PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article focuses particularly on the applications of PIV to turbulent open-channel flows, which have been conducted for the past decade in Hydraulics Laboratory of Kyoto University. In Section 2, we introduce our experimental setup and PIV/PTV algorithm. In Section 3, we apply the PIV measurements to reveal turbulence characteristics and coherent structures in open-channel flows as well as in vegetated canopy flows. For complex flow situations, various applications of PIV to compound open-channel flows and wind-induced water waves are considered to reveal coherent vortices. In Section 4, we discuss some advanced PIV measurements in open-channel flows. The free-surface-elevation fluctuations and velocity components were measured simultaneously with two sets of cameras to examine phase-averaged parameters of turbulence. A multi-layer scanning PIV was developed to reveal 3D turbulence structure in compound open-channel flows. Our discriminator PIV/PTV was applied successfully to sediment-laden open-channel flows and revealed the fluid/particle interaction and the relationship between coherent structures and sediment concentration. Finally, we conducted simultaneous measurements of velocity and dye concentration with a combination of PIV and LIF in vegetated open-channel flow, which enables us to examine turbulent scalar flux of a passive contaminant.     

Vertical mass and momentum transport in open-channel flows with submerged vegetations

The importance of flow and turbulence to the ecology of aquatic benthic organism has been widely reported. Aquatic vegetation is one of environmental variables that influence turbulence and the ecological condition of rivers. Aquatic canopies have the potential to greatly improve water quality through the removal of nutrients and trace metals. To describe the efficiency of this removal, we must be able to quantify the rate of vertical mixing. In fully submerged vegetation flows, coherent turbulent motions are generated near the vegetation edge and these large-scale eddies control the vertical exchange of mass and momentum. It is therefore important for river management to investigate hydrodynamic characteristics and coherent eddies in open-channel flows with vegetation canopies. Turbulence structure and transport mechanism of momentum in vegetated flows have been investigated intensively in the past decade.However, the effect of the submerged vegetation on the vertical mass transport and turbulent diffusion has not been fully investigated. Therefore, in the present study, continuous dye injection experiments were conducted to evaluate the mass transport structure in open-channel flow with rigid vegetation models by changing the vegetation density. A combination technique between PIV and planar laser-induced fluorescence (LIF) was developed by using two sets of CCD cameras, to measure the instantaneous velocity and concentration field simultaneously. The technique is capable of determining the turbulent scalar flux as well as the Reynolds stress, mean and fluctuating velocity and concentration fields. Consequently, the effects of coherent vortices on the vertical turbulent diffusivity were examined in detail.     

Industrial Policy in Japan

Japanese industrial policy had been well known to be about specific sectors and technologies. About 1990 economic growth stopped after decades of a remarkable process of catching up with the US. The potential to borrow technologies and ideas from other countries has become exhausted and Japan had to develop own technologies. The article descibes structural reforms in competition policy, corporate governance, management of intellectual property and mobility of researchers. Industrial policy has now more to do with horizontal policies and framework conditions than with targeting. Even if the “new economic growth strategy” – drawn up by the economics ministry [Ministry of Economy, Trade and Industry (METI)] and improved by government in 2006 – defines industrial areas with strong growth potential, these areas are obvious and there are no instruments available to promote them specifically. METI has become a proponent of government wide deregulation and will play as a leader of reforms.