Air/water two-phase flow test tunnel for airfoil studies

A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.Dedicated to the 60th Birthday of Professor Klaus Gersten     

Polysynthetically-twinned structures of enstatite and wollastonite

Crystal structures of clinoenstatite, orthoenstatite, wollastonite-1T and wollastonite-2M (parawollastonite) were refined to an R factor 3–4 percent level. Molar volumes at room temperature are 31.270(15), 31.315(8), 39.842(5) and 39.901(10) cm³/MSiO₃, in the above-mentioned order, indicating that one-layer polytypes (clinoenstatite and wollastonite-1T) are stable at higher pressures than two-layer polytypes (orthoenstatite and wollastonite-2M). The polytypic relation of the enstatite polytypes can be described by four twinning operations — b glide ∥ to (110), a glide ∥ to (001), twofold screw axis ∥ to a (of orthoenstatite) and a twofold screw axis ∥ to c. For the wollastonite polytypes, twinning operations are twofold screw axis ∥ to b and a glide ∥ to (010). Structural adjustments after twinning are not necessarily the largest at the twin boundary (true in enstatite but not so in wollastonite). In both cases octahedral sites that involve bridging oxygens tend to show relatively large changes. Lattice strain ellipsoids associated with twinning are also different for enstatite and wollastonite, which implies that wollastonite may react differently from enstatite to non-hydrostatic pressure.     

The distribution of Fe3+ and Ga3+ between two tetrahedral sites in melilites,Ca2(Mg,Fe3+, Ga,Si)3O7

The distribution of Fe³⁺ and Ga³⁺ between the two tetrahedral sites in three synthetic melilites has been studied by using ⁵⁷Fe Mössbauer spectroscopy. In the melilite, (Ca₂Ga₂SiO₇)₅₀ (Ca₂Fe³⁺GaSiO₇)₅₀ (mol %), the distribution of Fe³⁺ and Ga³⁺ in T1 and T2 sites is apparently random, which can be explained in terms of the electrostatic valence rule. However in the melilites, (Ca₂MgSi₂O₇)₅₂ (Ca₂Fe³⁺GaSiO₇)₄₂ (Ca₂Ga₂SiO₇)₆ and (Ca₂MgSi₂O₇)₆₂ (Ca₂Fe³⁺GaSiO₇)₃₆ (Ca₂Ga₂SiO₇)₂ (mol %), Fe³⁺ shows preference for the more ionic T1 site and Ga³⁺ for the more covalent T2 site. If the electronegativity of Ga³⁺ is assumed to be larger than that of Fe³⁺, the mode of distribution of Fe³⁺ and Ga³⁺ can be explained in terms of our previous hypothesis that a large electronegativity induces a stronger preference for the more covalent T2 site.     

Geomorphological study on a clastic accretionary prism: The Nankai Trough

Abstract The Nankai Trough, off southwest Japan, is one of the best sites for the study of geomorphic characteristics of a clastic accretionary prism. A recent multibeam survey over the central and eastern parts of the Nankai accretionary prism has revealed a large variation of the topography along the trough axis. Analysis of the bathymetric data suggests the existence of prism deformational features of different scales, such as depressions, embayment structures and cusps. These structures are the results of slope instability caused by basement relief of subducted oceanic plate. Unstable slopes recover by new accretion and development of a low angle thrust. Small-scale deformation due to the subduction of a small isolated seamount is then adjusted to the regional trend. By contrast, a 30 km indentation of the wedge observed in the eastern part of the Nankai Trough, the Tenryu Cusp, has seemed to retain its geometry. The subducted Philippine Sea plate has deformed greatly near the eastern end of the Nankai Trough, because of the collision between the Izu-Ogasawara (Bonin) arc and central Japan. Therefore, the indentation may be the result of the continuous subduction of a basement high, such as the Zenisu Ridge, which has been formed under north-south compression due to the arc-arc collision.     

Under‐ice salinity and stable isotope distribution of Saroma‐ko Lagoon,Hokkaido, northern Japan

In winter, lakes and lagoons at high altitudes or high latitudes have interesting hydrological cycles that differ from those in other seasons or in other regions, because water surfaces are covered with ice. Hydrological balances of lakes and lagoons are complex dynamic systems, and to elucidate them, isotopic tracers of water have been used as effective tools along with observations of precipitation, evaporation, inflows, and outflows. Here, to understand hydrological processes during freezing periods in the brackish Saroma‐ko Lagoon, Hokkaido, northern Japan, we examined horizontal and vertical distributions of salinity and isotope compositions of lagoon water and ice in 2005 and 2006. Horizontal and vertical gradients of salinity and isotope compositions were observed from the river mouth to the sea channel, and factors determining these distributions were considered. The mixing of freshwater and seawater and a freezing effect were presumed to be factors in relationships between salinity and isotopes and in relationships between surface waters and ice just above the water. A simple box model for water balance was constructed based on these putative factors to reproduce the distributions of salinity and isotope compositions of surface waters and ice. An evaluation of the model revealed that this hydrological system is controlled primarily by horizontal advection of the epilimnion, freshwater influx, and the ice growth rate. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal alteration of hydrated minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust

Abstract— Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture finegrained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light‐gas guns to impact into aerogels finegrained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at >6 km s^?1 similar to the flyby speed at comet P/Wild‐2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X‐ray diffraction (SR‐XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE‐SEM). SR‐XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR‐XRD and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 °C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 °C/μm were estimated near the surface of the grains (<2 μm thick) by TEM observation. Our data suggests that the interior of >4 μm across residual grains containing abundant materials that inhibit temperature rise would have not experienced >300 °C at the center.     

