100  kHz krypton-based flow tagging velocimetry in a high-speed flow

Area of Science:

• Fluid dynamics
• Laser-based diagnostics
• Spectroscopy

Background:

• Traditional velocimetry methods struggle with high-speed and hypersonic flows.
• Laser-induced fluorescence (LIF) techniques offer potential for advanced flow measurements.
• Krypton (Kr) has been explored as a potential tracer for flow velocimetry.

Purpose of the Study:

• To demonstrate Krypton (Kr)-based tagging velocimetry at a high repetition rate (100 kHz).
• To identify an optimal Kr two-photon excitation wavelength for efficient and long-lived fluorescence.
• To enable time-resolved velocity measurements in high-speed gas flows.

Main Methods:

• Utilized a custom-built burst-mode laser and optical parametric oscillator (OPO) system operating at 100 kHz.
• Investigated Kr two-photon-excitation transitions, identifying 212.56 nm as optimal.
• Employed single-laser-pulse tagging and detected long-lived fluorescence (∼40µs) from N2 via energy transfer.

Main Results:

• Achieved efficient Kr-based velocimetry with a 100 kHz repetition rate laser system.
• Identified the 212.56 nm Kr two-photon transition for optimal tagging.
• Demonstrated successful time-resolved velocity tracking in a high-speed Kr/N2 jet flow.

Conclusions:

• Kr-based tagging velocimetry at 100 kHz is feasible for high-speed flow diagnostics.
• The long-lived N2 fluorescence enables velocity tracking without a second laser pulse.
• This technique is suitable for time-resolved measurements in challenging high-speed and hypersonic flow regimes.