The growth of the atmospheric internal boundary layer

Elliott, William P.

doi:10.1029/tr039i006p01048

Cited by 317 publications

(237 citation statements)

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“…Figure 7(a) further includes least-squares fits of the three measures obtained from the LES results using a power law h − h 0 = ax p (with h, h 0 and x in metres). For all three estimates, we find that the exponents are close to the 0.8 power of Elliott (1958), i.e. 0.75, 0.71 and 0.74 for h(M), h(τ z ) and h(τ x ), respectively.…”

Section: Boundary-layer Flow Behaviourmentioning

confidence: 80%

“…In all three cases, the height evolution follows a slope close to 0.8 in the beginning of the farm. In cases S1 and S2, the slope increases slightly from the third turbine row onward, which might be related to outer-layer effects as the theoretical prediction of Elliott (1958) only holds in the surface layer. Figure 16(a) further shows that the growth rate is reduced when the IBL interferes with the inversion layer in cases S2 and S4.…”

Section: Flow Modification Under Low Inversion Layersmentioning

confidence: 98%

“…Further, the estimate h(M), based on the horizontal velocity, is lower than both estimates based on the shear stress, which agrees with the observation of Shir (1972) that velocity profiles adapt more slowly than stress profiles. Elliott (1958) observed that the IBL height grows as…”

Section: Boundary-layer Flow Behaviourmentioning

confidence: 99%

“…Several studies have argued that the adjustment of the ABL to the increased drag by the wind turbines is comparable to a surface-roughness transition (Crespo et al 1999;Frandsen et al 2006). Elliott (1958) was the first to study the adaptation of the flow close to the ground to a step change in surface roughness. He found that the internal-boundary-layer growth scales with the 0.8 power of the downwind distance, a result that is still commonly used in the wind energy community (see, e.g.…”

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confidence: 99%

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Boundary-layer development and gravity waves in conventionally neutral wind farms

2017

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While neutral atmospheric boundary layers are rare over land, they occur frequently over sea. In these cases they are almost always of the conventionally neutral type, in which the neutral boundary layer is capped by a strong inversion layer and a stably stratified atmosphere aloft. In the current study, we use large-eddy simulations (LES) to investigate the interaction between a large wind farm that has a fetch of 15 km and a conventionally neutral boundary layer (CNBL) in typical offshore conditions. At the domain inlet, we consider three different equilibrium CNBLs with heights of approximately 300 m, 500 m and 1000 m that are generated in a separate precursor LES. We find that the height of the inflow boundary layer has a significant impact on the wind farm flow development. First of all, above the farm, an internal boundary layer develops that interacts downwind with the capping inversion for the two lowest CNBL cases. Secondly, the upward displacement of the boundary layer by flow deceleration in the wind farm excites gravity waves in the inversion layer and the free atmosphere above. For the lower CNBL cases, these waves induce significant pressure gradients in the farm (both favourable and unfavourable depending on location and case). A detailed energy budget analysis in the turbine region shows that energy extracted by the wind turbines comes both from flow deceleration and from vertical turbulent entrainment. Though turbulent transport dominates near the end of the farm, flow deceleration remains significant, i.e. up to 35 % of the turbulent flux for the lowest CNBL case. In fact, while the turbulent fluxes are fully developed after eight turbine rows, the mean flow does not reach a stationary regime. A further energy budget analysis over the rest of the CNBL reveals that all energy available at turbine level comes from upwind kinetic energy in the boundary layer. In the lower CNBL cases, the pressure field induced by gravity waves plays an important role in redistributing this energy throughout the farm. Overall, in all cases entrainment at the capping inversion is negligible, and also the work done by the mean background pressure gradient, arising from the geostrophic balance in the free atmosphere, is small.

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Section: Boundary-layer Flow Behaviourmentioning

confidence: 80%

Section: Flow Modification Under Low Inversion Layersmentioning

confidence: 98%

Section: Boundary-layer Flow Behaviourmentioning

confidence: 99%

mentioning

confidence: 99%

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Boundary-layer development and gravity waves in conventionally neutral wind farms

2017

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“…When one roughness regime gives way to another, the flow near the ground gradually adjusts to the new surface characteristics. This process is often represented mathematically by local internal boundary layers (IBLs), which grow vertically downstream of a roughness boundary (Elliott 1958;Panofsky and Townsend 1964;Townsend 1965;Peterson 1969;Blom and Wartena 1969).…”

Section: Introductionmentioning

confidence: 99%

Could Crop Height Affect the Wind Resource at Agriculturally Productive Wind Farm Sites?

Vanderwende

Lundquist

2015

Boundary-Layer Meteorol

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The collocation of cropland and wind turbines in the US Midwest region introduces complex meteorological interactions that could influence both agriculture and wind-power production. Crop management practices may affect the wind resource through alterations of land-surface properties. We use the weather research and forecasting (WRF) model to estimate the impact of crop height variations on the wind resource in the presence of a large turbine array. A hypothetical wind farm consisting of 121 1.8-MW turbines is represented using the WRF model wind-farm parametrization. We represent the impact of selecting soybeans rather than maize by altering the aerodynamic roughness length in a region approximately 65 times larger than that occupied by the turbine array. Roughness lengths of 0.1 and 0.25 m represent the mature soy crop and a mature maize crop, respectively. In all but the most stable atmospheric conditions, statistically significant hub-height wind-speed increases and rotor-layer wind-shear reductions result from switching from maize to soybeans. Based on simulations for the entire month of August 2013, wind-farm energy output increases by 14 %, which would yield a significant monetary gain. Further investigation is required to determine the optimal size, shape, and crop height of the roughness modification to maximize the economic benefit and minimize the cost of such crop-management practices. These considerations must be balanced by other influences on crop choice such as soil requirements and commodity prices.

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Aeolian processes across transverse dunes. I: Modelling the air flow

Boxel

Arens

Dijk

1999

Earth Surf. Process. Landforms

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This paper discusses a two-dimensional second-order closure model simulating air flow and turbulence across transverse dunes. Input parameters are upwind wind speed, topography of the dune ridge and surface roughness distribution over the ridge. The most important output is the distribution of the friction velocity over the surface. This model is dynamically linked to a model that calculates sand transport rates and the resulting changes in elevation. The sand transport model is discussed in a separate paper.The simulated wind speeds resemble patterns observed during field experiments. Despite the increased wind speed over the crest, the friction velocity at the crest of a bare dune is reduced compared to the upstream value, because of the effect of stream line curvature on turbulence. These curvature effects explain why desert dunes can grow in height. In order to obtain realistic predictions of friction velocity it was essential to include equations for the turbulent variables in the model. In these equations streamline curvature is an important parameter.The main flaw of the model is that it cannot deal with flow separation and the resulting recirculation vortex. As a result, the increase of the wind speed and friction velocity after a steep dune or a slipface will be too close to the dune foot. In the sand transport model this was overcome by defining a separation zone.

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The growth of the atmospheric internal boundary layer

Cited by 317 publications

References 1 publication

Boundary-layer development and gravity waves in conventionally neutral wind farms

Boundary-layer development and gravity waves in conventionally neutral wind farms

Could Crop Height Affect the Wind Resource at Agriculturally Productive Wind Farm Sites?

Aeolian processes across transverse dunes. I: Modelling the air flow

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