“Plasma Tube” is proposed for nano particle transportation and for particle surface purification in this study. The well-controlled efficient nano particle transportation is realized by combining plasma actuation, electrostatic force and high oxidation potential of produced ozone in a tube. Nano particles in the plasma tube can be transported in axial direction with swirl. Nano particles near the inner electrode wall jump due to electrostatic force, which can suppress particle clogging in a tube. The characteristics of plasma induced flow, particle charging and ozone generation are experimentally clarified in this study for various electrode angles and electrical conditions. Finally, the powder transportation rate is quantitatively evaluated. The alumina powder with average diameter of 30 nm can be transported at the maximum rate of 2.8 mg/s at consumption power of as low as 0.35 W for the transportation distance of 100 mm.

View full abstract

Axial fluctuations in carrier concentrations cause detection noise during chemical analysis using flowing carrier streams. Here, we report a method of axial mixing using serially cascaded microchannel units with branches and junctions. Two branched channels in one unit differ in liquid residence time, and the time lags between the two branched channels are different for each unit. Each unit decreases the fluctuations in carrier concentration of the frequency associated with the time lag. The branched channels are in the form of spirals to induce the secondary flow that decreases axial dispersion and enhances the cancelling effect of the axial fluctuations from the branched channels. We evaluated the effect of secondary flow on the reduction in axial dispersion as a function of the Dean number in computational fluid dynamics simulations. Axial mixing in the prototype mixer was the most effective at a Dean number of 10. A prototype mixer whose volume was 52.5 mm³ reduced absorbance fluctuations from 27.2 to 5.0 mAU in a 0.1% trifluoroacetate aqueous: acetonitrile stream under these conditions. The frequency characteristics of the reduced absorbance fluctuations were evaluated through numerical simulations within a deviation of 20%.

View full abstract

This research presents a wind tunnel experiment for investigating three-dimensional flows in the vicinity of a blade in a Horizontal Axis Wind Turbine (HAWT) model. Though the design of the wind turbine blade has been recognized as a modern advance, most of them are based on two-dimensional sectional performance analyses. However, the actual flow around the rotating blade also has a flow effect from a span-wise direction that it is generated from centrifugal and Coriolis forces. A span-wise flow can change the boundary layer on the blade surface. The sectional performance strongly depends on the surface boundary layer. Thus, the actual flow characteristics and correct surface boundary layer in the vicinity of a wind turbine blade is important in designing a wind turbine blade with high performance. In this research, the test wind turbine was a three-bladed type. The test blade comprised four types of airfoils that were smoothly connected and distributed along the blade. The experimental investigation of the flow on the blade surface was performed by simultaneously measuring three-dimensional velocity components by the approach of a three-dimensional Laser Doppler Velocimetry (LDV) method: two LDV probes were used in the synchronized measurement of three-dimensional velocity components. Characteristics of the three-dimensional flow were investigated and visualized by velocity vector field, boundary layer and trajectory path. The results clarified that the three-dimensional flow for the inboard had higher values than the outboard. The two-dimensional relative velocity and the span-wise velocity for the optimum tip speed ratio and low tip speed ratio showed significant differences in the boundary thickness. The shape factor H had satisfactory results and could clearly separate laminar and turbulent regions. The flow trajectory seemed to be affected by the span-wise velocity at chord station y/c > 0.25.

View full abstract

Understanding and predicting the efficiency of displacement, i.e., the non-wetting phase saturation after drainage, is of great importance in many practical applications. In this study, we experimentally derive the empirical equations of the non-wetting phase saturation as a function of the capillary number, the Bond number, and the viscosity ratio. A series of laboratory experiments are conducted with a packed bed of glass beads. Several fluid pairs are used to change the viscosity ratio. However, the density of the non-wetting phase is lower than that of the wetting phase for all pairs. In the case of vertically upward injection, the non-wetting phase saturation decreases with the Bond number and increases with the capillary number for all fluid pairs. In the case of the unfavorable viscosity ratio, the non-wetting phase saturation is low because the displacement interface is always unstable. At a low capillary number, the capillary fingering enhanced by buoyancy results in low non-wetting phase saturation. In the case of the downward injection, if the viscosity ratio is favorable, the displacement front is always stable against the Darcy velocity. If the viscosity ratio is unfavorable, the displacement front is stable for low Darcy velocity, when the non-wetting phase saturation is high. When the Darcy velocity exceeds the critical velocity, the non-wetting phase saturation reduces.

