Damping with evolving tau

• Damping prescription as in Ohlmann+17, using t_{dyn}=3\times10^5s (about equal to the freefall time, while the sound-crossing time is about 7.5\times10^5s).

Reflecting hydro BCs, Multipole expansion Poisson BCs
​2d density ​2d density and velocity

Extrapolating hydro BCs, Multipole expansion Poisson BCs
​2d density ​2d density and velocity

Extrapolating hydro BCs, Periodic Poisson BCs
​2d density ​2d density and velocity

Periodic hydro BCs, Periodic Poisson BCs
​2d density ​2d density and velocity