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Turbulent Penetration in T-junction Branch Lines with Leakage Flow

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2014
Author Kickhofel John, Prasser Horst-Michael,
Project Temperature Fluctuations in Fluid and Pipe Walls induced by Turbulent Mixing
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Original article (peer-reviewed)

Journal Nuclear Engineering and Design
Volume (Issue) 276
Page(s) 43 - 53
Title of proceedings Nuclear Engineering and Design
DOI doi.org/t4g

Abstract

While the study of T-junction mixing with branch velocity ratios of near 1, so called cross flow mixing, is well advanced, to the point of realistic reactor environment fluid–structure interaction experiments and CFD benchmarking, turbulent penetration studies remain an under-researched threat to primary circuit piping. A new facility has been constructed for the express purpose of studying turbulent penetration in branch lines of T-junctions in the context of the high cycle thermal fatigue problem in NPPs. Turbulent penetration, which may be the result of a leaking valve in a branch line or an unisolable branch with heatlosses, induces a thermal cycling region which may result in high cycle fatigue damage and failures. Leakage flow experiments have been performed in a perpendicular T-junction in a horizontal orientation with 50 mm diameter main pipe and branch pipe at velocity ratios (main/branch) up to 400. Wiremesh sensors are used as a means of measuring the mixing scalar in adiabatic tests with deionized and tap water. The near-wall region of highest scalar fluctuations is seen to vary circumferentially and indepth in the branch a great deal depending on the velocity ratio. The power spectra of the mixing scalarin the region of turbulent penetration are found to be dominated by high amplitude fluctuations at low frequencies, of particular interest to thermal fatigue. Artificial velocity oscillations in the main pipe manifest in the mixing spectra in the branch line in the form of a peak, the magnitude of which grows with increasing local RMS.
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