Determining residence time is of major interest in the characterization, design or modeling of most chemical engineering processes, where a proper and homogeneous fluid distribution is often essential. A numerical method was used to obtain theoretical predictions of residence time spatial distributions and was validated by comparing with experiments. It was simulated first by solving continuity and momentum conservation equations, coupled with turbulence quantity transport equations, using the finite volume method. After calculating the flow configuration, the simulation was done by solving the transport equation of a passive scalar, the local mean age of the fluid or local mean residence time, which is the average time of a fluid particle to reach any point of the domain from a supply inlet. The result obtained is a spatial distribution of the local mean age of the fluid, which may be displayed as isocontours in the space domain considered. It was compared with measurements of mean residence times of tracers in a reactor to concretely assess the relevance of this method.