Experimental Measurement of Laminar Axisymmetric Flow Through Confined Annular Geometries With Sudden Inward Expansion

In this paper, separating and reattaching aqueous laminar flows produced by a sudden inward expansion within confined annular geometries are experimentally studied. The test geometries are based on a previous numerical study. The fluid flow structure at the expansion region is experimentally characterized using particle image velocimetry combined with refractive index matching. The detailed measurements of the velocity field, reattachment length, and relative eddy intensity are obtained for two different expansion ratios, 1.4 and 1.6. For both expansion ratios, the reattachment length is found to vary nonlinearly with the Reynolds number $(50<Re<600)$⁠, in line with numerical predictions. The eddy intensity is found to depend strongly on both the Reynolds number and expansion ratio with the relationship between the Reynolds number and the reattachment length being nonlinear. Overall, the corresponding numerical predictions are in good agreement with the measurements undertaken herein.