View full abstract

In this research, an inexpensive aerodynamic shape optimization of airfoil is performed for Darrieus type vertical axis wind turbine (VAWT). Computational fluid dynamics (CFD) evaluations of various airfoil shapes are treated inexpensively by considering the apparent flow velocity magnitudes and apparent angles of attack at multiple positions of VAWT airfoil, which includes some assumptions as two dimensional steady flows and no consideration about flow interactions between blade airfoils. Global optimal shapes are efficiently explored by using a Kriging response surface model approach. An optimal VAWT airfoil is obtained by the maximization of a proposed objective function. Since our objective function for this design optimization of VAWT airfoil can be primary decomposed into the terms of thrust force and pitching moment, another multi-objective optimization of thrust/pitching moment coefficients is also performed for detailed discussions about the obtained optimal airfoil. Analysis of variance is performed on the Kriging response surface model to extract design knowledge in this design optimization problem. The obtained optimal airfoil achieves a significant improvement in the aerodynamic performance compared with an existing airfoil. Finally, expensive unsteady CFD simulations are performed for the obtained airfoils, that take into account unsteady flow interactions between three blade airfoils. The results of the unsteady CFD simulations validate the effectiveness of the proposed aerodynamic shape optimization approach for VAWT airfoil.

View full abstract

We investigated the influence of the airfoil geometry on the performance of the plunging airfoil numerically. In the present study, two circular arc airfoils with the different thickness were used and the numerical calculations were carried out within the laminar flow region to obtain the data of the extremely small micro air vehicles. Moreover, the arbitrary Lagrangian-Eulerian method was adopted to solve the moving boundary problem. The calculation results are summarized as follows. (1) The thickness of the airfoil has a strong effect on the lift and thrust forces, and these forces for the thick airfoil are insensible to the change in the angle of attack compared with the ones for the thin airfoil. (2) The optimal oscillating frequency of the plunging airfoil has a strong relation to the conditions of the flying or swimming animals, birds, fish and insects.

View full abstract

In order to improve the aerodynamic performance of external side mirror of race car, the wake flow around three-dimensional bluff body is studied in this study. Firstly, the high-speed PIV was applied to measure turbulent wakes generated by asymmetric side mirror (called CT-cylinder) and semi-cylinder at a Reynolds number of 6,240 in the circulating water channel. These flow fields were evaluated by time-averaged, instantaneous and phase-averaged flow structures and the FFT analysis. And then, one- and two-dimensional wavelet multi-resolution techniques were used to analyze the instantaneous velocity and vorticity data in order to obtain the turbulent structures of various scales. It is found that the CT-cylinder generates smaller separation region and lower Reynolds shear stresses than that of semi-cylinder, and produces the asymmetric flow structure and aerodynamic downforce. In the wake of CT-cylinder, the size or shape of the vortices shed from upper and lower side is different and the vorticity of upper side is larger than that of lower side, causing asymmetry and high-intensity vertical velocity fluctuation. The most contribution to the Reynolds shear stress come from large-scale structures and account about 82.0 % for CT-cylinder wakes and 78.6 % for semi-cylinder wake. The relatively small-scale structures make less contribution to Reynolds shear stresses.

View full abstract

Predicting leak rate through porous compression packing rings is a significant challenge for the design of external sealing of valves. Although few studies have been conducted to predict the leak rate through these seals, there is no comprehensive standard procedure to be used to design and select suitable compression packings for a maximum tolerated leak for a given application. With the ubiquitous use of the yarned packing rings in the sealing of the valves, and the strict regulations on fugitive emissions and the new environment protection laws, quantification of leak rate through yarned stuffing boxes becomes more than necessary and a tightness criteria based design procedure must be developed. In this study a new approach to predict leak rate through compression packing rings has been developed. It is based on Darcy's model to which Klinkenberg's slippage effect is incorporated. The predicted leak rates are compared to those measured experimentally using two different graphite-based packing rings subjected to different compression levels and pressures. A good agreement is found between the predicted and the measured leak rates which illustrates the validity of the developed model.

View full abstract

Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent 34th America's Cup in 2013 featuring AC72 catamarans with multi-element wing sail yachts sailing at unprecedented speeds, interest in wing sail technology has increased substantially. Unfortunately there is currently very little open peer-reviewed literature available with a focus on multi-element wing design for yachts. The limited available literature focuses primarily on the structures of wings and their control, rather than on the aerodynamic design. While there is substantial available literature on the aerodynamic properties of aircraft wings, the differences in the flow domains between aeroplanes and yachts is significant. A yacht sail will operate in a Reynolds number range of 0.2 to 8 million while aircraft operate regularly in excess of 10 million. Furthermore, yachts operate in the turbulent atmospheric boundary layer and require high maximum lift coefficients at many apparent wind angles, and minimising drag is not so critical. This paper reviews the literature on wing sail design for high performance yachts and discusses the results of wind tunnel testing at the Yacht Research Unit at the University of Auckland. Two wings with different symmetrical profiles have been tested at low Reynolds numbers with surface pressure measurements to measure the effect of gap geometry, angle of attack and camber on a wing sail's performance characteristic. It has been found that for the two element wing studied, the gap size and pivot point of the rear element have only a weak influence on the lift and drag coefficients. Reynolds number has a strong effect on separation for highly cambered foils.

View full abstract