[Adam_PHD]

Hello, CFD's colleagues,
I encountered a problem with negative volume when I just start calculation Please help me out, how can I solve this issue ?.
- I plan to simulate diesel engine from IVC TO EVO so, I drew my geometry at 100 CA before TDC and when I used compression ratio tool in converge studio to check CR=18 , converge studio couldn't understand that my case is in 100 CA before TDC and gave me just 2 as CR and when I pushed to get 18 all bowl was damage..
I don't know if I have given a sufficient description.
Your help is highly appreciated

[MFGT]

Dont draw the geometry at any other crank angle positon than -180 (BDC).
CONVERGE will use your start time to move the piston to the correct position.

[Adam_PHD]

Thanks, MFGT,
you are right Converge CFD accept only BDC

[ksrivast]

Hello Adam,

Your triangle normals are not pointing into the fluid domain. Please check your triangle normals and fix them. Have a look at our STUDIO manual for more details on this.

CONVERGE requires that the surface file represent the maximum volume attainable during the simulation. For in-cylinder cases, this is at BDC. CONVERGE will assume piston is located at BDC in your provided surface file when the automatic piston motion is employed. Providing a start_time of -100 CA is sufficient. CONVERGE automatically moves to the piston to the appropriate location at the start of the simulation.

Sincerely,

Srivastava

[mohameditdh]

Dear ksrivast;
it works well now :, as you said it was the problem of triangle normals are not pointing into the fluid domain

thanks, a lot of the useful advice
Regards:

[Nitisha]

I am getting a warning that :
There might be an alignment issue between piston and cylinder liner. normal direction of triangles connected to piston should be perpendicular to direction of motion.
Since the normal always points normal to triangle area. What should I do if I dont have a flat shaped piston?

[ksrivast]

Hello Nitisha,

The warning is directed at the liner triangles, and not at those of the piston. The warning points to your liner being tapered/inclined. Make sure your liner is perfectly cylindrical. This can be checked by measuring the triangle normal of the liner triangles. Measure > Direction > Triangle normal. If your piston motion is along the Z-axis, the Cell Normal measured must be zero in the z-axis.

The best thing to do would be to reconstruct your liner. Do not loft between the piston edge and the head edge, since if there is a difference in diameters, this would result in a tapered liner. Use the Sweep option to construct triangles. Sweep to an amount just above TDC and loft the remaining gap. It would also be helpful to check if the Piston itself is aligned properly.

Hope this helps,

Sincerely,

Srivastava

[Nitisha]

Thank you, I checked the perpendicularity of the normals of the cylinder liner. I was able to resolve the issue.