Laminar flow in radial flow cell with small aspect ratios: Numerical and experimental study

Studies on the effect of wall shear stress on soil and biofilm attachment and removal from a surface are one of the many applications of radial axisymmetrical flow. The particular nature of this flow allows taking advantage of a wide range of wall shear Stress applied at the analyzed surface in a single experiment. This type of experiments provides a critical radius up to which soil removal occurs. Good models are, however, still needed to convert the experimental data into critical wall shear stress. Analytical models are already available for creeping flow but Computational Fluid Dynamics must be applied for experiments performed at higher Reynolds numbers. The present study is a numerical analysis of the radial axisymmetrical flow for aspect ratios of 0.125, 0.25, 0.5 and 1 with inlet pipe Reynolds numbers varying from 0 to 2000, aiming at computing the wall shear stress distribution at any distance from the center. The simulations provided a thorough description of the complex flow pattern encountered close to the inlet section, which were validated for the laminar regime by dye injection. A total of up to four recirculation zones were identified in both numerical and experimental investigations. The experimental positions of these recirculation zones corresponded well to the numerical predictions. Based on this work, a map of the flow for the different aspect ratios was developed, which can be particularly interesting for the design of experimental devices involving axisymmetrical flow.