CFD simulations of a calyx shape rain gauge in a uniform and turbulent wind tunnel environment

The airflow surrounding any precipitation gauge is deformed by the presence of the gauge body, resulting in increased flow velocity above the orifice of the instrument, which deflects the hydrometeors (liquid/solid particles) away from the collector. The main factors of influence are the gauge shape, the wind speed and the type of precipitation, including the particle size distribution (PSD). Currently to reduce the wind effect on precipitation collection wind shields are installed and rain gauges with aerodynamic shape are developed. The method employed in this study is based on the analysis of airflow patterns in the proximity of the gauge collector by means of Computational Fluid Dynamic (CFD) simulations. Validation of the numerical results is obtained by comparison with wind tunnel experiments. These simulations, to be coupled in future developments with a particle tracking model to introduce the dispersed phase (solid/liquid particles), will allow to quantify the Collection Efficiency (CE) of the gauge. The overall objective of the work that includes this study, is to derive suitable correction curves for operational purpose.