Wall Shear Stress in the Early Stage of Unsteady Turbulent Pipe Flow |
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| Authors: | S. He C. Ariyaratne |
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| Affiliation: | 1Chair in Thermofluids, Dept. of Mechanical Engineering, Univ. of Sheffield, Sheffield S1 3JD, UK; formerly, Reader, School of Engineering, Univ. of Aberdeen, Aberdeen AB24 3UE, Scotland (corresponding author). E-mail: s.he@sheffield.ac.uk
2Research Fellow, School of Engineering and Design, Univ. of Sussex, Brighton BN1 9QT, United Kingdom; formerly, Research Fellow, School of Engineering, Univ. of Aberdeen, Aberdeen AB24 3UE, Scotland, E-mail: c.ariyaratne@sussex.ac.uk
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| Abstract: | Conventionally, wall shear stress in an unsteady turbulent pipe flow is decomposed into a quasi-steady component and an “unsteady wall shear stress” component. Whereas the former is evaluated by using “standard” steady flow correlations, extensive research has been carried out to develop methods to predict the latter leading to various unsteady friction models. A different approach of decomposition is used in the present paper whereby the wall shear in an unsteady flow is split into the initial steady value and perturbations from it. It is shown that in the early stages of an unsteady turbulent pipe flow, these perturbations are well described by a laminar-flow formulation. This allows simple expressions to be derived for unsteady friction predictions, which are in good agreement with experimental and computational results. |
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| Keywords: | Shear stress Friction Unsteady flow Pipe flow Turbulence |
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