Study of the fluid mechanics of aerodynamic microparticle sampling

Thesis (Ph.D.)--University of Washington, 2020It is no secret that there is significant room for improvement when it comes to security at airports and other secure locations. One area with considerable room for improvement is in the passenger screening for the presence of illicit materials. Traditional swabbing methods used for sampling can be inconvenient and ineffective. Non-contact sampling can offer improvements over traditional sampling methods by increasing speed and effectiveness. Aerodynamic sampling uses a combination of impinging jets to remove particles from the surface of interest and suction to direct the removed particles onto a collection substrate or directly to a detector of choice. This offers improvements over swabbing as there is less room for contamination of the sampling substrate, removes user bias, and allows for sampling of larger areas in less time. To design an effective non-contact surface sampler, one must characterize several distinct phenomena; the flow field of impinging jets, the necessary flow conditions for the removal of micro-particles resting on a surface, and the aerodynamic forces experienced by particles under these conditions. This dissertation focuses on (i) characterization of wall shear stress from axisymmetric underexpanded impinging jets, (ii) development of equations for the wall jet velocity profile and wall shear stress of planar underexpanded impinging jets, (ii) development of a method for calculating the adhesion force of spherical microparticles, and (iv) formulations of aerodynamic forces on non-spherical particles in a boundary layer