On The Fluid Dynamics of Virtual Impaction and The Design of a Slit Aerosol Sampler

It has been long established that Reynolds number effects can lead to flow instabilities and/or transition from laminar to turbulent flow regimes. The nature of free shear jets is well understood and heavily covered in the fluid mechanics literature. On the other hand, the study of confined nozzles presents some challenges and is still a developing area of research. In this work, we focus on quasi-impinging jets, such as the ones feeding into a virtual impactor. Virtual impactors


1 Introduction
1.1 Literature Review
1.1.1 Virtual Impactors
1.1.2 Hydrodynamic Stability of Jets
1.1.3 Particles in Turbulence
1.1.4 Thesis Synopsis
2 Two-dimensional Theoretical Study
2.1 Equations of Fluid Motion
2.2 Equation of Particle Motion
2.3 Numerical Setup
2.3.1 Geometry & Flow Conditions
2.3.2 FLUENT Code
2.3.3 Particle Tracking Code
2.4 Results
2.4.1 Time Averaged Flow
2.4.2 Aerosol Collection & Loss
2.4.3 Unsteady Flow
2.4.4 Particle-Eddy Interaction
iii3 Large Eddy Simulation
3.1 Overview of the Method
3.2 Mathematical Formulation
3.3 Residual Stress Tensor Modeling
3.3.1 The Lagrangian Dynamic Subgrid Scale Model
3.4 Model Validation
3.4.1 Fully Developed Turbulent Channel Flow
3.4.2 Turbulent Flow Past a Square Cylinder
4 LES of Round Slit Virtual Impactor
4.1 Geometry & Flow Conditions
4.2 Virtual Impaction Statistics
4.3 Free Boundary Layer Properties
4.4 Particle Transport
4.4.1 Description of Wind Tunnel Experiment
4.4.2 Efficiency Characterization
4.4.3 Segregation and Preferential Concentration
5 Summary, Conclusions, & Recommendations
5.1 Summary of Two-dimensional Study
5.1.1 Conclusions
5.2 Summary of LES Studies
5.2.1 Conclusions
5.3 Recommendations
A User Defined Function (UDF) for the Convective Boundary Condi-tion
A.1 Validation

Author: Charrouf, Marwan

Source: University of Maryland

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