Thermo-fluid dynamic simulations of the Hotplate precipitation gauge and wind tunnel experiments

The present study addresses the aerodynamic response of the recently developed “Hotplate” precipitation gauge when exposed to the wind. The Hotplate gauge employs two heated plates to provide a reliable method of precipitation measurement. The measuring principle is based on an algorithm to associate the latent heat needed to evaporate the snow, or the rain, and the precipitation rate. The presence of the instrument body immersed in a wind field is expected to induce significant deformations of the airflow pattern near the gauge, with an impact on the associated catching efficiency. Indeed, the fall trajectories of the hydrometeors when approaching the gauge can be deviated away from the collecting plate resulting, in general, in some underestimation of the precipitation rate. This work is based on Computational Fluid Dynamics (CFD) simulation of the airflow field around the gauge for different wind speeds, to identify areas where the wind-induced updraft, local acceleration and turbulence are significant. The performed CFD airflow simulations use the URANS SST k-ω approach, and are the initial modelling step to quantify the associated undercatch. These will be possibly coupled in future developments with particle tracking models to derive suitable correction curves for operational purposes. Due to the specific measurement principle exploited by the “Hotplate” gauge, thermo-fluid dynamic simulations are addressed as well. Dedicated tests have been performed in the wind tunnel facility available at the Department of Civil, Chemical and Environmental engineering DICCA, University of Genoa to validate simulation results. Numerical results indicate that the presence of wind is a relevant source of systematic bias and its effect must be corrected by adopting suitable correction curves as a function of the wind velocity. An assessment of the airflow patterns developing around the gauge at various wind velocity regimes is provided in this work and wind tunnel tests allowed for a substantial validation of the numerical results.