Abstract ：

Multi-wire-to-cylinder corona discharge was studied for better understanding of the electrohydrodynamic phenomena which directly relate to the performance of heat transfer enhancement. A unipolar approximation model was established and numerical simulations were conducted to determinate the heat transfer and velocity distribution of ionic wind. The numerical and experiments results show good agreement. It indicates that higher applied voltage and more corona wires can help decreasing thermal boundary layer thickness and increasing velocity gradient of boundary layer, resulting in the enhancement of heat transfer. When the applied voltage increases from -7 kV to -11 kV and the number of wire increases from corona wire number 1-3, there will be a 39.8% decrease of the thickness of thermal boundary layer. In the condition of U = -11 kV, the maximum local forced convection heat transfer coefficient for corona wire number N = 3 is 12 times and the average value is 8 times higher than that of natural convection. (C) 2017 Elsevier Ltd. All rights reserved.

Keyword ：

Boundary layer Electrohydrodynamic Field synergy Heat transfer enhancement

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Abstract ：

Air pollution caused by particles with small size has been a global concern because of threats to human health. A feasible way to remove these super fine suspended particles is using electrostatic precipitation technology. Herein, the PIV was used to measure the particle velocity distribution. By analyzing the particle motion trend in high electric field, a process of particle charging loss was observed. This phenomenon cannot be explained by current particle charging theories. Our conclusions may improve the understanding of particle charging processes.

Keyword ：

electric field flow field particle charging PIV super fine particles

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Abstract ：

It is of significance to study the movement of solid - gas mixed flow of small particle size in the high electric field region for explaining such insulation accidents as contamination deposition, gap breakdown, unknown flashovers, and the like occurring on power line insulators surface. Based on artificial simulation experiments, we applied the particle image velocimetry (PIV) technology to investigate the flow-electric field coupling movement of low-speed mixed flow, comprehensively compare the effects of electric field uniformity, voltage levels, wind speed and other factors on the distribution of flow field. The results show that the effect of non-uniform electric field on the flow field is apparently stronger than that of uniform electric field. It increases with the applied electric field increasing, and decreases a little with the wind speed increasing. In the uniform electric field, the particles have a trend to move to the cathode plate, while in the non-uniform electric field, they are evidently charged under the action of corona and prone to moving toward the anode plate. In contrast, the effect of the AC electric field on the flow field is weaker than that of the DC electric field. However, it still has obvious manifestation. These relevant conclusions play an active role for in-depth research on the external insulation characteristics of HV power grid in sand dust environments such as pollution deposition and distribution on the surface of insulation string, breakdown of the air gap, etc., especially the charged mechanism of small sized dust and sand particles.

Keyword ：

artificial simulation experiments flow-electric field coupling Gas-solid two-phase flow particle image velocimetry

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Abstract ：

在传统大涡模拟算法的基础上引入显式滤波技术,有效地控制了截断误差.对对流项和湍流应力项进行二次显式滤波,并对湍流应力的分解形式作了相应改进.以三维平板通道为计算模型编写了二阶精度计算程序,对传统、显式滤波大涡模拟2种算法的计算结果进行了对比,并就亚滤波模型的重建程度对计算精度的影响进行了探讨.计算结果表明:2种算法对流线方向平均速度分布模拟差异不大,但显式滤波大涡模拟算法可明显改进脉动速度分布;随着对亚滤波模型重建程度的提高,平均速度和脉动速度分布均有明显改进.

Keyword ：

大涡模拟 显式滤波 亚滤波模型

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Abstract ：

对前向多翼式离心风机建立了性能及流场测试台位,性能试验重复性良好.用粒子图像速度场仪(Particle image velocimetry,PIV)技术对蜗舌附近速度矢量场做了详细的变工况测量及分析.结果表明,蜗舌附近的主要流动特征由冲向蜗舌的速度矢量方向及蜗舌周围滞止区的影响范围所决定.小流量时,滞止区影响范围主要在蜗舌间隙流道内,造成速度矢量向叶轮内偏斜,蜗舌下游易形成分离旋涡而恶化;大流量时,滞止区影响范围偏向蜗壳出口流道,蜗舌间隙流动较好.此外,在蜗舌间隙沿轴向不同位置返回蜗壳的流量也不同,这主要与叶片不同段做功能力不同有关.

Keyword ：

PIV 多翼式叶轮 离心风机 速度场 蜗舌

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针对自由曲面三元叶轮的特点,将鼓锥形刀具引入到三元叶轮粗加工中,提出了基于动态模型的刀位生成算法.该算法引入时间因素,即时计算各时间节点叶轮特征曲面,建立了动态模型模拟加工过程,能真实地反映刀具与叶轮的空间关系,降低了加工病害发生的可能性;采用等距离偏置法生成走刀轨迹,进而计算粗加工刀位信息,并通过干涉检验进行刀位修正.由于鼓锥形刀具与被加工曲面具有良好的曲率匹配性,从而增大了加工带宽,可实现宽行线接触加工.与此同时,通过对进刀深度、偏置距离的合理优化,避免走刀冗余,减少了刀迹总长度,从而提高了加工效率.实例证明由此生成的粗加工刀位具有高效、可靠的特点,效率比同直径球头刀具等距离偏置法提高约27.5%.

Keyword ：

粗加工 刀位 动态模型 自由曲面

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Abstract ：

对前向多翼式离心风机建立了性能及流场测试台位.性能试验及流场测试表明,性能试验重复性良好,曲线符合理论性能曲线.用粒子图像速度场仪技术对叶片尾迹区及蜗壳出口横截面上的二次流做了详细的变工况测量与分析.结果表明:叶片尾迹区脉动强度达20%～70%;在设计工况附近叶片尾迹影响区域小,在非设计工况下叶片尾迹影响区域大,尾迹区域占到蜗壳径向宽度的15%～25%,约是叶片弦高的2～3倍;在蜗壳横截面上明显存在二次流旋涡;沿着蜗壳旋出方向二次流对称分布,但是到达出口时,小流量下两侧旋涡结合成一个旋涡,大流量下两侧旋涡一直保持到蜗壳出口.

Keyword ：

二次流 粒子图像速度场仪 前向多翼式离心风机 旋涡 叶片尾迹

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