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Proposing Institution

Zentrum f. angewandte Raumfahrttechnologie u. Mikrogravitation (ZARM)/Uni Bremen
Project Manager

Dr. Daniel Feldmann
Am Fallturm
28359 Bremen
Turbulent flows feature large and very large scale coherent motions (LSM/VLSM) carrying a substantial part of the kinetic energy. Large scale fluid motions are rather shaped by boundary conditions, geometry and source of driving than by universal small scale processes. To go beyond state-of-the-art modelling and controlling strategies for turbulent wall-bounded flows, LSM and VLSM must be correctly accounted for. Within the newly installed priority programme "Turbulent Superstructures" funded by the German Research Foundation (DFG), we aim to extend dynamical-systems approaches to high Reynolds number (Re) pipe flows to identify exact coherent solutions (ECS) forming the skeleton of LSM and VLSM in turbulent pipe flow. The remarkable similarity of typical structures observed in experiments at large Re and ECS at low Re hints at a connection worth pursuing. Very recently, first successful steps were accomplished in extending dynamical-systems approaches beyond the transitional regime in Couette, Poiseuille, and homogeneous shear flows. Instead of computing ECS by directly solving the Navier-Stokes equations with Newton-Krylov methods, we follow the successful road of first applying a spatial filter to the Navier-Stokes equations in order to eliminate the small-scale motions before seeking for exact solutions: We plan to conduct regular as well as overdamped large-eddy simulations (LES) of turbulent pipe flow up to Re=130000 by varying the constant Cs of a simple but robust Smagorinsky model towards unphysically high values to quench smaller-scale active structures and isolate the presumably self-sustaining LSM and VLSM from the full spectrum of turbulent motions. This allows us to readily detect recurrences in the flow field by symmetry reduction, which are then converged to ECS of the full Navier-Stokes equations using a Newton-Krylov hookstep method and continuation in the Cs-Re-plane.

Impressum, Conny Wendler