Changes between Version 253 and Version 254 of WikiStart


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Oct 21, 2016, 3:55:19 PM (7 years ago)
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peakall3je
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    121121'''Particle Imaging Velocimetry (PIV)'''
    122 A Spectra-Physics xxxx laser in conjunction with 3 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the floor of the channel. The light sheet can then be racked in the vertical through a series of steps through the use of a motorized traverse (tilted at 3.5 degrees to match the slope of the channel) and a mirror; the laser is pointed down at the mirror producing the light sheet. The laser light sheet positions are then synchronized with the PIV cameras. The field of view extends from close to the upstream end of the first bend, towards the mid-point of the second bend. Later experiments used larger seeding particles, 200 micron polystyrene particles for the flow seeding. These work very well for these situations where the measurement area is larger than 2 square metres. The PIV cameras consist of one Dalsa camera and two PCO cameras. These use xxx objective lenses.
     122A Spectra-Physics Millennia ProS 6W YAG continuous laser (532 nm) in conjunction with 3 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the floor of the channel. The light sheet can then be racked in the vertical through a series of steps through the use of a motorized traverse (tilted at 3.5 degrees to match the slope of the channel) and a mirror set at 45 degrees. The laser has another set of optics to point the light sheet down at the mirror, producing the light sheet. There is a glass window that enables the laser beam to go through the surface of the water tank. A 3D animation of the laser is in the ‘videos’ subfolder of the Photos folder. The laser light sheet positions are then synchronized with the PIV cameras. The field of view extends from close to the upstream end of the first bend, towards the mid-point of the second bend. Later experiments used larger seeding particles, 200 micron polystyrene particles for the flow seeding. These work very well for these situations where the measurement area is larger than 2 square metres. The three PIV cameras consist of one Falcon1 camera (Falcon 4M, CMOS 2432*1728 pixels, 10 bits) over the upstream part – with a 35 mm objective lens, PCO2 over the first bend with a 35 mm objective lens, and PCO3 over the most downstream part of the PIV measurement area, which has a 20 mm objective lens. 15 slices in the vertical are taken, and these are repeated multiple times. The two PCO cameras are PCO.edge5.5 CMOS cameras (2560*2160 pixels). The general approach is to have the lowest slice at approximately 2 cm above the floor, and then there are 2.5 cm heights between each successive level. These varied over time however, so there are a number of slightly different setups – see below. The sequence starts at the highest point, and then steps down through the flow, to the bottom, before switching back to the top again. Heights of laser slices [22/09/16 – 2.5 cm but after that 12/10/2016 and 14/10/2016 and 19/10/2016 all at basal 2 cm.
    123123
    124124== 3.2 Definition of time origin and instrument synchronisation ==
    125125
    126 This section relates to the main experiments, and not the test experiments (see diary entries for details of earlier experiments). Conductivity as measured in the inlet box (Probe C1) is seen to vary initially due to mixing within the input box, and because a higher input rate is used in the first minute of the experiment (~11-13 L/s in the main experiments – see Section 6) than later in the flow (~6 L/s). This initial pulse is intended to help to clear fluid out of the inlet box. The time origin is judged to be that point at which the value of this conductivity probe (C1) becomes approximately constant. The timings and synchronisation of the ADV, UVP and the Siphons are controlled with the aid of a stopwatch which is started at the time origin. PIV is then initiated soon after the time origin (approximately 0 minutes) to approximately 10 minutes run time. The timing of PIV initiation can be determined retrospectively, relative to the time origin, because the traverse initiation (that runs the ADV) is specifically linked to the time origin (ADV measurements start at 15 minutes and runs to 35 minutes), and both the traverse and the PIV are tied into the main control software. Thus knowing the time difference between the traverse initiation and the PIV initiation, and subtracting this from 15 minutes provides the PIV initiation relative to the time origin. The UVP and Siphon data are independent as their outputs are not directly tied into the Coriolis control software in the same way that the traverse is. Siphons are initiated after 5 minutes, and the cross-stream UVPs are started at 5 minutes (run until 15 minutes), whilst the downstream UVPs are started at 25 minutes are run until 35 minutes. For 19/10 and 20/10 files the start of the PIV integrates directly with the time origin, all other aspects as before.
