Yoshihiro Kubota

Aerodynamic Particle Resuspension Due to Human Foot and Model Foot Motions

Human foot motions such as walking and foot tapping resuspend the particulate matter on the floor and redistribute it, increasing the particle concentration in air and affecting the indoor air quality. The objective of this article is to experimentally investigate the mechanism of particle resuspension and redistribution due to human foot motion from focusing on aerodynamic effect. In particular, we have examined generation and deformation of a vortex produced by foot motion and how it is affected by the shape of the shoe sole. The experimental methods used were particle visualizations and particle image velocimetry (PIV) measurements in air, supplemented by dye flow visualization in water. The flow visualizations with human foot tapping and stomping were performed to elucidate the particle resuspension in real situations. In the laboratory experiment, the foot was modeled as either an elongated plate or a prosthetic foot wearing a slipper, moving normal to the floor downward or upward. The particle resuspension and redistribution were associated with the wall jet between the foot and floor and the vortex dynamics. With the elongated plate foot model and the slipper, three-dimensional vortex structure strongly affected the particle redistribution and its direction. Copyright 2013 American Association for Aerosol Research

An Experimental Investigation of the Flowfield and Dust Resuspension Due to Idealized Human Walking

In order to address how human foot movement causes particles to be resuspended from the floor, particle flow visualization and particle image velocimetry (PIV) measurements were performed on a simplified model of the human walking motion; a disk moving normal to the floor. Flow visualization of particles, seeded initially on the ground, indicates that particles are resuspended by both the downward and upward motions of the walking process. On both the upstep and the downstep, particle resuspension occurs due to a high velocity wall jet, forming between the wall and the disk in general accord with the mechanism for particle resuspension put forth by Khalifa and Elhadidi (2007, Particle Levitation Due to a Uniformly Descending Flat Object, Aerosol Sci. Technol., 41, pp. 33-42). Large-scale ring vortex structures were formed on both the downstep and the upstep, and did not cause particle resuspension, but were extremely effective at quickly moving the already resuspended particles away from the wall. By varying the seeding of the particles, it was determined that only particles underneath and toward the outer edge of the disk are resuspended.

Splash Formation by a Spherical Body Plunging into Water

Splashes caused by a spherical body plunging into water were investigated experimentally using a high speed CMOS camera. We categorized types of splash according to impact velocities of the sphere. Three types of splash were found: Type-I is a thin spire-type splash, Type-II is a mushroom-type splash with many droplets, and Type-III is a crown-type splash with many droplets. The reaction to the concave water surface attached to the sinking sphere is a cause of the Type-I splash. The film flow climbing up the sphere is a dominant cause of the Type-II splash. The velocity of the film flow, which is proportional to the impact velocity of the sphere, affects the fingers of the film flow, detaching of droplets, and maximum height of the Type-II splash. The Type-III crown-type splash is characterized by water jets with many droplets. A bulky air column in water is formed behind the sinking sphere, and longitudinal ridges and ripples on the surface of the air column were observed.

Some remarks on surface conditions of solid body plunging into water with particle method

BackgroundThe water splash patterns strongly depend on the surface conditions of the solid object. The present paper discusses the influence of the surface conditions of the solids falling into the water on the formation of the splashes, employing the experimental method with the high speed video camera and the numerical approach by the particle method.MethodsWe propose two engineering models for calculating the Navier–Stokes flows to distinguish the different surface conditions of the solids falling into the water. One is to add the attractive or repulsive force between the water and the surfaces of the solids, and the other is to consider the swelling ratio as the slip condition, which causes the different wall shear stresses at the interfaces between the solids and the water.ResultsThe above models are successfully employed to study the effects of the differences of the surface conditions of the falling objects on the splash formations.ConclusionsWe have successfully calculated the splashes caused by the different surface conditions of spheres using the MPS method.

