Length and time scales of response of sediment suspensions to changing flow conditions

Dorrell, Robert M.; Hogg, Andrew J.

Abstract

Turbulent suspensions of sediment are investigated to establish the characteristic length and time scales on which they adjust from one state to another. The suspensions are modeled by using a simple closure for the turbulent fluctuations in which the average flux of sediment is treated as a diffusion process. A key dimensionless settling parameter, which is closely related to the Rouse number, measures the magnitude of the settling to diffusive fluxes of particles. It is shown how the length and time scales on which the suspension responds are a function of the settling parameter and the assumed form of the eddy diffusivity, and that the predictions are broadly in accord with laboratory experiments. It is further established analytically that, in the regimes of the settling parameter much greater or much less than unity, the timescale of response is independent of the form of the eddy diffusivity. This motivates the use of simple eddy diffusivity laws to provide generic insight to the unsteady evolution of complex suspension and sedimentation problems.

Citation

Dorrell, R. M., & Hogg, A. J. (2012). Length and time scales of response of sediment suspensions to changing flow conditions. Journal of Hydraulic Engineering, 138(5), 430-439. https://doi.org/10.1061/%28asce%29hy.1943-7900.0000532

• Journal Article Type: Article
• Acceptance Date: Apr 4, 2011
• Online Publication Date: Nov 10, 2011
• Publication Date: May 10, 2012
• Deposit Date: Aug 12, 2018
• Journal: Journal of Hydraulic Engineering
• Print ISSN: 0733-9429
• Publisher: American Society of Civil Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 138
• Issue: 5
• Pages: 430-439
• DOI: https://doi.org/10.1061/%28asce%29hy.1943-7900.0000532
• Keywords: Boundary conditions; Suspended sediment; Eddy (fluid dynamics); Motivation; Flow duration; Particles; Diffusion; Parameters (statistics)
• Public URL: https://hull-repository.worktribe.com/output/733515
• Publisher URL: https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29HY.1943-7900.0000532