SUBMERSIBLE PIV SYSTEM USING FIBER OPTIC LASER DELIVERY AND A DIGITAL CAMERA

摘要

A submersible particle image velocimetry (PIV) system for use in oceanographic field studies has been designed and built. The primary purpose of this instrument is to measure the characteristics of the continental shelf bottom boundary layer including the velocity profile, Reynolds stresses, vorticity distribution, dissipation and turbulence spectra. Fiber optic laser delivery is used in this system. The choice of a laser and optical fiber to transmit the large energies required for PIV imaging is discussed. The laser is a dual-head, flashlamp pumped dye laser which generates up to 350 mJ/pulse. The optical fiber has a core diameter of 400μm. To date, the highest energy output transmitted through this fiber without damage has been 126 mJ/pulse. The coupling and collimating optics required to avoid fiber damage and to maintain low output beam divergence are outlined. A digital camera with 1024×1024 pixel resolution (15 pairs of frames per second) is used for data acquisition. Other components of the system include: a digital compass and biaxial clinometer to provide an accurate reference frame; a high precision pressure sensor to give depth and wave height measurements; and a high-speed serial data link for data transmission and system control. The entire system is mounted on a hydraulic scissor jack and a motorized turntable to allow alignment with currents and traversing of the boundary layer.