Abstract
This study of a lee wave event over three-dimensional (3D) mountainous terrain in Lantau Island, Hong Kong, using a simulation combining mesoscale model and computational fluid dynamics (CFD) model has shown that (1) 3D steep mountainous terrain can trigger small scale lee waves under strong wind condition, and the horizontal extent of the wave structure is in a dimension of few kilometers and corresponds to the dimension of the horizontal cross-section of the mountain; (2) the life cycle of the lee wave is short, and the wave structures will continuously form roughly in the same location, then gradually move downstream, and dissipate over time; (3) the lee wave triggered by the mountainous terrain in this case can be categorized into “nonsymmetric vortex shedding” or “turbulent wake,” as defined before based on water tank experiments; (4) the magnitude of the wave is related to strength of wind shear. This study also shows that a simulation combining mesoscale model and CFD can capture complex wave structure in the boundary layer over realistic 3D steep terrain, and have a potential value for operational jobs on air traffic warning, wind energy utilization, and atmospheric environmental assessment.
Highlights
Lee wave is one of the key indicators of how mountains affect air flows [1]
Based on the authors’ previous studies, this paper leverages the advantageous application of computational fluid dynamics (CFD) in microscale numerical simulation to perform a detailed simulation on the “vortex/wave shedding” case in Lantau Island raised by Chan [17] and to analyze the process of lee wave formation triggered by 3D mountainous terrain under strong wind condition
(1) As a typical 3D steep mountainous terrain, Lantau Island can trigger small scale lee waves under strong wind condition. Both radar observation and CFD numerical simulation captured clear evidences of lee waves, and some waves are in a formation of rotor
Summary
Lee wave is one of the key indicators of how mountains affect air flows [1]. It has significant impact on aviation safety, wind energy utilization, and air pollution. From analysis of Doppler radar data, Chan [17] noticed significant lee waves in Lantau Island, Hong Kong, under a typical strong wind condition, and he took it as “vortex/wave shedding.”. Compared with simple and idealized mountains [12] or semi-2D ridges [14] discussed in previous numerical studies, the terrain of Lantau Island is far more complex and realistic, which makes the lee wave case observed in this. Based on the authors’ previous studies, this paper leverages the advantageous application of computational fluid dynamics (CFD) in microscale numerical simulation to perform a detailed simulation on the “vortex/wave shedding” case in Lantau Island raised by Chan [17] and to analyze the process of lee wave formation triggered by 3D mountainous terrain under strong wind condition
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