Illustration of the outer boundary conditions imposed on the computational domain with the color map representing the density, while arrows show the sign of the radial velocity of the matter in the outer part of the computational domain at a time: t = 0.29P_BBH. On the one hand, the gas is allowed to exit the computational domain without modifying its density; whereas on the other hand, the inflowing gas can enter the computational domain with a density set to a value very close to the density floor. Such conditions are designed to mimic the ambient medium standing outside of the disc and to prevent any artificial input of gas from the exterior of the domain.