On Tuesday, 28 January 2020 at 11.00 Cedrick Ansorge will talk on the topic “Turbulent Ekman flow as virtual lab in geophysical fluid dynamics”

Location:  Gyrhofstraße 8a (Gebäude 158a), Room 1.105 (1st floor), 50931 Cologne

Abstract: The atmospheric boundary layer (ABL) is the lowest part of the atmosphere that is directly linked to the surface through vertical turbulent exchange, typically the lowest 100 to 1000m. There, turbulent mixing is the main vertical transport mechanism for heat, water, momentum and any kind of air constituent. Besides turbulence, the ABL is a multi-physical system comprising also radiative, miro-physical, chemical and other processes on scales from the multi-kilometre range down to the Kolmogorov scale of turbulent motion at the sub-millimetre range in three spatial dimensions. Both the multiphysical complexity and the broad-scale nature are prohibitive for a brute-force approach to numerical modelling of the system. Truncated representations of the ABL are thus inevitable when numerically modeling the ABL.
I will introduce turbulent Ekman flow–the doubly periodic flow over a flat rotating plate—that physically truncates the ABL to its fluid-mechanical core, the Navier–Stokes equations with appropriate boundary conditions. The governing equations are solved by a highly scalable numerical algorithm that is being used on up to 250,000 compute cores to represent the turbulent flow on grids that routinely use 3 × 230 collocation points in space. The reduced physical complexity allows for high-fidelity turbulence simulations where the entire range of turbulent motion is represented directly–without need for turbulence closure. We can thus study the ABL under conditions for which classical approaches to represent turbulence fail–such as partial or complete laminarization and transitional flows.