Computational Analysis of Missile Flight Through Rain

Our problem is to determine whether raindrops can survive the shock environment ahead of missile optical components to a degree that they become a damage concern. An initial assessment made for this proposal indicates that the relevant time scales measure in 5-20 microseconds and the Weber numbers (a measure of breakup regime and intensity) reach out to 2 106. We demonstrate that the relevant breakup regime is shear-induced entrainment, occurring on a time scale that allows minimal deformation of the drop as a whole, while mass loss is taking place as a fine mist emanating from the frontal surface area of the drop. Thus, our simulations will focus on the a priori prediction of interfacial instabilities, from “nucleation” occurring spontaneously at the appropriate wavelengths, the early, linear regime of growth, to the non-linear development of the resulting waves and their breaking to produce the mist. We provide evidence that our numerical tools are uniquely suitable (being endowed with all necessary features) for such a task, the proposed simulations will be of breakthrough quality, and the resulting software will have great impact in many other areas of defense/technology requiring aerobreakup predictions at supersonic speeds.