Raindrop demise in a high-speed projectile flowfield
This research examined current approaches used to model raindrop demise in high-speed missile flowfields. Historical correlations derived from shock tube data do not capture all of the critical non-dimensional parameters and temporal droplet shape change and as such are not accurate. In addition, while droplet demise studies in shock tubes provide valuable data for code validation, it was established that the data cannot be directly used to develop projectile induced droplet demise estimates. A numerical approach was developed based on the Smooth Particle Hydrodynamics-C (SPHC) code to model the entire temporal evolution of the macroscopic droplet demise process from shock crossing to catastrophic break-up. As part of this effort, an extended algebraic equation of state was developed for water including the supercooled region. A series of unit problems was simulated to verify that the numerical method was able to capture the required flow field instabilities and relevant physics inherent in drop demise. The numerical approach was then used to investigate the internal environment of the water drop during the demise process. Highlights of this investigation included the capture of wave instabilities on the surface of the drop, wave crest stripping of small water droplets, the likely cause of the lateral droplet dilation, and the internal temporal droplet pressure and velocity distribution. The SPHC simulations suggest that for a Weber number range of 5000–40,000, the Kelvin-Helmholtz instability is the primary mechanism driving mass stripping and that spherical droplets are stable against Rayleigh-Taylor instabilities. This conclusion is supported by recently obtained droplet demise empirical data.
0548: Mechanical engineering