Susumu Kobayashi

• Saitama Institute of Technology

This paper reports on the influence of underwater explosion depth on the disintegration of thin polystyrene plate attached microbubbles subjected to the underwater shock wave and the primary bubble induced by the explosion. The underwater explosion is created by the electrical discharge. The thin plate motion caused by the interaction of underwater...

We consider the problem of internal structure of the triple point appearing in Mach reflection, which is considered to be important for the cause study of the von Neumann paradox as well as the shock reflection itself in rarefied gas. We investigate it in an adequately made finite region near the triple point and use analytical approach rather than...

The singular nature of the flow near the triple point is investigated analytically based on a solution of the steady 2D Navier–Stokes equations system in polar coordinates, with special attention on the cause of the Neumann paradox. It gives a centered fan-like flow from the triple point in widening the slip flow region. Angles and curvatures of th...

Oblique shock reflection phenomena have long been studied both theoretically and experimentally. In ordinary situations, incident shock is considered to be reflected off some solid hard material. In this case, the deformation of the reflection surface is negligible even if the pressure rise is high, and the boundary condition can be easily assigned...

Oblique shock reflection has been well investigated when the reflecting wedge is solid. In that case, the acoustic impedance is extremely high and no transmitted wave is considered. However, the acoustic impedance of elastic materials is not so high compared with metal that some inherent reflection characteristics can be expected.

In this study, we conducted experiments using a shock tube to investigate how the thickness of soft reflecting material affects the reflected shock wave of oblique shock reflection. Results indicated that transition to Mach reflection (MR) is delayed when the reflecting surface is silicone, compared with that when the surface is rigid. Regarding th...

When a shock wave is incident on an obstacle, it is not only reflected back but also transmitted into the obstacle itself. The transmitted shock wave has not been fully investigated so far, compared with the reflected shock wave. In actual situations, the behavior and the characteristics of the transmitted shock wave are also of importance. In batt...

In recent years, products are being downsized. So, machines that manufacture them need to be miniaturized as well. However, monitoring the cutting state in machining small parts is quite difficult. In this study, an acoustic emission (AE) technique was used to detect AE signals generated during cutting which could be very useful for monitoring the...

Regular reflection (RR) and Mach reflection (MR) are theoretically both possible in the dual-solution domain of oblique shock reflection. The physical difference between the two types of reflection is the pressure behind the reflected shock wave: that of MR is lower than that of RR for strong shock reflection. The magnitude relation of these pressu...

Friction and wear phenomena between metals are very complex because various influence factors affect them. So, it is very difficult to predict friction coefficient and wear amount correctly. In this study, the formation process of metallic transfer layer was investigated by an in situ observation and various measurements with a pin-on-disk-type sli...

Because a lot of factors are controlled as for friction and wear phenomena between solids, it is complex and the forecast is difficult. There is a transfer film formation as the one phenomenon. The transfer film is a film formed to the entire friction surface with the transfer and remaining of the transfer particle in the friction surface, and the trib...

Analyses of oblique reflection of shock waves assume ideal model wedges are utilized. The surface of the model wedge is smooth and the wedge tip is sharp. However, in reality, the model wedges used in experiments are never ideal

This paper experimentally investigates the validity of self-similarity of strong shock reflection phenomena in a shock tube. The models used for the shock-tube experiment are ordinary wedges with various reflecting wedge angles. The triple-point trajectory is approximately a straight line through the wedge apex for each reflecting wedge. However, a...

In oblique shock reflection, when an incident shock Mach number and/or a reflecting wedge angle are small, the reflection configuration differs from Mach reflection (MR) and is known as von Neumann (NR). It is characteristic in that a Mach stem is tangentially connected with the incident shock at a triple point, the reflected wave is weak, and a sl...

Oblique shock reflection phenomena have been long considered to preserve selfsimilarity. However, the authors’ investigation of von Neumann reflection [1] was a turning point that cast doubt on self-similarity. The von Neumann reflection is a new type of oblique reflection first referred to by Colella and Henderson [2]. This reflection is geometric...

