|
|||||
|
|
Mass Transport in Shallow Turbulent Wake Flow by Planar Concentration Analysis Technique |
|
| Authors: | Carl F v Carmer Andreas C Rummel Gerhard H Jirka |
| Affiliation: | 1Research Associate, Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), 37073 Goettingen, Germany; presently, Research Institute for Optronics and Pattern Recognition (FGAN-FOM), Gutleuthausstrasse 1, 76275 Ettlingen, Germany. E-mail: carmer@fom.fgan.de 2Research Assistant, Institute for Hydromechanics, Univ. Karlsruhe, Karlsruhe, Germany and DICAT, Univ. Genova, Genova, Italy. E-mail: rummel@ifh.uka.de 3Professor and Director, Institute for Hydromechanics, Univ. Karlsruhe, Karlsruhe, Germany. E-mail: jirka@uka.de |
| Abstract: | A planar concentration analysis (PCA) system is used for observing the transport and mixing of a tracer mass in a shallow turbulent free-surface wake flow of a large cylindrical obstacle. The nonintrusive, fieldwise PCA measuring technique is applied to evaluate depth-averaged mass concentrations by making use of light attenuation due to absorption and scattering processes related to a dissolved tracer mass. The scalar fields are decomposed into a low-frequency quasiperiodic part, the coherent flow, and a randomly fluctuating part. From accompanying near-surface velocity measurements, large-scale coherent structures are identified and related to the coherent mass fields. This allows one to assess the role of the large-scale vortices for advection and diffusion in shallow wake flows. The time–mean wake flow displays a self-similar spanwise distribution both for mass and velocity. The longitudinal development of shallow wakes initially shows the growth of unbounded wakes; in the wake far field an attenuated behavior applies. |
| Keywords: | Shallow water Mass transport Turbulent diffusion Vortices Flow measurement Dye |