MEASURING TURBULENCE IN A NATURAL BOUNDARY LAYER USING A FIELD-BASED PARTICLE TRACKING VELOCIMETRY SYSTEM (Invited Presentation)

Our capability to model and measure fluid flow and transport in aeolian field environments have steadily increased over the last decade. Improvements in modeling efforts using probabilistic modeling theory direct numerical simulations, and field-derived coefficients for semi-empirical models show the tremendous advancement in our ability to predict windblown sand. Instrumentation designed to measure fluid flow and aeolian transport in both wind tunnel and field environments have substantially improved in form factor, sampling frequencies, and the use of new, innovative techniques that provide higher resolution observations with minimal disruption to the process of aeolian transport. These improvements in modeling and measurement point to a severe need to relate turbulence to sand transport, particularly in field environments.

Here, we introduce F-PTV, a Field-based Particle Tracking Velocimetry system. The field-based system is capable of providing the first unobtrusive measurements of turbulence and the resulting sand transport by wind in a field environment and consists of 3 integral components: (1) an illuminated volume, (2) neutrally-buoyant seeding material in the form of helium bubbles, and (3) 4 high speed cameras. The laser beam is directed to the surface through a fiber-to-volume optics collimator and directs a defocused beam vertically down to create an ellipsoidal cone of light over the sampling area. Cameras capture the scattered light from helium bubbles and sand particles passing through the illuminated volume, enabling us to track individual helium bubbles and sand grains to resolve turbulence and transport in a natural boundary layer.