Collaborative Research: Dust Entrainment Processes by Convective Vortices and Localized Turbulent Structures: Experimental and Numerical Study

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Dust in the atmosphere plays a significant role in modulating weather, air quality, and climate. Most studies of the lofting of dust from the surface have focused on steady wind conditions. However, there are obvious examples of other types of dust lifting mechanisms, such as dust devils, that occur in situations where the wind flow is more complicated. This research project will combine high-resolution numerical modeling with laboratory experiments to study dust devils and convective vortices and how they entrain dust from the surface. The long-term impact of the project will be to improve the prediction of dust entrainment, which has a significant climate impact. The research team will also conduct a significant education and outreach effort, with graduate and undergraduate students, outreach to K-12 students, and a virtual mini-symposium including international partners. The project plans to enhance diversity through specific programs that recruit underrepresented undergraduate students.The primary objective of this project is to identify and characterize the fundamental mechanisms triggering the entrainment of dust in the non-equilibrium conditions that depart from a canonical, well-investigated scenario of a fully-developed boundary layer flow that assumes both spatial homogeneity and statistical stationarity. An example of a non-equilibrium condition is a dust devil, which is a vortical structure that can lift significant amounts of dust. The research team will, through a combination of laboratory experiments and numerical simulations, characterize and identify the role of individual dust lifting processes in the physics of sediment entrainment by dust devils and convective vortices. The laboratory experimental setup consists of a vortex generator with three-dimensional particle image velocimetry (PIV) and particle tracking velocimetry (3D-PTV) systems. The computational aspect of the project will use an open-source spectral-element method (SEM) code Nek5000 which was co-developed by one of the researchers. The laboratory and numerical techniques would be used to answer the following questions:1. What is the effect of a horizontal spatial inhomogeneity of mean and fluctuating properties of the carrier flow turbulence on dust entrainment mechanisms in non-canonical vortex flows? What is the role of the competing forces, such as aerodynamic, pressure gradient, cohesion, gravity and electric forces in the dust entrainment processes?2. What is the role of the particle size, Stokes number and the size distribution modality? Would the main mechanisms be different or similar for inertial particles of different sizes?3. What kind of agreement is expected between experimental and computational results in a representation of multiphase flow turbulence? What is the source and value of uncertainties?4. What are the implications for modeling? How well the global (local) sediment fluxes are correlated with the global (local) vortex flow variables? This information is critical for developing improved sediment flux parameterizations for simulation models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.