Investigation of the upstream and downstream flow in a bent pipe using time-resolved three-dimensional particle tracking velocimetry

Sundstrom, LRJ, Seddighi, M ORCID: 0000-0003-4941-5111 and Larsson, IAS (2026) Investigation of the upstream and downstream flow in a bent pipe using time-resolved three-dimensional particle tracking velocimetry. Experimental Thermal and Fluid Science, 175. ISSN 0894-1777

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Abstract

Turbulent flow through a (Formula presented) bend with a curvature ratio (Formula presented) has been investigated experimentally using time-resolved three-dimensional particle tracking velocimetry (PTV) at (Formula presented). Fluorinated ethylene propylene tubes were installed upstream and downstream an opaque bend, and index-matching was achieved using a mixture of 94.1% of water and 5.9% of glycerol. The PTV measurements have been performed both before and after the bent section in order to provide further understanding of bent flow in general, and the swirl-switching phenomenon in particular. From the streamline pattern in the upstream tangent it is shown that the effect of the bend is minor for distances exceeding about two pipe diameters upstream from the bend. In the downstream tangent, elongated quasi-streamwise vortices have been identified using the λ2[jls-end-space/]-criterion on time-averaged data, and it is conjectured that the dynamics of these vortices might play an important role in the dynamics of the swirl-switching. This is in line with previously performed direct numerical simulations (DNS) of flow in toroidal pipes. To further characterize swirl-switching, two and three-dimensional proper orthogonal decomposition have been performed. It is shown that the cross-stream in-plane mode shapes do not differ significantly between the two approaches. Similarly as found in DNS, the mode shapes in the bend symmetry plane exhibit wave-like structures. These structures are shown to vary in time at a Strouhal number of (Formula presented) .

Item Type:	Article
Uncontrolled Keywords:	Bent pipe flow; 4D PTV; Swirling flows; 4012 Fluid Mechanics and Thermal Engineering; 40 Engineering; 09 Engineering; Mechanical Engineering & Transports; 40 Engineering
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Engineering and Built Environment
Publisher:	Elsevier
Date of acceptance:	8 April 2026
Date of first compliant Open Access:	1 September 2026
Date Deposited:	01 Sep 2026 15:51
Last Modified:	01 Sep 2026 15:51
DOI or ID number:	10.1016/j.expthermflusci.2026.111751
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29274

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