Synthesis of highly dense and fine-grained aggregates of mantle composites by vacuum sintering of nano-sized mineral powders

Synthesized mineral powders with particle size of <100 nm are vacuum sintered to obtain highly dense and fine-grained polycrystalline mantle composites: single phase aggregates of forsterite (iron-free), olivine (iron containing), enstatite and diopside; two-phase composites of forsterite + spinel and forsterite + periclase; and, three-phase composites of forsterite + enstatite + diopside. Nano-sized powders of colloidal SiO₂ and highly dispersed Mg(OH)₂ with particle size of ≤50 nm are used as chemical sources for MgO and SiO₂, which are common components for all of the aggregates. These powders are mixed with powders of CaCO₃, MgAl₂O_4, and Fe(CO₂CH₃)₂ to introduce mineral phases of diopside, spinel, and olivine to the aggregates, respectively. To synthesize highly dense composites through pressureless sintering, we find that calcined powders should be composed of particles that have: (1) fully or partially reacted to the desired minerals, (2) a size of <100 nm and (3) less propensity to coalesce. Such calcined powders are cold isostatically pressed and then vacuum sintered. The temperature and duration of the sintering process are tuned to achieve a balance between high density and fine grain size. Highly dense (i.e., porosity ≤1 vol%) polycrystalline mantle mineral composites with grain size of 0.3–1.1 μm are successfully synthesized with this method.     

Non-equilibrium Condensation ina Primordial Solar Nebula: Formation of Refractory Metal Nuggets

We present a theoretical investigation of non-equilibrium condensation of refractory metalsinthe primordial solar nebula, in relation to the origin of “Fremdlinges” included inCAIs. Todescribe the nucleation process of grains from vapor, weadopted asemi-phenomenological modelmodified fromthe classical nucleation theoryby the introductionof the second virial coefficient of vapor. This modelachieves excellent agreement with nucleation rate experiment. However,the second virial coefficients are unknown for a vapor of refractory metals. To overcome this, weexpress the nucleation rate by theuse of the chemical potential of dimersinsteadof the second virial coefficient.On the basis of this new nucleation theory,we have performed numerical simulations ofnon-equilibrium condensation of refractory metals andfind thattheircondensation temperatures, T_c, decrease considerably in comparison withequilibrium condensation. Even if the characteristiccooling time scale is aslarge as 1×10⁵ years, the decrease in T_c isfrom 200 to 400 Kfor rare elements such as W, Re,and Os. This remarkablenon-equilibrium behaviormainly stemsfromthelow totalpressure in the primordial solar nebula. From our new modelwealso obtainthe typical size ofgrainsformed in condensation. We findthatthe cooling time should be ?1×10⁵ years for sub-micron-sized or largerrefractory metal nuggetsto form.     

Evaluation of urban thermal environments in commercial and residential spaces in Okayama City, Japan, using the wet-bulb globe temperature index

We estimated wet-bulb globe temperature (WBGT) using measured meteorological data to understand the bioclimates of human living spaces during the summer season. Our research focused on commercial and residential areas of Okayama City, Japan (population ～700,000). The commercial spaces (CO) mainly consisted of multi-story office buildings, whereas the residential spaces (RE) consisted of one- or two-story residential buildings. On a fine day with southeast winds, the spatially averaged WBGT measured in the CO was higher than that in the RE. The difference was statistically significant and would have caused noticeable discomfort and a high risk of heat disorder for occupants of the CO over the long term. For instance, at 1900 Japan Standard Time (JST), the maximum difference in the WBGT between the CO and RE sites was 2.0°C (23.5°C for the CO and 21.5°C for the RE). From 1800 to 1900 JST, the wet-bulb temperature in the CO was still 1.5–2.0°C higher than that in the RE, even though both areas had the same dry-bulb temperature. This indicates that the CO retained greater amounts of water vapor for longer periods compared to the RE. The wet-bulb temperature in the CO increased rapidly at most observation points when the southeast sea breeze arrived. In contrast, in the RE, the wet-bulb temperature decreased until evening. This difference was caused by moist air transported from a river about 1 km upwind from the CO. The moist air forced an increase in the WBGT and elevated the risk of heat disorder in the CO. The spatially averaged globe temperature of the CO at 1500 JST was 6.2°C lower than that at the RE, causing the WBGT of the CO to decrease. The results suggest that the higher WBGT in the CO was caused by higher wet-bulb temperatures. On a day with southwest winds, the CO and RE showed no difference in WBGT because the river was not included in the upwind source area.