Effect of Angle of Attack on the Performance of an Airborne Counterflow Virtual Impactor

Abstract

A three-dimensional model has been developed within the framework of the commercial computational fluid dynamics program, FLUENT R , to investigate the collection efficiency of an airborne counterflow virtual impactor (CVI). The model assumes steady-state, isothermal, compressible, and turbulent flow. Particle trajectories are computed based on the Lagrangian discrete phase model (DPM). In addition to predicting the effects of flight velocity and counterflow rate on the particle collection efficiency, as do prior models, the model quantifies the effect of flight attack angle on the particle collection efficiency. With an angle of attack as small as 5 • , the CVI collection efficiency drastically degrades at large particle sizes, and only particles with intermediate sizes are collected. Smaller particles do not have sufficient inertia to fight the counterflow, and larger particles tend to impact the CVI inner walls and are lost to the CVI walls. The modeling results show that the alignment between the free stream flow and the CVI inlet is critical to the performance of the CVI.

Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals

“…This self-governing feature and portability of the PCVI system is especially advantageous over the regular CVI to provide constant residual-laden flows to the downstream instruments during studies in a controlled laboratory setting (China et al, 2015;Hiranuma et al, 2011;Slowick et al, 2011;Crawford et al, 2011;Gallavardin et al, 2008;Kim and Raynor, 2009;Cziczo et al, 2003Cziczo et al, , 2009DeMott et al, 2003) and a ground-based field application (Kupiszewski et al, 2015;Worringen et al, 2015;Vogel et al, 2013;Corbin et al, 2012;Richardson et al, 2007). In particular, the separation of small ice crystal residuals (∼ 4 µm) from diesel soot has been demonstrated with a combination of a compact ice chamber and the PCVI in China et al (2015). Moreover, among the aforementioned PCVI studies, Crawford et al (2011) and Gallavardin et al (2008) have used the PCVI connected to the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud simulation chamber at the Karlsruhe Institute of Technology (KIT) in Germany.…”