergence issues if you try to use a velocity inlet/outlet arrangement.

Im running stagnation inlet and pressure outlet. You think mass flow inlet with preasure outlet will.be.better?

fluid23 · August 25, 2015, 08:50

that would be my choice, I think.

August 22, 2015, 05:56	steady in cylinder simulations: having problems with the mesh and simulation settings	#1
shaoyikai813 New Member yikai shao Join Date: Mar 2015 Posts: 15 Rep Power: 11	Hello everyone, I am doing inlet port design as my uni project with star ccm+. I am having problems now but my supervisor is away. First of all I am planning to simulat two engine speed, 4500rpm and 14500rpm. There is not a option of velocity outlet. How can I simulate different engine speed? Currently, I am having pressure outlet with negtaive number which makes outlet avg velocity around the piston mean velocity at that engine speed. Is it right way to do? Secondly, I have mesh error when I use corse mesh such as 3mm base mesh. As picture shows below: It is fine if I use fine mesh like 1mm. It getting worse as base mesh getting bigger. I created the geometry in Solidoworks and input into ccm with STEP file. The last is the simulations are not converging with any of mesh size. The polt of outlet mass flow showing wave. The model I used: Thank you in advance.

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August 24, 2015, 08:12		#2
shaoyikai813 New Member yikai shao Join Date: Mar 2015 Posts: 15 Rep Power: 11	All good now. Solved mesh error with decrease min gap between two parts to 0.5mm. And results became stable as well.

August 24, 2015, 11:53		#3
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	FYI, I think you can specify a velocity outlet by giving a negative value. I know this can be done with a mass flow inlet as an outlet, I would assume that it would work for velocity as well.

August 25, 2015, 08:45		#6
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	I wouldn't do 2 inlets. You can have one downstream or one upstream. The opposing inlet/outlet should be either a pressure outlet or stagnation inlet. Chances are you will have some convergence issues if you try to use a velocity inlet/outlet arrangement.

August 25, 2015, 08:50		#8
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	that would be my choice, I think.