Water Tank Experiments on Stratified Flow over Double Mountain-Shaped Obstacles at High-Reynolds Number

Author(s)

Ivana Stiperski, Stefano Serafin, Alexandre Paci, Hálfdán Agustsson, Anne Belleudy, R. Calmer, Kristian Horvath, Christoph Knigge, Johannes Sachsperger, Lukas Strauss, Vanda Grubisic

Abstract

In this article,we present an overviewof theHyIV-CNRS-SecORo (Hydralab IV-CNRS-Secondary Orography and Rotors Experiments) laboratory experiments carried out in the CNRM (Centre National de Recherches Météorologiques) large stratified water flume. The experiments were designed to systematically study the influence of double obstacles on stably stratified flow. The experimental set-up consists of a two-layer flow in the water tank, with a lower neutral and an upper stable layer separated by a sharp density discontinuity. This type of layering over terrain is known to be conducive to a variety of possible responses in the atmosphere, from hydraulic jumps to lee waves and highly turbulent rotors. In each experiment, obstacles were towed through the tank at a constant speed. The towing speed and the size of the tank allowed high Reynolds-number flow similar to the atmosphere. Here, we present the experimental design, together with an overview of laboratory experiments conducted and their results. We develop a regime diagram for flow over single and double obstacles and examine the parameter space where the secondary obstacle has the largest influence on the flow. Trapped lee waves, rotors, hydraulic jumps, lee-wave interference and flushing of the valley atmosphere are successfully reproduced in the stratified water tank. Obstacle height and ridge separation distance are shown to control lee-wave interference. Results, however, differ partially from previous findings on the flow over double ridges reported in the literature due to the presence of nonlinearities and possible differences in the boundary layer structure. The secondary obstacle also influences the transition between different flow regimes and makes trapped lee waves possible for higher Froude numbers than expected for an isolated obstacle.

Organisation(s)

Department of Meteorology and Geophysics

External organisation(s)

National Centre for Meteorological Research, Icelandic Meteorological Office, Gottfried Wilhelm Leibniz Universität Hannover, National Center for Atmospheric Research (NCAR), Leopold-Franzens-Universität Innsbruck, MeteoServe Wetterdienst GmbH, Meteorological and Hydrological Service, Zagreb

Journal

Atmosphere

Volume

8

No. of pages

19

ISSN

2073-4433

DOI

https://doi.org/10.3390/atmos8010013

Publication date

01-2017

Peer reviewed

Yes

Austrian Fields of Science 2012

105206 Meteorology

Keywords

ASJC Scopus subject areas

Environmental Science (miscellaneous)

Portal url

https://ucrisportal.univie.ac.at/en/publications/0a992179-6c3d-4ad3-962a-3afdb47d50e5