Controlled spherical deuterium droplets as Lagrangian tracers for cryogenic turbulence experiments

Area of Science:

• Fluid Dynamics
• Turbulence Research
• Cryogenics

Background:

• Lagrangian particle tracking is essential for studying turbulence at small scales.
• Challenges include high-resolution imaging and suitable tracer particles.
• Seeding cryogenic liquid helium flows with micrometer-sized, density-matched particles is difficult.

Purpose of the Study:

• To develop methods for generating suitable tracer particles for cryogenic fluid dynamics.
• To create controlled liquid spherical droplets of deuterium for seeding liquid helium flows.
• To investigate droplet generation techniques for Lagrangian particle tracking.

Main Methods:

• Utilized surface tension to generate controlled liquid deuterium droplets over a liquid helium bath.
• Developed a continuous mode technique using Rayleigh-Taylor instability to fragment a liquid jet.
• Developed a drop-on-demand mode technique using piezoelectric transducer-generated pressure pulses.

Main Results:

• Continuous mode: Droplet diameter distribution of 2 ± 0.25DN (DN=20 μm nozzle diameter) with a production rate >30 kHz.
• Drop-on-demand mode: Narrower droplet diameter distribution of 2.1 ± 0.05DN with a production rate of 500 Hz-2 kHz.
• Investigated initial droplet trajectories and shapes using back-light illumination.

Conclusions:

• Successfully generated deuterium droplets suitable for seeding liquid helium flows.
• Two distinct methods offer trade-offs between production rate and droplet size control.
• These techniques advance the capability for high-resolution turbulence studies in cryogenic fluids.