Session MA - Turbulent Boundary Layers V.
MIXED session, Tuesday afternoon, November 23
Grand I, Westin Seattle
Particle Image Velocimetry (PIV) measurements were performed in the turbulent boundary layer just above and within a mature corn canopy. Data were acquired at several heights, each at 4 Hz for 17min. The Kolmogorov length \textit\eta is about 0.4mm while the Taylor length scale is about 40mm. The Taylor microscale Reynolds numbers range between 2000-3000. The sample area is 18x18 cm, and the vector spacing is 2.8 mm. The mean flow profiles, Reynolds stresses, and turbulent flux (triple correlation) terms are consistent with those found in the literature. By combining the time series with the instantaneous velocity distributions we construct energy spectra that extend over 6 orders of magnitude of length scales. They exhibit an inertial range extending over three decades of wavenumbers. The small-scale spatial spectra reveal local isotropy for \textit\kappa _1\textit\eta > \quad \sim 10^-3. Quadrant-Hole analysis shows that the contribution of sweeps to the Reynolds stresses, dissipation and production are consistently higher than those of the ejections. Furthermore there is a strong correlation between conditionally sampled vorticity magnitude and dissipation. On the other hand, dissipation is only weakly correlated with the Reynolds stresses.
Sponsored by NSF.