Vortex formation by a vibrating cantilever

Choi, Minsuk; Cierpka, Christian; Kim, Y.-H.

doi:10.1016/j.jfluidstructs.2012.03.004

Cited by 63 publications

(24 citation statements)

References 20 publications

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“…Vorticity plots for the smooth surfaced fan are largely consistent with existing literature on oscillating fan aerodynamics [1,6,8]. Vortex formation is driven by the pressure differential across the fan tip.…”

Section: X-y Plane Measurementssupporting

confidence: 81%

The Influence of Surface Roughness on the Flow Fields Generated by an Oscillating Cantilever

Conway

Punch

2018

EPJ Web Conf.

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Abstract. With the current trend of miniaturisation of electronic devices, piezoelectric fans have attracted increasing interest as a means of inducing forced convection cooling, instead of traditional rotary solutions. Although there exists an abundance of research on various piezo-actuated flapping fans in the literature, the geometries of these fans all consist of a smooth rectangular cross section with thicknesses typically of the order of 100 µm. The focus of these studies has primarily been on variables such as frequency, amplitude and, in some cases, resonance mode. It is generally noted that the induced flow dynamics are a direct consequence of the pressure differential at the fan tip as well as the pressure driven 'over the top' vortices generated at the upper and lower edges of the fan. Rough surfaces such as golf ball dimples or vortex generators on an aircraft wing have proven to be beneficial by tripping the boundary layer and energising the adjacent airflow. This paper aims to examine the influence of surface roughness on the airflow generation of a flapping fan, and to determine if the induced wake can be manipulated or enhanced by energising the airflow around the fan tip. Particle-Image Velocimetry (PIV) is carried out on mechanically oscillated rigid fans with surfaces consisting of protruding pillars and dimples. A smooth rigid fan surface is also investigated as a control. No significant difference was noted between the smooth and roughened fans through observation of the induced flow fields. Both fans produced results that were largely consistent with the existing literature on oscillating cantilevers. The results of this paper may be used to inform the design of piezoelectric fans and to aid in understanding the complex aerodynamics inherent in flapping wing flight.

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Section: X-y Plane Measurementssupporting

confidence: 81%

The Influence of Surface Roughness on the Flow Fields Generated by an Oscillating Cantilever

Conway

Punch

2018

EPJ Web Conf.

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“…A few researchers succeeded in simulating the 3D flow around a vibrating plate, they adopted tetrahedral mesh with spring-based dynamic mesh and re-meshing techniques to implement the movement of the plate. Therefore, the simulated counter-rotating vortex was weaker than the experimentally measured one, even though the overall heat transfer rate agreed well between 3D simulations and the experiments.This study is a continuation of the previous works [3][4][5] to calculate the 3D flow around a piezoelectric fan with minimizing the numerical dissipation caused by the mesh movement. Therefore, only hexahedral mesh was generated around the fan, and its movement was implemented by the spring-based dynamic mesh technique only without using the re-meshing.…”

mentioning

confidence: 88%

“…His experimental results clearly showed the formation of counter-rotating vortices by a piezoelectric fan. Choi et al [3][4][5] conducted two-dimensional numerical simulations to obtain the flow around a piezoelectric fan and validated their results with the experimental data of Kim et al [2]. Based on the numerical simulations, they investigated the exact moment of vortex separation from the fan and the effects of phase difference and distance between two fans on the flow generation.…”

