3-D particle tracking? There's an app for that

August 21, 2017
3-D particle tracking? there's an app for that
An example of the three-color tracer particle image captured using a smartphone for tomographic particle image velocimetry measurements. Credit: KAUST

Using four low-cost smartphone cameras and some simple colored backlighting, KAUST researchers have dispensed with expensive research-grade camera equipment and dangerous lasers to construct a tomographic particle image velocimetry (PIV) system that is capable of quantitative flow visualization. The proof-of-concept study demonstrates the research power of everyday devices, and puts a state-of-the-art tool within easy reach of a broader group of researchers and educators.

Tomographic PIV is regarded as the holy grail of experimental fluid mechanics: it allows fields to be observed in three dimensions at fine spatial resolution by tracking the motion of tracer using an array of digital cameras. The technique involves lighting up the fluid volume with a high-intensity laser and recording the light scattered by the tracer particles using expensive, high-speed, high-sensitivity cameras. These images are then processed by simple tomographic reconstruction algorithms to reproduce the position of the particles and track their motion over time to give the 3-D velocity field.

"Having access to tomographic PIV for the first time allows the calculation of full vortex structures in a turbulent flow," says Sigurdur Thoroddsen who led the research team. "This can benefit many applications involving turbulence, such as mixing or reducing drag for flows over airfoils or Formula 1 cars and even studying swimmers and flying animals.

"But the technique is prohibitively expensive for many researchers," continues Thoroddsen. "We believe that it should be possible to use mainstream consumer devices to produce high-quality research on various flow problems."

The smartphone PIV system consists of four 41-megapixel smartphone cameras positioned at different angles around the flow volume—in this case a glass tank filled with moving water and polystyrene tracer particles forming a vortex ring flow. To overcome the low sensitivity of the phone cameras, the cameras were set up to photograph the shadows of the tracer particles cast by blue, green and red LED lights, imprinting in the same image all three colors (see image). The results compare well with those obtained using a commercial tomographic PIV system, with deviations in circulation flow of less than 8 percent.

"With the addition of optical zoom as seen on some of the latest phones, and the ability to take '4k' video clips or even slow-motion video, we expect to see a significant increase in the possibilities of this approach," says Thoroddsen. "We have already pre-ordered the latest phones to extend our work."

Explore further: Image: A laser-sharp view of blended wing body plane design

More information: Andres A. Aguirre-Pablo et al. Tomographic Particle Image Velocimetry using Smartphones and Colored Shadows, Scientific Reports (2017). DOI: 10.1038/s41598-017-03722-9

Related Stories

Image: A laser-sharp view of blended wing body plane design

October 14, 2016

Engineers at NASA's Langley Research Center in Hampton, Virginia, used lasers inside the 14- by 22-Foot Subsonic Tunnel to map how air flows over a Boeing Blended Wing Body (BWB) model – a greener, quieter airplane design ...

Team finds reason behind defects in 3-D printing

August 2, 2017

High-speed images of a common laser-based metal 3-D printing process, coupled with newly updated computer models, have revealed the mechanisms behind material redistribution, a phenomenon that leads to defects in printed ...

Recommended for you

Carefully crafted light pulses control neuron activity

November 17, 2017

Specially tailored, ultrafast pulses of light can trigger neurons to fire and could one day help patients with light-sensitive circadian or mood problems, according to a new study in mice at the University of Illinois.

Strain-free epitaxy of germanium film on mica

November 17, 2017

Germanium, an elemental semiconductor, was the material of choice in the early history of electronic devices, before it was largely replaced by silicon. But due to its high charge carrier mobility—higher than silicon by ...

New imaging technique peers inside living cells

November 16, 2017

To undergo high-resolution imaging, cells often must be sliced and diced, dehydrated, painted with toxic stains, or embedded in resin. For cells, the result is certain death.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.