Dotted-line FLEET for two-component velocimetry

Area of Science:

• Fluid Dynamics and Aerodynamics
• Laser-Based Measurement Techniques
• Turbulence Research

Background:

• Femtosecond Laser Electronic Excitation Tagging (FLEET) is an established unseeded velocimetry method.
• Traditional FLEET measures single velocity components along a line or multiple components at a single point.
• Existing methods lack the capability for dense spatial velocity profiling with multi-component measurements.

Purpose of the Study:

• To develop and demonstrate a novel dotted-line FLEET technique.
• To combine the spatial resolution of line measurements with the multi-component capability of point measurements.
• To enable two-component velocity measurements using a single camera setup.

Main Methods:

• A single beam path was utilized to generate multiple simultaneous laser spots.
• A periodic mask with rectangular slits was employed to create the dotted pattern.
• Measurements were conducted downstream of a turbulent, supersonic nitrogen free jet.

Main Results:

• Successfully implemented a dotted-line FLEET configuration generating up to seven simultaneous spots.
• Achieved spot spacing of approximately 0.9 mm with diameters ranging from 150 to 350 µm.
• Computed and presented both streamwise and radial velocity components.

Conclusions:

• The dotted-line FLEET technique effectively merges line-based dense profiling with point-based two-component velocimetry.
• This advancement allows for more comprehensive velocity field characterization in complex flows.
• The method offers a significant improvement over previous FLEET configurations for detailed flow analysis.