Hydroxyl tagging velocimetry method optimization: signal intensity and spectroscopy

Area of Science:

• Fluid dynamics
• Laser-based diagnostics
• Combustion science

Background:

• Hydroxyl tagging velocimetry (HTV) is a proven nonintrusive technique for molecular velocity measurements.
• Previous demonstrations show HTV's capability in both room temperature and flame environments.

Purpose of the Study:

• To investigate and discuss the spectroscopy and relative signal intensities of different hydroxyl tagging velocimetry (HTV) read techniques.
• To determine implications for optimizing HTV performance in various conditions.

Main Methods:

• Utilized well-characterized jets of air (nonreacting) and hydrogen-air diffusion flames (reacting).
• Generated a 7x7 OH line grid via single-photon photodissociation of H2O using a 193 nm ArF excimer laser.
• Revealed the grid using a read laser sheet and fluorescence from specific OH transitions (A2sigma+(v'=3, 1, or 0) <-- X2pi(i)(v''=0)) at ~248, ~282, or ~308 nm.

Main Results:

• Presented a detailed analysis of the spectroscopy for different OH pumping schemes.
• Quantified and discussed the relative signal intensities associated with each read technique.
• Identified optimal conditions for HTV operation based on spectral and intensity data.

Conclusions:

• The choice of read laser wavelength significantly impacts signal intensity and HTV performance.
• Understanding the underlying spectroscopy is crucial for maximizing the effectiveness of HTV.
• HTV is a versatile tool for nonintrusive velocity measurements in diverse environments.