Basic tutorial for solving a simple heat transfert problem. 

The initial condition of the problem is represented in sketch.PNG: a gas flows into a porous material (Tg < Ts) due to an applied pressure gradient (Poutlet < Pinlet). We want to determine the gas velocity, the density variation of the gas, and the temperature distribution in the domain over time of the gas and the solid.  

This tutorial will solve the problem first with the compressibleDarcy2T solver (OpenFoam), then with a Fenics script, 
and finally it will compare the different results. 

Type ./Allrun in the terminal to execute the tutorial and plot the fields at a certain time step. 


N.B. Due to stability problems, Fenics needs a smaller time step than the one of openFoam --> Fenics computational time is higher. (Fenics solve all the equations coupled, whereas openFoam solves the equations decoupled) 


