Understanding stress distributions in flows is essential yet remains challenging due to the lack of direct measurement techniques. Here, we introduce a birefringence-based method in which dispersed nanoparticles respond to local shear, enabling visualization of stress fields around rising bubbles. The observed retardation patterns capture distinct regions of stress concentration, boundary-condition transitions, and stagnation phenomena. This stress-oriented approach moves beyond conventional velocity-based analyses, providing new opportunities to probe hidden mechanical aspects of fluid-structure interactions and complex flow environments.
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