Simulating spray deposition on plant canopies within a wind tunnel

Three-dimensional computer modelling techniques are being used to develop a probabilistic model of turbulence-related spray transport around various plant architectures to investigate the influence of plant architectures and crop geometry on the sprayapplication process. Plant architecture models that utilise a set of growth rules expressed in the Lindenmayer systems (L-systems) formalism have been developed and programmed using L-studio software. Modules have been added to simulate the movement ofdroplets through the air and deposition on the plant canopy. Deposition of spray on an artificial plant structure was measured in the wind tunnel at the University of Queensland, Gatton campus and the results compared to the model simulation. Further trials are planned to measure the deposition of spray droplets on various crop and weed species and the results from these trials will be used to refine and validate the combined spray and plant architecture model.

Measurement of the aerodynamic performance of a scramjet-powered vehicle in a shock tunnel

A force balance system for measuring lift, thrust and pitching moment has been used to measure the performance of fueled scramjet-powered vehicle in the T4 Shock Tunnel at The University of Queensland. Detailed measurements have been made of the effects of different fuel flow rates corresponding to equivalence ratios between 0.0 and 1.5. For proposed scramjet-powered vehicles, the fore-body of the vehicle acts as part of the inlet to the engine and the aft-body acts as the thrust surface for the engine. This type of engine-integrated design leads to a strong coupling between the performance of the engine and the lift and trim characteristics of the vehicle. The measurements show that the lift force increased by approximately 50% and centre-of-pressure changed by approximately 10% of the chord of the vehicle when the equivalence ratio varied from 0.0 to 1.0. The results demonstrate the importance of engine performance to the overall aerodynamic characteristics of engine-integrated scramjet vehicles and that such characteristics can be measured in a shock tunnel.

Dispersal of soredia from individual soralia of the lichen Hypogymnia physodes (L.) Nyl. in a simple wind tunnel

Dispersal of soredia from individual soralia of the lichen Hypogymnia physodes (L.) Nyl. was studied using a simple wind tunnel constructed in the field. Individual lobes with terminal soralia were placed in the wind tunnel on the adhesive surface of dust particle collectors. Air currents produced by a fan were directed over the surface of the lobes. The majority of soredia were deposited within 5 cm of the source soralium but some soredia were dispersed to at least 80 cm at a wind speed of 6 m s-1. Variation in wind speed had no statistically significant effect on the total number of soredial clusters deposited averaged over soralia but the mean size of cluster and the distance dispersed were greater at higher wind speeds. The number of soredia deposited was dependent on the orientation of the soralium to the air currents. More soredia were deposited with the soralium facing the fan at a wind speed of 9 m s-1. Moisture in the form of a fine mist reduced substantially the number of soredia deposited at a wind speed of 6 m s-1 but had no effect on the mean number of soredia per cluster or on the mean distance dispersed. The data suggest: (1) that wind dispersal from an individual soralium is influenced by wind speed, the location of the soralium on the thallus and the level of moisture and (2) that air currents directed over the surfaces of thalli located on the upper branches of trees would effectively disperse soredia of H. physodes vertically and horizontally within a tree canopy. © 1994.