Influence of head shape of solid body plunging into water on splash formation

We experimentally investigated the influence of a head shape of a solid body plunging into water on splash formation. Three different head shapes were tested: a hemisphere, cone, and circular cylinder. A hemisphere as a tail shape is common to all three head shapes. We captured images of splash formation using a high-speed CMOS camera. We found that a film flow generated at an early stage when a body impacts the water surface influences subsequent events until the splash sequence is completed. We explain the origin of the film flow according to the principle of conservation of momentum. The film flow as the primary splash originates from water displaced by the head. The meridian line, which connects the head to the tail of the body, affects separation of the film flow and causes the secondary splash. The air cavity generated when the body plunges into the water is also influenced by the head shape. The tertiary splash is formed by a reaction of the air cavity, which is detached from the body. We found that the secondary dome-type splash obstructs growth of the tertiary splash. Thus, we conclude that the head shape affects all events of the splash.Graphical Abstract

Pulsatile Jet Ejected from Lips

The mechanism of sound generation by lips is studied for basic understandings of biological sound. The sound is similar to buzzing, and is known as a sound which is generated when the trumpet player blows breath to a mouth piece. The sound and vibration of lips are observed experimentally by using a microphone with a high directivity and a high-speed CCD camera. The flow through the opening of lips are observed by using a smoke visualization. The vibration of the lips model is also observed by a high-speed CCD camera with 1000 fps. The lips model shows interesting motion by jetting the compressed air. The cyclic motion of the opening and closing is observed. The frequency of motion relates the natural frequency of the model. The oscillation causes the pulsating sound that is superimposed higher frequencies. The digon shape of nozzle relates the higher frequency sound.

Influence of Water-Splash Formation by a Hydrophilic Body Plunging Into Water

The objective of this study is to understand the relationship between water-splash formation and the surface conditions of bodies plunging into the water’s surface by considering hydrophilicity strength. A hydrophilic body (constructed with hydrogel), as well as an acrylic resin body, was created to understand the influence of hydrophilicity on splash formation. The strength of hydrophilicity was determined by investigating degrees of swelling. We obtained consecutive images of splash formation by using a high-speed CMOS camera. We show that water-splash formation is related to water-film formation by studying: 1) droplets formed at the film edge, 2) mushroom-or dome-type splashes caused by film impinging, and 3) crown-type splash caused by film separation. The strength of hydrophilicity affects the splash-formation process of the mushroom- and crown-type splashes. The difference in formation process is caused when the film velocity increases with hydrophilicity. As the film velocity increases with strong hydrophilicity, the film flow separates from the body surface and an air cavity forms. Crown-type splashes form with hydrophilic bodies because such film separation occurs. Moreover, the relationship between the strength of hydrophilicity and film velocity was examined empirically. These results indicate that the hydrophilic body does not alter the splash-formation process.Copyright

Effects of Wall Condition of a Plunging Body on Splash

Splashes generated by hydrogel sphere were simulated numerically and experimentally for investigating the effects of slip like mucus of living things. Numerical simulation using MPS (Moving Particle Semi-implicit) method was carried out. We defined the slip ratio as the swelling degree of hydrogel and installed the slip ratio into the MPS method. The swelling degree is the ratio of the weight of water against that of hydrogel. We simulated the splashes generated by the hydrogel spheres which had the different swelling degree plunging into water. As the evaluation of swelling degree on the surface of actual hydrogel spheres we also tested by using the hydrogel spheres plunging into water experimentally. The height of splash as a result of reaction of the air cavity became higher according to the increase of the swelling degree. The speed of hydrogel sphere sinking in water tank was also quicker in the numerical simulation. The reason of these results was that the velocity of water around the hydrogel sphere became quicker due to the slip on the surface.© 2011 ASME

Aerodynamic Particle Resuspension due to Human and Model Foot Motions

Human foot motions such as walking and foot tapping detach the particulate matter on the floor and redistribute it, increasing the particle concentration in air. The objective of this paper is to experimentally investigate the mechanism of particle resuspension and redistribution due to human foot motion. In particular, generation and deformation of vortex produced by the foot motion and how they are affected by the shape of sole have been examined. The experiments were carried out by particle flow visualization and the Particle Image Velocimetry (PIV) measurements in air, and dye flow visualization in water. The flow visualizations with human foot tapping and stomping were also carried out in order to elucidate the particle resuspension in real situations. In a laboratory experiment, the foot was modeled either as an elongated plate or a foot wearing a slipper, moving normal to the ground downward or upward. To focus on the aerodynamic effect, the model foot was stopped immediately above the floor before contacting the floor. The results indicated that the particles were resuspended both in downward motion and in upward motion of the foot. The particle resuspension and redistribution were associated with the wall jet between the foot and floor and the vortex dynamics. With an elongated plate, three-dimensional vortex structure strongly affected the particle redistribution.Copyright