Particle Image Velocimetry (PIV) is an ideal technique to characterize turbulent flow structures at smaller scales, such as the dissipation rate of turbulent kinetic energy (TKE), rate of strain, and vorticities. It is, however, difficult to be adapted to field studies due to the requirement of high power lasers, high performance CCD cameras and full-fledged image acquisition computer systems, which are not suitable for submersible configurations. The PI's propose an alternative solution by using a class IIIb Diode Pumped Solid State (DPSS) laser which is powered by batteries. A light sheet is created by steering the continuous-wave laser beam through a rotating mirror, thus ensuring adequate light energy for illuminating small particles (~10 mm to ~100 mm) in natural waters while at the same time keep the exposure time of particle short to avoid blurred images. A preliminary system has been built with an ultra-mobile computer and a USB-based signal generator.
The PI?s propose to improve the prototype UWMPIV system, so it can measure flows with higher speed and turbulence level and can adapt its orientation with shifting mean flow direction to avoid measurement error induced by out-of-plane motions. The improved system will be compact, versatile and allow for long-term observations (several days). The UWMPIV will be set up as a free-floating system that measures the vertical profiles of small-scale turbulence structures, including the dissipation rate, enstrophy and surface divergence immediately below the air-water interface. The purpose is to provide understanding of free surface turbulence and its effects on gas transfer through the air-water interface.
Broader Impacts:
The PIs do a very good job of outlining how this compact in-situ PIV system will be used in education and public outreach. As well as being used for labs and case studies in various civil engineering courses, the proposal has money for two graduate students. The collaboration with Discovery World at Pier Wisconsin sounds like an excellent opportunity to reach the public. PIV could provide a very different perspective of ocean flows, as it resolves 2D fields with exceptional detail. This is very seldom achieved with typical ocean observations, which are generally sparse.
