When designing an aerial application, it is critical to have accurate information on the size of droplets produced by an atomizer. To conform with ever-tightening regulations on pesticide use, atomizers must be configured to produce very specific droplet spectra depending on method of control, intended target and meteorological conditions. High confidence in the droplet spectrum for a given atomizer configuration allows an operator to optimize their program for specific situations, reducing the amount of product used and lessening environmental impact. Despite its significance, a droplet spectrum is difficult to measure directly in the field. Modern tanker aircraft fly at speeds in excess of 270 km/h and have atomizers mounted on a boom beneath the wing. This unfortunately makes a very poor platform for mounting droplet sizing instrumentation.

The H.J. Irving – J.J.C Picot Wind tunnel removes the problems associated with testing sprays on real aircraft in flight. It is an open-circuit, subsonic, aerodynamics research platform capable of mounting full-size spray delivery systems and testing droplet spectra for a variety of products at real aircraft speeds. By testing in the wind tunnel instead of the field, an applicator is able to test a small amount of product in a controlled environment to predict atomizer and droplet behaviour before a project is initiated.

The 1m diameter, 5m long test section and movable atomizer mount provide a platform for mounting popular brands of hydraulic, rotary and electrically powered atomizers. Precision electronic monitoring equipment continuously records and displays parameters such as wind speed, boom pressure, atomizer rpm, and product flow rate to ensure that these important parameters remain constant during a test. A variable frequency drive unit powers a 185 kW electric motor that turns the tunnel’s 9-blade, 1.4m axial flow fan, producing test-section speeds up to 288 km/h. At the tunnel output, a bank of high-efficiency moisture collectors remove droplets from the exiting airstream.

Droplet size distributions are measured using a Sympatec Helos-Vario/KF laser particle size spectrometer. This device is used to quickly sample the spray and calculate droplet size distributions based on scattering of laser light by the droplets in the spray. The Vario is mounted to a vertical axis traversing system and its laser beam is projected across the tunnel through glass viewports. This enables operators to move the Vario and measure different regions of the plume while the atomizer remains in a fixed location. With minimal knowledge of fluid properties, the Helos-Vario/KF can be used to accurately and repeatably determine the droplet size spectrum for a variety of products, existing and experimental.

In addition to providing droplet spectrum measurement services, Forest Protection Limited (FPL) is working with students and faculty at UNB on cutting-edge droplet research and the development of international standards. This is being done with the aid of a state-of-the-art 3D Phase Doppler Interferometer (PDI) from Artium Technologies. The 3D PDI is able not only to measure the size of droplets, but also their velocity in 3 dimensions. It is hoped through this research to gain a better understanding of fluid flow dynamics and droplet behaviour in the complicated and turbulent wake of atomizers.

The wind tunnel was placed in its current location in 2003 and underwent significant modification in 2008 with funding from FPL, the Atlantic Innovation Fund and SERG-I. The tunnel was inaugurated in 2008 and officially opened September 16, 2009.

To request information about the H.J. Irving - J.J.C. Picot Wind Tunnel and how it can help with your project, please contact us.