Effects of Lens Geometry and Nozzle Dimensions on Aerodynamic Focusing
Harrison Griffin, Mustafa Hadj Nacer, Salix Bair, Bjoern Bingham, W. Patrick Arnott, Judith Chow, John Watson, XIAOLIANG WANG,
University of Nevada, Reno Abstract Number: 104
Working Group: Instrumentation and Methods
AbstractStraight-edge thin plate orifices (90° half angle) are used as the focusing elements in most aerodynamic lenses. They are simple to fabricate and have fewer boundary layer effects as compared to other geometries such as capillaries, converging nozzles, and diverging nozzles. The focusing performance of these other geometries has not been systematically evaluated. This study used computational fluid dynamics (CFD) simulations and Lagrangian particle tracking to investigate aerodynamic focusing of converging and diverging orifices with half angles ranging from 30° to 150° at two Reynolds numbers (50 and 100) and three Mach numbers (0.03, 0.1, and 0.3). The results show that the optimal Stokes number (St
o) for near-axis particles have small differences between the straight-edge orifice and the converging or diverging orifices, indicating small changes in focusing behavior for different lens geometries. This study also investigated the effects of the dimensions of the exit nozzle on particle terminal trajectories in the vacuum chamber. The nozzle has a cylindrical constriction upstream of the exit orifice. Several nozzle radial aspect ratios and lengths of the constriction were simulated in a two-dimensional axisymmetric domain for a range of flow conditions. The nozzle geometry that generates the least divergent particle beam in the vacuum chamber is identified.