Experimental and Numerical Study of Swirling ... - Solid Mechanics

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Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Chapter 3 mounted, is not fitted with the traverse. Laser cavity and cameras are mounted on the same traverse with their positions fixed relative to each other. Thus the traverse moves only laser and the cameras at the required measuring planes in axial direction (Z-axis). 3.5.1 Alignment and Calibration The NewWave ® Solo Nd:Yag pulse laser device (120 mJ pulses @ 15 Hz, Wavelength 532 nm) is mounted on the traverse in a way that the laser sheet is perpendicular to the cylinder. The laser sheet is aligned with the laser light reflected from the cylinder wall. This ensures that the laser sheet is perpendicular to the cylinder. Two Dantec HiSense cameras with 1344 x 1024 pixels and pixel size of 6.45μm are equipped with 60 mm focal length lenses and green light filters. Both cameras, mounted on the same traverse, are at one side of the laser sheet and the cylinder is placed between the two cameras (Figure 3.13). The calibration target is attached on a disc of same diameter as the internal diameter of the cylinder and is slided inside the test cylinder. The calibration target is kept aligned with the laser sheet at only one of the measuring cross-sectional position and considering the test cylinder being axially aligned; same calibration is used for all the other measuring cross-sections. The cameras were focused on a rectangular target plane within the pipe diameter, avoiding measurements close to the cylinder wall due to strong reflections of the laser light. In order to capture all the measuring positions, two position configurations for the cameras are used (Figure 3.10). Due to angle of view, for the measuring positions near the outlet in camera configuration 1, camera view is blocked by the cylinder outlet wall and thus configuration 2 is used. For each configuration, calibration is performed at single measuring position. Dantec DynamicStudio® software is used for PIV measurements and data processing. Calibration was performed using 3rd Order XYZ-Polynomial Imaging model which is capable of handling distortion caused by the lens or curved windows (DynamicStudio ® user manual). In order to account for the possible misalignment of the calibration target with the laser sheet, disparity error correction is performed. For configuration 2, calibration and calibration refinement processes are repeated and is used only for the positions near the outlet. One half of the test cylinder wall behaves like a concave reflecting surface and laser light reflections from the internal walls make a very bright spot near the concave wall facing the laser light (Figure 3.14). This will increase uncertainty in the measurement in that region. The F-number is set to 8 for the camera receiving the forward scatter and for the camera receiving the backward scatter, F-number is set to 4. 42 Experimental Setup
Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging Processs for 2-Stroke Marin ne Diesel Engin nes Figu ure 3.14: Wall Reflection Effect t on PIV im mages (View from m Backw ward Scatter Came era. Cylinder wall locati ion is an illustrat tion and not n in true scale.) ) Figu ure 3.15: Seedin ng Setup Illustr ration. Cylinder wall 3.5.2 Seeding g Setup Chapter 3 The see ed generator co ontains 75/25 % by volumee glycerol-Watter solution annd size dist tribution of se eeding dropletts is in range oof 2-3 μm. Forr a uniform annd adequat te seeding, th he particles shhould mix prooperly with thhe incoming aair entering g the inlet sec ction. For this purpose a meetal frame, diaameter 860 mm and wid dth 150 mm, is mounted aroound the inlett section (Figuure 3.15). 43 Experimental Setup
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DTU Mechanical Engineering Section
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Experimental and Numerical Study of Swirling ... - Solid Mechanics

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