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This paper describes a simple and reliable method of improving the surface insulation strength of a spacer used in vacuum. The method is to roughen the spacer surface to an average roughness [R.sub.a] higher than 1 or 2 [micro]m. The material of the spacer examined is Si[O.sub.2], PMMA, PTFE or [Al.sub.2][O.sub.3] and their shape is a right cylinder with 10 mm in height and 54 mm in diameter. The spacer is subjected to a ramped dc voltage and its surface charging is observed by using an electrostatic probe embedded in the cathode. It has been found that [R.sub.a] decisively affects the charging, which decreases as [R.sub.a] increases. Increasing [R.sub.a] larger than about 2 [micro]m suppresses the charging until a higher applied voltage is reached, thus improving the insulation property. Index Terms--Charging, flashover voltage, insulating spacer, roughness, vacuum.

Phthalocyanine rare-earth metal complexes were examined for their optical properties.

Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the effect of the inlet boundary layer (IBL) on the flow. A duct with six struts and the same geometry as that used to connect compressor spools on our experimental small two-spool turbofan engine was investigated. A curved downstream annular passage with a similar meridional flow path geometry to that of the centrifugal compressor has been fitted at the exit of S-shaped duct. Two types of the IBL (i.e., thin and thick IBL) were used. Results showed that large differences of flow pattern were observed at the S-shaped duct exit between two types of the IBL, though the value of 'net' total pressure loss has not been remarkably changed. According to 'overall' total pressure loss, which includes the IBL loss, the total pressure loss was greatly increased near the hub as compared to that for a thin one. For the thick IBL, a vortex pair related to the hub-side horseshoe vortex and the separated flow found at the strut trailing edge has been clearly captured in the form of the total pressure loss contours and secondary flow vectors, experimentally and numerically. The high-pressure loss regions on either side of the strut wake near the hub may act on a downstream compressor as a large inlet distortion, and strongly affect the downstream compressor performance. There is a much-distorted three-dimensional flow pattern at the exit of S-shaped duct. This means that the aerodynamic sensitivity of S-shaped duct to the IBL thickness is very high. Therefore, sufficient care is needed to design not only downstream aerodynamic components (for example, centrifugal impeller) but also upstream aerodynamic components (LPC OGV).

Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the influence of the shape of the downstream passage located at the exit of the duct on the flow. A duct with six struts and the same geometry as that used to connect the compressor spools on our new experimental small two-spool turbofan engine was investigated. Two types of downstream passage were used. One type had a straight annular passage and the other a curved annular passage with a meridional flow path geometry similar to that of the centrifugal compressor. Results showed that the total pressure loss near the hub is large due to instability of the flow, as compared with that near the casing. Also, a vortex related to the horseshoe vortex was observed near the casing. In the case of the curved annular passage, the total pressure loss near the hub was greatly increased compared with the case of the straight annular passage, and the spatial position of this vortex depends on the passage core pressure gradient. Furthermore, results of calculation using an in-house-developed three-dimensional Navier-Stokes code with a low-Reynolds-number k - [Epsilon] turbulence model were in good qualitative agreement with experimental results. According to the simulation results, a region of very high pressure loss is observed near the hub at the duct exit with the increase of inlet boundary layer thickness. Such regions of high pressure loss may act on the downstream compressor as a large inlet distortion, and strongly affect downstream compressor performance.

This paper presents a series of trials of direct detection of the transition process of a squeeze film, from the contacting state into the floating one. The material was initially placed on the surface of a vibrator constituting a squeeze air film. Three electrical trials were performed to certify whether the material could be elevated after the vibrator was excited. When this is done, clearance is expected between the surfaces of the test material and the vibrator. This may be regarded as the equivalent of a change in electrical resistance from almost zero to infinity, with a kind of parallelplate capacitor being formed. First, detection through DC current was carried out. The experimental result, however, reveals that the resistance never does become infinite, although the equivalent contacting area calculated from this value is very small. Second, detection through DC voltage was performed by terminating the clearance with parallel resistance. The experimental results verify the appearance of the floating state. Third, the average clearance could be detected by regarding it as a parallel-plate type capacitor. Here a Langevin type piezoelectric transducer was used as the vibrator. Through these experimental results an important fact was observed: the waveform of the voltage applied to the transducer is closely related to the movement of the clearance in the time domain.