  We study the hydrodynamical behavior occurring in the turbulent interaction
zone of a fast moving red supergiant star, where the circumstellar and
interstellar material collide. In this wind-interstellar medium collision, the
familiar bow shock, contact discontinuity, and wind termination shock
morphology forms, with localized instability development. Our model includes a
detailed treatment of dust grains in the stellar wind, and takes into account
the drag forces between dust and gas. The dust is treated as pressureless gas
components binned per grainsize, for which we use ten representative grainsize
bins. Our simulations allow to deduce how dust grains of varying sizes become
distributed throughout the circumstellar medium. We show that smaller dust
grains (radius <0.045 micro-meters) tend to be strongly bound to the gas and
therefore follow the gas density distribution closely, with intricate
finestructure due to essentially hydrodynamical instabilities at the
wind-related contact discontinuity. Larger grains which are more resistant to
drag forces are shown to have their own unique dust distribution, with
progressive deviations from the gas morphology. Specifically, small dust grains
stay entirely within the zone bound by shocked wind material. The large grains
are capable of leaving the shocked wind layer, and can penetrate into the
shocked or even unshocked interstellar medium. Depending on how the number of
dust grains varies with grainsize, this should leave a clear imprint in
infrared observations of bowshocks of red supergiants and other evolved stars.
