Conventional computational fluid dynamics (CFD) methods for simulating the flow through automotive exhaust catalysts assume a monolith resistance based on one-dimensional laminar flow. This underpredicts the flow maldistribution in the monolith. Incorporation of an additional pressure loss accounting for entrance effects improves predictions for the maximum flow velocity within the substrate.

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This study examines the effect of pulsating flow on the flow distribution through contoured substrates. Three ceramic contoured substrates of equal volume were assessed. Two of the substrates were cone shaped with different cone angles and one had a dome shaped front face. The flow distribution was measured for a range of flow rates and pulsation frequencies. Computational Fluid Dynamics (CFD) simulations were also performed. It is shown how a contoured substrate can provide improvements in flow uniformity and that they are less sensitive to changes in flow rate and pulsation frequency when compared to the case of a standard substrate. Improvements in the prediction of flow distribution are reported when substrate "entrance effects" are accounted for.

Conversion efficiency, durability and pressure drop of automotive exhaust catalysts are dependent on the flow distribution within the substrate. This study examines the effect on flow distribution using substrates which feature contoured front faces. Three ceramic contoured substrates of equal volume were assessed. Two of the substrates were cone shaped with different cone angles and one had a dome shaped front face. Pressure drop and flow distribution was measured for a range of flow rates and substrate positions. Computational Fluid Dynamics (CFD) simulations were also performed to provide insight into flow behaviour. It is shown how a contoured substrate can provide improvements in flow uniformity and pressure drop when compared to the case of a standard non-contoured substrate.