小直径円管内を伝播する衝撃波の干渉計測

In this study, we developed a diaphragmless driver section with two pistons to generate the shock wave in small diameter tubes. An optical system using a He-Ne laser is constructed for the definition of a main piston opening time. The trajectories of main piston are measured under the several initial driver pressures. Additionally, the motion equation for the main piston is derived from a simple motion model. Moreover, the laser differential interferometer is constructed for the contactless measurement of the shock waves. The shock waves generated by our diaphragmless driver section, propagating in 2 and 3 mm inner diameter tubes are measured by the laser differential interferometer. The Mach number of the shock wave and the density ratio across the shock wave can be calculated by the interference signal obtained from the shock wave measurement. Additionally, the Mach number distributions along the axial direction of the tubes and the relation between the shock wave location and time (shock wave diagram) are obtained. Consequently, it is attributed to the fact that the friction effect between the test gas and the inner wall of the tubes becomes larger with decreasing the inner diameter of the tube.

Recently, the micro-shock waves have attracted attention of researchers in several fields of science. It is well known that the shear stress and the heat transfer between a test gas and a wall lead to significant deviations from the normal theory of a shock wave propagating in a small diameter shock tube[1][2]. In our previous research, we developed a diaphragmless driver section using a rubber valve, and estimated the valve opening characteristics[3]. In addition, the shock wave measurements in the driver pressure range from 0.1 to 0.2 MPa were made in 1 and 3 mm inner diameter shock tubes with rubber valves, while the shock wave measurements in small diameter tubes were performed at a relatively low driver pressure[4][5][6]. At relatively high driver pressures over 0.5 MPa, shock wave measurements using the diaphragmless driver section with the rubber valve are very difficult to perform, because of the structural properties of the section. The technique of two pistons for diaphragmless driver section, which was invented and applied by Oguchi, et al.[7] and Maeno, et al.[8]. Its technique is successfully used especially in the larger diameter shock tube and initial pressure ratio, and has some accomplishments[9][10]. They concluded that, the diaphragmless driver section with two pistons is capable of producing the shock waves and is very convenient at the driver pressure range from 0.3 to 0.9 MPa, and there are some advantages over the convential shock tube as high reproducibility, and so on. However, there are no reports about applying this technique for generation of the shock wave in the small diameter tube. In this study, we simultaneously measured the velocities of shock waves and the density ratios across the shock wave, generated by originally developed diaphragmless driver section with two pistons, propagating in 2 and 3 mm inner diameter tubes by using laser differential interferometer.

Recently, the micro-shock waves have attracted attention from researchers in several fields of science. It is well known that the shear stress and the heat transfer between a test gas and a wall lead to significant deviations from the normal theory of a shock wave propagating in a small-diameter shock tube [1, 2]. In our first research, we developed a diaphragmless driver section using a rubber valve, and estimated the valve opening characteristics as the first step towards clarifying the shock wave characteristics propagating in the small-diameter tube [3]. As a second step, the shock wave measurements in small-diameter shock tubes were performed at a relatively low driver pressure by using the driver section with rubber valve [4–6]. However, at relatively high driver pressures over 0.5 MPa, shock wave measurements using the diaphragmless driver section with rubber valve are very difficult to perform, because of the structural properties of the rubber valve.