mentioning

confidence: 99%

Flow Generation by a Piezoelectric Fan

Oh¹,

Jeon²,

Choi³

2017

World Congress on Mechanical, Chemical, and Material Engineering

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Extended AbstractSince Toda [1] firstly introduced a vibrating flat plate, many researchers have conducted experiments to understand its effects on the heat transfer around a small heat source. Recently, it is relatively easy to make a vibrating plate with piezoelectric materials. When AC power is applied to a flat plate on which the piezoelectric material is deposited, the plate moves back and forth so that this movement can generate a small airflow to cool a small electric device. That's why a vibrating plate with the piezoelectric material is called as 'piezoelectric fan'.Although most of researchers had been focusing on the heat transfer enhancement with a piezoelectric fan, Kim et al. [2] tried to understand the flow generated by the fan and measured two-dimensional velocity field using LDV (Laser Doppler Velocimetry). His experimental results clearly showed the formation of counter-rotating vortices by a piezoelectric fan. Choi et al. [3][4][5] conducted two-dimensional numerical simulations to obtain the flow around a piezoelectric fan and validated their results with the experimental data of Kim et al. [2]. Based on the numerical simulations, they investigated the exact moment of vortex separation from the fan and the effects of phase difference and distance between two fans on the flow generation. A few researchers succeeded in simulating the 3D flow around a vibrating plate, they adopted tetrahedral mesh with spring-based dynamic mesh and re-meshing techniques to implement the movement of the plate. Therefore, the simulated counter-rotating vortex was weaker than the experimentally measured one, even though the overall heat transfer rate agreed well between 3D simulations and the experiments.This study is a continuation of the previous works [3][4][5] to calculate the 3D flow around a piezoelectric fan with minimizing the numerical dissipation caused by the mesh movement. Therefore, only hexahedral mesh was generated around the fan, and its movement was implemented by the spring-based dynamic mesh technique only without using the re-meshing. From the numerical results, it was found that the endwall has a significant effect on the flow around the fan. The clearance flow between the sides of the fan and the endwalls forms two alternating vortices. These vortices finally merged with the counter-rotating vortices generated at the plate tip, causing very complex flow near the endwall. These vortex motions make the axial velocity increase at the mid-span but decrease near the endwall. These flow structures around the piezoelectric fan have not been clearly resolved by tetra elements with the re-meshing technique in previous researches.

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“…Acikalin et al (6) discovered that the natural convection heat transfer coefficient increased by 100% using piezoelectric fans. They conducted experiments using a mobile phone with a 40 × 5.7 × 3.8 cm 3 flow channel.…”

Section: Introductionmentioning

confidence: 99%

Heat Flow Field Analysis of the Effects of Vertical Piezoelectric Fan Placement on Heat Convection in Pin-Fin Heat Sink

2017

Sensors and Materials

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Keywords: electronic cooling, computational fluid dynamics, horizontal piezoelectric fan, heat sink Piezoelectric fans make use of the inverse piezoelectric effect to actuate the rotation of blades. These fans have the advantages of small size, low power consumption, and low noise output. In this study, we used the commercial computational fluid dynamics (CFD) software ANSYS CFD/ Fluent to simulate a transient flow field in order to explore the impact of each column on the heat flow of a rectangular-channel piezoelectric fan installed inside each columnar radiator. The aim of this study was to find the best position for the piezoelectric fan cooling radiator. In the numerical simulation, the pressure radiator fan blade tip-to-tip distance (L g ), height of the piezoelectric fan center from the flow channel plate (H w ), fin row (n), radiator fin width (W f ), and the fin gap (G) were used for the vertical piezoelectric fan to obtain the Niu Saier number (N u ) and thermal resistance (R th ). Cyclical swings of the piezoelectric fan impede the uninterrupted flow of impact energy transfer on the boundary layer. At the tip of the blade actuation direction, the fluid reciprocating stroke, that is, the direction of the flow field, was pulled, and the front tip of the blade generated a vortex forming an entrained flow, but the hot and cold air were effectively mixed. The results showed that when the height of the center of the piezoelectric fan in relation to the flow channel plate was increased, the dissipation performance decreased comparatively. Furthermore, when a pressure fan was placed in front of the radiator, the height from the base center to the flow channel of the piezoelectric fan was reduced.

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Vortex formation by a vibrating cantilever

Cited by 63 publications

References 20 publications

The Influence of Surface Roughness on the Flow Fields Generated by an Oscillating Cantilever

The Influence of Surface Roughness on the Flow Fields Generated by an Oscillating Cantilever

Flow Generation by a Piezoelectric Fan

Heat Flow Field Analysis of the Effects of Vertical Piezoelectric Fan Placement on Heat Convection in Pin-Fin Heat Sink

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