Sealing scenarios in Two-Stroke enigne simulation

CFDer_1 · October 23, 2024, 06:40

Hello Converge community,

I have started a simulation for a two-stroke engine and would like to share some thoughts with you about the sealing scenarios. Your recommendations are really appreciated.

- The first scenario, as mentioned in the example of the two-stroke engine in Converge (also in the manual), a seal should be generated from the circumference of piston surface to the cylinder, as well as from the ports (their edges) to the piston skirt. As I understand it, this scenario will prevent any mixture or exhaust flow in the clearance between the piston and cylinder. My concern is, whether this scenario will reduce the accuracy of the piston skirt temperature or not, as it would prevent any heat transfer (by convection) between the piston skirt and the flow field from the ports. In the reality, when the piston reaches the ports, there is a contact between the flow (mixture or exhaust) and the piston skirt.

- The second scenario that I would like to discuss (in the attached photo in this link: https://ibb.co/7KRhv16 ), involves creating a seal from the piston surface to the cylinder and from the piston bottom to the cylinder (assuming the piston is a regular closed cylinder), while having no seal between the ports and the piston skirt. This will allow that the flow from the ports touchs the piston skirt (heat transfer), but also will cause a trapped flow along the piston skirt, when the whole piston is above or under the level of the ports.

So what are the disadvantages of this scenario? It is my pleasure to exchange the ideas with you.
Note: the clearance in the photo is bigger just to indicate the idea.

Thanks in advance,
Regards,

DrDuncan · March 18, 2025, 18:19

Hello David!
I think the challenge in scenario 2 is that the seals will break when they reach the port and have an open edge. Presumably if the seal is small then the errors should also be minor. You might also consider the use of general intersection handling. That is only available as a hidden feature (allow_intersections: 1 in hidden.in) in v3.1 and v4 but it will be available in sealing.in once v5 is released.

October 23, 2024, 06:40	Sealing scenarios in Two-Stroke enigne simulation	#1
CFDer_1 New Member David Join Date: Sep 2024 Posts: 17 Rep Power: 2	Hello Converge community, I have started a simulation for a two-stroke engine and would like to share some thoughts with you about the sealing scenarios. Your recommendations are really appreciated. - The first scenario, as mentioned in the example of the two-stroke engine in Converge (also in the manual), a seal should be generated from the circumference of piston surface to the cylinder, as well as from the ports (their edges) to the piston skirt. As I understand it, this scenario will prevent any mixture or exhaust flow in the clearance between the piston and cylinder. My concern is, whether this scenario will reduce the accuracy of the piston skirt temperature or not, as it would prevent any heat transfer (by convection) between the piston skirt and the flow field from the ports. In the reality, when the piston reaches the ports, there is a contact between the flow (mixture or exhaust) and the piston skirt. - The second scenario that I would like to discuss (in the attached photo in this link: https://ibb.co/7KRhv16 ), involves creating a seal from the piston surface to the cylinder and from the piston bottom to the cylinder (assuming the piston is a regular closed cylinder), while having no seal between the ports and the piston skirt. This will allow that the flow from the ports touchs the piston skirt (heat transfer), but also will cause a trapped flow along the piston skirt, when the whole piston is above or under the level of the ports. So what are the disadvantages of this scenario? It is my pleasure to exchange the ideas with you. Note: the clearance in the photo is bigger just to indicate the idea. Thanks in advance, Regards,

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March 18, 2025, 18:19		#2
DrDuncan New Member Joshua Join Date: Mar 2025 Posts: 2 Rep Power: 0	Hello David! I think the challenge in scenario 2 is that the seals will break when they reach the port and have an open edge. Presumably if the seal is small then the errors should also be minor. You might also consider the use of general intersection handling. That is only available as a hidden feature (allow_intersections: 1 in hidden.in) in v3.1 and v4 but it will be available in sealing.in once v5 is released.