We study turbulent flows in pressure-driven ducts with square cross-section through direct numerical simulation in a wide enough range of Reynolds number to reach flow conditions which are representative of fully developed turbulence (Re 1000). Numerical simulations are carried out over very long integration times to get adequate convergence of the flow statistics, and specifically to achieve high-fidelity representation of the secondary motions which arise. The intensity of the latter is found to be on the order of 1 %–2% of the bulk velocity, and approximately unaffected by Reynolds number variation, at least in the range under scrutiny. The smallness of the mean convection terms in the streamwise vorticity equation points to a simple characterization of the secondary flows, which in the asymptotic high-Re regime are approximated with good accuracy by eigenfunctions of the Laplace operator, in the core part of the duct. Despite their effect of redistributing the wall shear stress along the duct perimeter, we find that secondary motions do not have a large influence on the bulk flow properties, and the streamwise velocity field can be characterized with good accuracy as resulting from the superposition of four flat walls in isolation. As a consequence, we find that parametrizations based on the hydraulic diameter concept, and modifications thereof, are successful in predicting the duct friction coefficient.

Turbulence and secondary motions in square duct flow / Pirozzoli, Sergio; Modesti, Davide; Orlandi, Paolo; Grasso, Francesco. - In: JOURNAL OF FLUID MECHANICS. - ISSN 0022-1120. - 840:(2018), pp. 631-655. [10.1017/jfm.2018.66]

Turbulence and secondary motions in square duct flow

Pirozzoli, Sergio
;
Modesti, Davide;Orlandi, Paolo;
2018

Abstract

We study turbulent flows in pressure-driven ducts with square cross-section through direct numerical simulation in a wide enough range of Reynolds number to reach flow conditions which are representative of fully developed turbulence (Re 1000). Numerical simulations are carried out over very long integration times to get adequate convergence of the flow statistics, and specifically to achieve high-fidelity representation of the secondary motions which arise. The intensity of the latter is found to be on the order of 1 %–2% of the bulk velocity, and approximately unaffected by Reynolds number variation, at least in the range under scrutiny. The smallness of the mean convection terms in the streamwise vorticity equation points to a simple characterization of the secondary flows, which in the asymptotic high-Re regime are approximated with good accuracy by eigenfunctions of the Laplace operator, in the core part of the duct. Despite their effect of redistributing the wall shear stress along the duct perimeter, we find that secondary motions do not have a large influence on the bulk flow properties, and the streamwise velocity field can be characterized with good accuracy as resulting from the superposition of four flat walls in isolation. As a consequence, we find that parametrizations based on the hydraulic diameter concept, and modifications thereof, are successful in predicting the duct friction coefficient.
2018
pipe flow boundary layer; turbulence simulation; turbulent boundary layers
01 Pubblicazione su rivista::01a Articolo in rivista
Turbulence and secondary motions in square duct flow / Pirozzoli, Sergio; Modesti, Davide; Orlandi, Paolo; Grasso, Francesco. - In: JOURNAL OF FLUID MECHANICS. - ISSN 0022-1120. - 840:(2018), pp. 631-655. [10.1017/jfm.2018.66]
File allegati a questo prodotto
File Dimensione Formato  
Pirozzoli_turbulence-and-secondary_2018.pdf

solo gestori archivio

Tipologia: Versione editoriale (versione pubblicata con il layout dell'editore)
Licenza: Tutti i diritti riservati (All rights reserved)
Dimensione 2.74 MB
Formato Adobe PDF
2.74 MB Adobe PDF   Contatta l'autore
Pirozzoli_preprint_turbulence-and-secondary_2018.pdf

accesso aperto

Note: https://doi.org/10.1017/jfm.2018.66
Tipologia: Documento in Pre-print (manoscritto inviato all'editore, precedente alla peer review)
Licenza: Creative commons
Dimensione 4.92 MB
Formato Adobe PDF
4.92 MB Adobe PDF

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: https://hdl.handle.net/11573/1092642
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 110
  • ???jsp.display-item.citation.isi??? 94
social impact