Fumio Higashino

Numerical Investigation of Supersonic Flows Around a Spiked Blunt Body

In supersonic flow, a spike attached to the nose reduces the drag of a blunt body. In this paper, supersonic flows around a spiked blunt body are numerically simulated to examine the effects of the spike length, Mach number, and angle of attack. Three-dimensional thin-layer compressible Navier-Stokes equations are solved using a highresolution upwind scheme with LU-ADI time-integration algorithm. The computed results show that the drag of the spiked blunt body is significantly influenced by the spike length, Mach number, and angle of attack. Scales of the separated region are not significantly influenced by the freestream Mach number. For the spiked blunt body at angle of attack, the flowfield becomes complex with spiral flows. The computed results are in reasonable agreement with experimental data.

Experiments on the interaction of a pair of cylindrical weak blast waves in air

This paper reports the results of experiments and computations on the interaction of a pair of cylindrical blast waves in air. The waves were generated by exploding wires, and both symmetrical and unsymmetrical interactions were observed. The experimental data includes schlieren photographs of the wave interactions, their radii, shock Mach number and pressure versus time, as well as various cross plots and data on the shock regular/irregular interaction transition condition. The flow fields were computed with the help of the “Total Variation Diminishing” (TVD) method, and appear to represent the experimental results reasonably well. Some attention is also given to the blast scaling laws of the type discussed by Sakurai (1965) and Oshima (1960).

Pressure wave propagation by gas expansion in a high vacuum tube

In this article we describe an unsteady tube flow model which accounts for the effect of contracted flow around the entrance orifice of the tube which was developed with the aim of preventing vacuum hazards at scientific experimental facilities. Setting an atmospheric pressure drop between the outside and inside of the vacuum tube makes the model applicable to high vacuum, although the model is based on continuous fluid dynamics. We installed an orifice on the inlet end of the tube in the model, and investigated the orifice aperture effect on the propagation velocity of pressure waves.

A numerical study on implosion of polygonally interacting shocks and consecutive explosion in a box

Implosion of polygonally interacting shock system and consecutive explosion in a box with the square cross section were investigated numerically by using a TVD finite difference scheme of shock capturing family. Results obtained from initially regular‐polygonal form from the equilateral triangle to the octagon are shown in this paper.

Three-Dimensional Flow Computation Around a Projectile Overtaking a Preceding Shock Wave

A numerical simulation of the e owe eld around a projectile overtaking a preceding shock wave is carried out by solving the three-dimensional, thin-layer Navier ‐Stokes equations. A domain decomposition method with the fortie ed solution algorithm interface scheme is used to supply reasonable grid cone gurations for such an unsteady e owe eld. Computed results show that complicated interaction e owe elds are observed while overtaking the shock wave. The results of the two- and three-dimensional e owe eld computations are compared, and the characteristic features of the three-dimensional e owe eld are shown. Time histories of the aerodynamic forces show that the projectilesuffers strong asymmetric forces while overtaking theshock wave, which may makethetrajectory of the projectile unstable.

On the Development of a Two-Dimensional Color Schlieren Method

A two-dimensional color schlieren method developed by Settles (1970) is one of the best visualized technique of compressible flow field. By using this method, direction of density gradient is indicated by three primary colors (red, blue and green) and three neutral colors (yellow, purple and blue-green). The clear neutral colors are required to survey the direction precisely. The optical setup consists of a flash, a ring-shaped tricolor filter mask, a couple of parabolic mirrors, a pinhole and a still camera. The quality of a developed color image by this method depends on three parameters; diameter of the pinhole D1, diameter of the filter mask D2 and thickness of the color band D3. We clarified suitable values of these parameters. The following results are obtained from this study: (1) D1 influences the visible area and sensitivity, (2) D2 influences developed color image, (3) D3 influences brightness.

THREE-DIMENSIONAL COMPUTATION OF THE FLOW INDUCED BY A PROJECTILE OVERTAKING A SHOCK WAVE

A numerical simulation of the flow field around a projectile overtaking a preceding shock wave is carried out by solving the three-dimensional thin-layer Navier-Stokes equations. A domain decomposition method with the FSA (fortified solution algorithm) interface scheme is used to supply reasonable grid configurations for such unsteady flow filed. Computed results show that the complicated interaction flow fields are observed during the overtaking. The results of the two- and three-dimensional flow field computations are compared, and the characteristic features of the three-dimensional flow field are shown. Time histories of the aerodynamic forces show that the projectile suffers strong asymmetric forces during the overtaking which may make the trajectory of the projectile unstable.

On-dimensional Numerical Simulation of a Compression Wave Induced by a Train Entering a Tunnel.

One-dimensional unsteady Euler equations are solved for the investigation of the flow field induced by a train entering a tunnel. The effect of the moving train is included in the basic equations as an area change in time. The equations are discretized by the finite difference method, and the calculations are performed for trains with various speeds, cross-sectional areas and nose area gradients. Effects of these parameters on the strength of a compression wave and the maximum pressure gradient are studied. Computed strength of the compression wave shows good agreement with the theoretical 1-D analysis and the axisymmetric numerical simulation. The one-dimensional flow model is validated through the comparison of computed pressure gradient with multidimensional numerical simulations.

Interaction of Boundary Layer with Shock Wave in Unsymmetrical Supersonic Nozzle.

The study of unsymmetrical nozzle flow is important not only for basic research in gas dynamics but also for mechanical applications. In the present study, six kinds of unsymmetrical nozzles which had different divergence angles and wall lengths were used to analyze the effect of the nozzle configuration and Mach number at the nozzle entrance on the flow. The effects of Mach number at the nozzle entrance and the divergence angle of the nozzle on the oscillation of shock wave were investigated experimentally. Furthermore, the effect of wall length on the direction of the flow was investigated. A schlieren optical system, and a Mach-Zehnder interferometer composed of an Argon laser (CW) as the light source with acousto optic modulators (AOM) were employed for visualization of the flow.

Study on Unsymmetrical Supersonic Nozzle Flows.

The shape of scramjet-engine utilized for a space vehicle may be unsymmetrical in general. Supersonic flows generated in such asymmetric nozzle are very unstable due to pseudo-shock waves. To analyze the effects of the nozzle contour on the flow, three kinds of nozzle configuration were examined experimentally. The interaction of supersonic expansion flows in the nozzle with the boundary layer developed on a nozzle wall was investigated by applying a Mach-Zehnder interferometer. This used an Argon-Ion laser with an electro-magnetic shutter (AOM and EOM) as the light source. The frequency of the pseudo-shocks was not affected by the flow velocity at the nozzle entrance but was affected by the nozzle configuration. It is possible to measure the density distribution in supersonic un-steady flow fields quantitatively by using the present optical system.