Session Cj - Experimental Techniques.
ORAL session, Sunday, November 23
310, Moscone Center
An off-axis holographic PIV system has been developed for the study of turbulence and complex flow phenomena. An automated image processing system is used for measuring the velocity distribution of a fully developed turbulent flow in a square duct at Re_h = 1.23 \times 10^5. A single 3-D vector map consists of 97x97x87 vectors. Improvements in analysis procedures using image compression enable reconstruction of the hologram at a magnification of 500 pixels/mm and about 100 pixel displacements between exposures, improving accuracy without payoffs in analysis time. The data is used in a study of subgrid-scale motion and modeling. The 3-D structure of fields such as subgrid dissipation and subgrid stress divergence is evaluated, giving a significantly more complete picture than our previous 2-D studies. As a preliminary step, it is shown that quantities such as the mean energy dissipation, its modeled counterpart using existing models such as the Smagorinsky and similarity models, and correlation coefficients, are in the expected range of values. Qualitative observations on the structure of the SGS force field are made.