Analyzing the large scale flow in a precessing cylinder and its ability for dynamo action

We carried out ultrasonic Doppler measurements of a precession driven flow in a cylindrical cavity. The experimental studies were conducted in a downscaled water experiment to analyze the possibility of hydrodynamic dynamo action in a planned large-scale liquid sodium experiment. The azimuthal and axial mode decomposition close to the outer rim reveals a significant peak for the axi-symmetric flow component with axial wavenumber k=2 in a narrow region of the precession ratio. At this peak, dynamo action is predicted for the DRESDYN sodium experiment. Specifically we analyze the ultrasonic measurement data which were transferred via slip rings from the vessel rotating about two axes. By post-processing the azimuthal dependence of the flow was extracted from the ultrasonic data. The utilized workflow eliminates the slight variations over time of the operating conditions and of the frame rate of the data acquisition. The downscaled water experiment was operated in a wide range from Re=10000 to 1.6·106, showing a very good agreement with direct numerical simulations at their upper limit of Re=10000.