Institut für Meteorologie und Klimaforschung

Seminar über Aerosolphysik (IMK-AAF)

Ansprechpartner: Prof. Dr. T. Leisner, Dr. H. Saathoff, Dr. R. Wagner

Das Seminar findet - soweit nicht extra angekündigt - Montags um 11:00 Uhr im Seminarraum 150 des IMK-Gebäudes 326 (Campus Nord) statt.

Veranstaltungskalender

 
Vortrag

Wind tunnel experiments on natural and collision induced oscillations of raindrops

Dienstag, 26. November 2013, 15:00-0:00
KIT Campus Nord, IMK
Gebäude 435, Raum 2.05
From recent years, an overview of experimental investigations of water drops which were freely floating in the air stream of the Mainz vertical wind tunnel will be given. Efforts were made to characterize the microphysics of raindrops including their shapes and axis ratios, oscillation modes and frequencies, and internal circulation. A first series of experiments was carried out with pure water drops which serve as basis for further intercomparisons of microphysical properties. The shapes and oscillation frequencies of raindrops with different sizes from 0.6 to 7 mm diameter were compared to theoretical results. It was shown that the average drop shape is appropriately estimated by an aerodynamic model of quiescent water drops. Atmospheric raindrops do generally not consist of pure water but may contain additional substances which modify the surface tension and, thereby, influence drop deformation as well as breakup and coalescence, and, thus, the formation of precipitation. A second series of measurements with drops having reduced surface tensions resulted in variations of the terminal velocity, drop shape, mean axis ratio, oscillation modes, frequencies, and amplitudes. It was shown that the microphysical models used to compute the above parameters for pure water drops is also suited for raindrops with different surface tensions. Furthermore, depending on the existence of a surfactant film on the surface, drops exhibit the presence or absence of internal circulation. In a third series of measurements, the shape and oscillation behaviour of raindrops after collision were investigated. Water drops with 2.5 mm diameter were freely floated at their terminal velocities in the wind tunnel while they were colliding with 0.5 mm diameter droplets which were carried along with the air stream. The collision efficiency and its dependence on the Weber number and on the eccentricity of the colliding drops showed good agreement with numerical studies. Results regarding the amplitude of the axis ratio variation, the active oscillation modes and their frequencies, and the decay of the oscillation after collision will be presented.
Diese Veranstaltung ist Teil der Reihe Karlsruher Meteorologisches Kolloquium
Referent/in
Dr. Miklós Szakall

Universität Mainz
Institut für Atmosphärenphysik
Veranstalter
Institut für Meteorologie und Klimaforschung
Karlsruher Institut für Technologie (KIT)
Hermann von Helmholtz Platz 1
76344 Eggenstein-Leopoldshafen
Tel: 0721-608-0
E-Mail: sekretariat does-not-exist.imk-asf kit edu
Servicemenü

Hinweise

"CS" - KIT-Campus Süd (Universität), Gebäude 30.23 (Physikhochhaus), Seminarraum 13/2

"CN" - KIT-Campus Nord (Forschungszentrum), Gebäude 435 (IMK), Raum 2.05

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