The radioactive particles in the cloud of near-earth nuclear explosion diffuse and settle under the driving of wind at different heights, causing a wide range of radioactive contamination. Traditional fallout prediction models are based on ideal terrain and meteorological conditions, which can not solve the problem of prediction of radioactive contamination under complex conditions. This paper introduces the research progress of the authors' team on the numerical prediction of radioactive contamination under complex conditions in the past 10 years. Firstly, the numerical simulation method of atmospheric transport and settlement of radioactive particles is established based on the gas-solid two-phase flow model. Then the raindrop collision model and cascade downscaling technique are used to realize the prediction of radioactive contamination in rainfall weather and complex terrain conditions respectively. Finally, the numerical prediction ability of radioactive contamination under complex conditions is used to calculate the distribution law of contaminated radiation environment, and some significant results are obtained.

Based on conservation of mass and momentum, a fluid dynamics model of debris motion from a near-space nuclear detonation is established. Many influence factors are considered, such as energy dissipation, air density as a function of height, gravity, increasing air temperature caused by X-ray deposition and radiation cooling. A computation program is developed. The expansion and upward motion of debris in TEAK and ORANGE tests are calculated. Evolution of typical parameters such as central height, maximum horizontal radius, ascending velocity, and shape of debris are given. They are in accordance with experimental data. The model provides delayed radiation source parameters for ionospheric effect and artificial radiation band effect.