engleski

Water tank experiments on stratified flow over double mountain-shaped obstacles at high-Reynolds number

We present an overview of the HyIV-CNRS-SecORo laboratory experiments carried out in the CNRM large stratified water flume. The experiments were designed to systematically study the influence of double obstacles on stably stratified flow. The experimental setup consisted of a two-layer flow in the water tank, with a lower neutral and an upper stable layer separated by a sharp density discontinuity. A series of 395 experiments performed for a range of Froude numbers Fr extending from 0.17 to 1.4, and for non-dimensional inversion heights H/Zi from 0.3 to 1.3, in the stratified water tank successfully reproduced the range of phenomena expected to occur with this type of layering, such as trapped lee waves, rotors, hydraulic jumps, lee wave interference and flushing of the valley atmosphere. Here we present the first results of the laboratory experiments with a special focus on lee wave interference and coupling between lee wave amplitude and rotor strength. 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. Particle-image velocimetry (PIV) is used to obtain the velocity field. 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 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.

water tank, stratified flow, obstacles

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