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Coherent Structures in Compound Open-Channel Flows: Experimental Investigation Using Dpiv

Author(s): Joachim V. Lukowicz; Jurgen Kongeter

Linked Author(s): Jürgen Köngeter

Keywords: Compound Open-Channel Flows; Coherent Structures; Digital Particle Image Velocimetry (DPIV)

Abstract: Digital Particle Image Velocimetry (DPIV) is used for experimental investigation of large scale coherent structures in compound open-channels. In a straight flume images of particles in a horizontal plane are recorded with a CCD-camera and evaluated to reveal instantaneous velocity fields. Afterwards, data is validated using an advanced dynamic filter algorithm. To obtain fluctuating velocity fields different decomposition techniques are applied and compared. The mean-bulk Galilean decomposition proves best and is used for further analysis. Instantaneous fluctuating velocity fields are examined regarding occurrence of vortical structures using spacetime correlation. Especially if vortices can not be identified by visualisation spacetime correlation analysis is a useful tool. Observed structures are not only transported with the mean flow but also have momentum in the lateral direction. This leads to interaction processes with streaks indicating strong influence of the shear layer. Vortices are characterised by extreme values of vorticity. Vorticity as well as rotational speed of observed structures well fit the Oseen vortex equation.


Year: 1999

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