Jiro Funaki

Basic Characteristics of Autorotating Flat Plate in Flow

In the present study, the authors conduct subsonic wind‐tunnel experiments, in order to investigate the effect of a depth‐to‐width ratio λ upon the tumbling of a simple two‐dimensional rectangular‐cross‐section prism. The authors carry out both flow visualisation and velocity measurement using a hot‐wire anemometer, together with the synchronised measurement of a prism’s attack angle α, which are analised using a phase‐averaging technique. As a result, there are two modes for λ<0.6 and λ⩾0.6. For λ<0.6, large‐scale two vortices are emitted during one prism’s rotation, although the dominant velocity fluctuation has the period corresponding to one prism’s rotation, namely, is in 360° cycle of α. For λ⩾0.6, large‐scale four vortices are emitted during one prism’s rotation, although the dominant velocity fluctuation has the period corresponding to a half prism’s rotation, namely, is in 180° cycle of α. Especially, for λ = 0.5, we can see transition‐process features between the two modes. For λ<0.6, momentum d...

Measurements of Minute Unsteady Pressure on Three-Dimensional Fan with Arbitrary Axis Direction

The present study is a fundamental approach to develop the measuring technology for minute fluctuating pressures on the three-dimensional blade surfaces of the fan which rotates with an arbitrary rotation-axis direction. In this situation, we are required to correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures. The working fluid is air. A pressure transducer rotating with an arbitrary attitude is closely sealed by a twofold shroud system. The rotational motion with an arbitrary attitude is produced by fixing the pressure transducer to the cantilever which is connected to a motor-driven disc of 500mm in diameter and 5mm in thickness. As a result, we have quantitatively determined main governing effects upon the non-effective component of the pressure-transducer signal.

On Sloshing Modes in Equilateral-Polygonal-Section Containers (1st Report, Unified Classification)

This is the first part of a pair of the studies which report the vertical sloshing, that is, the liquid surface motion in container oscillating in the vertical direction, concerning various equilateral-polygonal-section containers : namely, octagonal, heptagonal, hexagonal, pentagonal, square and trianglar containers together with a circular container, in order to generalise their sloshing modes. As a result, the authors classify the sloshing modes based on the circular-container sloshing modes, referring to computational and experimental results. This modal classification has some advantages over that based on the square-section-container sloshing modes. The present computation is based on the discrete singularity method. In the second part, the proposed modal classification is shown to be useful to predict the eigen frequencies.

Aspect-Ratio Effects and Unsteady Pressure Measurements inside a Cross-Flow Impeller

In the present experimental study, the authors try to clarify the characteristics of the flow around and inside a cross-flow impeller in a typical geometry, over a wide parameter range of an aspect ratio . In order to eliminate the complicated casing factors, the impeller rotates in open space without any casings. As a result, by using hot wire anemometer measurements and by conventional flow visualisations with a particle image velocimetry technique, the authors show that both the outflow rate and the maximum vorticity attain the maximum for

Hydrogen Production by Bio-Fuel Steam Reforming at Low Reaction Temperature

The authors reveal the dominant chemical reactions and the optimum conditions, supposing the design of ethanol steam-reforming reactors. Specifically speaking, experiments are conducted for Cu/ZnO/Al2 O3 catalyst, together with those for Ru/Al2 O3 catalyst for reference. Using a household-use-scale reactor with well-controlled temperature distributions, the authors compare experimental results with chemical-equilibrium theories. It has revealed by Shinoki et al. (2011) that the Cu/ZnO/Al2 O3 catalyst shows rather high performance with high hydrogen concentration CH2 at low values of reaction temperature TR . Because, the Cu/ZnO/Al2 O3 catalyst promotes the ethanol-steam-reforming and water-gas-shift reactions, but does not promote the methanation reaction. So, in the present study, the authors reveal that the Ru/Al2 O3 catalyst needs high TR > 770 K for better performance than the Cu/ZnO/Al2 O3 catalyst, and that the Ru/Al2 O3 catalyst shows lower performance at TR < 770 K. Then, the Ru/Al2 O3 catalyst is considered to activate all the three reactions even at low TR . Furthermore, concerning the Cu/ZnO/Al2 O3 catalyst, the authors reveal the influences of liquid-hourly space velocity LHSV upon concentrations such as CH2 , CCO2 , CCO and CCH4 and the influence of LHSV upon the ethanol conversion XC2H5OH , in a range of LHSV from 0.05 h−1 to 0.8 h−1 , at S/C = 3.0 and TR = 520 K. And, the authors reveal the influences of the thermal profile upon CH2 , CCO2 , CCO , CCH4 and XC2H5OH , for several LHSV’s. To conclude, with well-controlled temperatures, the reformed gas can be close to the theory. In addition, the authors investigate the influences of S/C.Copyright

Thermal Characteristics of Heavy-Hydrocarbons-Fuel Reactor for Fuel Cell System

We has successfully developed a small and simple steam-reforming reactor for n-dodecane as a heavy-hydrocarbons fuel. The reactor satisfied the target thermal conditions. Under the conditions, we have measured the inside temperature profile and the reaction performance. The reaction becomes more active at the position where the temperature T>600°C. At steam-to-carbon S/C≥5.0, hydrogen-molecule ratio R H2 is nearly-constant to about 70%. From a practical point of view, the best operating condition is at S/C ≥ 5 for present reactor.

