Mamoru Oike

The effect of abrasive grain size on the transition between abrasive and adhesive wear

Abstract Experiments were carried out in which SiC abrasives with a grain size range of 3–150 μm were inserted between sliding metals. The metals were pure aluminium, copper, iron, nickel and zinc. The test geometry was a tube end against a flat surface. The effect of grain size can be classified into three regimes. In the first, where abrasive grains are larger than a critical size d c (about 50 μm), the wear rate is independent of grain size. In the second regime the wear rate decreases as abrasive grains become smaller than d c to a limit at a transition grain size d t (about 10 μm). In the third regime the wear rate is high and independent of abrasive grain size. The wear debris consists of large metal flakes with abrasive particles mixed in. Although abrasive particles are present, the wear is primarily adhesive, and the action of the abrasive particles is to promote the removal of metallic wear debris from the contact region.

Tribo-characteristics of self-lubricating ball bearings for the LE-7 liquid hydrogen rocket-turbopump

The tribo characteristics of self-lubricating 40-mm-bore ball bearings with a retainer of glass cloth-polytetrafluoroelhylene (PTFE) laminate, which has elliptical pockets with a large pocket clearance, were tested under thrust loads at speeds up to 50000 rpm, 2 million DN, in liquid hydrogen (LH2) and in liquid nitrogen (LN2). During testing, the bearing torque, outer-race temperature, and electric resistance between the inner and outer races were monitored to verify the formation and rupture of a PTFE transfer film. Testing showed that the bearings having the elliptical retainer pockets were superior to the conventional bearings with circular pockets. It was determined that at the maximum inner race spinning velocity of about 5 mls a PTFE transfer film could sustain the maximum Hertz stress, up to about 2000 N/mm2, in LH2, without severe film rupture resulting in bearing seizure. In LN2, the critical load capacity of PTFE transfer film with bearing seizure was about 2700 N/mm2. Presented as a Society of...

Tribo-Characteristics of Cryogenic Hybrid Ceramic Ball Bearings for Rocket Turbopumps: Bearing Wear and Transfer Film©

The self-lubricating performance of the two types of modified, angular-contact 25-mm-bore ball bearings, i.e., a hybrid ceramic bearing with Si3N4 ceramic balls and an all-steel bearing, was evaluated based on wear inspection as well as X-ray photoelectron spectroscopic (XPS) analysis of transfer films. These bearings had been tested in liquid hydrogen (LH2), liquid oxygen (LO2), or liquid nitrogen (LN2) at speeds to 50,000 rpm and thrust loads to 2840 N. In LH2, both the hybrid ceramic and all-steel bearings demonstrated excellent wear performance made possible by the thick transfer film consisting of PTFE (polytetrafluoroethylene)/CaF2 or CaF2/FeF2, in which CaF2 and FeF2 were tribocatalytically formed by the reducing ability of LHτ This film was generated from a glass cloth-reinforced PTFE retainer. In LO2, the all-steel bearing exhibited excellent wear performance as the result of the intense formation of a Cr2O3 layer beneath an extremely thin PTFE transfer film. By contrast, the hybrid ceramic beari...

Tribo-characteristics of cryogenic hybrid ceramic ball bearings for rocket turbopumps : Self-lubricating performance

Experiments were conducted to investigate and compare the self-lubricating performance of two types of modified, 25 mm-bore ball bearings: a hybrid bearing with Si3N4 ceramic balls, and an all-steel bearing. The modified bearings had a single outer land-guided retainer with elliptical pockets and a narrow axial pocket clearance to reduce wobbling of the retainer. The bearings were tested under high thrust loads to 2840 N and at speeds up to 50,000 rpm in liquid hydrogen (LH2), liquid oxygen (LO2), or liquid nitrogen (LN2). Testing showed that the bearing torque of the modified all-steel bearing was drastically decreased to about one-half that of the conventional double outer land-guided bearing at a speed of 50,000 rpm in LH2 Furthermore, the hybrid bearing had relatively stable variation of bearing torque and better load capacity than those of the all-steel bearing in both LH2 and NH2. However, in LO2, the all-steel bearing exhibited excellent performance with high load capacity at high speeds, contraste...

Numerical Analysis of Two-Phase Pipe Flow of Liquid Helium Using Multi-Fluid Model

The two-dimensional characteristics of the vapor-liquid two-phase flow of liquid helium in a pipe are numerically investigated to realize the further development and high performance of new cryogenic engineering applications. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model are presented and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the two-phase flow of liquid helium is shown in detail, and it is also found that the phase transition of the normal fluid to the superfluid and the generation of superfluid counterflow against normal fluid flow are conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. According to these theoretical results, the fundamental characteristics of the cryogenic two-phase flow are predicted. The numerical results obtained should contribute to the realization of advanced cryogenic industrial applications.

