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| Titel |
Effect of roughness and porosity on geometry and kinematics of lock-exchange gravity currents |
| VerfasserIn |
Elena Gatto, Claudia Adduce, Rui M. L. Ferreira |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152830
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| Publikation (Nr.) |
 EGU/EGU2017-17719.pdf |
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| Zusammenfassung |
| Gravity currents generated by lock-exchange are an important research tool to understand key
features of flows driven by a density may be naturally caused by interaction of geophysical
nature but may also be triggered by adverse anthropic actions, from oil spills to pollution
related turbidity. Research on the fundamental geometrical and kinematic features
of these currents is still necessary, especially when they propagate on complex
geometries.
The purpose of this work is to investigate the shape and the velocity of propagation of
gravity currents over rough beds and over rough-porous beds. To attain this objective,
different initial conditions were specified, namely smooth bed, rough bed composed of a
single layer of 2 mm glass beads and rough and porous bed composed of 4 layers of the same
beads.
The dimensions of the channel are 300 × 19,6 × 40 cm in which a steel gate is inserted to
define the lock. Two initial mixtures were tested: 1015 and 1030 kgm−3. The density is
measured with a pycnometer on a high precision balance. The mixture is composed of fresh
water, salt and rhodamine, to allow for visualization and measurements based on image
analysis.
A high-speed video system camera was used to record the motion of the current. The
camera has a 50 mm lens and a sampling frequency of 100 fps. Gray-level images were
obtained with 8 bit depth. Calibration of gray-levels was performed pixel by pixel to mixture
concentrations. The current is examined in three positions: immediately after the gate
((x−x0)∕x0 = 0 to 3), in the middle ((x−x0)∕x0 = 5 to 8) and at the end of the
channel((x − x0)∕x0 = 10 to 13).
It is shown that the celerity of the gravity current wave front varies with the different
boundary conditions. Indeed, the current is faster for the smooth bed and slower for the rough
bed conditions. No appreciable effects of porosity were registered on the wave celerity. The
shape of the current varied slightly between the rough and the porous-rough tests, indicating a
minor loss of mass to the porous bed.
Acknowledgements
This research was partially supported by Portuguese and European funds, within
programs COMPETE2020 and PORL-FEDER, through project PTDC/ECM-HID/6387/2014
and Doctoral Grant SFRH/BD/97933/2013 granted by the National Foundation for Science
and Technology (FCT). |
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