Direct numerical simulation of a turbulent 90° bend pipe flow

Zhi-xin, Wang; Schlatter, Philipp; Chung, Yongmann M.

doi:10.1016/j.ijheatfluidflow.2018.08.003

Cited by 40 publications

(20 citation statements)

References 26 publications

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“…The low frequency mode that was present fort 10 has been suppressed. Since this low frequency mode is thought to originate from the large-scale structures upstream of the bend [12], one possible explanation for this observation is the turbulence-suppressing effects of stable stratification, which reduce the kinetic energy contained within the large structures. Figures 12 and 13 show contours of the normalised axial velocity 0.05D from the wall, for timest = 0 andt = 30, respectively.…”

Section: Swirl-switchingmentioning

confidence: 99%

Thermal transients in a U-bend

Skillen

Zimoń

Sawko

et al. 2020

International Journal of Heat and Mass Transfer

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We study numerically the propagation of a hot thermal transient through a Ubend via an ensemble of wall-resolved large eddy simulations. Conjugate heat transfer between fluid and solid domains is accounted for. The flow is in a fully turbulent mixed convection regime, with a bulk Reynolds number of 10, 000, a Richardson number of 2.23, and water as the working fluid (Prandtl number = 6). These conditions lead to strong thermal stratification, with buoyancyinduced secondary flows, and the generation of a large and persistent recirculation region.The evolution of Dean vortices as the thermal transient passes is studied. It is found that baroclinic vorticity generation dominates over a large period of the transient, due to the thermal inertia of the wall. Gravitational buoyancy leads to a reversal of the counter-rotating vortex pair. The impact of this reversal on the swirl-switching and secondary-current losses is assessed. It is found that low frequency modes are suppressed in the reversed-vortex state.

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Section: Swirl-switchingmentioning

confidence: 99%

Thermal transients in a U-bend

Skillen

Zimoń

Sawko

et al. 2020

International Journal of Heat and Mass Transfer

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“…The DNS data are generated by a massively paralleled MPI (Message Passing Interface) code, Nek5000 (Fischer, Lottes & Kerkemeier 2008) using the spectral element method (SEM). The incompressible Navier-Stokes equations are solved in Cartesian coordinates to avoid the singularity issue associated with the cylindrical coordinates at the pipe centreline (Jung & Chung 2012;Wang et al 2018). A semi-implicit time scheme solves the viscous terms implicitly using a third-order backward differentiation (BDF3) and the nonlinear terms by a third-order extrapolation (EXT3).…”

Section: Numerical Simulationmentioning

confidence: 99%

Uniform-momentum zones in a turbulent pipe flow

2019

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“…Given the fact that the existence of backflow events has been established beyond doubt in canonical wall-bounded flows, in this study we aim at evaluating the effect of a nonzero cross-stream velocity distribution (i.e., secondary flow) on such backflow events. The flow through curved pipes is characterised by a strong in-plane secondary flow of Prandtl's first kind driven by the centrifugal force and accompanied by a pressure gradient, which has a strong impact on the kinematics and dynamics of the flow [34,35]. This makes the toroidal pipe a very interesting flow case regarding backflow events.…”

Section: Introductionmentioning

confidence: 99%

Backflow events under the effect of secondary flow of Prandtl's first kind

et al. 2020

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A study of the backflow events in the flow through a toroidal pipe at friction Reynolds number Re τ ≈ 650 is performed and compared with the results in a straight turbulent pipe flow at Re τ ≈ 500. The statistics and topological properties of the backflow events are analysed and discussed. Conditionally averaged flow fields in the vicinity of the backflow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the azimuthal wall-shear stress when compared to the pipe flow. In the region around the backflow events, critical points are observed. The comparison between the toroidal pipe and its straight counterpart also shows fewer backflow events and critical points in the torus. This is attributed to the secondary flow of Prandtl's first kind present in the toroidal pipe, which is responsible for the convection of momentum from the inner to the outer bend through the core of the pipe, and back from outer bend to the inner bend along the azimuthal direction. These results indicate that backflow events and critical points are genuine features of wall-bounded turbulence, and are not artefacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

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Direct numerical simulation of a turbulent 90° bend pipe flow

Abstract: Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.

Cited by 40 publications

References 26 publications

Thermal transients in a U-bend

Thermal transients in a U-bend

Uniform-momentum zones in a turbulent pipe flow

Backflow events under the effect of secondary flow of Prandtl's first kind

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