Simultaneous Measurement of Velocity and Fluctuating Pressure in a Turbulent Wing-tip Vortex Using Triple Hot-film Sensor and Miniature Total Pressure Probe

We have developed a probe-system for simultaneous measurement of three velocity components and pressure in turbulent flows. A miniature total pressure probe is placed adjacent to the sensors of a triple hot-film probe in order to achieve the spatial resolution which is equivalent to that of the triple hot-film probe itself. The instantaneous static pressure is calculated from measured velocity and total pressure by means of a newly developed processing method based on the Bernoulli equation for unsteady flows. The measurements were undertaken in a turbulent wing-tip vortex flow. The look-up table method is employed for the calibration of the hot-film probe so accurate velocity data could be obtained over a wide range of the flow-attack angles. It is also demonstrated that the present probe-system is capable of measuring fluctuations in both velocity and pressure in the 20?C650 Hz frequency range. The distribution of the fluctuating pressure obtained by this indirect method is in good agreement with the results from direct measurements of static pressure, demonstrating the promising performance of the present method. Furthermore, an improvement in the ability to make measurements of the velocity?Cpressure correlation across the wing-tip vortex is achieved. This improvement is possible because the effects of lateral velocity components are properly taken into account in the present formulation. The investigation regarding the transport equation budget for turbulent kinetic energy shows an anomalous structure of turbulence in this flow, mainly due to the meandering of the vortex, and the measurement of pressure diffusion is found to play an important role in the characterization of this kind of flow.     

Preparation of organic/inorganic hybrid and hollow particles by catalytic deposition of silica onto core/shell heterocoagulates modified with poly[2-(N,N-dimethylamino)ethyl methacrylate

The organic/inorganic hybrid particles PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) were prepared by catalytic hydrolysis and subsequent polycondensation of tetraethoxysilane in the poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA) layers grafted on the PSt/P(St-CPEM)(θ) core/shell heterocoagulates. The micron-sized PSt core and the submicron-sized P(St-CPEM) shell particles bearing ATRP initiating groups were synthesized by dispersion polymerization of styrene (St) and emulsifier-free emulsion polymerization of St with 2-chloropropionyloxyethyl methacrylate (CPEM), respectively. The raspberry-shaped PSt/P(St-CPEM)(θ) heterocoagulates with a controlled surface coverage (θ=0.51, 0.81) were prepared by hydrophobic coagulation between the core and the shell particles in an aqueous NaCl solution near the T(g) of P(St-CPEM). Surface modification of heterocoagulates was carried out by ATRP of DMAEMA from the shell particles adsorbed on the core particles. Silica deposition was performed by simply adding tetraethoxysilane to a water/methanol dispersion of PSt/P(St-CPEM)(θ)-g-PDMAEMA. The SEM and TGA revealed that the resulting PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2) composites maintain a raspberry-like morphology after deposition of silica onto the PDMAEMA layer grafted on heterocoagulates. The micron-sized, raspberry-shaped or the submicron-sized, hole-structured silica hollow particles were obtained selectively by thermal decomposition of the PSt/P(St-CPEM)(θ)-g-PDMAEMA/SiO(2). The oriented particle array was fabricated by dropping anisotropically perforated silica particles onto a glass substrate settled at the bottom of a bottle filled with chloroform.     

LES Study of Flow Between Shrouded Co-rotating Disks

Large eddy simulations of turbulent flow between shrouded co-rotating disks, representing a simplified model of a hard disk drive, are performed. The computation domain surrounds a complete disk and is bounded at top and bottom by half a disk. Therefore, it is possible to compute the fluctuating pressure field surrounding the middle disk. Also, the influence of the shroud geometry is taken into account by comparing a flat shroud wall and a wall with rib chambers. In the flat shroud case, the fluctuating pressure on the upper- and lower-surface of a disk indicates a strong correlation with fluid motion travelling across the disk-tip clearance region. However, in the ribbed shroud case the organized flow structure that is observed in the flat shroud case disappears and the fluctuating pressure acting on the surface of the disk is remarkably diminished.     

Stereo PIV measurement of a finite, flapping rigid plate in hovering condition

Qualitative and quantitative flow visualizations were performed on a flapping rigid plate to establish a quantitative method for flow observation and evaluation of the force in the near field of a flapping wing. Flow visualization was performed qualitatively with dye visualization and quantitatively with velocity measurements using stereo particle image velocimetry (PIV) on three planes near the tip of the plate along its chord and oriented normally. By ensemble averaging the velocity fields of the same phase angles, they represent a portion of the volume near the tip. Measurements were conducted with two flapping frequencies to compare the flow structure. The second invariant of the deformation tensor visualized the leading edge and mid-chord vortices around the plate appearing due to flow separation behind the plate while other vortical structures were visualized by streamlines. These structures appear to be related to the dynamics of the leading edge vortex. Force analysis by integrating the phase-averaged velocity field within a chosen control volume showed increases in the maxima of the magnitudes of the non-dimensional unsteady force terms on the edge of the plate at the angles after the end of each stroke. The non-dimensional phase-averaged momentum flux was similar for both flapping frequencies.     

