US Department of Defense

 

Date of this Version

2013

Citation

Procedia Engineering 58 ( 2013 ) 223 – 231; doi: 10.1016/j.proeng.2013.05.026

Abstract

The U.S. Army AMRDEC has been performing research focusing on both analytical modeling and obtaining validation data through experimentation. The focus of this research is to understand both the impact event, and the associated material damage mechanisms. A key aspect of weather encounter modeling is that the local vehicle flow field environment alters the impact boundary conditions with time. Therefore, an analytical model must be able to include not only the vehicle flow field, but also the time accurate embedded flow field surrounding the droplets as they alter shape prior to impact. The impact event is highly dependent on the actual droplet shape at impact, and therefore extensive modeling and testing was required to obtain data suitable for code validation. The empirical testing effort consisted of single droplet impacts, high-speed rocket sled testing, and testing in a ballistics range. The data presented focuses on the data collected at the ballistics range for Mach numbers ranging from 2 to 7 for various shapes. The core analytical effort was developed by extensive modifications of the Smoothed Particle Hydrodynamics C-Code (SPHC) from Stellingwerf Consulting, augmented with an improved water equation of state that included the super-cooled regime to augment the fidelity of the impact physics for rain drops at high altitudes. The analytical model demonstrates that the temporal distortion of water in a post-shock environment and the impact events for various projectiles can be captured with reasonable accuracy. The next step is to obtain data within the shock layers of relevant vehicle shapes in order to obtain the detailed demise and coupled flow field physics in order to validate the model in a realistic environment. The data presented reveals the droplet shape change and demise characteristics inside the shock structures for missile domes and sphere-cone designs, along with the complex embedded shock structure and impact physics associated with these events. This data forms a subset of empirical data that can be used for the fully-coupled full-scale impact events on flight vehicles.

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