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Direct numerical simulations of laminar and transitional flows in diverging pipes

Dhanush Vittal Shenoy (Complexe de Recherche Interprofessionnel en Aérothermochimie, Institut National des Sciences Appliquées, INSA Rouen Normandie,Saint Etienne du Rouvray, Haute-Normandie, France)
Mostafa Safdari Shadloo (Complexe de Recherche Interprofessionnel en Aérothermochimie, Institut National des Sciences Appliquées, INSA Rouen Normandie,Saint Etienne du Rouvray, Haute-Normandie, France)
Jorge Peixinho (LOMC, CNRS and Université Le Havre Normandie and Laboratoire PIMM, CNRS, Arts et Métiers, CNAM, HÉSAM Université, Paris, France)
Abdellah Hadjadj (Complexe de Recherche Interprofessionnel en Aérothermochimie, Institut National des Sciences Appliquées, INSA Rouen Normandie, Saint Etienne du Rouvray, Haute-Normandie, France)

International Journal of Numerical Methods for Heat & Fluid Flow

ISSN: 0961-5539

Article publication date: 19 July 2019

Issue publication date: 15 January 2020

Abstract

Purpose

Fluid flows in pipes whose cross-sectional area are increasing in the stream-wise direction are prone to separation of the recirculation region. This paper aims to investigate such fluid flow in expansion pipe systems using direct numerical simulations. The flow in circular diverging pipes with different diverging half angles, namely, 45, 26, 14, 7.2 and 4.7 degrees, are considered. The flow is fed by a fully developed laminar parabolic velocity profile at its inlet and is connected to a long straight circular pipe at its downstream to characterise recirculation zone and skin friction coefficient in the laminar regime. The flow is considered linearly stable for Reynolds numbers sufficiently below natural transition. A perturbation is added to the inlet fully developed laminar velocity profile to test the flow response to finite amplitude disturbances and to characterise sub-critical transition.

Design/methodology/approach

Direct numerical simulations of the Navier–Stokes equations have been solved using a spectral element method.

Findings

It is found that the onset of disordered motion and the dynamics of the localised turbulence patch are controlled by the Reynolds number, the perturbation amplitude and the half angle of the pipe.

Originality/value

The authors clarify different stages of flow behaviour under the finite amplitude perturbations and shed more light to flow physics such as existence of Kelvin–Helmholtz instabilities as well as mechanism of turbulent puff shedding in diverging pipe flows.

Keywords

Acknowledgements

This work was granted access to HPC resources of IDRIS/GENCI. The authors also acknowledge the access to HPC resources of CRIANN (Centre Régional Informatique et d’Applications Numériques de Normandie). The authors gratefully acknowledge financial support from LabEx (Laboratoires d’Excellence), EMC3 (Energy Materials and Clean Combustion Centre) through the project INTRA.

Citation

Vittal Shenoy, D., Safdari Shadloo, M., Peixinho, J. and Hadjadj, A. (2020), "Direct numerical simulations of laminar and transitional flows in diverging pipes", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 30 No. 1, pp. 75-92. https://doi.org/10.1108/HFF-02-2019-0111

Publisher

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Emerald Publishing Limited

Copyright © 2019, Emerald Publishing Limited