76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023;
Washington, DC
Session A36: Bubbly Flows I
8:00 AM–9:57 AM,
Sunday, November 19, 2023
Room: 202B
Chair: Roberto Zenit, Brown University
Abstract: A36.00007 : Extension of Inertial Subrange in Turbulent Bubbly Jet at Low Void Fraction*
9:18 AM–9:31 AM
Abstract
Presenter:
Kyung Chun Kim
(Pusan National University)
Authors:
Kyung Chun Kim
(Pusan National University)
Hyunduk Seo
(Pusan National University)
Turbulent bubbly jets at Reynolds number 3,000 with low void fraction (≤ 1%) are measured by using time-resolved three-dimensional Particle Tracking Velocimetry and Eulerian reconstruction techniques. The evolution of the mean flow characteristics shows good agreement with the Eulerian-Eulerian DNS of a bubbly jet at the same condition. As the jet flows downstream, the bubble-populated region resides inner interface of the shear layer. Hence, there is a separation between the bubbles and the shear layer. The phase separation occurs earlier with a lower void fraction. After the phase separation, typical coherent structures appear around the shear layer. The identified vortical structures are correlated with the alternating pattern of the axial liquid accelerations. The alternating pattern gets sparse as the jet has higher axial liquid velocity due to the bubbles and vortical structures are drifted by the slip velocity of the bubbles. The wake instability has a strong correlation with the spanwise (radial and azimuthal) motion of the bubbles. In high-frequncy range, all the spectrums collapse with -5/3 slopes. In the liquid phase energy spectra plotted against the wavenumber, bubbly jet cases have an extended cascading process after the Taylor microscale (λ) of the single-phase jet. The extension of the cascading process is regardless of velocity components but a higher void fraction induced a small hill in high-frequency scale. To identify the effect of the bubbles in terms of scales, premultiplied energy spectra normalized by the axial mean liquid velocity are calculated. Inside the jet core, a plateau after the peak of the band regardless of the initial void fraction. At the shear layer, there are still lifted tails of the energy spectra at high wavenumber region depending on the void fraction, but no distinctive plateau. The interactions extended the energy cascading process beyond the wake instability frequency from bubbles. It is concluded that a small amount of bubbles in the jet shows different turbulent characteristics to buoyancy dominant flow.
*This work was supported by the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT) (No. 2020R1A5A8018822).