Particle Image Velocimetry Results

Initial PIV results of Swirler 304545 are presented to show the three-dimensional (3D) vector field and vorticity downstream of the nozzle with a 4-inch confining tube. These results were obtained by averaging 100 images, as the instantaneous images could not be used to discern the dominant structure of the flow field. The mean axial, tangential, and radial velocity components vorticity and 3D vector are shown in Fig. 10.7. 

The vorticity mapping (Fig. 10.7rf) suggests that the intense vortical region develops at 1.5-2 nozzle diameters downstream of the nozzle. This strong vortex could contribute to the stabilization of the flame. 

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Figure 10.7 Particle Image Velocimetry results on a streamwise plane downstream of Swirler 304545 at 68 scfm, 2-inch diameter exhaust nozzle, and Lmi = O" (a) mean axial velocity component (6) mean tangential velocity component (c) mean radial velocity component (d) vorticity and (e) 3D vector. (Refer color plate, p. VIII.)...

Figure 10.7 Particle Image Velocimetry results on streamwise plane downstream of Swirler 304545 at 68 scftn, 2-inch diameter exhaust nozzle, and (a)...

Recently Lin et al. (1996) applied the VOF method to study the time-dependent behavior of bubbly flows and compared their computational results with experimental data obtained with a particle image velocimetry (PIV) technique. In their study the VOF technique was applied to track several bubbles emanating from a small number of orifices. Lin et al. reported satisfactory agreement between theory and experiment. 

Fig. 20.3 Water currents generated by the courtship stationary paddling of male blue crab. View from above, the male performing courtship stationary paddling. Particle imaging velocimetry was used to visualize water currents generated by this behavior. Arrows indicate the direction of the currents, with the length of the arrows being proportional to the velocity. Results show that the water current was directed away from the male at a mean velocity of 3.1 cm/s. From Kamio et al. (2008), reproduced with permission of The Journal of Experimental Biology...

Various flow visualisation techniques have been utilised to obtain experimental results from local gas hold-ups and bubble size distributions (BSD) in a gas-liquid mixed tank. Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA), Capillary suction probe (CSP), High-speed video imaging (HSVI) and Electrical Resistance Tomography (ERT) techniques have been applied. The applicability of various techniques is dependent on the location of the measurement, the physical properties of the gas-liquid flow, the gas hold-up and the size of the tank. 

By confining the fluidized bed in one direction and using a translucent waU, visual access is restored so that the bed behavior can be studied fuUy and non-intrusively using optical techniques, such as particle image velocimetry (PIV) or digital image analysis (DIA), which are discussed in detail below. With these techniques, it is possible to obtain information on the instantaneous flow fields, but it remains difficult to translate the 2D results quantitatively to 3D. As a learning tool that allows to see and verify different aspects of the bed behavior (e.g., bubble size distribution, instantaneous particle fluxes) however, such techniques are unrivaled. The main focus of this chapter therefore lies on these optical techniques. 

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