In the so-called modern linear stability analysis based on a spatial evolution model, the origin of unstable wave responsible for spontaneous liquid jet disintegration is attributed to an infinitesimal amplitude of perturbation inevitably introduced within an injector. This implies that the jet disintegration is a one-way process caused by an almighty noise. Against this belief, author’s research group conducted ISS experiments, in which a microgravity plug-flow jet, assumed in the classical Rayleigh’s analysis, was realized in order to validate our proposal that any liquid jet can spontaneously disintegrate thanks to a self-destabilizing causality loop formation along the jet. Unlike the modern linear stability analysis prediction, covenctively unstable waves observed for all jet issue speeds tested had the phase velocity equal to the jet velocity, and they played an important role to result in various quasi-steady jet disintegration states. This paper first examines why the noise concept was necessary in the modern linear stability analysis, and then presents the 1D jet model numerical simulations which support our experimental observations and reveal their underlying physics. It is found that the spatial evolution model does not describe the physically reasonable unstable wave formation process even for a forced jet such as an ink-jet printer.

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We attempt to apply a Lattice Boltzmann Method to sloshing analysis in a circular tank under microgravity conditions. Numerical simulations are effective tools to predict sloshing phenomena in a propellant tank in microgravity conditions. In order to realize the analysis of such phenomena, a numerical method that conserves the fluid volume accurately, copes with large deformation of the gas-liquid interface, and properly expresses the surface tension and wettability is required. To satisfy these requirements, we have focused on the method combining the Lattice Boltzmann Method (LBM) and Phase Field Method (PFM). The Conservative-Allen-Cahn (CA-C) equation is employed as the interface tracking equation, and the velocity-based LBM is employed as the Lattice Boltzmann Method to compute the pressure and velocity fields. In addition, the Interpolated Bounce Back is applied for the no-slip condition around the curved surfaces, and the cubic boundary condition is applied for the wetting condition. It is verified that the present method has good volume conservation and can express wettability with high accuracy. Finally, using the present method, several analyses of sloshing phenomena in a circular tank under microgravity conditions have been carried out, and it is confirmed that the phenomena varies significantly depending on the equilibrium contact angle.

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Abstract: A continuous screw reactor for hydrogen reduction of lunar soil simulant was assembled. The water production rates were measured with different reduction conditions. Reduced simulants were analyzed by XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), and EDS (Energy dispersive X-ray spectroscopy). The effect of reduction temperatures in the range of 1173-1373 K in 3 vol% hydrogen was clarified. The highest water production rate at the steady-state is obtained at 1273 K. The water production rate becomes higher with the higher reduction temperature up to 1273 K. It becomes lower at the temperature above 1273 K because Na-rich components in lunar simulant melt and it inhibits the hydrogen diffusion. The impact of hydrogen concentrations between 3-10 vol% was revealed with the fixed reduction temperature of 1273 K. The reaction rate has linear relationship to the hydrogen concentration. The reduced lunar simulant contain α-Fe, and the amount increases with higher hydrogen concentrations. The reduced ilmenite has porous structures due to the vacancy of oxygen. This work suggests the continuous hydrogen reduction system as a promising process to acquire oxygen on the moon.

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Studies to understand the risk of dust explosions in a microgravity environment are required for lunar and planetary exploration. In order to propose safety protocols for dust explosions, microgravity tests are extremely effective. This project aims to develop an overarching experimental apparatus for microgravity experiments. For developing such an experimental system, the microgravity experimental apparatuses of dust explosion, and the results of flame propagation and flame quenching were first reviewed. A microgravity experimental apparatus consisting of a high-speed visualization system to simultaneously measure both the flame propagation and dust concentration was developed. Reduced-gravity experiments on the dust explosion of 20 μm aluminum powder have been carried out at a drop tower. The tests performed have allowed the simultaneous observation of the flame speed and flow velocity.

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