The periodic condition can be
 

The periodic condition can be defined as follows:
sides
{
type cyclic;
value uniform (0 0 0);
}
The entry term 'value' confused me. What is the exact meaning of this term?

The entry term 'value' gives t
 

The entry term 'value' gives the field value on the patch.

I use cyclic condition for 'Ga
 

I use cyclic condition for 'Gamma' when I solve RT instability with interFoam.
sides
{
type cyclic;
value uniform 0;
}

Does the entry 'value' act as only an initial setting? After I run 'setGammaDamBreak', the value of Gamma of boundary 'sides' will be not zero,but determined by 'setGammaDamBreak'. Is it right?

Of course it's only the initia
 

Of course it's only the initial value, did you really think all boundary condition values are fixed to the value given?

That is ok. ^_^. With your gam
 

That is ok. ^_^. With your gamma*(1-gamma) and gamma differencing scheme, I have got beautiful 3D RT instability interface structure. If I delete the gamma*(1-gamma) term and apply only the GD scheme, the sharp interface will be lost, right? I am not very clear with the effect on sharp interface intruduced by gamma*(1-gamma) term. How does it compress the interface?

By the way, if I use wall condition on my 'sides' boundary,
sides
{
type gammaContactAngle;
theta0 90;
thetaA 90;
thetaR 90;
uTheta 0.01;
value uniform 0;
}
Then here how the 'value' entry affect the values on the patch? Will the gamma on the patch change when time goes?

Why not find out for yourself,
 

Why not find out for yourself, you will learn more that way and without consuming other peoples time.