Flow through catalytic converters - laser Doppler anemometry versus computational fluid dynamics

Using laser Doppler anemometry (LDA) techniques, the flow velocities have been measured for a sudden pipe expansion into a square duct containing a catalyst situated downstream of the expansion. This geometry has been modelled using the computational fluid dynamics (CFD) code FLOW3D from Harwell. The results of the LDA data have been compared to those predicted by the CFD code. The CFD simulations are close to the experimental data though the CFD results predict more mal-distribution than observed with the LDA technique. Changing the turbulence modelling from the k-epsilon model to the Algebraic Reynolds Stress model improved the predictions significantly, with the magnitude of the recirculation matching the experimental data more closely. It was also found that the solution was not wholly grid independent, though variations were small.