Cycle Of Atmospheric Boundary Layer Research Articles

Numerical investigations into the idealized diurnal cycle of atmospheric boundary layer and its impact on wind turbine's power performance

The power generated by a wind turbine largely depends on the properties of wind resource. In this work, wind characteristics in different regimes occurring throughout the idealized diurnal cycle and its impact on wind turbine's power performance are investigated systematically by means of large-eddy simulation (LES), and blade element momentum method (BEM), respectively. Through a precursor simulation of the atmospheric boundary layer (ABL) over a homogenous surface throughout a day, it is found that the resulting shapes of wind profiles (including wind speed, wind direction and turbulence level) vary significantly at different time periods, induced by distinct stabilities of the atmosphere. The simulated wind field data are then applied to a NREL 5 MW wind turbine for its power evaluation. Due to variabilities in wind shear and turbulence, the equivalent (disk-averaged) wind speed is introduced for power prediction. It is found that the magnitude and fluctuation of turbine's diurnal power are closely related to the atmospheric stability. In general, the average power production is higher under convective conditions during the day than under stable conditions at night, with a difference approaching 24.4%. This indicates that wind energy resource assessment will close to reality and benefit from increased accuracy if atmospheric stability impacts are considered for turbine's power predictions.

Estimating natural ventilation potential for high-rise buildings considering boundary layer meteorology

The design of energy conservative buildings that incorporates natural ventilation (NV) strategy has become increasingly popular around the world. Natural ventilation is a key solution for reducing energy consumption of buildings and for maintaining a healthy indoor environment. However, the adoption of natural ventilation in high-rise buildings is less common. As rapid population growth and urbanization take place in cities, it is important to explore the substantial energy saving potential of high rises by utilizing natural ventilation. In this study, we have provided the early effort to estimate quantitatively the vertical profiles of NV potential for high rises at major cities from six climate zones in the U.S. (i.e., Miami, Houston, Los Angeles, New York City, Chicago, and Minneapolis), using an in-house boundary layer meteorology model. The diurnal cycle of atmospheric boundary layer (ABL) and local climate characteristics are found to have a great effect on the vertical structure of NV potential. In general, negative vertical gradients of NV hours are observed for all cities except Miami where the vertical distribution is nearly uniform. For example, the annual NV hour decreases from 7258 at ground level to 4866 at 300m above the ground in Los Angeles. Our analysis shows that outdoor temperature is a key meteorological parameter that determines vertical profiles of NV hours in New York City, Los Angeles, Chicago, and Minneapolis. In contrast, humidity plays a greater role in cities like Miami and Houston where the outdoor temperature is often favorable for using natural ventilation except in the summer. Among studied cities, Los Angeles provides the ideal climate (warm and dry) for utilizing natural ventilation, displaying the greatest NV potential (7258NV hours or 83% time of the year at ground level), followed by New York City with 3360NV hours. The remainder of the four studied cities display comparable numbers of NV hours of approximately 2500 at ground level. The methodology and findings from this study are intended to assist architects and policy makers in quantifying the potential energy savings of natural ventilation, and illustrating the importance of considering the vertical variations of elevated thermal environment in high-rise buildings across different climate zones in the U.S.

Large‐eddy simulation of a diurnal cycle of the atmospheric boundary layer: Atmospheric stability and scaling issues

A simulation of a diurnal cycle of atmospheric boundary layer (ABL) flow over a homogeneous terrain is performed using large‐eddy simulation (LES) with the Lagrangian scale‐dependent dynamic subgrid‐scale model. The surface boundary condition is derived from the field observations of surface heat flux from the HATS experiment (Horst et al., 2004; Kleissl et al., 2004). The simulation results display good general agreement with previous modeling and experimental studies with regard to characteristic features such as growth of the convective boundary layer by entrainment, nocturnal jet, and multilayered flow structure of the nocturnal regime. To gain a better understanding of the physical parameters affecting the statistics of the flow, we study the dependence of a subgrid parameter (dynamic Smagorinsky coefficient), resolved turbulent kinetic energy, and resolved vertical velocity variance upon atmospheric stability. The profiles of these turbulent variables plotted as a function of Obukhov length show “hysteretic” behavior that implies nonunique dependence. The subsequent use of local Richardson number as the scaling parameter shows a decrease in this “hysteresis,” but there is an increased scatter in the profiles with increasing height. Conversely, profiles plotted as a function of local Obukhov length (based on the fluxes at the local vertical level) show almost no hysteresis, confirming the validity of Nieuwstadt's local scaling hypothesis. Although the local scaling hypothesis was formulated for the stable boundary layer, we find that it applies to the entire stability range of the diurnal cycle.