## Fluids

#### Cylinder geometry warping during Piston motion

• geniusjimmy92
Subscriber

I want to perform a cold-flow analysis in a simple 2-valve IC engine with the 'In-cylinder' option turned off in dynamic mesh. I have defined the piston motion using UDF and applied it to the bottom surface plane of the cylinder. The thing is my geometry is a little different. It is a curved cylinder with angular sinusoidal piston velocity as shown in figure.

2 parts in geometry. Port1 is the upper cylinder head, Port2 is the lower cylinder. I named selection piston, inlet, outlet and cylinder wall. Wall-port1, Wall-port2 and Cylinder are 'deforming' while Piston remains rigid body (UDF). Minimum and Maximum length scales in Remeshing are equal to the initial element mesh size.

• Keyur Kanade
Ansys Employee
You are using tet mesh. So no need for layering. nPlease cross check your udf for giving motion to piston. nAlso please check the dynamic mesh zones defined. Please see help manual for more details about these commands. nRegards,nKeyurnGuidelines for Posting on Ansys Learning ForumnHow to access ANSYS help linksnn
• geniusjimmy92
Subscriber
Thank you for your reply.nnI understand now that if I use the tet mesh, I do not need layering option turned on.nMy UDF for piston motion is very simple. Kindly check it out if there's any mistake there. The piston motion works fine, its just the warping of cylinder during piston motion.nn#include udf.hnDEFINE_CG_MOTION(PistonMotion, dt, cg_vel, cg_omega, time, dtime)n{nreal omega;nomega = 617*sin(3.14159265/180*time/.000005);ncg_omega[2] = omega;n}nnAs for the dynamic mesh zones definition, I am facing problem here because I have tried almost every possible combination to go.nI have tried to keep the cylinder wall 'deforming' but that made the whole cylinder 'running away' along with the piston as can be seen in the fig.n
• Keyur Kanade
Ansys Employee
This looks UDF issue. nYou need to check UDF. Please see customization help manual for the same. nRegards,nKeyurnGuidelines for Posting on Ansys Learning ForumnHow to access ANSYS help linksnn
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