Large eddy simulation of flow over a three-dimensional hill with different slope angles

doi:10.1007/s11707-022-1048-4

Front. Earth Sci.

2024, Vol. 18

Issue (1) : 98-111 https://doi.org/10.1007/s11707-022-1048-4

Large eddy simulation of flow over a three-dimensional hill with different slope angles

Liang LI¹, Deqian ZHENG^1,^2,³(

), Guixiang CHEN^1,^2,³, Pingzhi FANG⁴, Wenyong MA⁵, Shengming TANG⁴

¹. School of Civil Engineering, Henan University of Technology, Zhengzhou 450001, China
². Henan International Joint Laboratory of Modern Green Ecological Storage System, Zhengzhou 450001, China
³. Henan Key Laboratory of Grain Storage Facility and Safety, Zhengzhou 450001, China
⁴. Shanghai Typhoon Institute of China Meteorological Administration, Shanghai 200030, China
⁵. Wind Engineering Research Center, Shijiazhuang Tiedao University, Shijiazhuang 050043, China

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Abstract

Slope variation will significantly affect the characteristics of the wind field around a hill. This paper conducts a large-eddy simulation (LES) on an ideal 3D hill to study the impact of slope on wind field properties. Eight slopes ranging from 10° to 45° at 5° intervals are considered, which covers most conventional hill slopes. The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy. The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed. The accuracy of the present method is verified by comparison with experimental data. The slope can affect both the mean and fluctuating wind flow fields around the 3D hill, especially on the hilltop and the leeward side, where a critical slope of 25° can be observed. The fluctuating wind speeds at the tops of steep hills (with slope angles beyond 25°) decrease with increasing slope, while the opposite phenomenon occurs on gentle hills. With increasing slope, the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface, resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence. The vortex shedding trajectory in the wake region becomes wider and longer, suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.

Keywords large eddy simulation inflow turbulence topographic wind field critical slope flow mechanism

Corresponding Author(s): Deqian ZHENG

Online First Date: 10 August 2023 Issue Date: 15 July 2024

Cite this article:

Liang LI,Deqian ZHENG,Guixiang CHEN, et al. Large eddy simulation of flow over a three-dimensional hill with different slope angles[J]. Front. Earth Sci., 2024, 18(1): 98-111.

URL:

https://academic.hep.com.cn/fesci/EN/10.1007/s11707-022-1048-4
https://academic.hep.com.cn/fesci/EN/Y2024/V18/I1/98

Tab.1 Fitting values of wind farm parameters

Fig.1 Schematic diagram of the mountain shape.

Fig.2 Computational domain of the numerical model.

Fig.3 Mesh distributions of the numerical model: (a) vertical plane grid and (b) horizontal plane grid.

Tab.2 Grid resolution

Fig.4 Comparisons of (a) normalized mean velocity and turbulence intensity profiles and (b) fluctuating wind speed spectrum.

Fig.5 Comparisons of the mean wind profiles (a) and turbulence intensity profiles (b) between results of large eddy simulation and wind tunnel test.

Fig.6 Time-averaged streamline of three-dimensional hills with different slopes. (a) 10°, (b) 15°, (c) 21.8°, (d) 25°, (e) 30°, (f) 35°, (g) 40°, and (h) 45° on the longitudinal section of y = 0.

Fig.7 Schematic diagram of the measurement point locations.

Fig.8 Profiles of the normalized mean velocities for the flow over 3D hill at different slopes. (a) x/L = −1.0, (b) x/L = −0.5, (c) x/L = 0, (d) x/L = 0.5, (e) x/L = 1.0, (f) x/L = −1.5, (g) x/L = 2.0, and (h) x/L = 2.5.

Fig.9 Profiles of the normalized fluctuating wind velocities for the flow over 3D hill at different slopes. (a) x/L = −1.0, (b) x/L = −0.5, (c) x/L = 0, (d) x/L = 0.5, (e) x/L = 1.0, (f) x/L = −1.5, (g) x/L = 2.0, and (h) x/L = 2.5.

Fig.10 Instantaneous vortex structure with Q = 1000 for different slopes. (a) 10°, (b) 15°, (c) 21.8°, (d) 25°, (e) 30°, (f) 35°, (g) 40°, and (h) 45°.

Tab.3 Vortex core coordinates

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[1]	Pingzhi FANG, Deqian ZHENG, Liang LI, Wenyong MA, Shengming TANG. Numerical and experimental study of the aerodynamic characteristics around two-dimensional terrain with different slope angles[J]. Front. Earth Sci., 2019, 13(4): 705-720.

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