Multi-point line focused laser differential interferometer for high-speed flow fluctuation measurements.

Area of Science:

• Fluid dynamics
• Optical metrology
• Laser diagnostics

Background:

• Accurate measurement of density fluctuations is crucial for understanding complex fluid phenomena.
• Conventional single-point interferometers lack the spatial resolution for detailed flow field analysis.
• Developing advanced diagnostic tools is essential for high-fidelity fluid flow research.

Purpose of the Study:

• To develop and demonstrate a multi-point focused laser differential interferometer (FLDI) for high-resolution density fluctuation measurements.
• To enable simultaneous density measurements along two distinct, configurable lines.
• To validate the instrument's performance in dynamic flow environments.

Main Methods:

• Modification of a single-point FLDI with cylindrical lenses to create two parallel, orthogonally polarized laser lines.
• Utilizing a 16-element photodiode array for signal detection and density fluctuation measurement.
• Incorporating a Nomarski prism and a second photodiode array for simultaneous dual-line measurements.
• Orienting measurement lines at any azimuthal angle in the focal plane.

Main Results:

• Successfully measured density fluctuations at 16 points along a line.
• Demonstrated simultaneous density measurements along two separated lines.
• Captured density disturbances and velocity of a laser-induced shock wave, validated with schlieren imaging.
• Acquired density disturbance data in the boundary layer of a flat plate in Mach 6 flow.

Conclusions:

• The multi-point FLDI is a capable tool for detailed, multi-point density fluctuation measurements.
• The instrument provides valuable data for analyzing transient phenomena like shock waves and boundary layer dynamics.
• This technology advances optical diagnostic capabilities in fluid mechanics research.