What is it about?
The characteristics of the ground, i.e., its roughness and the presence and size of ground elements (like buildings), have a strong influence on the flow field that develops at the near-ground level during extra-tropical cyclones, which are long-lasting and spatially wide structures whose characteristics are stationary (do not change with time) during the occurrence of the event. This research assesses whether the same can apply to thunderstorm winds, which are very intense and transient (non-stationary) extreme wind phenomena. This is addressed experimentally in one of the largest wind tunnel worldwide capable of reproducing 3D thunderstorm downbursts and tornadoes, the WindEEE Dome at Western University in Canada. Different surfaces were investigated to explore the change of kinematic and geometric characteristics of the downburst flow with changing the grade of roughness at the ground.
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Why is it important?
The very localized spatial and temporal structure of thunderstorm downbursts make them very difficult to be captured by classic anemometric instruments in nature. Furthermore, the very large heterogeneity of full-scale downburst records do not allow a clear characterization. In this perspective, controlled conditions such as large-scale wind tunnel testing in ad-hoc laboratory can provide fundamental insights into their modelling. Surface roughness is here proven to be a key element in the characterization of the downburst outflow impacting on the natural and built environment. Its contribution, which is impossible to assess in nature, is quantified in the present article at the largest geometric scales ever tested in a laboratory.
Perspectives
The quantification of the relation between the grade of ground obstruction (roughness) and the variation of key parameters in terms of wind-structure interaction (such as maximum wind speed and its height, turbulence level) will provide a fundamental contribution toward the formulation of a model of thunderstorm winds to include in the wind and civil engineering design codes. This will aid at improving the resilience of structures and infrastructure, environment, and communities and society.
Federico Canepa
Universita degli Studi di Genova
Read the Original
This page is a summary of: Effect of surface roughness on large-scale downburst-like impinging jets, Physics of Fluids, March 2024, American Institute of Physics,
DOI: 10.1063/5.0198291.
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