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0 0.05 0.1 0.15 0.2 0.25 0.3 60 64 68 72 76 80 84 88 92 96 100 104 d A [mm] N /N d Optical microscope Optical microscope Optical microscope Hologram Hologram SEM Pollen in water: Pollen in DC1: Dry pollen: Experimental study at increasing scales of the characteristics of corn (Zea Mays L.) pollen dispersal into the atmosphere R.van Hout, W. Zhu, J. Katz Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218 USA E-mail: [email protected], [email protected], [email protected] PIV flow measurements in a corn canopy At the field scale, PIV measurements just within and above a mature corn canopy provided vertical distributions of mean flow and turbulence parameters. Local isotropy was measured at scales smaller than 2m. Conditional sampled dissipation rate showed a strong correlation with the out-of-plane enstrophy, and only a weak correlation with the Reynolds shear stress. Turbulence production rate, on the other hand, showed weak dependence on small scale dynamics. van Hout, R., Zhu, W., Luznik, L., Katz, J., Kleissl, J., Parlange, M., 2005: PIV measurements in the atmospheric boundary layer within and above a mature corn canopy. Part A: Statistics and small scale isotropy. To be submitted to Journal of the Atmospheric Sciences. Zhu, W., van Hout, R., Katz, J., 2005: PIV measurements in the atmospheric boundary layer within and above a mature corn canopy. Part B: Quadrant Hole analysis. To be submitted to Journal of the Atmospheric Sciences. Setup Results: energy spectra 5 decades of length scales 3 decades inertial range Results: Quadrant-Hole Analysis Conditionally sampled dissipation rate ε H is strongly correlated with vorticity and weakly with the stresses and vice versa for the production. D H is conditionally sampled duration fraction. Acknowledgements: Mike Embry of the Wye Research and Education Center of the University of Maryland and to Mac Farms Inc. in Hurlock, MD, for generously granting us access to their corn field. Y. Rhonzes and S. King for design and technical expertise. L. Luznik for his help in carrying out the experiments. Wind tunnel study of canopy flow At intermediate scales, the structure of canopy turbulence was studied both in wind tunnel and in field experiments. A model canopy was placed inside a wind tunnel and PIV measurements of the flow structure were performed. Conditions were matched with those measured in the field. Setup Preliminary Results Good agreement between hot wire and PIV measurements Acknowledgements Brent Golden Joseph Kim Dr. H.S. Kang All JHU Lift and Drag coefficients A second system measured the drag and lift force on single pollen grains that are released into rotating Taylor Couette flow. Quadruple pulsed Particle Image Velocimetry (PIV) technique was applied to resolve the instantaneous velocities and the accelerations of the particles and the air, subsequently used to determine the drag and lift coefficients of these particles by balancing the forces acting on them. Setup of quadruple pulsed PIV Two cameras, 4 exposures Two perpendicularly Polarized Nd-YAG lasers Pollen injection mechanism releases pollen grains into annulus Preliminary results Counter-rotating cylinders, Constant outer cylinder Reynolds number Re o = 47000 and varying inner Reynolds number Re. Quadruple pulsed PIV images with Injected pollen grains have been acquired. Data processing is currently ongoing. Acknowledgements: Tim Garrison of York College, PA Tien Yi Cheng, JHU, MD Y. Rhonzes and S. King for the design and technical expertise. Method to measure pollen density At the pollen scale, a method was developed, based on Stokes flow settling, to measure the pollen density. By using two statistically similar particle batches in two different settling fluids (DC1 and 2), the particle density becomes only a function of settling velocity and fluid properties. van Hout, R., Katz, J., 2004: A method for measuring the density of irregularly shaped biological aerosols such as pollen. Aerosol Science 35, 1369-1384. Pollen Size distributions Setup Digital holography system to measure settling velocities. Results Acknowledgements Owen Loh, JHU Collimator Settling chamber Pollen Thermometer Kodak ES4.0 CCD camera (No lens) HeNe laser Focusing lens Spatial filter SEM Optical microscope Hologram Dry Dry DC1 Water DC1 Water N d 109 174 162 161 155 111 d A (µm) 71.2 78.1 79.6 89.2 83.6 93.1 σ d (µm) 4.7 3.6 3.4 3.8 5.0 4.3 1” Polarizing Beamsplitter Laser 1 Laser 2 Mirror Laser sheet optics Motor 2 Motor 1 Electric controls Pollen Laser sheet 2” Polarizing Beamsplitter Camera 1 Inner cylinder Outer cylinder Camera 2 Side view of camera setup Cam. 1 Cam. 2 2” Polarizing Beamsplitter Shear Generator Active grid Model corn field Uniform shear Uniform air velocity Stalks, h = 25cm Increasing length scales DC 1 DC 2 Deionized water N s 787 487 486 U s [mm/s] 1.40 2.89 0.48 σ s [mm/s] 0.16 0.31 0.08 ρ f [kg/m3] 827 at 19°C 766 at 20°C 998 at 20°C µ [kg/ms] 8.90x10 -4 at 19°C 5.13x10 -4 at 20°C 1.00x10 -3 at 20°C Re 0.10 0.34 0.04 Corn Pollen Density ρ p [kg/m3] 1.14x10 3 ± 0.05x10 3
