The parameterisation of turbulence in the marine environment

Jack Hardisty,Ross Jennings

doi:10.1080/20464177.2016.1260892

Jack Hardisty, Ross Jennings

Open Access

https://doi.org/10.1080/20464177.2016.1260892

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Abstract

ABSTRACTThere are many problems in the fields of flow modelling around structures and tidal stream energy yield analysis which require a thorough understanding of the turbulent and time-averaged flow speeds in marine environments. In this paper we examine the relationship between the turbulence intensity and mean tidal flow speed at a potential tidal stream power site. We report data from the Humber Estuary wherein an Acoustic Doppler Current Profiler were used to capture vertical profiles of the high frequency and mean tidal flow speeds throughout Spring and Neap, Flood and Ebb cycles. We show not only that our results extend earlier work but also suggest that the turbulence intensity, IT, can be described parametrically in terms of the mean flow, U, by an inverse power function where the coefficient appears to be dependent upon the anisotropic nature of the turbulence. For the data reported here, the coefficient has value of about 17–18 and the exponent lies between −0.6 and −1.0. Confirmation of this relationship should not only improve engineering design work and energy yield analyses in turbulent tidal flows but also be applicable to other problems such as the prediction of sediment mass transport and pollution dispersal in estuarine management studies.

Highlights

There are many problems in the fields of marine engineering, sediment transport, pollution dispersal, flow modelling and energy yield analysis which require a thorough understanding of the turbulent and time averaged flow speeds and directions in the marine environment
The instantaneous flow is taken as the sum of tidal and turbulent components and recent work has focussed on the identification of relationships between the turbulence intensity and the mean tidal flow speed (e.g. Thomson et al (2012), MacEnri et al (2013) and McCaffrey et al (2015))
In the analogous case of observations at wind energy sites, the key parameter is again identified as the turbulence intensity measured at turbine hub height and this has been shown to correlate with turbine performance and structural fatigue (Thomson et al (2012), Mycek et al (2014))

Summary

Introduction

There are many problems in the fields of marine engineering, sediment transport, pollution dispersal, flow modelling and energy yield analysis which require a thorough understanding of the turbulent and time averaged flow speeds and directions in the marine environment. Computational or laboratory models are able to simulate the basic flows. It is not possible, at present, to directly model the turbulence at all of the relevant scales. The effects of turbulence on both the structure and the efficiency of tidal stream power devices have been studied and the analysis of field data is being used to identify general metrics which describe the relationship between the flow speed and the turbulence. In the analogous case of observations at wind energy sites, the key parameter is again identified as the turbulence intensity measured at turbine hub height and this has been shown to correlate with turbine performance and structural fatigue (Thomson et al (2012), Mycek et al (2014))

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