Planar Doppler Velocimetry for Large-Scale, Low-Speed Flows

The proposed effort will extend the capabilities of Planar Doppler Velocimetry (PDV) to enable measurement of flow fields 7 ft. x 7 ft. in area with a velocity resolution of 1 ft/s, providing a solution to the experimental characterization of large flow fields near parachute canopies and their wakes. The predicted improvements in velocity resolution come from increased well depths of state-of-the-art CCD cameras, which enable a greater range of photonic signal levels with an associated increase in signal-to-noise ratio, and from the use of continuous-wave (cw) lasers that allow signal averaging to eliminate speckle noise. PDV is ideally suited to large flow fields, since the technique does not require individual seed particles to be resolved, so the observation ranges are limited only by the signal levels obtained. Commercially available high-power, single-mode cw lasers now provide large enough signals for the extended ranges needed to cover large flow fields. Investigations during the Phase I effort have demonstrated that the desired velocity resolution should be achievable in a full-scale prototype.