Why you Should Use High-Speed Cameras for Visualizing Fluid Mechanics (with examples)

Fluid mechanics describes the flow of fluid whether at rest or in motion¹. The surface of the earth is covered approximately by 75% water and its atmosphere consists of air, a mixture of gasses. There is a wealth of nature and man-made applications related to this subject. If you think about it, it is difficult to pinpoint an application that does not involve a fluid flow phenomenon. The flight of an airplane, the liquid flow used to produce electric power, the flow in the arteries and the droplet ejection for printing are all fluid flow problems. 

This fascinating discipline has a sound theoretical foundation. Yet, the fundamental equations that describe fluid motion are difficult to solve by analytical means. Only a few exact solutions are available and they relate to highly simplified situations. Nevertheless, to validate theoretical models empirical evidence is required. In this aspect the field of fluid mechanics is rich in experimental methods, many of which have been available for decades now. If interested, take a look at the books by Merzkirch² and Smits³, they discuss different flow visualization techniques, listed in the references section at the end of this blog.

The Beginning of High-Speed Photography

One of the many techniques available is the use of images to analyze fluid motion. The technique goes back to the 19th century with the pioneer work by Muybridge to settle a discussion related to horse galloping⁴. Back then, it was speculated that a horse keeps at least one hoot on the ground when galloping. Surprisingly, his results portrayed a different story. First, the pictures showed that for a brief time the four legs of the horse are in the air. In addition to that, the footage depicted a rather complex motion of the horse’s limbs. It also showed no strongly synchronized motion of the two front members or of the rear ones. Muybridge’s work was not unnoticed. Soon, other people realized the value of the technique to analyze fast-occurring events. In the last few decades the use of high-speed footage has extended to a large number of fields in science and engineering.

Benefits of using High-Speed Cameras to analyze Fluid Motion

By using a high-frame rate of recording researchers can gain a deeper understanding of phenomena under study. High-speed cameras can record a larger number of frames per second than regular cameras. This provides the user with detailed visualization of fast-evolving fluid flow phenomena. Hence, these remarkable devices can reveal intricate flow patterns, turbulence, vortices, and other interesting flow features.

Moreover, the use of high-speed cameras combined with flow visualization techniques, i.e. PIV, has significantly improved our understanding of a large number of topics related to turbomachinery⁵, forensic analysis⁶ and multiphase flow research⁷, among others. Similar things can be said about the schlieren technique, changes of fluid density can be observed at time scales that are beyond the regular temporal resolution of commercially available cameras. In addition to that, both Particle Image Velocimetry (PIV) and schlieren are non-intrusive techniques which makes them attractive for different studies of fluid motion.

How High Speed Cameras are used by Academic Researchers and Universities

Impact of a Droplet onto a Cubic Pillar

Whether research studies are conducted at a large corporation, academic institution or military facility, fluid flow research can be demanding in terms of economic resources. Due to this, not all universities or colleges can offer students to get them involved in cutting edge research projects. However, some recent publications show it is possible to conduct high-caliber research work incorporating cost-effective equipment. In particular we want to mention a couple of studies that have been conducted making use of a cost-effective approach. Ren et al⁸ evaluated the impact of a droplet onto a cubic pillar experimentally and with numerical simulations. The team recorded the droplet impact using two Photron cameras as well as a Chronos 1.4 color camera. For the numerical results that used an in-house developed package, Free Surface 3D (FS3D), their numerical results agree well with their experimental results. Ren et al have managed to unravel how the point of impact between the droplet and micropillar strongly affects both the location and volume of entrapped gas.

Particle Image Velocimetry 

Luberto and Payrebrune⁹ recently proposed a low-cost particle image velocimetry. The spatial resolution of their system is comparable to professional systems. Moreover, they do not use a high power laser for the illumination of tracer particles, an attractive feature in terms of safety. For their experimental work, they used a Chronos 1.4 high-speed camera. Then they processed the PIV data using the MATLAB-based package PIV-lab. The authors supplemented their work with CFD (Computational Fluid Dynamics) simulations using the open source package openFOAM. Similar to the work by Ren, the relevant feature of their work is that they demonstrate it is possible to carry out competitive research work with cost-effective equipment. More importantly, they present their results in open access journals, thus making their results available to a wide audience.

These research studies resonate with our mentality here at Kron Technologies. We are also committed to provide cost-effective imaging solutions of top quality. This is not something taken lightly, our systems are employed in prestigious academic, industrial and research facilities all over the world. 

References

1. White, F.M., 2002. Fluid mechanics, 5th edition. McGraw-Hill. 
2. Merzkirch, W., 2012. Flow visualization. Elsevier.
3. Smits, A.J., 2012. Flow visualization: techniques and examples. World Scientific.
4. Tsuji, K., 2018. The micro-world observed by ultra high-speed cameras. Springer International Publishing, Cham. https://doi. org/10, 1007, pp.978-3.
5. Yamamoto, F. and Ishikawa, M., 2022. A Review of the Recent PIV Studies.
6. Comiskey, P.M., Yarin, A.L. and Attinger, D., 2017. High-speed video analysis of forward and backward spattered blood droplets. Forensic Science International, 276, pp.134-141.
7. Cely, M.M.H., Baptistella, V.E. and Rodriguez, O.M., 2018. Study and characterization of gas-liquid slug flow in an annular duct, using high speed video camera, wire-mesh sensor and PIV. Experimental Thermal and Fluid Science, 98, pp.563-575.
8. Ren, W., Foltyn, P., Geppert, A. and Weigand, B., 2021. Air entrapment and bubble formation during droplet impact onto a single cubic pillar. Scientific Reports, 11(1), pp.1-11.
9. Luberto, L. and de Payrebrune, K.M., 2021. Examination of laminar Couette flow with obstacles by a low-cost particle image velocimetry setup. Physics of Fluids, 33(3), p.033603.