To overcome defects of conventional hybrid rocket motors such as poor mass ratio and low combustion efficiency, the authors propose a new idea of design. The point of this idea is that the motor uses ‘wet towel propellant’, in which liquid oxidizer fills gap space in the fuel bed consisting of plastic fibers or films. Specific impulses of the propellants are estimated theoretically with HAN and LOX as liquid oxidizer. To investigate pressure sensitivity of the burning rates of the propellants, burning rates of LOX-polyaramid propellants are measured in a pressure range of 0.1 to 2MPa with a specially designed strand burner. A striking feature in the experimental results is that the enhancement of the burning rate with ambient pressure is as big as the pressure exponent being larger than one. Further innovation is necessary for realization of the proposed idea.
For the space-debris protection problem, it is very important to understand the multi-phase transformation phenomena including elastic and plastic deformation caused by hyper-velocity impact. In this paper, the numerical simulation code, CRATE-2D, was developed to reproduce the hyper-velocity impact phenomena, employing the SPH (Smoothed Particle Hydrodynamics) Method. First, simulation on the impact between a polyethylene projectile and an aluminum target at the impact velocity of 5km/s was performed. Aluminum was assumed to behave as fluid under the high pressure and high temperature condition created by such a high-speed collision. The calculated crater geometry shows a good agreement with the one created by a light-gas gun in our experiment. Second, the impact between a polyethylene projectile and a duralumin bumper at 2.16km/s was simulated. Johnson-Cook model and a simple instantaneous failure model were employed for taking account of material strength and failure criteria. As a result, the kinetic energy distribution of the secondary debris, which reveals the energy transformation mechanism on the hyper-velocity impact, was obtained.
Interlaminar delamination at edge of circular hole is most important to care in design of composite material structures among many kinds of defect damaged in the machining holes. Following five items are described in this paper. (1) Experiment conducted with three kinds of CFRP (P3060, P2190, APC-2) to get data of delamination growth and of residual strength, (2) An improvement on delamination growth law to give a better correlation between experimental data and estimated results, (3) The upper limit, unexpectedly very high, of load under that delamination does not grow, (4) Confirmation of an analytic method of residual strength on the assumption that Euler buckling occurs in an outer delaminated laminate and (5) Considarations to damage tolerance design of composite material structures.
The flow around a sphere rising in a cylindrical pipe is numerically analyzed upon the axisymmetricity assumption. The sphere goes upward with constant velocity or with constant accerelation. The spherical coordinate mesh is attached to the sphere, however finite difference solution on the mesh is only auxiliary to a overset mesh method and does not affect on the cylindrical coorinate solution by HSMAC scheme. In the constant accerelation case whether the wall shear has its peak above or below the sphere depends upon whether the sphere velocity become larger than the background velocity or smaller than the latter. The qualitatively good agreement of sphere surface pressure is obtained with the existing experiment in the axisymmetric jet. Such assessment of the method predicts the applicability of the overset mesh method for calculation for the bubble or sedimendation of body in the pipe.
A ground facility was developed for simulation of material and space plasma interaction and for study of spacecraft charging and discharge phenomena. The space plasma simulator consisted of a vacuum tank 0.7m in diameter ×1.5m long, two turbo-molecular pumps with pumping speeds 5 and 3m3/s, respectively, achieving some 10-4Pa, and an electron cyclotron resonance plasma source of a magnetic-field-expansion plasma accelerator. Oxygen or nitrogen plasma properties of plasma density, electron temperature, ion incident energy, ion freestream velocity and atomic oxygen flux were measured. The simulator was found to have a high potential for ground tests.
The purpose of this paper is to control edge tone generated by flow of a jet-wedge system. An attempt to control the edge tone has been carried out by attaching projecting objects to the nozzle exit. It is found that the edge tone is reduced even though a pair of projecting objects is attached to the nozzle exit. In addition, the effect of attached projecting objects upon the spectrum intensity of predominant frequency of the pressure fluctuation at the wedge is examined. We also found that the spectrum intensity decreases with the increase of the number of projecting objects. The spectrum intensity is minimized at the point which is located downstream from the position of the attached projecting objects.
The response of an airfoil wake to acoustic forcing is examined experimentally for NACA0012 airfoil at moderate and high angles of attack, at a chord-Reynolds number Rc=23×104. At a moderate angle of attack α=10°, the flow is found to be highly receptive to acoustic forcings over a wide range of frequencies and the excited vortices can govern the downstream wake. At a stall angle α=16°, on the other hand, nearly periodic large-scale vortical structures appear and govern the wake without the forcing, indicating the appearance of the absolute instability in the near wake, not unlike that of bluff-body wakes. In this case, the small-amplitude external forcing can not control the vortex shedding except at and around the natural shedding frequency, suggesting that the stall is critically governed by the absolute (or global mode) instability under natural flow conditions without large-amplitude external forcings.