V-ONSET (Vertical Octagonal Noncorrosive Stirred Energetic Turbulence): A vertical water tunnel with a large energy dissipation rate to study bubble/droplet deformation and breakup in strong turbulence

Abstract

A vertical water tunnel facility has been constructed to study the dynamics of turbulent multiphase flow. The new system features several unique designs that allow us to study bubble deformation and breakup in strong turbulence: (i) The mean flow can be adjusted to balance the rising velocity of buoyant bubbles/droplets so that they can stay in the view area for an extended period of time. (ii) Turbulence is generated and controlled using a 3D-printed jet array that can fire 88 random high-speed momentum jets with the individual jet velocity of up to 12 m/s. This component allows us to attain turbulence with a high energy dissipation rate (≥0.1 m2/s3), which is orders-of-magnitude higher than most of the existing turbulent multiphase flow facilities. (iii) Turbulence generated in the test section is nearly homogeneous and isotropic, and the turbulent fluctuations are also decoupled from the mean flow. The resulting turbulence intensity can be varied between 20% and 80% with the speed of the mean flow at around 0.2 m/s. (iv) This system has an octagonal test section that allows six cameras to image and reconstruct the 3D shape of deforming bubbles/droplets in turbulence. The same set of cameras was also used for tracking tracers in the surrounding turbulent flow. Both the reconstruction and particle tracking were completed using our in-house codes that were parallelized to run on high-performance computing clusters efficiently.

Simultaneous measurements of deforming Hinze-scale bubbles with surrounding turbulence

“…Additional details concerning this set-up and its flow characteristics can be found in Masuk et al. (2019 b ).…”

“…The details of these statistics can be found in Masuk et al. (2019 b ). Here, we only show the measured longitudinal second-order structure function, i.e.…”

“…The test section was set much farther downstream of the jets (about 80d j ) to ensure that the jets were well mixed and turbulence becomes homogeneous and isotropic with very little spatial variation. Additional details concerning this set-up and its flow characteristics can be found in Masuk et al (2019b).…”

“…Before discussing bubble deformation and breakup, single-phase turbulence statistics in the tunnel needs to be characterised to ensure that the flow is close to homogeneous and isotropic, and the bubble size is within the inertial range of turbulence. The details of these statistics can be found in Masuk et al (2019b). Here, we only show the measured longitudinal second-order structure function, i.e.…”

“…Schematic of the V-ONSET vertical water tunnel; two insets show the 3-D model of the jet array used to fire high-speed water jets into the test section and a bubble bank to inject bubbles, respectively. Additional details concerning this facility can be found inMasuk et al (2019b).…”