Genesis and Features of Dust Devil Like Vortices in Convective Boundary Layers - A Comparative Study Using DNS/LES and Laboratory Experiments
Final Report Abstract
Dust devils are a frequent phenomenon of the atmospheric boundary layer. They often appear in deserts as near surface vortices with vertical axes, which can lift up dust due to their high velocities, and which mainly appear during daytime when the earth’s surface is strongly heated by the sun. Despite their well-known existence through simple observations, there is still a significant lack of sufficiently precise observations, as well as numerical and laboratory studies of dust devils. One of the main problems in observing dust devils in real nature is their random appearance and very small spatial scale with diameters often below 10 m. Within this project, dust devils have been studied both in the laboratory using a convection tank (Barrel of Ilmenau with a diameter of about 7 m) and with the help of high-resolution numerical simulations running at the same spatial scale as the tank. To our knowledge it was the first time that such structures have been generated in a laboratory experiment without stimulating their rotation by an artificial input of vorticity. Insofar, the project opens a chance to study the evolution process in a well-controlled laboratory environment. The simulations showed the existence of dust devils on such spatial scales for the first time, but could be run only for a few minutes due to the required numerical resources of several days CPU time on approximately 10.000 cores. The laboratory study allowed for observation times in the order of hours and was able to detect some very strong and large vortices with some similar features as found in the simulations, which is the first distinct evidence for naturally evolving vortices in a laboratory experiment. For a better comparison of statistical vortex features, longer runs of the simulation model and higher spatial resolution of the measurement technique in the laboratory experiment are required in the future. Furthermore, the numerical experiments were extended to the atmospheric scale. Main results of these simulations are that simulating dust devils with observed strength requires spatial model resolutions of 1 m and less. Only then, the near-surface thin layer of very hot air that appears in nature is adequately reproduced. Detachment of this layer generates very strong buoyancy and updrafts of more than 20 m s−1 that are known from observations. The simulations also helped to clarify how much dust devils contribute to the production of continental aerosols. While previous estimations showed a wide range from a few percent to more than 50 %, the simulation results give some hints that the contribution seems to be more at the lower end.
Publications
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(2019): Large-Eddy Simulationen von Staubteufeln mit beobachtbarer Intensität: Auswirkungen von Gitterweite, Hintergrundwind und Oberflächenheterogenitäten. DACH2019, Garmisch-Partenkirchen, Germany, 18–22 March
Giersch, S., Brast, M., Hoffmann, F., Raasch, S.
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(2019): Staubteufel. DACH2019, Garmisch-Partenkirchen, Germany, 18–22 March
Loesch, A., du Puits, R.
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(2019): Toward Large-Eddy Simulations of Dust Devils of Observed Intensity: Effects of Grid Spacing, Background Wind, and Surface Heterogeneities. Journal of Geophysical Research: Atmospheres, 124(14), 7697-7718
Giersch, S., Brast, M., Hoffmann, F., Raasch, S.
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(2020): Experimental investigation of Dust Devil like vortices with 3D particle tracking velocimetry. EGU General Assembly 2020, Online, 4–8 May
Loesch, A., du Puits, R.
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(2020): Genesis and Features of Dust Devil-Like Vortices in Convective Boundary Layers – A Numerical Study Using LES and DNS. EGU General Assembly 2020, Online, 4–8 May
Giersch, S., Raasch, S.
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(2021): Evolution and Features of Dust Devil-Like Vortices in Turbulent Rayleigh-Bénard Convection—A Numerical Study Using Direct Numerical Simulation. Journal of Geophysical Research: Atmospheres, 126(7), e2020JD034334
Giersch, S., Raasch, S.
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(2021): The Barrel of Ilmenau: A large-scale convection experiment to study dust devil-like flow structures. Meteorol. Z., p. 89 - 97, 30(1), 89-97
Loesch, A., du Puits, R.
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(2022): Experimentelle Untersuchung von Staubteufeln in einem Laborexperiment, DACH2022, Leipzig, Germany, 21–25 March 2022
Kaestner, C., du Puits, R.
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(2022): Observed dust devil-like flow structures in large-scale turbulent Rayleigh-Bénard convection. 20th International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, Lisbon, Portugal, 11–14 July
Kaestner, C., Schneider, J.D., du Puits, R.
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(2022): Staubteufelähnliche Wirbel in turbulenter Rayleighe Bénard Konvektion – Eine Studie unter Verwendung der direkten numerischen Simulation. DACH2022, Leipzig, Germany, 21–25 March
Giersch, S., Raasch, S.