Two-Phase Flow in Floating-Ring Seals for Cryogenic Turbopumps

A flow visualization study on the two-phase flow in floating-ring seals for cryogenic fluid was carried out to identify the two-phase flow area (A2) inside the sealing clearance induced by viscous frictional heating and the pressure drop. The effect of the two-phase flow area on leakage was investigated by comparing leakage measurements (Q) and the values of A2 obtained from observed results. A2 increased with increasing rotational speed; however, the increase of A2 did not always bring about a decrease in the mass leakage rate. Moreover, the effect of the two-phase flow on the reduction of leakage was discussed by comparing the measurements of Q with the computational results (Qliquid) obtained from the incompressible flow equation. It was confirmed that the effect of the two-phase state on the reduction in leakage can be broadly classified into the following two effects: effect of the all-liquid choked flow and effect of the two-phase flow area (A2) inside the sealing clearance. In a high degree of subc...

Experimental study on high-pressure gas seals for a liquid oxygen turbopump

An experimental study on high-pressure gas seals was carried out in order to investigate the feasibility of a liquid oxygen (LOX) turbopump rotating-shaft seal system for the LE-7 rocket engine of Japan. Floating-ring seals 50 millimeters in diameter were successfully operated under the following conditions: a maximum rotational speed of 25,000 rpm and a maximum sealed hydrogen gas pressure of about 15 MPa. The leakage rates obtained in the experiment were in good agreement with the analytical results obtained from the quasi-one-dimensional compressible flow equation. Observational results indicated that the housing sealing surface coated with rf (radio frequency)-sputtered molybdenum disulphide (MoS2) film was extremely effective in reducing the wear on the carbon sealing surfaces. A 100-millimeter-diameter double segmented hydrodynamic circumferential seal designed for a helium gas purge system was tested in order to investigate the wear process of the carbon segmented-rings. The seal was operated for a...

Numerical simulation of cavitating flow of liquid helium in a pipe using multi-fluid model

The two-dimensional characteristics of the cavitating flow of liquid helium in a pipe are numerically investigated to realize the further development and high performance of new cryogenic engineering applications. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model are presented and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the turbulent cavitating flow of liquid helium passing through the orifice is shown in detail, and it is also found that the phase transition of the normal fluid to the superfluid and the generation of superfluid counterflow against normal fluid flow are conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. According to these theoretical results, the fundamental characteristics of the cryogenic cavitating flow are predicted.

Rotor vibrations of turbopump due to cavitating flows in inducer

During the initial phase of the development of the LE7 liquid-oxygen turbopump, supersynchronous and subsynchronous shaft vibrations occurred. We experienced a very curious phenomenon, namely, that three types of shaft vibrations appeared in the tests of the turbopump under almost the same operating conditions. That is, only supersynchronous shaft vibration occurred, only subsynchronous shaft vibration occurred, or supersynchronous shaft vibration appeared just after subsynchronous vibration had disappeared concomitant with the decrease of inducer inlet pressure. First, it was clarified that the supersynchronous shaft vibration was caused by rotating cavitation which occurred in the inducer of the liquid oxygen main pump. However, considerable time was needed to identify the cause of the subsynchronous shaft vibration, because this vibration occurred under almost the same conditions as that which brought about the rotating cavitation. Finally, it was concluded that the subsynchronous shaft vibration was a cavitation-induced system oscillation, that is cavitation surge. In the present paper, we show how the subsynchronous shaft vibration was identified as cavitation surge. Some results of calculations will also be presented to explain the test results.

Dynamic Molecular Collision model for N2–He mixture

Dynamic Molecular Collision (DMC) model is extended to calculate collisions of N2 and He. An intermolecular potential is obtained as the sum of the two potentials between each atom of a N2 molecule and He. Lennard-Jones (12–6) potential is used as the interatomic potential and potential parameters are determined by combination rule. N2–He collisions are simulated in many cases by Molecular Dynamics (MD) method in order to construct the collision model between N2 and He. A collision cross section is determined based on a diffusion coefficient and a probability density function of energy after collision is determined by the MD method. In the present paper, moreover, this model is applied to simulations of the free jet expansion of N2–He mixture by Direct Simulation Monte Carlo (DSMC) method and the flow field is analyzed. Especially the number density and energy distributions at the axis of a free jet are analyzed in detail.