[dik]

hi all, I have a problem about simulating a shock absorber fluid.

here's the model, a very simplified model as a preliminary design only to test the general flow characteristics. the real model will be more complicated but understanding the basic phenomena is a very important step.



i've tried setting the Boundary Condition of 2,3,4,5 faces (piston) as downward moving wall -0.2 m/s (minus sign for downward motion on Y-axis), while faces 1,6 and the cylinder wall set as a stationary wall BC. the results for this setting is qualitatively incorrect, indicated by the unreasonably lower velocity at the four orifices (3) where according to continuity it shuold be higher than any other points in the model.

second trial, i set the BC of 6 as inlet velocity of 0.2 m/s (upward on Y-axis). and i set 1 as a pressure opening (default value, about 1 atm). the cylinder wall was a moving wall which velocity is the same with the inlet velocity of 1 (0.2 m/s upward) and the remaining is a stationary real wall. the result was more make sense, at least qualitatively correct at the orifices where it gave more velocity than other points. but the problem is: face 1 and 6 is in fact a wall, not openings. setting 6 as an opening will result an eliminated rebound effect due to the collision between the fluid and the wall. just consider a shock absorber, there's no atmospheric opening.

so, what should I do to make this simulation realistic (not only just seems realistic, but also show the real phenomena indeed).

what should the Boundary Conditions of the faces?

can somebody help me with this problem? you can use the numbers in the picture above to designate the face in your explanations.

Thanks for viewing this thread. I will be glad and highly appreciate if you post some reply. well, once again, thanks folks.