VELOCITY-MEASUREMENTS BY FLOW TAGGING EMPLOYING LASER-ENHANCED IONIZATION AND LASER-INDUCED FLUORESCENCE

A new flow tagging technique for measurements of gas velocities over a wide range of flow conditions is proposed. This method employs the la ser-based spectroscopic techniques of laser-enhanced ionisation (LEI) and laser induced fluorescence (LIF). Initially the flow to be studied is seeded with a small amount of sodium. The flow is then tagged by u tilising LEI to deplete a substantial fraction (80%) of the neutral so dium species in a well defined region upstream of the flow. Finally, s ingle laser pulse planar LIF is used to create a two-dimensional (2D) inverse image of the depleted tagged region downstream of the flow at a specific time delay. The feasibility of this method was demonstrated in two different types of air-acetylene flame by measuring instantane ous 2D flow structures. Flame velocities were determined with an accur acy of better than 10%.