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In the semiconductor device manufacturing process, wet cleaning is an important process that determines product yield. In this paper, spray cleaning in the wet process of semiconductor device manufacturing is described from the perspective of macroscopic fluid dynamics. When micrometer-order particles adhere to the substrate, the van der Waals force, as discussed in DLVO theory, is dominant. When these particles are removed by spraying, the fluid drag force on the particles is a major factor. In addition, in semiconductor device cleaning, it is not enough to simply increase the fluid drag; as a trade-off, increasing the fluid drag also increases the probability of pattern collapse and electrostatic damage. Thus, as semiconductor device miniaturization progresses, cleaning methods with even higher selectivity are needed. [ABSTRACT FROM AUTHOR]

Direct fuel injection spray is used to improve thermal efficiency and environmental performance in SI engines. A mixture is formed through momentum exchange between fuel droplets and ambient gas, along with mixing accompanied by droplets evaporation and diffusion. Both the droplets development derived from the liquid fuel atomization and the entrainment ambient air predominate the mixture formation process. The purpose of this study is to elucidate the momentum exchange characteristics of the spray formed by a single-hole injector for direct injection gasoline engines. To clarify the momentum exchange characteristics of spray droplets, the spray was visualized by optical experiments and the spray development process was analyzed. The parameters are injection pressure and ambient density. A comparison of experimental results and a model analysis of a single droplet movement was conducted, and different of deceleration characteristics were evaluated. In the case of the fuel spray, the induced ambient air by the spray tip droplets decreases the relative velocity between the spray droplets and the spray internal flow. A model for predicting the temporal variation of the spray tip penetration from the different of momentum exchange characteristics between the spray and the droplet was proposed.

Weakly nonlinear (i.e., finite but small amplitude) propagation of plane progressive pressure waves in compressible water flow uniformly containing many spherical gas bubbles is numerically investigated with a special attention to a drag force acting bubbles and translation of bubbles. The gas and liquid phases are flowing with initially independent velocities. Drag force and virtual mass force are introduced as interfacial momentum transports. Translation and spherically symmetric oscillations are considered as bubble dynamics. In this paper, under these assumptions, we numerically solve the KdVB (Korteweg-de Vries-Burgers) equation previously derived by ourselves (Yatabe et al., Phys. Fluids, 33 (2021), 033315) from basic equations based on a two-fluid model. The main results are summarized as follows: (i) The drag force acting on bubbles increases a dissipation effect of waves and drastically changes the phase and amplitude of waves. (ii) Although the translation of bubbles increases the nonlinear effect of waves, its contribution to waveform is quantitatively small. (iii) The effect of the drag force decreases with decreasing the initial void fraction and with increasing the initial bubble radius. That of the translation decreases with decreasing the initial void fraction, and is almost independent of the initial bubble radius. (iv) The spatiotemporal evolution of two type of dissipation effects (i.e., dissipation terms) due to the acoustic radiation and to the drag force is different tendency. [ABSTRACT FROM AUTHOR]

The effects of the configurations and structural parameters of the cylinder blade wind turbine driven by the steady lift force of the longitudinal vortex on its rotation and drag force characteristics were investigated. When the longitudinal vortex was formed stably behind the moving direction of the cylinder blade, a negative pressure region was generated between the cylinder blade and the wake ring-plate. This negative pressure region applies the drag force on the cylinder blade in the mainstream direction simultaneously with the driving force in the rotation direction. The drag force was generated by the irregular formation of the necklace vortex when the cylinder blade was fixed, but the drag force increased even more when the necklace vortex became stable with the rotation. A complicated behavior of drag coefficients with increasing flow velocity was observed for the single-cylinder blade due to the influence of the inner region of a ring-plate and the tip-ends of the cylinder blade. In the case of the stepped cylinder blades, in which the unnecessary region where the influence of the necklace vortex does not occur was removed, the drag coefficient remained almost constant regardless of the flow velocity, and the formation of the necklace vortex was stabilized. In the multiple stepped cylinder blade wind turbine, the rotational speed increased by the effect of adjacent blades. The drag force acting on the entire wind turbine increased with the increasing of the blade number, but the drag force per blade was almost constant.

The drag and lift forces acting on a droplet moving near a plane wall were numerically investigated using a three-dimensional direct numerical simulation (DNS) based on the marker and cell (MAC) method. The numerical results showed that the presence of the wall causes an increase in the drag force. The less viscosity ratio of the internal fluid to the external fluid caused the decrease in the wall-induced drag coefficient. The direction of the wall-induced lift force acting on a droplet near the wall changed depending on the viscosity ratio in the high Reynolds number cases. At low Reynolds numbers, the wall-induced drag and lift coefficients of a droplet had the similarity for different viscosity ratios, respectively.

