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基于高速摄像方法，开展了17–800℃范围内不同温度球体垂直入水实验研究.呈现了随球体温度变化所产生的复杂入水现象：在1.5 m/s入水速度条件下，实验所采用的室温球体不能产生空泡，当球体温度为300℃时空泡生成，增加到400℃空泡消失，继续提高温度至700℃空泡再次形成.根据传热学与流体动力学理论，分析了温度与速度变化对空泡形成的影响机理.结果表明随着温度的升高，球体与水之间的传热效率与传热方式发生改变，汽化生成的汽泡和蒸汽膜改变了周围流体流动的湍动性和球体表面的粗糙度、疏水性，这些变化均会影响空泡的形成；在1.5–3.8 m/s入水速度范围内，当球体具有较高温度时，能否形成入水空泡主要与球体的传热性能有关，速度的提高增强了球体与水的传热效率，使高速入水条件下的较低温度球体同低速入水条件下的较高温度球体入水现象相似，速度本身仅对生成空泡的形态有所影响.The present study aims to address the effect of sphere temperature on water-entry cavity. For this purpose, an experiment on vertical water-entry cavity of a heated sphere is conducted by utilizing a high-speed video camera. The temperature of the sphere ranges from 17℃ to 800℃. The complex flow phenomena of water entry, produced by a change in temperature of a sphere, is obtained for the first time. According to the finding, cavity is not formed around the room temperature sphere under the condition of the impact velocity of 1.5 m/s. When the temperature of the sphere is 300℃, the cavity appears, while it disappears when the temperature reaches up to 400℃. Interestingly, cavity appears again as the sphere is heated to a temperature of 700℃. The degrees of drag reduction of the sphere are different in various temperature conditions. Based on the theory of heat transfer and fluid dynamics, we analyze the mechanism for the influences of temperature and velocity on the forming of cavitation. The results show that the heat-transfer efficiency and heat-transfer mode between sphere and water change with the increase of temperature. Meanwhile the turbulent characteristic around the sphere, the surface roughness and hydrophobicity of the sphere are affected by the bubbles and vapor layer. In consequence, these characteristics influence the formation of cavity. The results of the effect of impact velocity on water-entry cavity reveal that the heat transfer performance plays a significant role in the forming of cavity, while the heat transfer efficiency is improved by the increase of impact velocity. The water-entry characteristics are similar to those in flow field under high temperature at low impact velocity as well as under low temperature at high impact velocity. The flow field of water entry looks similar under 330℃ at high impact velocity as well as under 400℃ at low impact velocity. Thus, an abnormal phenomenon appears. That is to say, the cavity size first decreases, and then disappears with the increase of impact velocity for the sphere at 330℃. The heat transfer performance can determine whether a cavity forms under the conditions of the impact velocity ranging from 1.5 m/s to 3.8 m/s. Meanwhile, the impact velocity itself can merely affect the cavity shape. The pitch-off time of the 300℃ sphere is irrelevant to impact velocity, which shows a good consistency with the literature result. Also, this research will be conductive to gaining an insight into the complex flow of water-entry with a heated sphere.
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Keywords:
- heated sphere /
- water-entry experiment /
- water-entry cavity /
- heat transfer mode
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[1] He C T, Wang C, He Q K, Qiu Y 2012 Acta Phys. Sin. 61 134701 (in Chinese)[何春涛, 王聪, 何乾坤, 仇洋2012 61 134701]
[2] Lu Z L, Wei Y J, Wang C, Sun Z 2016 Acta Phys. Sin. 65 014704 (in Chinese)[路中磊, 魏英杰, 王聪, 孙钊2016 65 014704]
[3] Liu D, He Q, Evans G M 2010 Adv. Powder Technol. 21 401
[4] Le Goff A, Quere D, Clanet C 2013 Phys. Fluids 25 043101
[5] Bell G E 1924 Philos. Mag. J. Sci. 48 753
[6] Gilbarg D, Anderson R A 1948 J. Appl. Phys. 19 127
[7] May A 1952 J. Appl. Phys. 23 1362
[8] Ueda Y, Tanaka M, Uemura T, Iguchi M 2010 J. Visualization 13 289
[9] May A 1951 J. Appl. Phys. 22 1219
[10] Worthington A M, Cole R S 1897 Philos. Trans. R. Soc. London 189 137
[11] Aristoff J M, Bush J W M 2009 J. Fluid Mech. 619 45
[12] Duez C, Ybert C, Clanet C, Bocquet L 2007 Nat. Phys. 3 180
[13] Marston J O, Vakarelski I U, Thoroddsen S T 2012 J. Fluid Mech. 699 465
[14] Zvirin Y, Hewitt G F, Kenning D B R 1990 Exp. Heat Transfer 3 185
[15] Gylys J, Skvorcinskiene R, Paukstaitis L, Gylys M, Adomavicius A 2015 Int. J. Heat Mass Transfer 89 913
[16] Vakarelski I U, Marston J O, Chan D Y C, Thoroddsen S T 2011 Phys. Rev. Lett. 106 214501
[17] Vakarelski I U, Patankar N A, Marston J O, Chan D Y C, Thoroddsen S T 2012 Nature 489 274
[18] Vakarelski I U, Chan D Y C, Thoroddsen S T 2014 Soft Matter 10 5662
[19] Li L X, Li H X, Chen T K 2008 Exp. Therm. Fluid Sci. 32 962
[20] Marston J O, Truscott T T, Speirs N B, Mansoor M M, Thoroddsen S T 2016 J. Fluid Mech. 794 506
[21] Ding H, Chen B Q, Liu H R, Zhang C Y, Gao P, Lu X Y 2015 J. Fluid Mech. 783 504
[22] Elbing B R, Winkel E S, Lay K A, Ceccio S L, Dowling D R, Perlin M 2008 J. Fluid Mech. 612 201
[23] Biance A L, Chevy F, Clanet C, Lagubeau G, Quere D 2006 J. Fluid Mech. 554 47
[24] Duclaux V, Caille F, Duez C, Ybert C, Bocquet L, Clanet C 2007 J. Fluid Mech. 591 1
[25] Ong C L, Thome J R 2011 Exp. Therm Fluid Sci. 35 873
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