Characteristics of energy production and dissipation around a bubble rising in water. (16th January 2019)

• Record Type: Journal Article
• Authors: Gumulya, M.; Joshi, J.B.; Utikar, R.P.; Evans, G.M.; Pareek, V.
• Is Part Of: Chemical engineering science. Volume 193(2019)
• Page Start: 38
• Page End: 52
• Publication Date: 2019-01-16
• Subjects: Bubble generated turbulence -- Turbulence in gas-liquid flows -- Bubble wake -- Shape oscillations -- Bubbly flows -- Volume-of-fluid method; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2018.08.059
• Languages: English
• ISSNs: 0009-2509

Abstract

Highlights: Numerical study on the rise behaviour of 3–5 mm bubbles in water ( Re = 800–1300). Chains of hairpin vortices formed at the wake of the bubble, creating velocity fluctuations. Average turbulent kinetic energy in the wake region is ≈1.4–4.8% of bubble kinetic energy. Turbulence production occurs at the near wake, with several regions of negative production. Small–scale dissipation occurs throughout the wake of the bubble. Abstract: A numerical simulation on the rise behaviour of a bubble rising in stagnant water at Re ≈ 800–1300 has been conducted. It is found that vorticity generated at the side of the bubble is transferred to the wake region, forming chains of hairpin vortices that are regularly shed and transported downstream. The resulting fluctuations in shape, trajectory, and rise velocity were found to conform well to experimental observations. The fluctuations in velocity resulting from the unsteady wakes were analysed through a fixed-frame approach about the centre of mass of the bubble. The average turbulent kinetic energy in the near wake region was found to be ≈1.4–4.8% with respect to the average kinetic energy of the bubble. The production of the turbulent kinetic energy was found to occur predominantly at the near wake region of the bubble, mostly as a result of normal and tangential gradients of the mean streamwise velocity. Interestingly, several regions of negative rate of energy production were identified, namely at the top and side interfaces of the bubble. Overall, the ratio of positive-to-negative production rate was found to be ≈2.4–3.1, resulting in a net conversion towards smaller-scale fluctuations from the mean flow. Small–scale dissipation was found to occur throughout the wake of the bubble.