Determination of terminal velocity of stack flow by numerical simulation

Recently, computational fluid dynamics (CFD) has been successfully applied to simulate the air pressure distribution inside vertical drainage system. In t his paper, the CFD application is extended to estimate the terminal velocity of water flowing inside a vertical drainage stack. The behaviour of annular drain is successfully captured. The average velocity of water at a pipe section is proposed to be determined by the weighted average of the velocities over the pipe section by considering the volume fractions of water over the section. The results show a good agreement with the empirical equations. This work further confirms the feasibility of applying CFD to simulate the behaviour of air and water flowing inside the drainage system.