Pulsating Flow Maldistribution within an Axisymmetric Catalytic Converter - Flow Rig Experiment and Transient CFD Simulation

This paper investigates the flow maldistribution across the monolith of an axisymmetric catalyst assembly fitted to a pulsating flow test rig. Approximately sinusoidal inlet pulse shapes with relatively low peak/mean ratio were applied to the assembly with different amplitudes and frequencies. The inlet and outlet velocities were measured using Hot Wire Anemometry. Experimental results were compared with a previous study, which used inlet pulse shapes with relatively high peak/mean ratios. It is shown that (i) the flow is more maldistributed with increase in mass flow rate, (ii) the flow is in general more uniformly distributed with increase in pulsation frequency, and (iii) the degree of flow maldistribution is largely influenced by the different inlet velocity pulse shapes. Transient CFD simulations were also performed for the inlet pulse shapes used in both studies and simulations were compared with the experimental data. For inlet pulse shapes with low peak/mean ratio, CFD predictions matched measurements fairly well in the bulk central region of the monolith. For inlet pulse shapes with high peak/mean ratio, agreement was less satisfactory. This is probably due to the inaccuracy of the Reynolds Averaged Navier Stokes (RANS) k-ε turbulence model under such conditions.