Simulation of chaff cloud dispersion and combustion by extending the CFD-DEM approach with chemical reactions

Pyrophoric chaff is a key countermeasure against infrared-guided missiles. A substantial quantity of metal chaffs is dispersed into the atmosphere, thereby forming a chaff cloud that obscures the infrared signatures of the carrier aircraft. The subsequent chemical combustion and kinematic diffusion of the chaffs within this process exert a significant influence on the temperature and morphology of the resulting chaff cloud. Therefore, it is necessary to model the chaff motion diffusion and temperature field considering aerodynamic forces, multi-body collisions, and chemical combustion. In this paper, the shrinkage reaction model is coupled on the basis of the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) framework. CFD is used to solve for the effect of airflow on chaff spontaneous combustion and motion. DEM simulates the physical phenomena of chaff- canister and chaff-chaff collision and heat transfer. Shrinking core model simulates the heat and mass transfer process of reactive metal oxidation and exothermic heat transfer. In this paper, a horizontally scattered chaff cloud was simulated. The diffusion laws in the horizontal and vertical directions, as well as the transient temperature field at different separation moments were analyzed. According to the simulation results, the chaff rapidly warms up and accelerates the diffusion process when exposed to airflow. Within 0.5s, the chaff transforms into a conical cloud, and the peak combustion temperature is attained within 1.9s. This model has the capacity to ascertain the position, orientation, and temperature of the chaff at any given moment, thereby furnishing an efficacious solution for the calculation of infrared characteristics, such as the dynamic radiation intensity of the chaff cloud.