Effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

Kilpatrick, Ryan; Hangan, Horia; Siddiqui, Kamran; Parvu, Dan; Lange, Julia; Mann, Jakob; Berg, Jacob

doi:10.5194/wes-1-237-2016

Cited by 14 publications

(11 citation statements)

References 29 publications

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“…Roughness elements were raised in and around the contraction zone by 7.5 cm; in the sector in front of the experiment model, no roughness elements were used. The upstream profiles were measured with TFI Cobra Probes and show that the turbulence intensity at 5 m to 13 m (units of scaled heights) of 12%−13% matches the full-scale measurements in Berg et al (2011), see Kilpatrick et al (2016) for details on inflow profiles. An array of 3 IO Industries Flare 12M125 high-speed CMOS cameras (12 megapixels) was placed 3.55 m away from the laser sheet with the lens axes perpendicular to the light sheet (figure 2).…”

Section: Windeee Dome Configuration and Experimental Set-upmentioning

confidence: 90%

“…The Reynolds number based on the model height h is defined as Re =Ūh/ , where = 1.478 × 10 −5 m 2 s −1 is the kinematic viscosity of air at 20 • C andŪ is the mean wind speed, see Kilpatrick et al (2016). The value of the Reynolds number in this study is approximately 5 × 10 5 , which, as far as we are aware of, is the largest documented in the literature of boundary-layer studies of flow over the Bolund terrain or any forwardfacing step.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…The inflow was produced by the 60-fan wall, where rows 1, 2 and 4 were running at 50% and row 3 at 75% of full power (see Kilpatrick et al 2016, for specific details on the fan setup). Spires and roughness elements acted as turbulence generators.…”

Section: Windeee Dome Configuration and Experimental Set-upmentioning

confidence: 99%

“…In this paper, we present the results of a windtunnel experiment at the Wind Engineering, Energy and Environment (WindEEE) Dome at the Western University, Canada: the world's first three-dimensional wind testing chamber (Hangan 2014). We investigate the flow over a 1/25 scale model of the Bolund peninsula, Denmark, which has been investigated in some detail by Kilpatrick et al (2016).…”

Section: Introductionmentioning

confidence: 99%

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For wind turbines in complex terrain, the devil is in the detail

Lange

Mann

Berg

et al. 2017

Environ. Res. Lett.

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The cost of energy produced by onshore wind turbines is among the lowest available; however, onshore wind turbines are often positioned in a complex terrain, where the wind resources and wind conditions are quite uncertain due to the surrounding topography and/or vegetation. In this study, we use a scale model in a three-dimensional wind-testing chamber to show how minor changes in the terrain can result in significant differences in the flow at turbine height. These differences affect not only the power performance but also the life-time and maintenance costs of wind turbines, and hence, the economy and feasibility of wind turbine projects. We find that the mean wind, wind shear and turbulence level are extremely sensitive to the exact details of the terrain: a small modification of the edge of our scale model, results in a reduction of the estimated annual energy production by at least 50% and an increase in the turbulence level by a factor of five in the worst-case scenario with the most unfavorable wind direction. Wind farm developers should be aware that near escarpments destructive flows can occur and their extent is uncertain thus warranting on-site field measurements.

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Section: Windeee Dome Configuration and Experimental Set-upmentioning

confidence: 90%

Section: Experimental Set-upmentioning

confidence: 99%

Section: Windeee Dome Configuration and Experimental Set-upmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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For wind turbines in complex terrain, the devil is in the detail

Lange

Mann

Berg

et al. 2017

Environ. Res. Lett.

