Shallow-flow visualization analysis by proper orthogonal decomposition

Abstract

The identification of the spatial characteristics and the shedding frequencies of coherent structures in shallow flows usually involves the use of sophisticated equipment for velocity measurements such as laser Doppler anemometry or particle image velocimetry. In this work, a simple and low-cost alternative for the quantitative characterization of quasi two-dimensional shallow coherent structures is presented. The technique is based on the image pre-processing of flow visualizations and post-processing by means of the proper orthogonal decomposition. As an illustration of the method, the analysis of a shallow flow in the wake of a cylinder with a vortex-street pattern is presented. The method is able to discriminate concentration patches attached to the vortices and their advection, providing frequencies in excellent agreement with a previous study.

Keywords:

• Coherent structure
• cylinder wake
• flow visualization
• POD
• shallow flow

Acknowledgements

The authors acknowledge the information provided by Prof. Lawrence Sirovich on the POD technique, Dr Alex Liberzon for his help on the programming aspects and the support of Mr Frederic Prinz during the flow visualization experiments. The financial support for this work provided by the German Research Foundation (DFG Grant JI 18/18-1) is gratefully acknowledged.

Additional information

Notes on contributors

Wernher Brevis

Present address: Structural and Civil Engineering Department, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield, S1 3JDUK

Manuel García-Villalba

Present address: Universidad Carlos III de Madrid, Bioingeniería e Ingeniería Aeroespacial, Leganés 28911, Madrid Spain.