An experimental study of three-dimensional vortical structures between co-rotating disks

In this study, we experimentally investigate the flow between co-rotating disks in a stationary cylindrical enclosure. Here, the gap between disks is much narrower than disk radius. This flow is often non-axisymmetrical and complicated. This flow sometimes induces magnetic-head oscillations in disk storage devices of PCs. We carry out flow visualisations using a high-speed camera, and time-successive three-dimensional PIV (Particle Image Velocimetry) analyses of visualised pictures. We focus on the relation and combination of axial modes with circumferencial modes. Tested cases are two, that is, A (Re = 1.2 × 104 and δ = 0.12) and B (Re = 1.0 × 105 and δ = 0.20). Here, Re is the rotating Reynolds number, and δ is a non-dimensional gap. Case A is in axial mode II and circumferencial mode 8-9, and case B is in axial mode III and circumferencial mode 4. Axial modes are related with the symmetry of a pair of toroidal-vortical structures and circumferencial modes are related with the radial fluctuation of these structures as well as the solid-body-rotation core. As a result, in case A, the vortical structures are mainly influenced by axial mode (II) in the z direction, but not influenced by both axial mode (II) and circumferencial mode (8-9) in the r direction. In case B, the vortical structures are mainly influenced by axial mode (III), but influenced by circumferencial mode (4) in the r direction.

Unsteady and Three Dimensional PTV Measurements of Flow Structure in a Suction Pump

We attempt to reveal the unsteady three‐dimensional flow structure in a suction sump with the vertical‐wet‐pit‐pump configuration. In the present study, we consider the simultaneous measurement of a three‐dimensional particle tracking velocimetry (3D‐PTV) with another velocimetry, that is, an ultrasonic velocity profiler (UVP), using common tracer particles. This simultaneous measurement is expected to be a suitable method for the accuracy check of the 3D‐PTV. At first, we have successfully found the suitable condition for simultaneous measurements with high accuracy. Then, we have revealed the concerning unsteady three‐dimensional flow structure at various instants, quantitatively.

Numerical and Experimental Study on Aerodynamic Characteristic of Basic Airfoils at Low Reynolds Numbers

The aerodynamic characteristics of airfoils have been researched in higher Reynolds‐number ranges more than 106, in a historic context closely related with airplanes’ and fluid‐machinery developments in the last century, however our knowledge is not enough at low and middle Reynolds‐number ranges. So, in the present study, we investigate such basic airfoils as a NACA0015, a flat plate and the flat plates with modified fore‐face and after‐facegeometries in a Reynolds‐number range of 102–105, using two‐ and three‐dimensional computations together with wind‐tunnel and water‐tank experiments. Especially, we show their flow fields at Re = 1.0×102.

Flow Characteristics and Structures of Three-Dimensional Unsteady Thermal Convection in a Container

In this study, we numerically investigates the flow and thermal characteristics of the three-dimensional thermal convection in a cubic cavity heated below in the gravitational field, concerning about spatially-averaged kinetic energy K , Nusselt number Nu and flow structure. We assume Prandtl number Pr = 7.1 (water) and Rayleigh number Ra = 1.0×104 – 3.5×105 . As a result, we have specified two of three important values of the Rayleigh number which demarcate different flow bifurcations and are referred to as the second and third critical Rayleigh numbers Rac2 and Rac3 . We have found that Rac2 and Rac3 are roughly 2.6×105 and 3.1×105 , respectively. We have observed a histerisis effect upon the value of Rac2 with chaotic behaviour at Ra ≈ Rac2 , and revealed flow structures. In addition, we investigate the relationship between Ra and the oscillatory-convection frequency. The increasing rate of the K mean with increasing Ra shows a different manner from that of Nuinflow-ave, mean . That is, the former is progressive and the latter is asymptotic, as Ra increases. Both the values of K mean and Nuinflow-ave, mean in oscillatory flow tend to be smaller than those in steady flow, respectively. Then, there exist small jumps/drops of K mean and Nuinflow-ave, mean at Ra = Rac2 .Copyright