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“…For steep slopes, wind tunnel results indicate that at a distance ( x ) ~0.8‐1.2 H upstream of the forward facing steps, there is a recirculation zone and a second detached circulation forms at the cliff close to the ground . The downwind bubble of enhanced turbulence extends to a downwind distance x = 0.3‐2.5 H for a smooth step and x = 1‐2 H , z = 0.5 H for a roughness discontinuity while flow became reattached at a distance of x = 1.5–5 H downstream of the cliff at a height ( z ) between z < 0.36 H (Sherry et al) and z ~0.5 H (Ren and Wu) . The reattachment zone is typically less well defined, and the reattachment length is reduced over rough surfaces .…”

Section: Introductionmentioning

confidence: 99%

The impact of wind direction yaw angle on cliff flows

Barthelmie

Pryor

2018

Wind Energy

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The behavior of flow close to a cliff at heights relevant to wind turbines is explored using observations and simulations from a field experiment conducted at the Wind Energy Institute of Canada Prince Edward Island field site. There are 4 wind turbines located approximately 100 m from a 12 m high cliff and a fifth turbine located 500 m inland. During the field experiment, ongoing mast‐based observations were supplemented with additional sonic anemometers and Doppler lidars. Consistent with wind tunnel measurements and previous model simulations, a small speedup in the flow (~3‐5%) at the turbine hub‐height (of 80 m) is observed when the flow is perpendicular to the cliff. The objective here is to determine the degree to which the magnitude of the speedup, or horizontal distance over which it is manifest, changes as the flow deviates from the perpendicular impingement angle (ie, for nonzero yaw angles). Results indicate that the zone of deceleration upwind of the cliff and the downwind acceleration zone are maintained with flow ±25° to the perpendicular. Further, there is little change in the relative magnitude of either the wind speed or the turbulence intensity with modest deviations from perpendicular flow. However, as the angle from the perpendicular increases (ie, flow becomes increasingly parallel to the coast), the impact on wind speed and turbulence intensity decreases and is manifest over narrow and spatially less coherent regions.

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Measurement of spectra over the Bolund hill in wind tunnel

et al. 2017

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We have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock-up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3-component hot-wire velocimetry, 2-component particle image velocimetry, and a high-precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270 • wind direction and for two Reynolds numbers, Re h 1 = 4.25×10 4 and Re h 2 = 8.21×10 4 , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density S ii = fS ii ∕u 2 i changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies n h ≈ 0.01 − 0.02, which could be a signature of a weakened "flapping" phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value −5/3, was found to be correlated with the hill geometry. KEYWORDS atmospheric boundary layer, complex terrain, wind energy, wind tunnel simulation 1 INTRODUCTION The Bolund experiment, run by RISØ-DTU in 2007, is probably the most relevant test case of flow models oriented to wind energy analysis over highly complex terrains, in neutral conditions and nonaffected by Coriolis forces. 1,2 Bolund is a reference case to identify flow patterns and to validate numerical and physical models, due to the number and quality of sensors installed on the full-scale hill and the amount of numerical and physical analyses available such as literature. 1-6 Bolund is a small hill of about 130 m × 75 m × 12 m, surrounded by water with a long uniform fetch for most of the upstream directions of interest (see Figure 1-left). A large amount of periods with nearly neutral atmospheric conditions can be found in the full-scale database provided by RISØ-DTU. These characteristics convert Bolund into an ideal case for wind tunnel modeling without considering flow stratification effects.The escarpment facing westerly winds is one of the main geometric characteristics of Bolund (see Figure 1). The escarpment height varies slightly for the 200 • to 295 • wind direction interval, being roughly equal to the maximum height of the island, h = 11.73 m. Flow detachment at the escarpment has been observed in the full-scale experiment 1,7 and in wind tunnel tests. 4,8 Reproducing the flow characteristics in this region has revealed to be a challenge, particularly at lower heights, where the interaction between the turbulent inflow and the detachment dynamics is highly complex. Most of the numerical and physical models have failed to reproduce the high reduction in the mean wind speed and the high increment in the turbulent kinetic energy (TKE) found in the full-scale experiment in met mast M6 at 2 m height for 270 • wind direction, see Figure 2. ...

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Effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

Cited by 14 publications

References 29 publications

For wind turbines in complex terrain, the devil is in the detail

For wind turbines in complex terrain, the devil is in the detail

The impact of wind direction yaw angle on cliff flows

Measurement of spectra over the Bolund hill in wind tunnel

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