Turbulent Transport of Suspended Particles and Dispersing Benthic Organisms: The Hitting-time Distribution for the Local Exchange Model

✍ Scribed by JAMES N. MCNAIR

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 266 KB
• Volume: 202
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1006/jtbi.1999.1057

✦ Synopsis

Fine particles suspended in turbulent water exhibit highly irregular trajectories as they are bu!eted by #uid eddies. The Local Exchange Model provides a stochastic di!usion approximation to the randomlike motion of such particles (e.g. dispersing benthic organisms in a stream). McNair et al. (1997, J. theor. Biol. 188, 29) used this model to derive equations governing the mean hitting time, which is the expected time until a particle hits bottom for the "rst time from a given initial elevation. The present paper derives equations governing the probability distribution of the hitting time, then studies the distribution's dependence on a particle's initial elevation and two dimensionless parameters. The results show that for "ne particles suspended in moderately to highly turbulent water, the hitting-time distribution is strongly skewed to the right, with mode(median(mean. Because of the distribution's thick upper tail, there is a signi"cant probability that a particle's hitting time will greatly exceed the mean. The results also show that the position of the mode depends strongly on a particle's initial elevation but, compared to the median or mean, is relatively insensitive to the particle's fall velocity.