research

Growth of Vorticity of a Moving Elastic Airfoil and Their Characteristics of Dynamic Forces

Many studies on the flow field around moving airfoils have been carried out using experimental and numerical approaches. These flow fields are a typical example of unsteady flow and have thus attracted attention. The present authors have previously qualitatively and quantitatively characterized vortex structures that form in the wake of a rigid airfoil with pitching, heaving, and a combination of both motions. The flow field around an elastic moving body has recently attracted attention from the viewpoint of insect flight, aquatic animal swimming, and the development of micro air vehicles. The flow field around an elastic body can be modeled as a coupled problem between the fluid and structure (fluid/structure interaction, FSI), with a series of phenomena, motions, structural deformations, and the generation, growth, and development of vortices repeated continuously. Now, we are trying to understand the growth of the vorticity of the elastic moving airfoil and their characteristics of the dynamic forces using not only the PIV measurement but also the Fluid-Structure interaction simulation by ANSYS/ANSYS-CFX

Three-dimensional Vortex Structure Formed by a Sweeping Jet from a Fluidic Oscillator Ejected into a Main Flow

Flow separation can be a major factor in the performance degradation of fluid-based processes, as it can result in several deleterious effects, such as vibration and noise. Recently, an active flow separation control device based on a fluidic oscillator that does not require electric power has been reported. This device is able to generate a sweeping jet over a wide spatial range as well as fluid oscillations, and its internal structure eliminates the need for a drive unit. Furthermore, the development of 3D printing technology has enabled the rapid design of these fluidic oscillators, so these units are expected to have applications in flow separation control. Many studies of flow separation control techniques using a fluidic oscillator have been reported. However, these prior studies all focused on the dynamic forces acting on an airfoil in conjunction with a fluidic oscillator. There have been no studies regarding the flow structure of the sweeping jet emitted by a fluidic oscillator, and the separation flow control mechanism associated with fluidic oscillators is not well understood. The goal of the present study was to examine the flow structure produced by interactions between the sweeping jet from a fluidic oscillator and a primary flow. This was accomplished by performing stereo particle image velocimetry (PIV) measurements of a flow field produced by a sweeping jet to the main flow. These assessments allowed quantitative visualization of the development of the 3D vortex structure resulting from the interaction.

Breakup Mechanism of Bubble Cloud

The flow field that forms at gas–liquid interfaces is strongly three-dimensional and extremely non-stationary, and it is considered difficult to understand. Among the types of gas–liquid two-phase flows, cross-flows, in which a fluid (gas phase) is blown into a main flow (liquid phase) having a velocity, are used to some mechanical applications via a chemical reaction. In recent years, several studies have been conducted on gas–liquid two-phase cross-flows using both experimental and numerical approaches. However, these studies have focused on the shape of bubbles. The mechanism of their breakup mechanism of the bubbles in the mainstream has not been understood. In this study, qualitative/quantitative experiments and numerical simulation are performed to clarify the bubble breakup mechanism. The three-dimensional dynamic behavior of the gas–liquid interface was captured by the numerical simulation using the commercial software ANSYS CFX and the particle image velocimetry (PIV).

Characteristics of Dynamic Forces Generated by a Flapping Butterfly Wing Related with the Dynamic Behavior of the Vortex Rings

The flow field around the butterfly wing is one of the most common unsteady flows around the moving elastic body. Because the butterflies fly by skillfully controlling their wings, which deform elastically, and vortices are generated around their bodies. The elastic wing motion of the flying butterflies produces a dynamic fluid force by manipulating the flow field around wing. Recently, the complex flow structures around the flapping insect wings have been visualized clearly using quantitative flow visualization techniques. The authors visualized the dynamic behavior of vortex rings that forms over the tethered flapping insect wings, Cynthia cardui and Idea leuconoe, using two-dimensional PIV. Moreover, the authors visualized a three-dimensional vortex structure in the wake of free-flight Cynthia cardui and Idea leuconoe using scanning PIV. Furthermore, the authors directly measured the dynamic lift of tethered flapping butterflies using a six-axes sensor. However, the characteristic of the dynamic forces generated by the flapping butterfly have not been understood sufficiently. The purpose of the present study is to understand quantitatively the characteristics of dynamic forces generated by the flapping butterfly wing related with the dynamic behavior of the vortex ring by the dynamic force measurement using six-axes sensor and the PIV measurements.

 

Development of Artificial Muscle based on Conducting polymer

Actuators, or artificial muscles, based on conducting polymers (CPs), constitute the base for the development of promising polymeric sensing motors, tools for surgeons, or zoomorphic and anthropomorphic soft robots. They are electrochemical devices; the CP oxidation/reduction drives the exchange of ions and solvent with the electrolyte causing reversible volume variations and device actuation. Some electrochemical characterizations of these actuators have been already investigated. Moreover, some asymmetric bilayers constituted by two different conducting polymers, CP1/CP2, thus both reactive, have been described. In this study, three bilayer muscles (PPy-ClO4(Lithium perchlorate)/PPy-DBS (dodecyl benzyl sulphonate), PPy-ClO4/tape, and PPy-DBS/tape) are characterized during potential cycling in aqueous solutions. The dynamo-voltammetric (angle vs potential) and coulo-dynamic (charge vs potential) results give the reaction-driven ionic exchanges in each PPy film. Our aim in this work is to investigate the characterization of the three selected bilayer muscles, cooperative and antagonist dynamic effects.

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