14th International Symposium on Particle Image Velocimetry – ISPIV 2021
August 1–5, 2021

Phase separation and flow measurement of dilute
bubbly jet with 2-D PIV and LIF

Hyunduk Seo1, Kyung Chun Kim1∗

1 Pusan National University, School of Mechanical Engineering, Busan, South Korea
∗ kckim@pusan.ac.kr

Abstract
A measurement technique with a combination of PIV and LIF is suggested to measure gas-phase and liquid-
phase separately to resolve flow structures of a bubbly jet. In the bubbly jet, distribution of the bubble
population shows a Gaussian-like function but translated outward. Spreading nature of each phase does not
correspond to each other due to lack of the number of bubbles to be redistributed.

1 Introduction
Investigations on the bubbly jet and plume have been conducted with several techniques. Among those
techniques, ADV and LDV can provide 3-component velocity information, but there is a disadvantage of
disturbing the flow or complex tuning for the gas phase. Shadowgraphy, which is a kind of optical tech-
niques, has been widely used to analyze bubbles, but it cannot resolve the specific structure inside the
bubbly flow due to overlapped bubbles in an imaging plane. In this study, we investigate bubbly jet with 2-D
PIV and LIF techniques, which can analyze the structure of bubbly jet inside the core region of the bubbly
jet with a low void fraction (Dulin et al., 2012).

2 Method

Figure 1: Schematic of experimental setup for (a) PIV (b) LIF

The schematic of the experimental setup is shown in Fig. 1. Gas phase information was calculated from
highlighted bubble edge. The air-water mixture was injected into a 1 m3 cubic tank from the outlet of 20
mm. Diameter of bubbles was around 1.7 mm.

3 Result
Radial profiles of the axial velocity mostly show good agreement with Gaussian-like distribution (Fig. 2
(a)). Fig. 2 (b) shows the evolution of the centerline velocity of the bubbly jet along streamwise direction.



The figure shows an acceleration of the bubbly jet and a potential core collapse in the early stage of the flow.
Higher void fraction results in much intense acceleration and earlier collapse of the potential core. It implies
that buoyancy of bubbles results in the acceleration of the bubbly jet (Morton and Middleton, 1973).

Figure 2: Axial mean velocity profiles (a) radial distributions of velocities (b) centerline velocity with height

In Fig.3, the population of bubbles is concentrated next to the centerline of the bubbly jet in a form of
translated Gaussian function. Position of the center of each Gaussian function spreads out as the bubbly jet
flows. It does not significantly spread out in the far-field. It contrasts to the spreading of the liquid phase
structures with linear self-similarity respect to the height.

Figure 3: Radial population of bubbles with height

4 Conclusions
Each phase in bubbly jet is successfully measured by the combination of PIV and LIF. The bubbly jet looks
like an annular truncated cone shape due to different spreading nature of each phase. It is attributed to the
low void fraction condition where the redistribution of bubbles does not sufficiently occur.

Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant, which is funded by
the Korean government (MSIT) (No. 2021R1A2C2012469, NRF-2018-Global Ph.D. Fellowship Program).

References
Dulin VM, Markovich DM, and Pervunin KS (2012) The optical principles of PFBI approach. AIP Confer-

ence Proceedings 1428:217–224

Morton BR and Middleton J (1973) Scale diagrams for forced plumes. Journal of Fluid Mechanics 58:165–
176


	Introduction
	Method
	Result
	Conclusions