Краткое описание

Flow visualization has been one of the most powerful techniques in experimental fluid mechanics for investigating qualitative aspects of coherent structures in turbulent shear flows. Various types of conditional sampling techniques for signals by the hot-wire velocimetry and the laser Doppler velocimetry (LDV) have been designed to provide quantitative information on detailed turbulence structures of flows. However, it is still hard to obtain structural information by the point-measurement due to the considerably large spatial extent as well as a random appearance of vortices. The recent development of computers and image processing systems have enabled researchers to obtain quantitative as well as qualitative data from the flow visualization simultaneously. Furthermore, a time-series measurement of whole flow field would be a powerful tool for analyzing and understanding the nature of turbulence. It is important for clarification of turbulent motion to investigate the spatial distributions of velocity fluctuations and the detailed structure of adjacent velocity fluctuations. For example, the instantaneous velocity vector and vorticity lead to clarify the relation between the coherent structure of a turbulent shear flow and the turbulent mixing.