An experimental and numerical investigation has been performed to study the evolution of shock waves undergoing a sudden expansion in one direction while restricted in the second. Experimental data are gathered and studied for shock waves undergoing the sudden 4:l area expansion in air for Mach numbers of 1.5 and 2.0. Detailed, time-accurate measurements of the shock wave and vortex core location as well as wall pressure data are presented. In addition, the evolving flow structure through the time-accurate flowfield imagery is also presented. The results of these experiments are compared to twodimensional numerical simulations specific to the Mach 1.5 and 2.0 initial conditions and geometry. The direct comparisons of the experimental work and numerical simulations provide insight into flowfield phenomena such as viscous dissipation and sh&&/vortex interaction. The data presented in this effort further elucidates key modeling questions by providing time-accurate flow visualization and pressure data of a two-dimensional shock wave undergoing a sudden expansion in a confined chamber. * Aerospace Engineer, Senior Member AIAA ’ Senior Principal Consultant, Associate Fellow AIAA ’ Research Engineer, Member AIAA ’ Professor & Department Chairman, Associate Fellow AIAA ‘I Associate Professor ’ Associate Professor, Senior Member AIAA ‘* Assistant Professor This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Background Gas dynamics of fast, transient characteristics includes issues such as shock wave reflections, vorticity production, shock-vortex interaction, energy exchange between shock and turbulence, and shock focusing (Chang and Kim, 1995). Figure 1 illustrates the sudden area expansion of a shock wave within a confined domain indicating these interesting fluid dynamic phenomena. These phenomena occur at time scales ranging from microseconds to milliseconds. This paper presents a focused look at sudden shock wave expansion within a confined chamber and the interaction of that shock wave with other fluid dynamic features. Both experimental and numerical tools have been adopted. Recent investigations of this type of gas dynamic flow, given by Jiang et al. (1997), present experimental and numerical simulations of a circular shock tube generated flow undergoing a sudden expansion. Figure 1 highlights the salient flow features of such a sudden expansion. Here it is seen that as the initial shock wave travels down the shock tube (Figure 1) it will undergo a sudden area expansion into a confined area (Figure lb-d), the flowfield gives rise to two important features. First, a “starting jet”, characterized by the formation of a vortex ring, Mach disk, and shear layer’ appear. Second, this precursor shock reflects off the confining walls of the expansion chamber and interacts with the starting jet flowfield. It is clearly seen in Figure 1 that this reflected shock splits once it interacts with the primary vortex ring, which gives rise to secondary shock waves. This shock/vortex/shear layer interaction is also shown in Figure 1. Here the reflected shock splits when it interacts with the primary vortex ring. It was also American Institute of Aeronautics and Astronautics (c)2000 American Institute of Aeronautics & Astronautics or published with permission of author(s) and/or author(s)’ sponsoring organization. observed by Jiang et al. (1997) that once the reflected shock wave passes through the developing shear layer that the shear layer splits, it is moved into the jet flow, and it is convected downstream. This allows another shear layer to form from the jet exit forming another weaker vortex ring. This is referred to as shear layer splitting and is largely an inviscid phenomenon (Jiang et al., 1997) Another phenomenon noted by Jiang et al. (1997) is the shock/shear layer interactions. It is noted that a vortex ring in the shear layer induced a shock wave and the shock wave separated the vortex ring from the shear layer. This is most often noted in strongly expanded free jets. Due to the strong influence of vortex dynamics and compressibility, the turbulence structure can be fruitfully assessed via an evaluation of viscous dissipation.

The flow patterns and heat transfer coefficients of R-22 and R-134a during evaporation in small diameter tubes were investigated experimentally. The evaporation flow patterns of R-22 and R-134a were observed in Pyrex sight glass tubes with 2 and 8 mm diameter tube, and heat transfer coefficients were measured in smooth and horizontal copper tubes with 1.77, 3.36 and 5.35 mm diameter tube, respectively. In the flow patterns during evaporation process, the annular flows in 2 mm glass tube occurred at a relatively lower vapor quality compared to 8 mm glass tube. The flow patterns in 2 mm glass tube did not agree with the Mandhane’s flow pattern maps. The evaporation heat transfer coefficients in the small diameter tubes (d i < 6 mm) were observed to be strongly affected by tube diameters, and to differ from those in the large diameter tubes. The heat transfer coefficients of 1.77 mm tube were higher than those of 3.36 mm and 5.35 mm tube. Most of the existing correlations failed to predict the evaporation heat transfer coefficient in small diameter tubes. Therefore, based on the experimental data, the new correlation is proposed to predict the evaporation heat transfer coefficients of R-22 and R-134a in small diameter tubes.

In this study, we have performed TiN coating for a free piston to decrease the abrasion resistance between the free piston and a housing, consisted of a main piston. The thickness of the TiN layer on the surface is 2 μm. The opening time of the main piston is measured by using the surface-coated free piston. As a consequence, the opening time of the main piston is achieved 500 μs for 2 mm stroke. Additionally, the shock wave has been generated in the glass tubes with 2, 3, and 4 mm diameter to confirm the shock wave propagation. The shock wave measurements are performed at the several points along the axial direction of the tube by using laser differential interferometer. Consequently, the shock wave propagation is confirmed by using the surface-coated free piston. Moreover, the experimental efficiency is drastically improved especially at the initial experimental process. However, TiN coating partly disappeared by repeated use.

Large diameter tubes have been used until comparatively lately. However, small diameter tubes are largely used because of their high efficiency in heat transfer and low cost, recently. This study focuses on the experimental research of the heat transfer coefficients during evaporation process of R-22 and R-134a in small diameter tubes. The evaporation heat transfer coefficients were measured in smooth horizontal copper tubes with ID 1.77, 3.36 and 5.35 mm. The evaporation heat transfer coefficients in the small diameter tubes (ID ＜7 ㎜) were observed to be strongly affected by the size of tube diameters and to differ from those of general predictions in the large diameter tubes. The heat transfer coefficients of ID 1.77 ㎜ copper tube were higher by 20 and 30 % than those of ID 3.36 ㎜, ID 5.35 mm copper tubes respectively. Also, it was found that it was very difficult to apply some well-known previous predictions (Shah's, Jung’s, Kandlikar's and Oh-Katsuda’s correlation) to small diameter tubes. Based on the data, the new correlation is proposed to predict the evaporation heat transfer coefficients of R-22 and R-134a in small diameter tubes.

