This study investigates oblique entry pressure loss in automotive catalyst monoliths. Experiments have been performed on a specially designed flow rig using different lengths of monolith (17—100 mm) over a range of Reynolds number and angles of incidence (0–75°). Losses were found to be a function of Reynolds number and angle of incidence and a general correlation has been derived. Computational fluid dynamics predictions of the flow distribution across axisymmetric catalyst assemblies have been performed. Incorporating the oblique entry loss provided much better agreement with experimental data with the assumption that such losses were constant above an angle of incidence of 81°.

Flow measurements are presented across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser. Particle image velocimetry measurements were obtained in the diffuser and the flow distribution within the monolith was obtained from hot wire anemometry at the monolith exit. Flow separation at the diffuser inlet resulted in the formation of a jet that traversed the diffuser before spreading just prior to entering the monolith. The jet featured a potential core and saddle-type velocity profiles. A free shear layer separated the jet core from two large recirculation regions that developed in the diffuser narrowing the potential core. The flow field in the main body of the diffuser was observed to be independent of Re in contrast to that within the monolith. Increasing monolith length gave greater flow uniformity in the monolith as a consequence of jet spreading. Comparing the axial velocity flow profiles ∼ 3 mm upstream of the monolith to that downstream showed that significant flow redistribution occurred as the flow entered the monolith, resulting in more flow entering peripheral channels. It is inferred that pressure loss arising from oblique entry into monolith channels significantly affects the flow distribution within the monolith.