The effect of a cross wind when sampling dust particles through an orifice in the base of a horizontal cylinder

Air containing particles is sucked into an orifice in the underside of a bulky sampling head which is idealized for analysis in two dimensions as a horizontal cylinder with a line sink. Equations are given for the motion of particles around and into the sink when a wind blows past in a horizontal direction; the fluid motion is ideal and the inertia of the particles, which are settling under gravity, is neglected. Particle trajectories are calculated when the wind velocity is of the same magnitude as the rate of fall of the particles.