[elia.p]

Good morning to everybody,

I am doing my master thesis on a semi-active control for a secondary damper for a train and i have to check the quality of the numerical model with a CFD simulation by using Fluent. The model of the damper I created is very simple and is composed by a cylinder divided in 2 chambers separated by a piston on which i have 3 valves controlling the fluid flow from one chamber to the other one.



The flow through the valve must be a linear function of the difference of pressure (dP) between the two chambers: when the dP is less then a certain dPx the valve should be closed, then the flow should increase linearly till a certain value of pressure dPy is reached and then the flow must be constant for increasing pressure (this law simulate the real behavior of the valve, who is regulated by a spring).

First i tried to model the valve with a simple porous jump boundary condition , but in this case i could not reproduce the real behavior, because also for small value of dP i had flow through the valves and by increasing dP indefinitely also the flow increased indefinitely (not good). I think the best way to solve my problem is to use an UDF function which calculates the flow receiving by input the pressures in the two chambers, but i have no idea how to write it, also if i read the fluent guide to uff it is still very unintelligible for me.

I ask your help to write me the very general structure i have to give to this function.

Thank you,
Elia