CHAPTER 4
                  INTERFACE EDUCTION USING LIGHT SHEET

    This chapter describes a simple method used to characterize the air water interface of the facility under different combinations of air and water speeds. The results are helpful in determining the amount of fluctuations in the air-water surface at a particular condition. A measure of both root mean squared amplitude and slope are obtained using a high-resolution camera in conjunction with a pulsed laser light sheet. A simple edgedetection algorithm is employed to determine the location of the air-water interface. The aim is to educe quantitative information of the air-water interface.

                                Experimental Set-up

    The experimental set-up consists of a pulsed Nd:YAG laser and a digital camera (TSI model PIVCAM), as shown in Figure 4-1. The Nd:YAG and associated optics generate a thin light sheet (-Imm thick) required to illuminate the air-water interface. The camera resolution is 1016 by 1000 pixels and acquires image pairs that are synchronized with the laser. To enhance the scattering at the air-water interface, a fluorescent dye Eosine Y is used. Some of the critical parameters used with the laser and camera are listed in Table 4-1. A span of little less than 4.5 in. is covered (corresponding to the range of 5.5 in.-IO in. from the splitter plate), yielding a spatial resolution of 209 pixels/in. and 223 pixels/in. in horizontal and vertical world coordinates, respectively.

    As shown in the camera is Figure 4-1, the camera is positioned to obtain a perspective view of the air-water surface. A perspective view avoids an overlap between the desired