Large eddy simulation of microbubble dispersion and flow field modulation in vertical channel flows

Turbulent liquid–gas vertical channel flows laden with microbubbles are investigated using large eddy simulation (LES) two-way coupled to a Lagrangian bubble tracking technique. Upward and downward flows at shear Reynolds numbers of Re τ = 150 and 590 are analyzed for three different microbubble diameters of 110, 220, and 330 μm. Predicted results are compared with published direct numerical simulation results although, with respect to comparable studies available in the literature, the range of bubble diameters and shear Reynolds numbers considered herein is extended to larger values. Microbubble concentration profiles are analyzed, with the microbubbles segregating at the wall in upflow conditions and moving toward the channel centre in downflow. The various forces acting on the bubbles, and the effect of the flow turbulence on the bubble concentration, are considered and quantified. Overall, the results suggest that the level of detail achievable with LES is sufficient to predict the fluid structures impacting bubble behavior. Therefore, LES coupled with Lagrangian bubble tracking shows promise for enabling the reliable prediction of bubble-laden flows that are of industrial relevance

Long-period (12 sec) volcanic tremor observed at Usu 2000 eruption: Seismological detection of a deep magma plumbing system, Eos Trans

[1] From a temporal deployment of a broadband seismic network at Usu volcano, Japan, we observed long-period (12 sec) volcanic tremors during the first few weeks of the eruptive activity which started in the end of March, 2000. The source of these long period tremors are located relatively deep at a depth of 5 km, and their amplitude variation well correlates with the uplift rate of the eruption area. We thus attribute these long period tremors to the flow induced vibration of a magma chamber and its outlet located around the source region of the long period tremors. This may be the first seismological detection of long-period (>10 sec) vibrations of a deep magma plumbing system

Hydrological and Chemical Budgets of Okama Crater Lake in Active Zao Volcano, Japan

The Okama Crater Lake is located in the highly active Zao Volcano on the boundary of Miyagi and Yamagata Prefectures, Japan. At present, the lake stays relatively calm with neither bubbling, steaming nor gas smell at a pH of 3.2–3.4, though the lake did change color with steaming from the water surface in 1939 as the result of one of Zao’s volcanic activities. In order to clarify the geothermal effect on Okama and the groundwater flow system below or around Okama, field observations were performed in 2019 and 2020. Groundwater inflow and outflow in Okama were separately evaluated by estimating the hydrological and chemical budgets of the lake, based on the hydrometeorology, water temperature and river inflow measured in the field. The average groundwater inflow and outflow were estimated at 0.012 m3/s and 0.039 m3/s during the non-rainfall periods of 2020, respectively. A surplus of groundwater outflow makes the lake level consistently decrease during non-rainfall periods or the completely ice-covered season. In the completely ice-covered periods, the water temperature consistently increased at 0–15 m above the lake bottom, which is probably due to thermal leakage from a hydrothermal reservoir below the lake bottom. The heat fluxes averaged over December 2019–April 2020 and December 2020–March 2021 were calculated at 2.5 and 2.9 W/m2, respectively. A coupling between the estimated groundwater inflow and the calculated geothermal heat flux was used to evaluate the temperature of inflowing groundwater

ASOBOI 97: Aso Seismic Observation with Broadband Instruments in 1997

In August 1997, we deployed a total of 24 broadband three-component velocity seismometers temporarily around Aso volcano in Kyushu, Japan. Most of these stations were located within 1 km of the first crater of Naka-dake and provided good azimuthal coverage to constrain the geometry of the source region of long-period (15s) tremors (LPTs). The spatial pattern of the observed LPTs amplitude reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack almost parallel to the chain of craters of Naka-dake (Yamamoto et al, 1999). This report summarizes details of the observations, as well as some of the characteristics of the observed data from the ASOBOI 97 expedition

ASOBO197 : 阿蘇山における広帯域地震観測 1997

In August 1997, we deployed a total of 24 broadband three-component velocity seismometers temporarily around Aso volcano in Kyushu, Japan. Most of these stations were located within 1 km of the first crater of Naka-dake and provided good azimuthal coverage to constrain the geometry of the source region of long-period (15s) tremors (LPTs). The spatial pattern of the observed LPTs amplitude reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack almost parallel to the chain of craters of Naka-dake (Yamamoto et al, 1999). This report summarizes details of the observations, as well as some of the characteristics of the observed data from the ASOBOI 97 expedition