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

Abstract

Abstract:In this article, we present an overview of the HyIV-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.

Adaptation of the meteorological model Meso-NH to laboratory experiments: implementations and validation

“…Unfortunately, due to budget cuts, the CNRM hydraulic flume was closed down, thus reducing the short-term prospects of this new numerical tool. However, there are still plans to use this tool in complement to past experiments conducted in this flume such as the one descrbied in Stiperski et al (2017). Moreover, other facilities conducting laboratory experiments are free to use our version of Meso-NH which can be downloaded on the website http://mesonh.aero.obs-mip.fr.…”

Computation of Density Perturbation and Energy Flux of Internal Waves from Experimental Data

“…Built in 1982, this flume was initially designed for applied studies of atmospheric flows over complex terrain. It soon became used for research purposes, in particular for studies [16][17][18][19] on internal waves and boundary layers. The present experiments were designed to study internal waves generated over multiple ridges.…”

Observation and simulation of mountain wave turbulence above Iceland: Turbulence intensification due to wave interference

“…The interaction and interference of mountain waves and their stability has previously been studied analytically (Grisogono et al ., 1993; Lee et al ., 2006), numerically (Vosper, 1996; Mayr and Gohm, 2000; Sharman and Wurtele, 2004; Grubišić and Stiperski, 2009; Stiperski and Grubišić, 2011) and in water tank experiments (Gyüre and Jánosi, 2003; Stiperski et al ., 2017). All these studies employed mountains that were distributed in the direction of the flow.…”