TURBULENT ELLIPTIC WAKES |
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| Authors: | M KIYA Y ABE |
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| Affiliation: | 1. Institut für Physik - NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, D-06120 Halle, Germany;2. Institut für Chemie – Organische Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, D-06120 Halle, Germany;1. Consumer and Clinical Radiation Protection Bureau, Health Canada, 775 Brookfield Road K1A 1C1, Postal Locator 6303B, Ottawa, Ontario, Canada;2. European Space Agency, ESA, European Astronaut Center, EAC, Crew Medical Support Office & Astronaut Division, PO Box 906090, 51127 Cologne, Germany;1. National Research Council of Italy–Institute of Science and Technology for Ceramics (CNR-ISTEC), Via Granarolo 64, I-48018 Faenza, Italy;2. National Institute of Materials Physics, P.O. Box MG-7, Bucharest, Magurele 077125, Romania;3. METAV-R&D S. A., P.O. 22, Bucharest, Romania;1. Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA;1. Department of Occupational and Environmental Health/Epidemiology, Bavarian Health and Food Safety Authority, Pfarrstr. 3, 80538 Munich, Germany;2. Bavarian Health and Food Safety Authority, Veterinärstr. 2, 85764 Oberschleißheim, Germany;3. Children Hospital and Children Polyclinic in the Dr. von Haunersches Children Hospital, Ludwig-Maximilians-University, Lindwurmstr. 4, 80337 Munich, Germany;4. Institute and Outpatient Clinic for Occupational, Social and Environmental Medicine, Ludwig-Maximilians-University Munich, Ziemssenstr. 1, 80336 Munich, Germany |
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| Abstract: | This paper describes results of an experimental study on turbulent wake of an elliptic disk set normal to the main flow, whose major diameter is 2·0 or 3·0 minor diameters, Reynolds number being 2·0×104on the basis of the minor diameter D. Two periodic components of velocity fluctuations were found in the wake. One is centred around the minor plane, being due to the alternate shedding of rolled-up, hairpin-like vortices. The other is centred around the major plane, which is likely to be due to a meandering motion of the wake. The axis switching, which is a cross-over of half-widths in the major and minor planes plotted against the streamwise distance, occurred at approximately 4·0 D downstream of the disk. The mechanism of the axis switching is different from that in elliptic jets, and it is proposed that it is due to a difference in the growth rate of the fundamental Fourier modes in the minor and major planes. The structure of the wake is studied by flow visualization and a survey of the time-mean velocity, turbulence intensities and Reynolds shear stresses. Wavelet analysis of the velocity fluctuations disclosed a low-frequency unsteadiness in the wake. This unsteadiness has different representative frequencies in the major and minor planes, being approximately one-fifth of the frequency of the corresponding periodic component in both planes. |
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