We report the first real-time observations of the entire fully developed laminar secondary flow field of aqueous 2% Viscarin GP-209NF (a $\lambda$-carrageenan polysaccharide) in a square duct as made using a modest rheological NMR imaging (rheo-NMR) apparatus. Simulations using the Reiner-Rivlin constitutive equation verify the results. An included rheo-NMR flow rate quantification study assesses the measurement precision. Rheo-NMR resolves slow flows superimposed on primary flows about 300 times greater, making it a universally accessible technique by which full secondary flow field data may be systematically gathered.

• Received 23 October 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.046001