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Non-Intrusive Frequency Measurements With Laser Shadowgraphy And Event-Based Schlieren Imaging Of Bluff Body Wakes In Compressible Flow

Max Nüßle (1), Felix Luc Ebertz (2), Nicklas Essig (1), Christof Schulz (2), Bernhard Weigand (1), Christoph Steinhausen (3)

1. Institute of Aerospace Thermodynamics, University of Stuttgart, Stuttgart, Germany
2. Institute for Energy and Materials Processes - Reactive Fluids, University of Duisburg-Essen, Duisburg, Germany
3. University of Duisburg-Essen, Essen, Germany


Event-based imaging is an emerging technology in thermodynamics and fluid dynamics. In this work, we are leveraging an event-based camera with a conventional schlieren set-up to investigate the vortex shedding dynamics behind a blunt central injector in a transonic nozzle flow. We offer different methods to evaluate the data stream of the event-based camera. Standard Fourier methods are not directly applicable to this data due to a non-constant time step. Therefore, the data needs to be treated with special care. Clusters of on- and off-events alternate and show the periodic nature of the wake. Using a clustering algorithm on the event groups also provides an estimation of vortex shedding frequency. These results are compared with laser shadowgraphy, a second novel method to measure the vortex shedding frequency in the wake. Both approaches to measuring the vortex shedding frequency are agreeing with each other within 1%. They each offer a simple set-up with comparatively low cost for their high temporal resolution.

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