Christel Hohenegger,  Postdoctoral Fellow, University of North Carolina at Chapel Hill

Diffusion-Induced Bias in Near-Wall Velocimetry.

Abstract:  Brownian fluctuations of the colloidal tracers used in many microscale velocimetry techniques yield effects that are typically isotropic in the bulk. In contrast, near-wall Brownian diffusion is strongly influenced by the wall because of the no-flux condition and hindered diffusion. These effects bias any measurement sampled by the colloidal tracers, potentially leading to significant overestimation of near-wall velocities. We use a Fokker-Planck description to generate probability density functions of the distances from a single wall sampled by matched particles present in the same window at both the start and end of a time interval. The importance of the resulting bias for experimental parameters is then quantified in terms of the size of the imaged region and measurement interva