Bubble clustering in turbulent boundary layer on a moving wall utilizing belt-driven system

For simulating the behavior of air bubbles injected into the turbulent boundary layer developed beneath the bottom of a ship, we propose a novel experimental system for a different driving force on flow from the bulk pressure gradient. In the proposed facility, the motion of a horizontal belt on the...

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Bibliographic Details
Published inJournal of Fluid Science and Technology Vol. 19; no. 2; p. JFST0013
Main Authors HORIMOTO, Yasufumi, MORI, Itsuki, PARK, Hyun Jin, TASAKA, Yuji, MURAI, Yuichi
Format Journal Article
LanguageEnglish
Published Tokyo The Japan Society of Mechanical Engineers 01.01.2024
Japan Science and Technology Agency
Subjects
Air bubbles
Air injection
Belt conveyors
Belt drives
Boundary layers
Bubble clustering
Bubbles
Bubbly drag reduction
Clustering
Driving ability
Frequency ranges
Frequency spectra
Frequency spectrum
Gas-liquid two phase flow
Moving walls
Pressure gradients
Ships
Torque
Towing
Turbulent boundary layer
Void fraction
Void wave
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Summary:For simulating the behavior of air bubbles injected into the turbulent boundary layer developed beneath the bottom of a ship, we propose a novel experimental system for a different driving force on flow from the bulk pressure gradient. In the proposed facility, the motion of a horizontal belt on the water surface as a moving wall is driven by a motor, and a turbulent boundary layer is developed beneath the belt. To show the usability of this belt-driven system for research on the bubble behavior in turbulent boundary layer, we investigated the bubble clustering beneath the moving belt. Bubble clusters are formed for sufficiently high values of the belt speed and the air injection rate. To quantify this bubble clustering, we calculated the frequency spectrum of the local projected void fraction to estimate the passing frequency of the bubble clusters at two fixed downstream positions and found that it has a peak in the frequency range which is identical to the void wave reported by previous towing model-ship experiments. In addition, our system has the advantage that the wall drag modification can be directly estimated from the torque measurement. The bubble clustering occurs in a parameter regime where the torque reduction ratio is relatively high, which is also consistent with the results of the previous towing experiments.
ISSN:1880-5558
1880-5558
DOI:10.1299/jfst.2024jfst0013