Plate penetration into dry granular materials is numerically studied using a large-scale discrete element method (DEM). To investigate the effects penetration angle on the interactions between particles and the plate, the simulations with the different angles from 0 (vertical penetration) to 60 degree are compared. The results show that the drag force acting on the plate increases with a decrease in the penetration angle. For all cases, the formation of shear bands from the plate tip to the free surface in the bed is confirmed. The analysis of energy consumption in the bed shows that most of the energy input to the bed by the plate is locally dissipated by sliding frictions between particles in shear bands. As the penetration angle decreases, the amount of energy dissipation due to the friction increases in the shear bands formed near the plate tip. [ABSTRACT FROM AUTHOR]

The interaction between dry granular materials and a plate is numerically studied using a large-scale discrete element method (DEM) simulation. In the simulation, a vertical flat plate is dragged horizontally through closely packed materials. To examine the effects of particle size on the drag force acting on the plate, five cases with different mean particle diameter Dp50 = 4.0, 2.0, 1.6, 1.2 and 0.8 mm are compared. The results show that for larger particles, the force randomly fluctuates as the plate advances while for smaller particles, the force oscillates with a larger amplitude. The analysis of angular velocity of the particles shows that the force oscillation is attributed to the evolution of shear bands formed only in the bed of the smaller particles. [ABSTRACT FROM AUTHOR]

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Dragonflies can perform both of gliding and flapping flight and have high maneuverability in spite of small-size. The aim of this study is to develop Micro Air Vehicle (MAV) based on the flight of dragonfly. The characteristics of wings are very important for development of MAV. Dragonfly wing is easy to be passively deformed in the tip side from the nodus in flapping flight, and thereby, aerodynamic force is generated effectively. In this study, the effect of passive deformation of wing on aerodynamic force was investigated using fluid-structure interaction analysis to develop the artificial wing suitable for dragonfly-like MAV. In this study, aerodynamic characteristics of wings in the gliding flight and aerodynamic force generated in flapping flight are numerically analyzed. In this analysis, nodus wing models, which can deform passively, and rigid wing model, which cannot deform, are used. Nodus wing model imitates the nodus structure; the tip side of this model is free to rotate around leading edge. As a result of gliding flight, the lift coefficient of the nodus wing was lower in low-angle of attack and was higher in high-angle of attack, compared to rigid wing. Moreover, the more flexible wings are, the more change. The gliding flight is low-angle of attack usually. Therefore, flexible wing is less suitable for the gliding flight than inflexible wing. As a result of flapping flight, the nodus wing made drag force generated during down stroke lower compared with the rigid wing. However, thrust forces generated during up stroke in both wings were the same. Therefore, flexible wing is more suitable for the flapping flight than inflexible wing. The wings of dragonfly-like MAV need to appropriate level of flexibility to upgrade the performance in both case of gliding and flapping flight.

The typhoon often causes a serious damage of the apple before harvest. Many apples fall from trees by the strong wind. These apples are bagged to protect them from insects and control sun light for the apples coloring while they are ripening on the tree. We conceive that the wind-force acting on the bagging apple exceeds one without bag. Thus, we investigate the drag coefficient CD of the bagging apple by measuring drag force acting on an apple model experimentally. The shear stress on a stem under the typhoon is estimated for understanding one of mechanism for dropping apple due to the strong wind. The shear stress of a stem whose apple encounters the maximum velocity recorded at the past typhoon is estimated by the obtained CD. The drag force of the bagging apple becomes bigger than that of the apple without the bag. The bagging apple is not a rotational symmetry so that the CD is different with the different wind direction. The angle against the flow of model with the bag is changed from 0 deg. to 90 deg. to understand the influence of shape, since CD depends on the geometry. The shear force acting on the stem depends on the drag. Thus, the shear stress is larger if the drag is larger. The obtained shear stress is compared with allowable shear stress of a real tree. We suggest that there is possibility to decrease damage if we can decrease the drag of the bagging.

The flow around a two-dimensional permeable porous plate placed normal to a horizontal flat wall was investigated with the aid of a laser Doppler velocimetry (LDV). The experiment was performed in a circuit-type wind tunnel having a test section of 200 mm in width and 200 mm in height. Three kinds of porous metal plate of different porosity and permeability were considered in the present work. Mean velocity vector fields in a streamwise wall-normal plane indicated that a recirculation region behind the porous plate moved to downstream with increasing in porosity. At the highest porosity,the recirculation region disappeared and a forward (streamwise) flow occupied in the whole region downstream of the porous plate due to the air flow permeation. These velocity profiles were compared to the theoretical analysis from Görtler, and it was found that the present results agreed with theoretical ones in the region where the forward flow dominated. A streamwise component of root-mean-square velocity fluctuation was enhanced just behind the porous plate with highest porosity. However, at farther downstream, it was weaker than that observed downstream of impermeable plate. Furthermore, a wall-normal fluctuating velocity decreased over the porous plate, although it rapidly increased immediately above the impermeable plate. To estimate a drag force acting on the porous plate, a simple technique based on a momentum balance of the flow was applied. The net body force was determined from the conservative form of the momentum equations by using the measurements of the velocity and pressure profiles. The results of the analysis showed a decrease in the drag force increasing permeability of the porous plate. The behavior of velocity field suggested that the permeable porous plate led to stable windbreak effect.