     126This section relates to the main experiments, and not the test experiments (see diary entries for details of earlier experiments). Conductivity as measured in the inlet box (Probe C1) is seen to vary initially due to mixing within the input box, and because a higher input rate is used in the first minute of the experiment (~11-13 L/s in the main experiments – see Section 6) than later in the flow (~6 L/s). This initial pulse is intended to help to clear fluid out of the inlet box. The time origin is judged to be that point at which the value of this conductivity probe (C1) becomes approximately constant. The timings and synchronisation of the ADV, UVP and the Siphons are controlled with the aid of a stopwatch which is started at the time origin. PIV is then initiated soon after the time origin (approximately 0 minutes) to approximately 10 minutes run time. The timing of PIV initiation can be determined retrospectively, relative to the time origin, because the traverse initiation (that runs the ADV) is specifically linked to the time origin (ADV measurements start at 15 minutes and runs to 35 minutes), and both the traverse and the PIV are tied into the main control software. Thus knowing the time difference between the traverse initiation and the PIV initiation, and subtracting this from 15 minutes provides the PIV initiation relative to the time origin. The UVP and Siphon data are independent as their outputs are not directly tied into the Coriolis control software in the same way that the traverse is. Siphons are initiated after 5 minutes, and the cross-stream UVPs are started at 5 minutes (run until 15 minutes), whilst the downstream UVPs are started at 25 minutes are run until 35 minutes. For 19/10 and 20/10 files the start of the PIV integrates directly with the time origin, all other aspects as before. For PIV analysis, the time origin of the experiment is worked out from the C1 conductivity probe in the input box, where it exhibits the initial sharp rise (near instantaneous) as the flow input starts.
    127127
    128128== 3.3 Requested final output and statistics ==
    129 Batch processed camera data in to .png files for those experiments from 18-43 that have PIV data, so that images are in a non-proprietary format. PIV analysis of the flow field through multiple horizontal slices in different Z-positions, for the non-rotating case, and for the rotating cases (experiments 18-43 as above), dependent on the quality of the captured PIV images.
     129Batch processed camera data in to .png files for those experiments from 18-43 that have PIV data, so that images are in a non-proprietary format. PIV analysis of the flow field through multiple horizontal slices in different Z-positions, for the non-rotating case, and for the rotating cases (experiments 18-43 as above), dependent on the quality of the captured PIV images. Average velocity vectors for the channel slices. Potentially information on vorticity would enable the smaller-scale vortical structures that are some obvious in the videos, to be identified.
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    131131[[BR]]
     
    141141 * 0_DOC: miscellaneous documentation and reports
    142142 * 0_MATLAB_FCT: specific matlab functions
    143  * 0_PHOTOS: photos of set-up
     143 * 0_PHOTOS: photos of set-up
     144 * •    0_PIV
     145  * o   Each ‘PIV’ folder contains subfolders for each of the 3 PIV cameras: Dalsa (sometimes Falcon1 – it’s the same thing); PCO2; PCO3 [these are named after the different brands of camera]. Other folders include PCO2.png and PCO3.png which contain processes images of the PCO cameras that are in a non-bespoke format. Other folders that can be within the Camera folder include: Dalsa.sback; Dalsa.sback_1; PCO2.png.civ; PCO2.png.civ_1; PCO2.png.civ_2; PCO2.png.sback: PCO2.png.sback_1; PCO3.png.sback_1. .sback files refer to those files where the background has been subtracted, then civ_1 contains images with the first PIV iteration as processed in UVMAT (Joel’s code) and shows the raw data – with or without the rejected vectors; vectors are shown in four colours, blue = best, green = medium, red = poor, and pink = false. A box can be clicked to hide the false vectors. Civ_2 uses a spline interpretation to interpolate between vectors, so long as they are close enough to the surrounding vectors. Then interpolates all the vectors onto a regular grid. Times for the .png images are in the XML files, or netcdf files.
     146 
    144147 * 0_Processing: UVP processing scripts in Matlab
    145148 * 0_REF_FILES: files of general use (calibration data, grids ...)