Partially filled pipes: experiments in laminar and turbulent flow



Ng, henry ORCID: 0000-0003-4926-7622, Cregan, Hope, Dodds, jonathan, Poole, rob ORCID: 0000-0001-6686-4301 and Dennis, DJC ORCID: 0000-0003-0214-7885
(2018) Partially filled pipes: experiments in laminar and turbulent flow. Journal of Fluid Mechanics, 848. 467 - 507.

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Abstract

Pressure-driven laminar and turbulent flow in a horizontal partially filled pipewas investigated using stereoscopic particle imaging velocimetry (S-PIV) in thecross-stream plane. Laminar flow velocity measurements are in excellent agreementwith a recent theoretical solution in the literature. For turbulent flow, the flowdepth was varied independently of a nominally constant Reynolds number (basedon hydraulic diameter,DH; bulk velocity,Uband kinematic viscosityν) ofReH=UbDH/ν≈30 000±5 %. When running partially full, the inferred friction factor isno longer a simple function of Reynolds number, but also depends on the FroudenumberFr=Ub/√gDmwheregis gravitational acceleration andDmis hydraulicmean depth. S-PIV measurements in turbulent flow reveal the presence of secondarycurrents which causes the maximum streamwise velocity to occur below the freesurface consistent with results reported in the literature for rectangular cross-sectionopen channel flows. Unlike square duct and rectangular open channel flow the meansecondary motion observed here manifests only as a single pair of vortices mirroredabout the vertical bisector and these rollers, which fill the half-width of the pipe,remain at a constant distance from the free surface even with decreasing flow depthfor the range of depths tested. Spatial distributions of streamwise Reynolds normalstress and turbulent kinetic energy exhibit preferential arrangement rather than havingthe same profile around the azimuth of the pipe as in a full pipe flow. Instantaneousfields reveal the signatures of elements of canonical wall-bounded turbulent flows nearthe pipe wall such as large-scale and very-large-scale motions and associated hairpinpackets whilst near the free surface, the signatures of free surface turbulence in theabsence of imposed mean shear such as ‘upwellings’, ‘downdrafts’ and ‘whirlpools’are present. Two-point spatio-temporal correlations of streamwise velocity fluctuationsuggest that the large-scale coherent motions present in full pipe flow persist inpartially filled pipes but are compressed and distorted by the presence of the freesurface and mean secondary motion

Item Type: Article
Uncontrolled Keywords: boundary layers, pipe flow boundary layer, turbulent flows
Depositing User: Symplectic Admin
Date Deposited: 07 Jun 2018 09:52
Last Modified: 06 Oct 2022 05:58
DOI: 10.1017/jfm.2018.345
Open Access URL: https://doi.org/10.1017/jfm.2018.345
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3022261