Single-beam velocimetry with dual frequency comb absorption spectroscopy.

Area of Science:

• Fluid dynamics
• Spectroscopy
• Combustion science

Background:

• Laser absorption Doppler velocimetry (LADV) traditionally uses a crossed-beam configuration.
• This configuration complicates spatial interpretation due to sampling different gas volumes.
• Errors from laser frequency drift and absorption model uncertainty are inherent challenges.

Purpose of the Study:

• To develop and demonstrate single-beam velocimetry for improved spatial interpretation.
• To achieve high-frequency accuracy and stability in velocimetry measurements.
• To validate measurements in a supersonic ramjet engine environment.

Main Methods:

• Utilized a portable dual comb spectrometer (DCS) with GPS-referencing for high frequency accuracy and stability.
• Developed and employed a new high-temperature water vapor absorption database.
• Performed single-beam velocimetry measurements in a supersonic ramjet inlet flow.

Main Results:

• Demonstrated successful single-beam velocimetry measurements in a supersonic ramjet.
• Achieved average measurement differences of 19 m/s compared to concurrent crossed-beam measurements.
• Estimated DCS and database contributions to the measurement difference as 1.6 m/s and 13 m/s, respectively.

Conclusions:

• Single-beam velocimetry with DCS provides a viable alternative to crossed-beam methods.
• The developed system offers improved spatial interpretation and high accuracy.
• This technique has potential applications in advanced propulsion systems and high-temperature flow diagnostics.