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Research Papers: Flows in Complex Systems

Siting Wind Turbines Near Cliffs: The Effect of Ruggedness

[+] Author and Article Information
Jerome Rowcroft

Department of Mechanical and
Aerospace Engineering,
Monash University,
Clayton 3800, Victoria, Australia
e-mail: Jerome.Rowcroft@monash.edu

David Burton

Department of Mechanical and
Aerospace Engineering,
Monash University,
Clayton 3800, Victoria, Australia
e-mail: David.Burton@monash.edu

Hugh. M. Blackburn

Department of Mechanical and
Aerospace Engineering,
Monash University,
Clayton 3800, Victoria, Australia
e-mail: Hugh.Blackburn@monash.edu

John Sheridan

Department of Mechanical and
Aerospace Engineering,
Monash University,
Clayton 3800, Victoria, Australia
e-mail: John.Sheridan@monash.edu

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received December 3, 2017; final manuscript received August 10, 2018; published online October 4, 2018. Assoc. Editor: Jun Chen.

J. Fluids Eng 141(3), 031104 (Oct 04, 2018) (13 pages) Paper No: FE-17-1778; doi: 10.1115/1.4041231 History: Received December 03, 2017; Revised August 10, 2018

Wind farms have often been located in close proximity to coastal cliffs to take advantage of the consistent wind regimes associated with many coastal regions, as well as to extract any available increase in flow speed that might be generated by such cliffs. However, coastal cliffs are often rugged as a result of erosion and the natural shape of the landform. This research explores the impact of the three-dimensional cliff topography on the wind flow. Specifically, wind tunnel testing is conducted, modeling the naturally occurring ruggedness as sawtooth lateral variations of various amplitudes applied to a forward facing step (FFS). Surface shear stress visualization techniques have been employed to derive the flow topology associated with different topographies, while pressure probe measurements are used to measure the development of wind speed and turbulence intensity (TI). Pressure probe measurements and surface pressure taps also assist to determine the lateral and vertical extents of the vortex structures identified. In particular, flow fields characterized by the probe measurements were consistent with vortex bursting that is described by various researchers in the flow over delta wings. Such bursting is observed as a stagnation and corresponding expansion of the vortex. Based on these observations, recommendations are provided for the siting of wind turbines near analogous cliffs.

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Figures

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Fig. 1

Schematic of Monash University 450 kW wind tunnel

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Fig. 2

Experimental domain

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Fig. 3

Inflow conditions: Panel 1—velocity and stream-wise TI; Panel 2—stream-wise integral length scale, and Panel 3—natural log of height plotted against natural log of velocity, with the gradient giving the power law exponent, α

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Fig. 4

Demonstration of build-up technique. Four instances are shown. Intermediate steps are omitted for brevity. Flow is from bottom of page to top.

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Fig. 5

Surface shear stress visualizations for the four A/λ ratios used, from left to right A/λ = 0.325, 0.5, 0.625, and 1

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Fig. 6

Schematic of flow topology compared with photograph of streaks, with descriptions of topological and geometric parameters

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Fig. 7

Flow topology over a FFS with sawtooth leading edge. From left to right, A/λ = 0.325, 0.5, 0.65, and 1. Flow is from bottom of page to top. Saddle points can be identified based on direction arrows. Stable nodes and foci – points of convergence are indicated by lighter colored dots and spirals. A close-up of the trough region for the A/λ =  1 case is shown in the inset.

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Fig. 8

Vortex growth angle as a function of Sawtooth half angle. Vortex growth angle is measured at the sawtooth peak, between the crest and the primary attachment line.

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Fig. 9

Surface pressure coefficients overlaid with flow topology; measurement locations denoted by circles

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Fig. 10

Speed-up contours above the A/λ = 0.325 topography

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Fig. 11

Turbulence intensity ratio contours above the A/λ = 0.325 topography

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Fig. 12

Speed-up (top) and TI ratio (bottom) measurements over the A/λ = 0.5 case

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Fig. 13

Siting approach over rugged cliffs. Gray dashed lines represent a distance of half a step height. The gray arrow represents the region where the wind turbine rotor might extend.

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