In this paper, experimental results were reported to investigate a behavior of combustion wave when a shock wave was transmitted into a combustible premixed gas of oxygen and hydrogen. In general, phenomena occurring in the premixed gas would be classified into four types, i.e. (a) the shock wave was just transmitted without causing ignition for the shock wave propagated with low-Mach number, (b) the gas was ignited behind the shock wave and a deflagration wave was propagated following the shock wave, (c) the deflagration wave was transited to a detonation wave behind the shock wave, (d) a detonation wave was directly initiated just behind incident shock wave having high-propagation Mach number. In this study, a shock wave produced by a detonation-driven shock tube was transmitted into a premixed gas of oxygen and hydrogen varied with an equivalence ratio, initial pressure of premixed gas and Mach number of the shock wave. As a result, the phenomena of combustion wave were classified using a cell-size of steady-propagating detonation wave. For sensitive gases having small cell-size, the detonation wave was directly initiated behind the shock wave even though the Mach number of the shock wave was relatively low. Empirical equations to evaluate a Mach number and temperature behind shock wave were obtained, which are threshold parameters to cause detonation wave behind transmitted shock wave.

A Large Eddy Simulation of Plate-Fin and Tube Heat Exchangers with Small Diameter Tubes

From previous works on the shock Mach number attenuation along small size diameter tubes, two different power-law correlations in laminar and turbulent flows in shock tube are proposed in this paper for describing this attenuation and the shock wave behavior. These correlations are based on a local scaling ratio built from driven gas conditions, hydraulic diameter tube, and shock wave propagation distance. A comparison to numerical and experimental existing data is presented and discussed.

This research deals with nonlinear interactions between the transient motion of a rigid body and unsteady fluid flow in a small diameter tube under the action of constant force. This problem becomes very important when the small diameter and complex tube is designed in many systems of micro machine. The analytical model consists of incompressible viscous fluid flow in a small diameter tube at low Reynolds number, and a sphere is released at the center of the tube under the condition that the velocity of the sphere is zero. So as to understand non-linear fluid-solid interaction, the appearance of flow field and the motion of a sphere are observed. The marker-and-cell (MAC) method is also used to calculate numerically the equations governing the interaction between the motion of the sphere and the unsteady fluid flow.

This research deals with nonlinear interactions between motion of a rigid body and fluid flow in a small diameter tube. It is supposed that such a problem becomes very important when the small diameter and complex fluid tube is designed in many systems of micro machine. The analytical model consists of incompressible viscous flow in a small diameter tube at low Reynolds number, and a sphere is released at center of the tube with static. So as to understand Non-linear Fluid-Solid Interaction, it is very important to measure the appearance of flow field and the behavior of a sphere.

Transonic turbine stage flows are strongly influenced by shock waves. The oblique trailing edge shock generated at the pressure side impinges on the suction side of the neighboring airfoil leading to a significant alteration of the Mach number distribution. On film cooled turbine airfoils this shock interacts with the local cooling film. The present study deals with the investigation of this kind of shock wave – film cooling interaction. Experiments are conducted in a high pressure high temperature transonic test rig which allows setting engine realistic Reynolds numbers and Mach numbers, as well as temperature and density ratios. The generic test rig simulates a transonic region of an airfoil passage with the advantage of accessibility for optical measurement techniques. Coolant is ejected from a row of 5 cylindrical and 5 fanshaped holes at different locations relative to the position of shock impingement. Blowing ratios are varied within a range of 0.25&amp;lt;M&amp;lt;1.5. A simulated suction side Mach number distribution is generated with a Mach number Mam = 1.45 upstream and Mam = 1.14 downstream of the shock. Experimental data presented comprise spatially resolved and laterally averaged film cooling effectiveness and heat transfer coefficients within the vicinity of the interaction zone.

For the measurement of ultrasonic shock waves with amplitudes near 40 MPa, two different hydrophones were constructed. The first is a high-bandwidth PVDF membrane hydrophone with a capacitively coupled signal. The second is a small acousto-optic fiber hydrophone which measures the shock-wave-induced variation of the refractive index of a liquid at the front end of the fiber. The properties of the hydrophones are compared. The first, with a sensitivity of 6 mV/MPa, demonstrates high durability and a 20-MHz bandwidth. The second has equally good characteristics and additionally measures the creation and the time dependence of cavitation bubbles in the liquid. >

Wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes with surface and nonlocal effects