A non-intrusive dye-based color differentiation technique for particle tracking velocimetry (PTV) in large-scale air flows

摘要

This paper describes a novel method for measuring large-scale airflows using a photographiic color PTV technique with neutrally buoyant bubbles. It is intended for measuring instantaneous entrained air velocities in large-scale sprinkler and fire-induced flows. The technique uses two Nd:YAG laser pulses, the first of which is a 532nm (green) pulse and the second is a 3ttnm (UV) pulse. Directional ambiguity in the velocity measurements is eliminated through the use of color differentiation. Color differentiation is accomplished byusing a fluorescent dye in the bubble solution that makes them fluoresce in the yellow-green with the green laser sheet and in the blue with the UV laser sheet. This method is much more efficient and convenient as The use of small neutrally buoyant bubbles (approx 2mm dia.) as seed particles and high-resolution color photography also enables PTV measurements over a large area ( approx 1m x 1m). Problems encountered due to widely different intensities of the green and the UV beams were solved by synchronizing the camera shutter. A generalization of this technique is presented so that it can be effectively used in both high and low velocity airflows. This technique is validated by making a ir entrainment measurements in classical axisymmetric jet flows.