Air resonance enhanced multiphoton ionization tagging velocimetry

Area of Science:

• Aerodynamics and Fluid Mechanics
• Laser-Based Diagnostics
• Spectroscopy

Background:

• Accurate flow velocity measurements are critical for understanding aerodynamic phenomena.
• Traditional velocimetry techniques can be intrusive or limited in certain flow regimes.
• Laser-based methods offer non-intrusive alternatives for flow characterization.

Purpose of the Study:

• To demonstrate and characterize a novel flow tagging velocimetry technique: Air resonance enhanced multiphoton ionization (REMPI) tagging velocimetry (ART).
• To validate ART's capability for pointwise velocity measurements in both quiescent and supersonic flows.
• To investigate the fundamental physics and parameters influencing ART performance.

Main Methods:

• Utilized a wavelength-tunable laser to selectively ionize molecular oxygen via resonance-enhanced multiphoton ionization (REMPI).
• Induced avalanche ionization in molecular nitrogen, generating fluorescence from nitrogen bands.
• Analyzed fluorescence emissions for flow tagging and performed pointwise velocity measurements in a Mach 1.5 supersonic nozzle flow.

Main Results:

• Successfully demonstrated ART velocimetry in quiescent and supersonic flow environments.
• Characterized key aspects including oxygen resonance effects, nitrogen fluorescence spectrum, minimal flow perturbation from laser energy deposition, and fluorescence lifetime.
• Achieved pointwise velocity measurements in a Mach 1.5 supersonic flow.

Conclusions:

• Air resonance enhanced multiphoton ionization (REMPI) tagging velocimetry (ART) is a viable technique for non-intrusive flow velocity measurements.
• ART shows promise for applications in both low-speed and high-speed aerodynamic research.
• Further characterization confirms the robustness and potential of ART for advanced flow diagnostics.