Large eddy simulation of a T-Junction with upstream elbow: The role of Dean vortices in thermal fatigue

R Tunstall,D Laurence,R Prosser,A Skillen

doi:10.1016/j.applthermaleng.2016.07.011

R Tunstall, D Laurence + Show 2 more

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https://doi.org/10.1016/j.applthermaleng.2016.07.011

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Abstract

Turbulent mixing of fluids in a T-Junction can generate oscillating thermal stresses in pipe walls, which may lead to high cycle thermal fatigue. This thermal stripping problem is an important safety issue in nuclear plant thermal-hydraulic systems, since it can lead to unexpected failure of the pipe material. Here, we carry out a large eddy simulation (LES) of a T-Junction with an upstream bend and use proper orthogonal decomposition (POD) to identify the dominant structures in the flow. The bend generates an unsteady secondary flow about the pipe axis, known as Dean vortex swirl-switching. This provides an additional mechanism for low-frequency near-wall temperature fluctuations downstream of the T-Junction, over those that would be produced by mixing in the same T-Junction with straight inlets. The paper highlights the important role of neighbouring pipe bends in T-Junction thermal fatigue problems and the need to include them when using CFD as a predictive tool.

Highlights

Thermal stripping in cooling system pipework is a major safety challenge in the nuclear power industry
In the present work we focus on nuclear plant thermal-hydraulics systems, Dean vortex swirl-switching may be of relevance to mixing problems in a wide range of other applications, such as oil and gas pipelines, internal combustion engines and process plants
Temperature fluctuations below 10Hz are associated with an increased risk of thermal fatigue problems in nuclear plant thermal-hydraulics systems [1]; the T-Junction considered could be susceptible to this safety issue

Summary

Introduction

Thermal stripping in cooling system pipework is a major safety challenge in the nuclear power industry. Experimental studies of the turbulent mixing that occurs in such T-Junctions have been performed by Brucker [5], Walker et al [6], Kamide et al [7] and by numerous workers at the Vattenfall R&D facility [8, 9, 10]. These studies describe how temperature fluctuations are generated downstream of the junction by the turbulent mixing of the two fluid streams

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