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Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences

Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences
Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences
Marine current energy conversion can provide significant electrical power from resource-rich sites. However since no large marine current turbine arrays currently exist, validation of methods for simulating energy extraction relies upon scaled down laboratory experiments. We present results from an experiment using porous fences spanning the width of a recirculating flume to simulate flow through large, regular, multi-row marine current turbine arrays. Measurements of fence drag, free surface elevation drop and velocity distribution were obtained to validate a method for parameterising array drag in the distributed drag approach, which is typically implemented in regional scale models. The effect of array density was also investigated by varying the spacing between fences. Two different inflow conditions were used; the first used the flume bed in its natural state, whilst the second used roughness strips on the flume bed to significantly enhance ambient turbulence intensity to levels similar to those recorded at tidal sites. For realistic array densities (<0.07), a depth averaged formulation of effective array drag coefficient agreed within 10% of that derived from experimental results for both inflow conditions. The validity of the distributed drag approach was shown to be dependent on longitudinal row spacing between porous fences and ambient turbulence intensity, two features that determine the level of wake recovery downstream of each porous fence. Finally a force balance analysis quantified the change in bed drag as a result of the presence of porous fence arrays. Adding arrays to the flow gave an increase in bed drag coefficient of up to 95% which was 20% of the total added bed and array drag coefficient. Results have implications for regional scale hydrodynamic modelling, where array layout along with site specific characteristics such as turbulence intensity and bed profile determine the validity of the distributed drag approach for simulating energy extraction.
Porous fence; Distributed drag method; Array density; Bed drag; Regional scale modelling
298-316
Coles, Daniel, Stephen
58e46bef-2a32-4b6e-b78b-7efede2a93ab
Blunden, Luke
28b4a5d4-16f8-4396-825b-4f65639d2903
Bahaj, Abubakr
a64074cc-2b6e-43df-adac-a8437e7f1b37
Coles, Daniel, Stephen
58e46bef-2a32-4b6e-b78b-7efede2a93ab
Blunden, Luke
28b4a5d4-16f8-4396-825b-4f65639d2903
Bahaj, Abubakr
a64074cc-2b6e-43df-adac-a8437e7f1b37

Coles, Daniel, Stephen, Blunden, Luke and Bahaj, Abubakr (2016) Experimental validation of the distributed drag method for simulating large marine current turbine arrays using porous fences. International Journal of Marine Energy, 16, 298-316. (doi:10.1016/j.ijome.2016.10.001).

Record type: Article

Abstract

Marine current energy conversion can provide significant electrical power from resource-rich sites. However since no large marine current turbine arrays currently exist, validation of methods for simulating energy extraction relies upon scaled down laboratory experiments. We present results from an experiment using porous fences spanning the width of a recirculating flume to simulate flow through large, regular, multi-row marine current turbine arrays. Measurements of fence drag, free surface elevation drop and velocity distribution were obtained to validate a method for parameterising array drag in the distributed drag approach, which is typically implemented in regional scale models. The effect of array density was also investigated by varying the spacing between fences. Two different inflow conditions were used; the first used the flume bed in its natural state, whilst the second used roughness strips on the flume bed to significantly enhance ambient turbulence intensity to levels similar to those recorded at tidal sites. For realistic array densities (<0.07), a depth averaged formulation of effective array drag coefficient agreed within 10% of that derived from experimental results for both inflow conditions. The validity of the distributed drag approach was shown to be dependent on longitudinal row spacing between porous fences and ambient turbulence intensity, two features that determine the level of wake recovery downstream of each porous fence. Finally a force balance analysis quantified the change in bed drag as a result of the presence of porous fence arrays. Adding arrays to the flow gave an increase in bed drag coefficient of up to 95% which was 20% of the total added bed and array drag coefficient. Results have implications for regional scale hydrodynamic modelling, where array layout along with site specific characteristics such as turbulence intensity and bed profile determine the validity of the distributed drag approach for simulating energy extraction.

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Accepted/In Press date: 10 October 2016
e-pub ahead of print date: 11 October 2016
Published date: December 2016
Keywords: Porous fence; Distributed drag method; Array density; Bed drag; Regional scale modelling
Organisations: Energy & Climate Change Group, Southampton Marine & Maritime Institute, Education Hub

Identifiers

Local EPrints ID: 408746
URI: http://eprints.soton.ac.uk/id/eprint/408746
PURE UUID: a244481a-db67-4d74-aad8-f736ef2aa05f
ORCID for Luke Blunden: ORCID iD orcid.org/0000-0002-0046-5508
ORCID for Abubakr Bahaj: ORCID iD orcid.org/0000-0002-0043-6045

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Date deposited: 27 May 2017 04:03
Last modified: 18 Feb 2021 17:14

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