Numerical study of time-periodic mixing ventilation : effect of amplitude

Conventional ventilation methods often supply fresh air to the room with a steady supply flow rate, which might induce stagnant recirculation cells and stagnation zones that are characterized by high concentrations of contaminants. This paper presents computational fluid dynamics (CFD) simulations of isothermal mixing ventilation with a transient supply flow rate in a generic room. The time-periodic supply flow rate is described by a sine function with different amplitudes. It is shown that time-periodic forcing triggers the stagnant recirculation cells to continuously shift throughout the room, thereby reducing average (passive gaseous) concentration levels in the occupied zone volume compared to the steady supply of fresh air. The concentrations are lower when larger amplitudes are applied. The analysis indicates a reduction in contaminant concentration by up to 24% and an increase of the contaminant removal effectiveness by 24% for time-periodic supply conditions compared to steady supply, which offers new perspectives on healthy and sustainable ventilation for, among others, residential buildings, office rooms, ship cabins, train cabins and cars.