A series of Lagrangian numerical simulations is performed to examine the dispersion process in open channel flows and to explain through a simple conceptual model its systematic deviations from the ideal long‐term one‐dimensional regime even in the case of straight axis and fixed impervious bed. The starting point is represented by a suitably depth‐averaged transport equation, with generally nonlocal turbulent mixing, solved in terms of particles trajectories and their first‐ and second‐order moments. Input data refer to six rivers of southern Italy, for which the irregular section morphology is known from a field survey. As the governing equation predicts, and according to experimental observations, in the case of variable cross‐sectional diffusion the tracer cloud exhibits a permanent and asymmetric peripheral drift toward the shallow boundary zones, with a remarkable deceleration along the main flow direction. Longitudinal inertia moments tend to become linear after a period equal to twice the single river diffusive time and sometimes show an early anomalous change of slope. Transverse inertia moments experience an initial very fast increment as compared to the theoretical value corresponding to the uniform transverse concentration and, after a peak, tend to stabilize about a smaller constant. Centrifugal moments remain, in any case, relatively limited, indicating that longitudinal and transverse axes practically identify with the plume principal directions, no matter how irregular and asymmetric the river section is.

Effect of nonlocal transverse mixing on river flows dispersion: A numerical study

PANNONE, Marilena
2010

Abstract

A series of Lagrangian numerical simulations is performed to examine the dispersion process in open channel flows and to explain through a simple conceptual model its systematic deviations from the ideal long‐term one‐dimensional regime even in the case of straight axis and fixed impervious bed. The starting point is represented by a suitably depth‐averaged transport equation, with generally nonlocal turbulent mixing, solved in terms of particles trajectories and their first‐ and second‐order moments. Input data refer to six rivers of southern Italy, for which the irregular section morphology is known from a field survey. As the governing equation predicts, and according to experimental observations, in the case of variable cross‐sectional diffusion the tracer cloud exhibits a permanent and asymmetric peripheral drift toward the shallow boundary zones, with a remarkable deceleration along the main flow direction. Longitudinal inertia moments tend to become linear after a period equal to twice the single river diffusive time and sometimes show an early anomalous change of slope. Transverse inertia moments experience an initial very fast increment as compared to the theoretical value corresponding to the uniform transverse concentration and, after a peak, tend to stabilize about a smaller constant. Centrifugal moments remain, in any case, relatively limited, indicating that longitudinal and transverse axes practically identify with the plume principal directions, no matter how irregular and asymmetric the river section is.
File in questo prodotto:
File Dimensione Formato  
pannone_wrr_2010.pdf

non disponibili

Tipologia: Documento in Post-print
Licenza: DRM non definito
Dimensione 2.6 MB
Formato Adobe PDF
2.6 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/22517
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 10
  • ???jsp.display-item.citation.isi??? 10
social impact