Résumé
The aerological study of the natural entrance gallery of Saint-Marcel-d'Ardèche cave was undertaken in order to recommend optimal conditions for the hibernation of bats while maintaining climatic conditions of the cavity guaranteeing its good state of conservation. Temperature was recorded, outside and inside the cave, in the galleries of the natural and tourist entrances, since 2017 by the CDS07 (local caving NGO). A numerical modelling of temperatures and air currents was carried out over cold periods (mid-Sept. to mid-April) using the fluid mechanics software Ansys Fluent. The opening surface of the door closing the entrance to the cave is modular thanks to removable wooden panels. The current door opening is 1.9m². The Reynolds number has been calculated for different door opening surfaces; this number being, in all cases, greater than 2000, the regime is turbulent. Air speed changes were observed where the natural gallery changes geometry, and section, at 12 m and 24.8 m from the entrance. Considering as a first approximation, that the necessary conditions for the hibernation of bats are to have a stable temperature and absence of wind, we can recommend an opening of 3.8m².