Abstract:The laser Doppler technique, most frequently referred to as a laser Doppler anemometer (LDA) or laser Doppler velocimeter (LDV), is a wide‐spread technique for point‐wise velocity measurements in a flow with fluid markers. Some decisive advantages of the technique over more conventional probe‐based techniques can be mentioned: non‐intrusiveness, directional sensitivity, high spatial and temporal resolution, and high accuracy. In this chapter the fundamental principles of laser Doppler velocimetry will be intro… Show more
“…An advantage of the above described pulse-shadowgraphy technique is its ability to measure droplets independent of its sphericity and the liquid being transparent, while these conditions are mandatory for the conventional laser-based techniques. 33 The technique is well-suited in the present case where nonspherical droplets are obtained since the rotational speed is low (≤10,000 rpm), and in such case popular techniques such as phase Doppler particle analyzer or PDPA and interferometric laser imaging for droplet sizing or ILIDS are not suitable since their application is restricted to spherical droplets.Figure 3.(a) Gray scale raw shadowgraph image, (b) corresponding processed binary image, and (c) identified droplets and their size in the binary size (in μm).Figure 4.Influence of defocusing on imaging the calibration plate. Detected dots at (a) the best focal plane, (b) 0.25 mm linear distance away from the best focus plane (maximum DoF for 50 μm dot), (c) 0.5 mm linear distance away from the best focus plane (maximum DoF for 100 μm dot), and (d) 1.75 mm linear distance away from the best focus plane (maximum DoF for 250 μm dot).…”
Section: Methodsmentioning
confidence: 99%
“…An advantage of the above described pulse-shadowgraphy technique is its ability to measure droplets independent of its sphericity and the liquid being transparent, while these conditions are mandatory for the conventional laser-based techniques. 33 The technique is wellsuited in the present case where nonspherical droplets are obtained since the rotational speed is low (≤10,000 rpm), and in such case popular techniques such as phase Doppler particle analyzer or PDPA and interferometric laser imaging for droplet sizing or ILIDS are not suitable since their application is restricted to spherical droplets.…”
Section: Droplet Sizing By Pulse-shadowgraph Imaging Techniquementioning
The ability of the rotary slingers to achieve fuel atomization by employing the rotational speed of the turbine shaft obviates the use of high-pressure fuel pump and makes those a popular choice for small gas turbine engines. Such atomizers contain arrays of orifices on their outer periphery for injection of the liquid into the combustion chambers. In the present work, we experimentally investigate the influence of the choice of orifice size on primary liquid breakup dynamics and spray characteristics in slinger atomizers. Three slinger discs with the same disc size and number of orifices but with different orifice size, d o (= 1 mm, 1.5 mm, and 2 mm) are examined in a high-speed slinger test rig for a range of rotational speed (2000–10,000 rpm) and liquid feed rate (0.2–1 lpm). The operating conditions are relevant to part-load and engine relighting conditions for which the selection of geometric parameters of the injector may play a crucial role in achieving the atomizer performance. In the current work, the liquid breakup process in the vicinity of the slinger orifices was visualized using front light illumination technique, whereas the pulse-shadowgraph technique was employed for droplet sizing. It is found that smaller orifice size promotes column mode of liquid breakup which results in larger primary liquid breakup length and subsequently results in larger Sauter mean diameter. The results highlight that the orifice size is an important design parameter as the liquid atomization in slinger atomizers is sensitive to the selection of orifice size especially for lower range of rotational speeds.
“…An advantage of the above described pulse-shadowgraphy technique is its ability to measure droplets independent of its sphericity and the liquid being transparent, while these conditions are mandatory for the conventional laser-based techniques. 33 The technique is well-suited in the present case where nonspherical droplets are obtained since the rotational speed is low (≤10,000 rpm), and in such case popular techniques such as phase Doppler particle analyzer or PDPA and interferometric laser imaging for droplet sizing or ILIDS are not suitable since their application is restricted to spherical droplets.Figure 3.(a) Gray scale raw shadowgraph image, (b) corresponding processed binary image, and (c) identified droplets and their size in the binary size (in μm).Figure 4.Influence of defocusing on imaging the calibration plate. Detected dots at (a) the best focal plane, (b) 0.25 mm linear distance away from the best focus plane (maximum DoF for 50 μm dot), (c) 0.5 mm linear distance away from the best focus plane (maximum DoF for 100 μm dot), and (d) 1.75 mm linear distance away from the best focus plane (maximum DoF for 250 μm dot).…”
Section: Methodsmentioning
confidence: 99%
“…An advantage of the above described pulse-shadowgraphy technique is its ability to measure droplets independent of its sphericity and the liquid being transparent, while these conditions are mandatory for the conventional laser-based techniques. 33 The technique is wellsuited in the present case where nonspherical droplets are obtained since the rotational speed is low (≤10,000 rpm), and in such case popular techniques such as phase Doppler particle analyzer or PDPA and interferometric laser imaging for droplet sizing or ILIDS are not suitable since their application is restricted to spherical droplets.…”
Section: Droplet Sizing By Pulse-shadowgraph Imaging Techniquementioning
The ability of the rotary slingers to achieve fuel atomization by employing the rotational speed of the turbine shaft obviates the use of high-pressure fuel pump and makes those a popular choice for small gas turbine engines. Such atomizers contain arrays of orifices on their outer periphery for injection of the liquid into the combustion chambers. In the present work, we experimentally investigate the influence of the choice of orifice size on primary liquid breakup dynamics and spray characteristics in slinger atomizers. Three slinger discs with the same disc size and number of orifices but with different orifice size, d o (= 1 mm, 1.5 mm, and 2 mm) are examined in a high-speed slinger test rig for a range of rotational speed (2000–10,000 rpm) and liquid feed rate (0.2–1 lpm). The operating conditions are relevant to part-load and engine relighting conditions for which the selection of geometric parameters of the injector may play a crucial role in achieving the atomizer performance. In the current work, the liquid breakup process in the vicinity of the slinger orifices was visualized using front light illumination technique, whereas the pulse-shadowgraph technique was employed for droplet sizing. It is found that smaller orifice size promotes column mode of liquid breakup which results in larger primary liquid breakup length and subsequently results in larger Sauter mean diameter. The results highlight that the orifice size is an important design parameter as the liquid atomization in slinger atomizers is sensitive to the selection of orifice size especially for lower range of rotational speeds.
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