Changes between Version 58 and Version 59 of WikiStart

Sep 25, 2017, 10:36:18 AM (3 years ago)



  • WikiStart

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    494494Observations: The largest part of the current continued straight, but there was quite a strong return flow across the trough from the western corner of the trough to the southeastern corner of the trough.
     496== 7.11 Thursday 21 September ==
     497During the night, the tank was emptied. This day was used to fix the 5 probes for the vertical salinity profiles, they were set up and tested. The lower part of the source was covered with tape to only get a squared inflow. Then, the tank was filled up with salt water (density of 11.0 kg/m3) and turned into solid body rotation with T=50s.
     499== 7.12 Friday 22 September ==
     500Today, the baroclinic experiments started. The density of the inflow was 1.2 kg/m3 to get a density difference of 9.8 km/m3. We were told that it is easier to increase reduce the density difference by adding salt in the inflow than to decrease it (However, after all we can switch between the two quite easily). Due to the higher density, we used 60 micron particles in the ambient and the inflow water.
     502=== Experiment EXP29 ===
     503During this experiment, we started with a HS (20 min), run the profiles with the probes as soon as the inflow was established (while doing the HS) and did the vertical slice (2 min) and the scan afterwards.
     505The flow rate of 20 l/min (8.5mm diameter) gave a measured flow rate of 20 l/min.
     507Probes: downward velocity: 2 cm/s; upward velocity: 5 cm/s; break at the surface: 10s. In total 10 repetitions. The height of the probes are adjusted to follow the slope. They start about 20.5 cm above the slope so that only the probe furthest away from the coast touches the water, the others stay above the surface. During the profiles they get lowered by 19 cm.
     509Scans: 11 levels (55:-2:35) with 5 images at each level. dt = 100ms and dt1 = 1000ms. Exposure time was 30ms.
     511Observations: The flow was very fast and a nice clear front developed. In the beginning the water formed a vortex just after the first corner, and then most of the flow entered on the shelf between the first and the second corner. On the vertical slice, the front was clearly visible, but it was very steep, so that it may be above the laser sheets.
     513Note1: The vertical camera is too far up for the experiments with density difference, as the free surface is not visible. It will be put further down for the following experiments.
     515Note2:''' The second probe from the coast is not working properly!! '''
     517Note3: '''We have to remember that the source area is smaller and the flow therefore higher! '''
     519=== Experiment EXP30 ===
     520The flow rate was increased to 50 l/min (12.6mm diameter), which gave a measured flow rate of 53 l/min. The flow was very high and the dt therefore reduced to 50ms and Exposure time was reduced to 20ms after a few minutes (saved in Exp_B).
     522Probes: We kept the same setup as EXP29, but did now 20 profiles.
     524Observations: The flow turn onto the shelf at the second corner and followed the topography also on southern side of the topography. After a while, a vortex developed in the trough and parts of the main flow entered this vortex.
     526Note: In the beginning of the experiment, the water was still in motion from the previous experiment due to the density difference.
     528===  ===
     529=== Experiment EXP31 ===
     530The flow rate was increased even more to 80 l/min (14mm diameter), which gave a measured flow rate of 75 l/min. As in the previous experiment, the we always got too high flowrates for the 80 l/min - experiments with the 16mm diameter, we decided to now chose a smaller diameter. We were also concerned that it was not possible to do PIV with an ever faster flow, because it is not possible to use a dt < 50 ms and E<20!
     532Observations: All water turned onto the shelf at the 2nd corner and formed a vortex over the shelf. Some of the flow turned within the trough in a very wavy way (didn't follow the topography out of the trough again).
     534=== Experiment EXP32 ===
     535Now, we removed the corner and did an experiment with 50 l/min flow rate (12.6 mm), which gave 52 l/min. dt = 50ms, E=20ms.
     537Observations: The flow went straight around the 1st corner and followed the topography.
     539Notes: The water was still in motion in the trough from the previous experiment and due to the density difference. It looked like the particles started settling down, which may create vertical motion. It may be, that there was already a fresh water layer at the surface that influenced the flow, but also the laser height.
     541=== Experiment EXP33 ===
     542This experiment was with a low flow rate of 20 l/min and had to be stopped after a while as there was a too strong stratification. The laser then  got deflected downward at the interface between the two densities and was only about 1-0 cm above the topography on the shelf.
    496544  '''' ''6 - Table of Experiments: '''''