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PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED spiral coil INSERT

Journal of Hydrodynamics 2012年第4期24卷 518-525页

作者： TANG Yu-feng TIAN Mao-cheng ZHANG Guan-min School of Energy Source and Power Engineering Shandong UniversityJinan 250061China

The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry （PIV） measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Com- pared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous dis- turbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the redu- ction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enha- nced in this area.

关键词： Particle Image Velocimetry (PIV) spiral coil longitudinal vortices flow disturbance

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Comparison of three formulations for eddy-current problems in a spiral coil electromagnetic acoustic transducer

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Journal of Central South University 2016年第4期23卷 817-824页

作者：石文泽吴运新龚海赵志然范吉志谭良辰 State Key Laboratory of High Performance Complex Manufacturing(Central South University) Changsha 410083China School of Mechanical and Electrical Engineering Central South UniversityChangsha 410083China Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center Changsha 410083China School of Materials Science and Engineering Central South UniversityChangsha 410083China

Three differential equations based on different definitions of current density are compared. Formulation I is based on an incomplete equation for total current density （TCD）. Formulations II and {I1 are based on incomplete and complete equations for source current density （SCD）, respectively. Using the weak form of finite element method （FEM）, three formulations were applied in a spiral coil electromagnetic acoustic transducer （EMAT） example to solve magnetic vector potential （MVP）. The input impedances calculated by Formulation III are in excellent agreement with the experimental measurements. Results show that the errors for Formulations I ＆ II vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin ＆ proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ili to solve MVP when the coil diameter is less than twice the skin depth for Formulation I is a low cost and high efficiency calculation method.

关键词： electromagnetic acoustic transducer (EMAT) eddy current finite element method (FEM) skin and proximity effects spiral coil

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