Rotation of base grid
 

Hi everyone,

While reading some publications about grid sensitivity in engine applications, I discovered that tilting the base mesh in the direction of injection can lead to better convergence.

However, I encountered a problem: I couldn't find the base grid rotation settings. As a workaround, I simply rotated the geometry, but this introduced another issue related to piston movement along the Z-direction.

I would greatly appreciate any suggestions or ideas.

Best regards,

Amin

Hi Amin,


You can do this by using a inlaid mesh, either creating in Studio or importing from another software.
Basically, if you know the flow direction before conducting a simulation it is better to create a mesh parallel to that direction. In case of IC engine with employing a fixed embedding for spray, I don't think it will significantly affect your results.

Hi Hamed jan,

Thanks for your response. As you mentioned, there is no significant difference while using very small mesh near injector in liquid parcel simulations. However, it has some small benefits in gas direct injection simulations with very low time steps and near nozzle mesh size of 0.125. I agree with your suggestion that it’s not worth it to use external mesh.

I was wondering if there was any way to just simply tilt the base grid, without rotating the whole geometry which makes problem with calculating the piston motion and speed in the z direction.

Did you ever rotate any base grid with invalid mesh? If yes, I will appreciate if you give some suggestions.

Thanks again. Movagaf bashi Amin

Hello Amin,

CONVERGE uses a cartesian mesh which is aligned with the x, y, z direction. We do have an example case with multiple cylinders in V8 configuration where all cylinders are rotated. You can see how the piston motion is defined. You will also need to correctly define the direction of the valves. The example case can be found in File --> load example case --> Internal Combustion Engines --> Gasoline spark ignition PFI --> SI8 engine PFI SAGE V8 multi-cylinder transient RANS.

Another solution is as Hamed suggested, to use an inlaid mesh that is aligned with the injection.

Best,

Angela

Dear Angela,

I am very grateful to you and your team for helping the users of the product enthusiastically.
The examples of the software itself are the most complete reference for experts in this area.

Thank you, wishing you a wonderful day.

Regards

Hi Amin,

It may be worth noting that although the numerical diffusion is less of an effect with rotated mesh in the area near the injector, as soon as the spray changes direction due to walls for example, you will have numerical diffusion there. Rotating the entire grid may overall not be an improvement in convergence or accuracy.
"Multi-Dimensional Modelling of Mixture Preparation in a Direct
Injection Engine Fueled with Gaseous Hydrogen" by Addepalli et al may be interesting for you.

Friendly greetings,
Laurens