Diffusion-induced bias in near-wall velocimetry

Reza Sadr, Christel Hohenegger, Haifeng Li, Peter J. Mucha, Minami Yoda

Research output: Contribution to journalArticle

35 Citations (Scopus)


The Brownian fluctuations of the colloidal tracers often used in microscale velocimetry are typically isotropic in the bulk. In the near-wall region, however, these fluctuations are strongly affected by the hydrodynamic interaction with the wall and by the no-flux condition imposed by the wall. These wall effects can, under appropriate conditions, bias measurements based on 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 the matched particles that are 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 interval. We conclude with a brief discussion of the implications for near-wall velocimetry measurements.

Original languageEnglish
Pages (from-to)443-456
Number of pages14
JournalJournal of Fluid Mechanics
Publication statusPublished - 25 Apr 2007


ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this