Dynamics of a single bubble rising in a quiescent medium

• Published in: Experimental thermal and fluid science Vol. 132; p. 110546
• Main Authors: Hoque, Mohammad Mainul, Moreno-Atanasio, Roberto, Doroodchi, Elham, Joshi, J.B., Evans, Geoffrey M, Mitra, Subhasish
• Format: Journal Article
• Language: English
• Published: Philadelphia Elsevier Inc 01.04.2022; Elsevier Science Ltd
• Subjects: Diameters; Diffusion; Energy; Energy dissipation; Energy spectra; Energy spectrum; Fast Fourier transformations; Fourier analysis; Kinetic energy; Kinetic energy distribution; Particle image velocimetry; PIV; Single bubble; Turbulence; Turbulence kinetic energy budget; Velocity; Velocity distribution; Wavelengths; Wavelet transformation; Wavelet transforms; Energy spectrum; Turbulence kinetic energy budget; Single bubble; Wavelet transformation; PIV
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2021.110546

•Single millimetric size bubble motion in quiescent liquid studied using PIV.•Turbulence kinetic energy budgeting performed directly from measured velocity data.•Both small- and large-scale motions identified by discrete wavelet transformation method.•Energy spectrum showed -5/3 and -3 slope in large- and small-scale regime.•Turbulence production term not balanced by the energy dissipation rate alone. In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ∼ 2.77–3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.