Numerical Simulation of CL415 & Dash8 Airtanker Liquid Drop
Fighting wildland fires is a major issue for the protection of populations and environment with a need of more efficient means to fight fires. Airtankers are able to drop volumes of liquid (water or fire retardant) varying from less than 1m3 to several tens of m3, directly on fire or with the objective to form barriers of retardant to stop or reduce the fire propagation. However, the dynamics of a liquid dropped from an airplane has received few attentions in the scientific community, and related studies have mostly focused on Newtonian liquid jets injection in cross flow from millimetric injectors for combustion applications. For firefighting purpose, the liquid can be a retardant (a non Newtonian fluid) and the characteristic size of the delivery systems is of the order of a meter. The objective of this work is to demonstrate that Computational Fluid Dynamics (CFD) can be used to provide a deep understanding of the liquid fragmentation and dispersion when dropped from an aircraft. A numerical investigation is proposed for the analysis of airtanker performance and applied here to the biggest airtankers used in Europe: the Canadair CL-415 and the Dash-8. A numerical approach based on the Volume of Fluid method (VoF) is used to provide an accurate description of the tank discharge as well as to study the liquid ejection, fragmentation and atomization in air. The 3D unsteady resolution of the Navier-Stokes equations for both the liquid and the air allows us to provide a description of the main characteristics of the resulting liquid cloud, characterized by the vertical penetration of the liquid, its lateral expansion and the process of atomization.