The effects of transport properties (viscosity and thermal conductivity) and surface roughness were compared experimentally to investigate non-self-similar Mach reflection phenomena in weak shock waves. The effect of the transport properties was changed by varying the initial pressure ahead of the incident shock in experiments conducted at Karlsruh...

Up to the present, the von Neumann paradox has been mentioned only for weak shock waves, and the classical theories have been considered to be valid for strong shock waves. In the present paper, we discovered experimentally that the paradox also occurs in strong shock waves for the same reason as in weak shock waves. We also explain why it has not...

The mechanism responsible for the high pressures generated in gas phase during the shock wave interaction with granular layer on a wall was studied experimentally and numerically. The granular layer used in experiments was composed of spheres fixed to each other and to the wall of shock tube. The pressure under the spheres was measured, and the sho...

In order to shed light on the initial mechanism of dust entrainment behind a moving shock wave, the particles' motion behind a planar shock wave was investigated using horizontally placed shock tubes and a direct photographic technique synchronized with the shock wave motion. The drag coefficient measurement of an accelerating spherical particle (0...

This paper deals with the von Neumann paradox, an as yet unsolved major problem in supersonic gas dynamics. We conduct a series of experiments using a conventional shock tube and focus attention on the flow-field around the triple point at various locations of the incident shock wave. By measuring the position of the triple point and the angle made...

According to standard textbooks on compressible fluid dynamics, a shock wave is formed by an accumulation of compression waves. However, the process by which an accumulated compression wave grows into a shock wave has never been visualized. In the present paper, the authors tried to visualize this process using a model wedge with multiple steps. Th...

Recently, Mach reflection, which has long been considered to be a self similar phenomenon, turned out to exhibit non-self-similar characteristics by a series of detailed experiments with optical visualization technique. On the other hand, it is inferred by a numerical experiment, that the effect of transport properties (viscosity and thermal conduc...

The purpose of the present paper is to compare the characteristics of the weak Mach reflection (MR) and the so-called von Neumann reflection (vNR). A series of experiments was performed to investigate both reflections. Attention is focused on the flow properties around the triple point. By measuring the location of the triple point and the angle be...

In this paper, we consider the phenomenon of unsteady Mach reflection generated by a plane shock wave advancing over a straight wedge surface, with particular attention to the deviation of the flow field from the self-similar nature. We examine the observed change in angle between incident and reflected shocks, which is in contrast to the fact that...

In order to investigate a later stage of Mach reflection and to check the non-selfsimilar and unsteady behavior, we performed experiments in a shock tube with a cross-section of 185 mm square in Karlsruhe University. The reflection configuration was visualized by means of the infinite fringe spacing interferometry, which is similar to the Schlieren...

The unsteady behavior of the non-stationary weak shock reflection over a wedge was investigated. Two kinds of flow models just behind the reflection point for regular reflection and Mach stem for Mach reflection were introduced to explain the unsteady behavior of the wave configurations. Based on these models, viscous effects caused by the boundary...

The purpose of the present paper is to consider the von Neumann reflection (vNR) which takes place for a small incident shock Mach number and a small wedge angle. A series of experiments has been performed with ordinary smooth straight wedges and step-like wedges that simulate the former. The reflection configuration over the step-like wedge has su...

When we carry out shock reflection experiments over a wedge, it is inevitable that the wedge has a finite "radius of curvature" at its tip. Then the reflection will be truly unsteady at the tip, like the reflection over a circular cylinder. A series of shock reflection experiments has been carried out by the use of shock tube in order to investigat...

Method of prediction for a critical angle of transition from Mach reflection to regular reflection over an elliptic concave surface is investigated analytically. In the analysis, the relation between the position and the propagating velocity of a reflection point on the concave surface is used when the reflection is Mach reflection. Based on this r...

A series of experiments on the transition of a shock reflection was conducted using a conventional shock tube. Attention has been focused on the transition phenomenon during the propagation of an incident shock wave whose Mach number ranges from 1.10 to 1.40. The present detailed investigation has helped clarify the transition phenomenon from regul...

Shock reflection phenomena over nonstraight surfaces have been investigated. The models used in this experiment are ordinary circular cylindrical concave and convex wedges and step-like wedges which simulate the former. The step-like wedges were used to investigate the process of reflected-wave formation over circular cylindrical wedges (method of...

