Spontaneous and artificial void wave propagation beneath a flat-bottom model ship
Spontaneous and artificial void wave propagation beneath a flat-bottom model ship
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DOI：
10.1016/j.oceaneng.2020.107850
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发表时间：
2020-10-15
影响因子：
5
通讯作者：
Murai, Yuichi
中科院分区：
文献类型：
--
作者：
Tanaka, Taiji;Park, Hyun Jin;Murai, Yuichi
尽管气泡减阻在船舶上的实际应用已经开始普及，但尚不清楚气泡如何沿着空间发展的湍流边界层迁移。我们测量了一艘在 100 米长水箱中拖曳的 4 米长全透明平底模型船下方局部空隙率的时空分布，船速高达 3.00 m/s。气泡以恒定和周期性波动的气流速率注入湍流边界层。在恒定的流速下，2-5毫米的气泡会引起自发的空隙波，即局部空隙率的准周期波动，频率为4-8 Hz。当重复气泡注入在下游形成人造虚空波时，虚空波以船速的 47%-53% 传播。在传播过程中，我们发现当重复频率低于虚空波的自发频率时，虚空波的表观扩散系数可低至10(-4) m(2)/s，甚至为负值。这表明虚空波在应用于船体时持续数十米。
Although the practical use of bubbly drag reduction for marine vessels has begun to spread, it is unclear how bubbles migrate along spatially developing turbulent boundary layers. We measured the spatiotemporal distribution of the local void fraction beneath a 4-m-long fully transparent flat-bottom model ship towed in a 100-m-long water tank with a ship speed of up to 3.00 m/s. Bubbles were injected with both constant and periodically fluctuated air flow rates into the turbulent boundary layers. With constant flow rates, 2-5-mm bubbles caused spontaneous void waves, i.e., quasiperiodic fluctuation of the local void fraction, standing at 4-8 Hz. When repetitive bubble injection, which formed artificial void waves downstream, was applied, void waves propagated at 47%-53% of the ship speed. During the propagation, we found the apparent diffusion coefficient of the void wave taking values down to 10(-4) m(2)/s and even negative values when the repetition frequency was set lower than the spontaneous frequency of void waves. This indicates that the void waves persist for several tens of meter in application to ship hulls.