A visualization of airflow pattern around a maize plant --Cheng, WY, Cheng, PC, Walden, DB In order to study the airflow pattern around different organs of a maize plant, a small wind tunnel was constructed (Figure 1a). Three 16-inch box fans were stacked in series to provide different airflow velocities. Laminar flow was achieved by using a honeycomb panel constructed by using 5mm McDonaldR plastic beverage straws (Figure 1a). A Kestrel 3000 anemometer (Nielsen-Kellerman, Chester, PA) was used to determine the air velocity. Two 15cm spherical mirrors (f=150cm 1/10l) were used to construct a Schlieren optical set-up (Edmund Optics Inc., NJ) (Figure 1b). A 100W Hg lamp (XBO) was used as the light source; a SonyTM camcorder operated in night-vision mode with built-in IR illuminator disabled was used to acquire the Schlieren images (Figure 1c). Acetone vapor was generated and ejected from a set of specially made nozzles in the air stream. The acetone vapor has a different reflective index from surrounding air, hence it can be easily delineated from the surrounding air. Plants were placed downstream from the nozzle in the wind tunnel, and rotated to allow a study of multiple wind directions.

At 3 km/h and 4.6 km/h breeze conditions, a significant updraft flow pattern and turbulence were detected when the lamellar airflow encountered leaf blades (Figure 2b, 2c, 2d, and 2e, arrows). The turbulence in the leeward side suggests significant drag acting on the plant. We have also observed an interesting turbulent pattern occurring at the tassel region of the plant (Figure 2f, 2g, arrows). This turbulence caused the tassel and the dehiscing anthers to vibrate even at low wind velocities and, in conjunction with the leaf-generated updraft, may play an important role in the efficient dispersing of pollen grains. The leaf-generated updraft may also minimize pollen deposition on the surface of the leaf. Downward draft can be observed only at the basal part of a leaf blade; this downward draft may assist the airborne pollen grains attaching to the silk.

Due to the limitations on the size of the mirrors and the wind tunnel, our Schlieren optical study can only be performed on young plants and isolated plant parts such as the tassel. Nevertheless, the results demonstrate the potential application of Schlieren optics to the study of aerodynamic response and pollen dispersion of maize.

This article is part of a report by WYC for Siemens Westinghouse Science and Technology Competition (Semi Finalist) and Intel Science Talent Search (2001).

Figure 1. (a) Wind tunnel with straw plate and nozzle. (b) Schlieren optics layout, (c), Schlieren optical setup.

Figure 2. (a-g), Airflow pattern around a plant, L: leaf, T: tassel, white arrows: turbulence flow.
 
 


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