Entrainment effects in the well-mixed atmospheric boundary layer

Driedonks, A. G. M.; Tennekes, H.

doi:10.1007/bf00121950

Cited by 111 publications

(73 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Daytime atmospheric conditions are different. The daytime mean convective boundary layer height in the WRF control simulation is 1,268 m. Of this total height, the constant stress layer, the vertical depth over which the downward kinetic energy flux is considered negligible, typically constitutes the lowest 10% of the convective boundary layer (31,32). Therefore, during the daytime, the upper extent of the turbine rotors is likely to be within the constant stress layer.…”

Section: Resultsmentioning

confidence: 99%

Two methods for estimating limits to large-scale wind power generation

Miller

Brunsell

Mechem

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Wind turbines remove kinetic energy from the atmospheric flow, which reduces wind speeds and limits generation rates of large wind farms. These interactions can be approximated using a vertical kinetic energy (VKE) flux method, which predicts that the maximum power generation potential is 26% of the instantaneous downward transport of kinetic energy using the preturbine climatology. We compare the energy flux method to the Weather Research and Forecasting (WRF) regional atmospheric model equipped with a wind turbine parameterization over a 10 5 km 2 region in the central United States. The WRF simulations yield a maximum generation of 1.1 W e ·m −2 , whereas the VKE method predicts the time series while underestimating the maximum generation rate by about 50%. Because VKE derives the generation limit from the preturbine climatology, potential changes in the vertical kinetic energy flux from the free atmosphere are not considered. Such changes are important at night when WRF estimates are about twice the VKE value because wind turbines interact with the decoupled nocturnal low-level jet in this region. Daytime estimates agree better to 20% because the wind turbines induce comparatively small changes to the downward kinetic energy flux. This combination of downward transport limits and wind speed reductions explains why large-scale wind power generation in windy regions is limited to about 1 W e ·m −2 , with VKE capturing this combination in a comparatively simple way.generation limits | turbine-atmosphere interactions | wind resource | kinetic energy flux | extraction limits W ind power has progressed from being a minor source of electricity to a technology that accounted for 3.3% of electricity generation in the United States and 2.9% globally in 2011 (1, 2). Combined with an increase in quantity, the average US wind turbine also changed from 2001 to 2012; hub height increased by 40%, rotor-swept area increased by 180%, and rated capacity increased by 100% (2). Likely a combination of both the above-noted technological innovations and improved siting, the per-turbine capacity factor, the ratio of the electricity generation rate (MW e ) to the rated capacity (MW i ), increased globally from 17% in 2001 to 29% in 2012 (1, 2), making a recently deployed wind farm likely to generate about 70% more electricity from the same installed capacity.Combining climate datasets with these observed trends of greater-rated capacities and capacity factors, several academic and government research studies estimate large-scale wind power electricity generation rates of up to 7 W e ·m −2 (3-7). However, a growing body of research suggests that as larger wind farms cover more of the Earth's surface, the limits of atmospheric kinetic energy generation, downward transport, and extraction by wind turbines limits large-scale electricity generation rates in windy regions to about 1.0 W e ·m −2 (8-14). Ideally, these inherent atmospheric limitations to generating electricity with wind power could be considered without scenario-and technol...

show abstract

Section: Resultsmentioning

confidence: 99%

Two methods for estimating limits to large-scale wind power generation

Miller

Brunsell

Mechem

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…Figure 6 shows the evolution of the (quasi-steady) mixed-layer depth (z i ) defined as the height of minimum virtual potential temperature flux, and of the inversion layer depth (δ = h 2 -z i , where h 2 is the height where the virtual potential temperature flux goes to zero above z i ) obtained for the five simulations performed. Different authors have considered other definitions of mixed-layer depth, such as the height of maximum virtual potential temperature gradient, z g (Sullivan et al 1998, Fedorovich et al 2004a, or where the concentration of a bottom-up passive scalar reaches a threshold value, z s (Garratt 1992, Driedonks and Tennekes 1984, Bretherton et al 1999. It is important to notice that lower values of z i are obtained for all the simulations with the former method, z i < z g ≈ z s .…”

Section: Entrainment Flux Ratiomentioning

confidence: 99%

“…From 1970 onwards many researchers (Tennekes 1973, Stull 1976a, Zeman and Tennekes 1977, Tennekes and Driedonks 1981, Driedonks and Tennekes 1984, Fedorovich 1995, Sorbjan 1996, Pino et al 2003, 2006, Sorbjan 2004, Conzemius and Fedorovich 2006b) have concentrated on studying the value and possible evolution of the ratio of virtual potential temperature fluxes at the inversion level and at the surface, . The main goal of these studies was to understand the driving processes of the entrainment heat flux and subsequently to develop a suitable parameterization for the entrainment flux.…”

Section: Introductionmentioning

confidence: 99%

Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget

Pino

Arellano

2008

Acta Geophys.

View full text Add to dashboard Cite

A b s t r a c tEffects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasi-steady barotropic boundary layer were conducted by increasing the value of the constant geostrophic wind by 5 m s -1 until the geostrophic wind was equal to 20 m s -1 . The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due to the enhancement of the entrainment heat flux by the presence of shear.Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases.Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget terms is obtained with the scaling, especially for shear contribution.

show abstract

“…The process is of great importance for the dynamics of the ocean [1][2][3], atmospheric pollution [4,5], bio-mass production [6,7] and oil-spill propagation [6,8], among other applications.…”

Section: Introductionmentioning

confidence: 99%

Steady state model and experiment for an oscillating grid turbulent two-layer stratified flow

2017

View full text Add to dashboard Cite

Turbulence generated by an oscillating grid in a two-layer stably stratified system is a classical flow utilised to study various aspects of turbulence in presence of stratification without mean shear.This flow evolves in a quasi-steady state, in which the layer thickness and density difference evolves in a quasi-steady manner due to the large separation of timescales between the turbulence and the setup. We present an extension of the classical setup that enables full steady state conditions and in which the entrainment velocity can be prescribed separately from the Richardson number.We develop a theoretical box-model and show that the model is in good agreement with the experiments. The model allows to predict the transient response of the system for a variety of initial conditions and the imposed steady state. The new setup is necessary to obtain the steady position of the density interface, for example when using advanced optical techniques to measure the small-scale features of turbulence near the interface.

show abstract

Entrainment effects in the well-mixed atmospheric boundary layer

Cited by 111 publications

References 20 publications

Two methods for estimating limits to large-scale wind power generation

Two methods for estimating limits to large-scale wind power generation

Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget

Steady state model and experiment for an oscillating grid turbulent two-layer stratified flow

Contact Info

Product

Resources

About