Large-Eddy Simulations of the Flow Over an Isolated Three-Dimensional Hill

Liu, Zhenqing; Cao, Shuyang; Li, Heping; Ishihara, Takeshi

doi:10.1007/s10546-018-0410-2

Cited by 14 publications

(12 citation statements)

References 35 publications

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“…In this auxiliary simulation, the surface temperature is set to θ cw , while other parameters are kept the same as those for the flow over the SST front. This method of prescribing the inflow condition in a simulation with periodic boundary condition was used extensively in the literature, e.g., in the simulations of flows in an urban street canopy (Tseng et al., 2006), over a steep hill (Liu et al., 2019; Wan & Porté‐Agel, 2011), and past a wind turbine (Wu & Porté‐Agel, 2011).…”

Section: Computational Configuration and Methodsmentioning

confidence: 99%

Numerical Study of Near‐Surface Jet in the Atmospheric Surface Layer Over an Oceanic Temperature Front

et al. 2021

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The interaction between atmospheres and oceans plays an important role in the global climate. In a field experiment of atmospheric flows over the Gulf Stream, when the wind blew from the cold water to the warm water, we observed a near‐surface jet over the warm water. We then conducted direct numerical simulations and large‐eddy simulations of atmospheric turbulence in the vicinity of the front and captured the near‐surface jet in simulations for the first time. Analyses of the data obtained from the high‐resolution three‐dimensional simulations revealed the dominant generation mechanisms of the near‐surface jet, which are the strong vertical mixing by the enhanced streamwise rolls and the mean downward motion. Around the near‐surface jet, the magnitude of the negatively valued Richardson number significantly increases, indicating the dominance of buoyancy effects in the flow dynamics there. The development of the near‐surface jet suggests that the Monin‐Obukhov similarity theory (MOST) needs to be modified in representing marine atmospheric boundary layers over sea surface temperature fronts.

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Section: Computational Configuration and Methodsmentioning

confidence: 99%

Numerical Study of Near‐Surface Jet in the Atmospheric Surface Layer Over an Oceanic Temperature Front

et al. 2021

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“…It is obvious that no matter how steep the 3D hill is, two peaks appear on the vertical v profiles with one locating near the ground and the other locating in the region close to the shear layer. The LES by Liu et al has revealed the mechanism of the two peaks on v profiles [34], in which the secondary turbulence structures surrounding the major vortex core in the wake are believed to be the source. Two peaks of v still appear but get less obvious when the ground is rough.…”

Section: Fluctuations Of Spanwise Velocitymentioning

confidence: 99%

Large Eddy Simulations of the Flow Fields over Simplified Hills with Different Roughness Conditions, Slopes, and Hill Shapes: A Systematical Study

Liu

Wang

2019

Energies

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Turbulent flow fields over topographies are important in the area of wind energy. The roughness, slope, and shape of a hill are important parameters affecting the flow fields over topographies. However, these effects are always examined separately. The systematic investigations of these effects are limited, the coupling between these effects is still unrevealed, and the turbulence structures as a function of these effects are still unclear. Therefore, in the present study, the flow fields over twelve simplified isolated hills with different roughness conditions, slopes, and hill shapes are examined using large eddy simulations. The mean velocities, velocity fluctuations, fractional speed-up ratios, and visualizations of the turbulent flow fields are presented. It is found that as the hill slope increases, the roughness effects become weaker, and the roughness effects will further weaken as the hill changes from 3D to 2D. In addition, the fractional speed-up ratio at the summit of rough hills can even reach to three times as large as that over the corresponding smooth hills. Furthermore, the underestimation of the ratios of spanwise fluctuation to the streamwise fluctuation by International Electrotechnical Commission (IEC) 61400-1 is quite obvious when the hill shape is 3D. Finally, coherent turbulence structures can be identified for smooth hills, and as the hill slope increases, the coherent turbulence structures will experience clear evolutions. After introducing the ground roughness, the coherent turbulence structures break into small eddies.

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“…Compared to flow over gentle hills where the roughness is characterized by a single momentum roughness height value (e.g., Allen, 2006;Belcher & Hunt, 1998;Cao et al, 2012;H. Chen & Yi, 2012;Liu et al, 2016Liu et al, , 2019Pearse et al, 1981), the presence of porous tall forest canopies introduces new features on the leeward side such as within canopy mean recirculation.…”

Section: Introductionmentioning

confidence: 99%

The Effects of Canopy Morphology on Flow Over a Two‐Dimensional Isolated Ridge

Banerjee

et al. 2020

JGR Atmospheres

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Momentum and mass exchanges between the atmosphere and forests situated on complex terrain continue to draw significant research attention primarily because of their significance to a plethora of applications. In this paper, we investigated flows behavior on the leeward side of a twodimensional forested ridge under neutrally stratified conditions using large-eddy simulations (LESs). The goal is to understand how variations in leaf area index (LAI), vertical canopy foliage distributions, and forest edge positions affect mean/turbulent flow statistics, momentum fluxes, and onset of recirculation patterns. Although pressure perturbations are dominated by the hill shape, it is demonstrated here that changes in canopy foliage distribution modulate intensities and patterns of the leeward adverse pressure gradients. Such changes in the adverse pressure gradients alter the mean velocity streamlines including the patterns and magnitudes of the leeward downward mean vertical velocity and the velocity variances and momentum flux in the wake region. While a downwind recirculation zone develops in all cases, the details regarding the incipient location and recirculation zone size vary including positions of the separation and reattachment points. Furthermore, changes in the strength and depth of the zone occur due to canopyinduced changes in adverse pressure gradients, advection, and canopy drag. Because the recirculation zone impacts the local mean advective terms in momentum and scalar exchanges, the simulations here indicate that canopy morphology-induced changes in the leeward flows have significant implications to both measurements and models of biosphere-atmosphere exchange over complex terrain.

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Large-Eddy Simulations of the Flow Over an Isolated Three-Dimensional Hill

Cited by 14 publications

References 35 publications

Numerical Study of Near‐Surface Jet in the Atmospheric Surface Layer Over an Oceanic Temperature Front

Numerical Study of Near‐Surface Jet in the Atmospheric Surface Layer Over an Oceanic Temperature Front

Large Eddy Simulations of the Flow Fields over Simplified Hills with Different Roughness Conditions, Slopes, and Hill Shapes: A Systematical Study

The Effects of Canopy Morphology on Flow Over a Two‐Dimensional Isolated Ridge

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