Magnetic anisotropy of amorphous (Fe1−x Co x )78Si10B12 alloys

In order to better understand the problem of magnetic anisotropy in amorphous alloys produced by a rapidly quenching technique, in-plane magnetic anisotropy of amorphous (Fe_1−x Co _x (₇₈Si₁₀B₁₂ alloys was measured by means of a torque magnetometer using a disk specimen made from the amorphous alloy ribbon. The amorphous ribbons were prepared by a single roller type quenching apparatus. It was found that the anisotropy had mostly twofold symmetry in all the alloy cases, and that the concentrationx dependence of the anisotropy constant behaved differently from that of the magnetostriction. Moreover, the anisotropy did not disappear by subsequent annealing at high temperatures where the internal stress relief and the crystallization were completed.     

Ni-Zr amorphous alloys: Low temperature specific heat and superconductivity

The specific heat (C_p) of the amorphous alloys Ni_100-xZr_x for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature T_c, the enhanced density of states at the Fermi level N_γ(_F) and the Debye temperatures θ_D(0), θ_D(T) established. For the three superconducting compositions (x=75, 65, 55) N_γ(E_F increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states $\text{N}{}_0\text{(E}{}_{\mathrm{F}}\text{) =}\text{N}{}_{\mathrm{\gamma }}\text{(E}{}_{\mathrm{F}}\text{)}\text{(1 + λ}{}_{\mathrm{p}}\text{)}$ increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I²> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys.     

Soluble,crystalline, and thermally stable alkali CO2− and carbonite (CO22−) clusters supported by cyclic(alkyl)(amino) carbenes

The mono- and dianions of CO₂ (i.e., CO₂⁻ and CO₂²⁻) have been studied for decades as both fundamentally important oxycarbanions (anions containing only C and O atoms) and as critical species in CO₂ reduction and fixation chemistry. However, CO₂ anions are highly unstable and difficult to study. As such, examples of stable compounds containing these ions are extremely limited; the unadulterated alkali salts of CO₂ (i.e., MCO₂, M₂CO₂, M = alkali metal) decompose rapidly above 15 K, for example. Herein we report the chemical reduction of a cyclic (alkyl)(amino) carbene (CAAC) adduct of CO₂ at room temperature by alkali metals, which results in the formation of CAAC-stabilized alkali CO₂⁻ and CO₂²⁻ clusters. One-electron reduction of CAAC–CO₂ adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals [M(CAAC–CO₂)]_n (M = Li, Na, K, 2–4) analogous to the alkali CO₂⁻ radical, and two-electron alkali metal reduction affords dianionic clusters of the general formula [M₂(CAAC–CO₂)]_n (5–8) with reduced CO₂ units which are structurally analogous to the carbonite anion CO₂²⁻. It is notable that crystalline clusters of these alkali–CO₂ salts may also be isolated via the “one-pot” reaction of free CO₂ with free CAAC followed by the addition of alkali metals – a process which does not occur in the absence of carbene. Each of the products 2–8 was investigated using a combination of experimental and theoretical methods.

The direct chemical reduction of CAACCO2 adducts by alkali metals to yield multinuclear clusters is reported. The mono- and dianions of CO₂ have been studied for decades and are fundamentally important oxycarbanions and critical species in CO₂ fixation chemistry.     

Rate constants for the reactions of benzyl and methyl-substituted benzyl radicals with O2 and NO

Rate constants for reactions of benzyl, o-niethylbenzyl and p-meihylbenzyl radicals with O₂ and NO have been measured at room temperature. The radicals were generated by UV flash photolysis and the time decay measured by absorption at ≈ 300 nm. The rate constants are: benzyl (0.99 ± 0.07 and 9.5 ± 1.2), o-methylbenzyl (1.2 ± 0.07 and 8.6 ± 0.8) and p-mithyl-benzyl (1.1= 0.10 and 8.9 = 0.9) for O₂ and NO respectively in units of 10^?12 cm³ molecule^?1 s^?1.     

High-fidelity image reproduction using angular distribution of reflected spectral intensity

A method to reproduce images of an object under various observation conditions is presented. In this method, a series of multispectral images is captured by rotating the object under a point light source of which spectral power distribution and the position are known. The captured images are decomposed into diffuse and specular reflection component images based on the dichromatic reflection and the Lambertian models. Next, the incident angle of the illumination light and the angle between viewing direction and regular reflection are calculated based on observation geometry. Finally, the image under observation geometry is synthesized using the light-ray rearrangement technique. The experiments are carried out using two-dimensional objects, leather and fabric. Most of the synthesized images are shown to be the same as the images actually captured under the assumed illumination geometry, even if the object has complex reflection like fabric for which it is difficult to apply the reflection model used in computer graphics.     

II. Chemische Analyse anorganischer Stoffe

Ohne Zusammenfassung