Hideo Kashimura

Diffraction of a shock wave around a convex corner

The diffraction of a plane shock wave at a convex corner with a sharp edge was studied both experimentally and numerically, and the shape of the diffracting shock wave was classified into four different types according to the profiles of wall shocks. The domains and transition boundaries of these four types were shown in an incident shock Mach number‐diffraction angle plane. The flow field behind the diffracting shock wave was also investigated in the present experimental and numerical studies, and the characteristics of the second and the third shock waves which appeared in this perturbed region were discussed.

The self-induced oscillations of the under expanded jets impinging upon a cylindrical body

The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and computational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self-induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.

Hysteretic Phenomenon of Underexpanded Moist Air Jet

Moist air jets, corresponding to the range of moderately underexpanded to strongly underexpanded conditions, have been investigated with the help of computational fluid dynamics methods. The equations for nucleation rate and droplet growth are incorporated into the unsteady, compressible Navier-Stokes equations. A third-order total variation diminishing finite difference scheme with monotonic upstream schemes for conservation lows is employed to discretize the spatial derivatives of the governing equations. The experiment is performed to validate the computational predictions. The initial degree of supersaturation is changed to obtain different values of the relative humidity of moist air. The pressure ratio is changed to investigate the characteristic behavior of the jets generated during the transient processes of startup and shutdown. The results obtained show that underexpanded air jet produced during the startup transient of jet behaves different from the shutdown transient process, leading to a hysteretic phenomenon of underexpanded jet. It is also known that the moist air jet reduces the hysteretic phenomenon compared with the dry air jet, and that nonequilibrium condensation that occurs in the underexpanded moist air jet is responsible for these findings.

Propagation Characteristics of Compression Waves Reflected from the Open End of a Duct

The present study addresses the distortion of the compression wave reflected from an open end of a shock tube. An experiment is carried out using the simple shock tube with an open end. Computational work is also performed to represent the experimented flows. The second-order Total Variation Diminishing scheme is employed to numerically solve the unsteady, axisy-mmetric, inviscid, compressible governing equations. Both the experimented and predicted results are in good agreement. The generation and development mechanisms of the compression wave, which is reflected from the open end of the shock tube, are obtained in detail from the present computations. The effect of size of the baffle plate at the open-end that causes the reflection of the incident expansion wave is found negligible. A good correlation is obtained for transition of the reflected compression wave to a shock wave inside the tube. The present data show that for a given wave length of the incident expansion wave the transition of the reflected compression wave to a shock wave can be predicted with good accuracy.

Interaction between underexpanded supersonic jet and obstacle

When an underexpanded supersonic jet impinges on an obstacle, a self-induced flow oscillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related to the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, therefore, have to be understood to control the various noise problems. The characteristics of the oscillatory flowfield and the mechanism of an oscillation have to be studied further to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position on the mechanism of self-induced flow oscillation by the numerical analysis and the experiment, when the underexpanded supersonic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of self-induced flow oscillation depends on the pressure balance in the flowfield.

Characteristic of Hysteresis Phenomena on Shock Wave Structure in Overexpanded Axisymmetric Supersonic Jet

The overexpanded supersonic jet, formed under the overexpanded condition at the nozzle exit, is very important for industrial devices, the same way as an underexpanded jet. It has been reported, in a recent study, that hysteresis phenomena for the shock reflection type in a three-dimensional supersonic jet occur under the quasi-steady flow. Several papers have described the hysteresis phenomena for underexpanded supersonic jet. However, the characteristics and mechanism of the hysteresis should be discussed more clearly to understand this phenomenon. The purpose of this study is to clear the characteristic of the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method.

Numerical Investigation for Hysteresis Phenomena of Shock-Reflection in Overexpanded Axisymmetric Supersonic Jet

The overexpanded supersonic jet, formed under the overexpanded condition at the nozzle exit, is very important for industrial devices, the same way as an underexpanded jet. It has been reported, in a recent study, that hysteresis phenomena for the shock reflection type in a three-dimensional supersonic jet occur under the quasi-steady flow. Several papers have described the hysteresis phenomena for underexpanded supersonic jet. However, the characteristics and mechanism of the hysteresis should be discussed more clearly to understand this phenomenon. The purpose of this study is to clear the characteristic of the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method.

Hysteresis Phenomena of Mach Disk in Under-expanded Jet with Condensation

In the present study, a computational fluid dynamics work was performed to investigate the hysteresis phenomena of Mach disk in under-expanded axisymetric sonic jet with condensation. The axisymmetric conservational equation is solved by TVD(Total Variation Diminishing) scheme. A quasi-steady approach is employed to calculate the hysteresis loop for the diameter and position of Mach disk. The result shows the existence of hysteresis phenomena of Mach disk in under-expanded jet with condensation.

Visualization of Unsteady Flow near Open-End of Tube Caused by Discharge of Shock Wave

When the shock wave propagating the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end and the unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. This paper aims to clear the mechanism of generating the unsteady pulse jet near the open end and the numerical analysis carried out for the emission of propagating the shock wave from an open end of a tube in this study. The flow field is visualized by the computed shadowgraph method using the axisymmetric two-dimensional density distribution contained the axis, which is obtained by the numerical calculation. In this paper, the mechanism of generating the unsteady pulse jet and the characteristics of a pressure distribution in the flow field, the secondary and spherical shock waves behind the impulsive wave are discussed.

Visualization of Impulsive Wave Impinging on Perpendicular Flat Plate

The impulsive wave is made by the weak shock wave discharge from an open-end of a tube. In this study, the characteristics of the impulsive wave is described as the flow field of the impulsive wave impinging upon a flat plate is visualized. Numerical simulation is applied to model the flow field subject to unsteady, inviscid and compressible equations of axisymmetric form. Computer schlieren, shadowgraph and intergerogram images are created from the numerical data using the optical method of the experimental set-up. The results of the visualized images well clarified the reflective form variations of the impulsive wave at the flow field near the open-end of a tube and behind the impulsive wave reflected by the flat plate.