Mamoru Kikuchi

Influences of axial gap between blade rows on secondary flows and aerodynamic performance in a turbine stage

A study on the effects of the axial gap between stator and rotor upon the stage performance and flow field of a single axial flow turbine stage is presented in this paper. Three axial gaps were tested, which were achieved by moving the stator vane in the axial direction while keeping the disk cavity constant. The effect of the axial gap was investigated at two different conditions, that is design and off-design conditions. The unsteady three-dimensional flow field was analyzed by time-accurate RANS (Reynolds-Averaged Navier-Stokes) simulations. The simulation results were compared with the experiments, in which total pressure and the time-averaged flow field upstream and downstream of the rotor were obtained by five-hole probe measurements. The effect of the axial gap was confirmed in the endwall regions, and obtained relatively at off-design condition. The turbine stage efficiency was improved almost linearly by reducing the axial gap at the off-design condition.Copyright

Crystal structure of oligothiophene thin films characterized by two-dimensional grazing incidence X-ray diffraction

Crystal structure in an highly oriented organic thin film was determined using two dimensional grazing incidence X-ray diffraction (2D-GIXD). α,ω-Hexyl-distyryl-bithiophene (DH-DS2T) was chosen as the material for the structural analysis, because it is a typical organic semiconductor showing a high crystallinity and an ordered layer-growth behavior. A 2D-GIXD pattern over large range of scattering angles was obtained by using high-brightness synchrotron radiation in SPring-8 and high-sensitive 2D X-ray detector (PILATUS 300 K). The analysis of the observed 2D-GIXD pattern was made to clarify that the crystal structure of highly oriented DH-DS2T thin films belongs to a monoclinic unit-cell with a = 0.58 nm, b = 0.78 nm, c = 3.43 nm, and β = 94.3°, and the space group is determined to be P21/a by considering the extinction rule. Furthermore, by fitting the simulated Bragg peak intensities to the experimental data, the molecular structure is determined. In this structure, two molecules are included in the unit cell and they tilt about 25° against substrate normal.

A new instrumentation for in situ characterization of the charge transport and crystallographic properties in co-evaporated organic thin film transistor

ABSTRACT A new instrumentation was developed to study the in situ electrical and crystallographic properties of organic thin film transistor during vacuum deposition. We characterized pentacene (PEN) and perfluoro-pentacene (PFP) co-deposited organic thin film transistor with various mixing ratio using this equipment. Lattice parameters and crystal orientations of PEN and PFP alloyed phases (named σ-phase and λ-phase) were determined using an in situ two-dimensional grazing incidence X-ray diffraction (2D-GIXD) measurement. The observed 2D-GIXD patterns clarified that the σ-phase is in triclinic unit cell with the following lattice parameters: a = 0.67 nm, b = 0.75 nm, c = 1.58 nm, α = 95.7° β = 94.2° and γ = 84.0°. The c plane of σ-phase crystal is parallel to the substrate surface. The λ-phase is also in triclinic with the following lattice parameters: a = 0.66 nm, b = 0.69 nm, c = 1.56 nm, α = 109.5° β = 113.0° and γ = 81.5°. The a plane of λ-phase crystal was parallel to the substrate surface. It was also found the best symmetric hole and electron mobility (μh = 5.5 × 10−4 cm2V−1s−1 and μe = 5.1 × 10−4 cm2V−1s−1) were obtained at PEN: PFP = 1:1.

In-situ Observation of 2-Dimensional X-ray Diffraction of Organic Thin-film Growth by Synchrotron Radiation

Two-dimensional grazing incidence X-ray diffraction (2D-GIXD) is one of the powerful methods to analyze crystal growth and structure of organic thin films. In this report, we show some experimental examples of 2D-GIXD measurements on organic semiconductor thin-films performed at SPring-8. First, polymorphic transformation of pentacene depending on film thickness observed by means of in-situ real-time 2D-GIXD is shown. Secondly, real-time observation of change in structure during thin-film growth of oligothiophenes by means of 2D-GIXD is shown. Finally, a result of crystal structure analysis from 2D-GIXD data of polycrystalline an oligothiophene thin film is reported.

Two Dimensional Grazing Incidence X-Ray Diffraction of TIPS-Pentacene Thin Films

We report crystal structure of TIPS-pentacene thin films studied by two dimensional grazing incidence x-ray diffraction (2D-GIXD). Thin films were fabricated by dry and wet processes, and precisely compared the crystal structures of the fabricated films. Slight differences in the unit cell parameters are found in the films. Furthermore, a new polymorph is identified in the film fabricated at sufficiently low substrate temperature, − 166°C. The unit cell parameters of the new polymorph are determined by analyzing the 2D-GIXD pattern.

