Simulations of Ice Particle Impacts on a Hypersonic Forebody

Within their flight envelope, hypersonic vehicles can be exposed to environmental and atmospheric conditions that include meteorological particles and these particles can be damaging to a vehicle’s forebody, engine components, optical sensors, and radomes. Ice particles can be particularly problematic due to their large diameters and high capability for surface erosion and ice particles tend to appear at altitudes consistent with supersonic speeds for hypersonic vehicles. The objective of this study is to understand the trajectories and impacts for typical ice particles on the nose cone of a hypersonic vehicle traveling at supersonic speeds. The particle drag model used to determine the trajectory in a compressible flow considers effects of particle shape and Reynolds number (which were found to be greater than effects due to relative Mach number). Discrete velocity and temperature of the particles are tracked from up to the point of impact for a variety of ice sizes and shapes. The size was based on a volume-equivalent diameter, which is directly proportional to particle mass. The results indicate that particle trajectories are only weakly deflected by the surrounding flow before wall impact. Compared to column-like shaped ice, plate-like shaped ice particles impact the vehicle body at a somewhat lower speed and result in a lower impact fraction. This is a result of the larger drag coefficients for plate-like shaped ice. The inertia vs. drag balance can be incorporated using a Stokes number scaling for both velocity changes and collection efficiency. However, both shapes of particles have very high inertias for typical atmospheric sizes and thus tend to impact at speeds and angles consistent with freestream conditions. In addition, the ice particle temperature stays near freezing up to impact so that melting (phase change) effects are expected to be small. Finally, the temperature changes depend on particle mass and are relatively insensitive to particle shape.