A three-dimensional scanning stereoscopic particle image velocimetry for large-volume liquid flows

TL;DR

This paper presents a novel three-dimensional scanning stereoscopic PIV system using a rotating prism for large-volume liquid flow measurements, enabling high-density velocity field acquisition in a single scan.

Contribution

The introduction of a rotating prism-based SSPIV system that simplifies setup and allows fast, high-resolution 3D flow measurements in large volumes.

Findings

Captured 10^6 velocity vectors in a 100x100x100 mm^3 volume.

Demonstrated the system on a jet and rising sphere flow, capturing vortical structures.

Compared flow fields with numerical simulations, showing good agreement.

Abstract

We introduce a Scanning Stereoscopic Particle Image velocimetry~(SSPIV) system which incorporates a thin rotating prism to obtain three-dimensional velocity fields in a large cubical measurement volume. The system makes use of an arrangement where a laser beam is first laterally deflected using an even-faced prism, and then passed through a cylindrical lens rod to obtain light sheets for illumination. This eliminates the need for large rotating mirrors or heavy prisms and facilitates relatively fast rotation speeds of up to 4800 rpm for the prism, yielding three-dimensional, three-component velocity field over a large depth at relatively high particle seeding density. About $10^6$ velocity vectors (3D-3C) are obtained in a single volumetric-scan of $100 \times 100 \times 100$ mm$^3$. The method is demonstrated using two independent experiments, (1) a round jet at Reynolds number Re = 1000, and (2) the flow field around a freely rising sphere at a Reynolds number Re$_p$ $\approx$ 260, and the wake flow is compared with direct numerical simulations of a falling viscous droplet. The scanning gives time-resolved evolution of the large-scale vortical structures of the Re = 1000 jet, with spatial gradients captured fairly well. The three-dimensional flow field surrounding the refractive-index-matched rising sphere is shown to be steady and non-axisymmetric. The flow field and separation bubble are seen to be similar, but slightly shorter than that of the falling droplet case and the uniform flow past a fixed sphere case at a comparable Reynolds number.