Response of Stretched Cylindrical Diffusion Flame to Sinusoidal Oscillation of Air Flow Velocity

An experimental study investigated the characteristics of a stretched cylindrical diffusion flame, with a convex curvature with respect to the air stream, in response to periodic air flow velocity oscillation. The fuel was methane diluted with nitrogen, and the oxidizer air. The oscillation frequency was varied from 5 to 250 Hz. The results are summarized as follows. Though the fluctuation amplitude of the air stream velocity gradient was constant with respect to the frequency, the amplitude of the fuel stream increased. The fluctuation amplitude of the flame radius changed quasi-steadily from 5 to 25 Hz, and decreased with increasing frequency in the frequency range greater than 50 Hz. The flame luminosity did not respond quasi-steadily at 5 Hz, and the oscillation amplitude of flame luminosity was less than that of a steady flame, over the same velocity fluctuation range. The oscillation amplitude of luminosity peaked at 50 Hz, and was greater than that of a steady flame. It is considered that this complex change in flame luminosity with respect to frequency was closely related to the phase difference in the respective time variations in the ratio of flame thickness to radius, the velocity gradients of the air and fuel streams, and the magnitude of these values, with the ratio of flame thickness to radius related to the flame curvature effect, the velocity gradient of the air stream correlated to the flame stretch effect, and the velocity gradient of the fuel stream impacting the fuel transportation.

Development of a small telescope like PZT and effects of vibrations of mercury surface and ground noise

A PZT type telescope for observations of gravity gradient and lunar rotation was developed, and a Bread Board Model (BBM) for ground experiments was completed. Some developments were made for the BBM such as a tripod with attitude control system, a stable mercury pool and a method for collecting the effects of vibrations. Laboratory experiments and field observations were performed from August to September of 2014, in order to check the entire system of the telescope and the software, and the results were compared to the centroid experiments which pursue the best accuracy of determination of the center of star images with a simple optical system. It was also investigated how the vibrations of mercury surface affect the centroid position on Charge Coupled Device (CCD). The results of the experiments showed that the effects of vibrations are almost common to stars in the same view, and they can be corrected by removing mean variation of the stars; and that the vibration of mercury surface can cause errors in centroid as large as 0.2 arcsec; and that there is a strong correlation between the Standard Deviation (SD) of variation of the centroid position and signal to noise ratio (SNR) of star images. It is likely that the accuracy of one (1) milli arcsecond is possible if SNR is high enough and the effects of vibrations are corrected.

Enhancement of Water Cooling Performance in Narrow Flow Passages by Using Micro Heat Sinks With Miniature Vortex Generators

This study describes a possibility of an improvement of water cooling devices for high-power electronic devices such as inverters for electric vehicles by using a combination of micro heat sinks and miniature vortex generators. Power devices such as IGBT (Insulated Gate Bipolar Transistor) are widely used for controlling an operation of electronic vehicles and hybrid vehicles. Due to the improvement of the performance of the power devices, the heat dissipation density from these devices becomes higher. The water cooling is the commonest method for dissipating heat from the inverter of the electronic vehicles. Therefore the improvement of the water cooling technology is significantly needed in order to manage the increase of the heat dissipation density.We are now trying to develop a high-performance water cooling device for dissipating the high heat flux from the inverters in the electric vehicles by using a combination of a fine miniature heat sink and a miniature vortex generator. The combination of the miniature heat sink and the vortex generator may increase heat transfer performance of the heat exchanger while inhibiting an increase of pressure drop by generating a swirling turbulent flow in a clearance between the heat sink fins. In this study, the water cooling performance in the narrow flow passage, which simulates the flow passage in the water cooling device, with the miniature heat sink and the miniature vortex generators was investigated by using 3-dimentional CFD analysis. From the analysis, we conclude that the combination of the miniature heat sink and the vortex generator was effective for the heat transfer enhancement in the narrow flow passage of the water cooling device while inhibiting the generation of the pressure drop when we can use the combination with the appropriate manner.Copyright

Studies on High-Lift LP Turbine Airfoils of Aero Engines (Understanding of Boundary Layer Transitional Behaviour on Time-Space Diagram under the High Lift and Ultra High Lift Conditions)

This paper details experimental studies on the flow field around a linear cascade of low-pressure turbine airfoils whose solidity is changeable. Highly loaded low-pressure turbine (LPT) blades are one of the key paths to successful future aero-engines, however these blades are usually accompanied with separation bubble, eventually leading to the increase in aerodynamic performance. The purpose of this study is therefore to clarify any favorable effects of incoming wakes upon the aerodynamic loss of high-lift or ultra high-lift rotor blade cascade through the measurements of wake-affected boundary layers including separation bubble under low Reynolds number conditions. Cylindrical bars on the timing belts work as wake generator to emulate upstream stator wakes that impact the rotor blade. Hot-wire probe measurement is conducted over the blade suction surface to understand to what extent and how the incoming wakes affect the boundary layers containing separation bubble. Time-dependent transitional behaviors due to the wake passing are examined through the detailed inspection of several composite maps of flow properties displayed on time-space diagrams.