Shock-tube experiments have been performed in order to examine the mechanism to generate overpressures in porous materials such as a dust layer during the propagation of a shock wave over the pourous materials. Two different models for the porous materials were used: slitted-plates model and spherical-particles model. The former is composed of slit...

Experiments have been conducted to investigate the formation mechanism of the reflected shock wave over curved surfaces by means of step-like double wedges as well as ordinary double wedges. The step-like double wedge simulates variation in the wedge angle of a curved surface and it is composed of the first flat smooth slope and the second step-lik...

Oblique reflections of a weak shock wave have been investigated both theoretically and experimentally. A modified three-shock theory is introduced to explain the well-known von Neumann paradox for weak Mach reflection. As a physical reality, the triple point is not a mathematical point and the slipstream has a finite thickness. Consequently, the ef...

When a shock wave propagates over a dust layer, a dust entrainment into an air takes place behind the shock wave. In order to understand the mechanism responsible for the lift-up from a floor, spherical particles of identical diameter (about 0.4 mm) were laid in a straight line on the model floor before firing a shock tube. The incident shock wave...

The regular reflection of a shock wave over a porous layer has been investigated both theoretically and experimentally. Two model types are considered. One may be called a simple sink theory, in which the deflection angle is the only parameter taking the sink effect of the porous layer into consideration and the detail of the flow in the porous lay...

The present paper reports the experimental and theoretical results for oblique reflection of weak shock waves. We introduce a modified three-shock theory to explain the well-known von Neumann paradox for weak Mach reflection. The theory proposed here considers the effect of slipstream divergence immediate behind a triple point. By giving the angle...

Detailed experimental analysis has been made on shock reflection over a wedge with surface roughness in a shock tube. The incident shock Mach number M was 1.43. The experimental parameters were the reflecting wedge angle and the size of gutters. The wave structure is similar among model wedges. Detailed measurement into the triple point trajectory...

The oblique shock reflection over a multi-guttered model wedge is investigated at constant Mach number. The experimental parameters were the reflecting wedge angle and the depth of the gutter. It is found that, unlike the case of a smooth surface, the wave structure is not self-similar but similar with respect to the coordinate system made dimensio...

Abstract Results of oblique shock reflection over a particulate layer are reported. A variable parameter was the reflecting wedge angle. Other parameters such as an incident shock Mach number and a mean diameter of particles deposited on the wedge were fixed at 1.41 and 30mm, respectively. The wave structure is compared with that for a two-dimensio...

To find the mechanism for cooling hot semi-conductors in an alternator mounted on an automobile is important to improve performance of an automobile. The cooling fan on the front end of the alter-nator is installed to suck an air through inlets of the rear cover in order to cool down the hot semi-conductors just inside the rear cover. Thus the cool...

The shock reflection over a multi-guttered wedge is investigated. The result is compared with the case with a dusty surface. It is found the wave structure is not self-similiar but similar with respect to a nondimensional coordinate based on the pitch of gutters. The wave structure is essentially unsteady and the entire waves reflected from the bot...

Detailed experimental analysis was made on the shock reflection over a wedge with surface roughness in a shock tube. The roughness was made by gutters carved on the wedge. The incident shock Mach number was Ms=1.43. The experimental parameters were the wedge angle and size of gutters. The wave configuration in the neighborhood of the triple point o...

An experiment on ignition of pulverized coal particles was conducted by means of a shock tube. A pneumatic injection device was used for particle dispersion. The loci of the ignited particles were photographed together with direct shadowgraphs of dispersed particles. The influence of the state of the dispersed particles ('dispersity') on the igniti...

The experiment on oblique shock reflection has been carried out by means of a shock tube and a model wedge. The incident shock Mach number M was about 1.42 and the working gas was air. Waves were visualized and analyzed by schlieren photography. Attention was focused on the quantitative analysis of the unsteady behavior of the triple point. The evo...

The behavior of a disturbance wave with finite amplitude is considered in the course of its propagation through a gas carrying a great number of small solid particles nonuniformly distributed in space. The results reveal that the expansion waves always damp out due to the interaction between both phases, while the weak compression waves decay when...