.FCSys.Subregions.Examples.AirColumn

Information

This is a model of a vertical column of 10 × 10 × 10 m regions with N₂ gas. The upper boundary is held at 1 bar and the lower boundary has zero velocity. The initial pressure difference is zero, but a gas enters the upper boundary and a pressure difference develops due to gravity. There are oscillations due to the inertance and compression of the gas. After about 1.5 s, the pressure difference settles to L_y a_y m ρ as expected.

A temperature gradient is created due to the thermodynamics of the expanding and contracting gases. It takes much longer (over a year!) for the temperatures to equalize due to the size of the system and the low thermal conductivity of the gas. With a stiff solver, the model should simulate at this time scale as well.

The damping factor (k) can be used to scale the continuity (ζ) of the gas in the regions. The oscillations are dampened considerably at k = 100. However, with high values of the factor, the boundary pressures are decoupled from the pressures in the region because the nonequilibrium force is considerable.

Assumptions:

1. The central difference scheme is used (no upstream discretization).