[Show abstract][Hide abstract] ABSTRACT: Thin circular-arc blade is often used as a guide vane, a deflecting vane, or a rotating blade of low pressure axial-flow turbomachine because of its easy manufacture. Ordinary design of the blade elements of these machines is done by use of the carpet diagrams for a cascade of circular-arc blades. However, the application of the carpet diagrams is limited to relatively low cambered blade operating under optimum inlet flow conditions. In order to extend the applicable range, additional design data is necessary. Computational fluid dynamics (CFD) is a promising method to get these data. In this paper, two-dimensonal cascade performances of circular-arc blade are widely analyzed with CFD. The results have been compared with the results of experiment and potential theory, and useful information has been obtained. Turning angle and total pressure loss coefficients are satisfactorily predicted for lowly cambered blade. For high camber angle of , the CFD results agree with experiment for the angle of attack less than that for shockless inlet condition.
[Show abstract][Hide abstract] ABSTRACT: Experimental and numerical investigations were conducted for the internal flow of the stator of the diagonal flow fan. Corner separation near the hub surface and the suction surface of the stator blade are focused on. At low flow rate of 80% of the design flow rate, the corner separation between the suction surface and the hub surface can be found in both experimental and numerical results. Separation vortices are found in the computed oil flow on both suction and hub surfaces at 80% of the design flow rate in the three-dimensional numerical simulation.
[Show abstract][Hide abstract] ABSTRACT: In order to clarify the effect of tip clearance (TC) size on fan performance and the flow field at rotor outlet in a small
semi-open axial fan, the experimental investigation was carried out. The tip diameter of test fan rotor was 180mm and test
TC sizes were 1mm (TC=1mm) and 4mm (TC=4mm). Fan characteristics tests were carried out for two cases of TC size and three-dimensional
velocity fields at rotor outlet were measured using a single slant hot-wire probe at four flow-rate conditions. As a result,
it was found that the pressure — flow-rate characteristics curves for two cases showed almost the same tendency. However,
the ensemble averaged velocity profiles along radial measurement stations of TC=4mm largely changed compared with that of
TC=1mm in cases of small flow-rate condition. From the phase-locked averaging results, it was also found that the vortex existed
in the rotor outlet flow field of high flow-rate condition for each TC case. Compared with the vortices for TC=1mm and TC=4mm,
the vortex for TC=4mm was stronger than that for TC=1mm.
[Show abstract][Hide abstract] ABSTRACT: Experimental investigations were conducted for the internal flow of the stator of the diagonal flow fan. Corner separation
near the hub surface and the suction surface of the stator blade are focused on. At the design flow rate, the values of the
axial velocity and the total pressure at stator outlet decrease near the suction surface at around the hub surface by the
influence of the corner wall. At low flow rate of 80–90 % of the design flow rate, the corner separation between the suction
surface and the hub surface can be found, which become widely spread at 80 % of the design flow rate.
[Show abstract][Hide abstract] ABSTRACT: In order to improve the fan characteristics, especially efficiency and noise level of a small axial cooling fan with a large
tip clearance, the internal flow measurements with tip leakage vortex were carried out at fan rotor outlet using an I-type
hot-wire probe. The probe was set toward two directions, parallel and normal to the meridional plane of test fan, and the
two directional velocity components were measured. From the result of fan test it was found that the test fan didn’t have
the unstable characteristic with a positive gradient on its pressure — flow-rate curve. From the results of velocity measurement
it was observed that the tip leakage vortex exited at maximum efficiency flow-rate and large flow-rate conditions. However,
at small flow-rate conditions the tip leakage vortex was not observed and it was found that the flow field were enlarged toward
[Show abstract][Hide abstract] ABSTRACT: The objective of this paper is to present the effect of end plate on the performances of the impulse turbine for wave energy conversion by experimental investigation. The experiments have been performed by model testing under steady flow conditions in the study. And then, the performances of the impulse turbine with end plates have been compared with those of the original impulse turbine, i.e., the impulse turbine without end plate. As a result, it is found that the characteristics of the impulse turbine with end plates are superior to those of the original impulse turbine. Furthermore, the effects of end plate size and penetration on the turbine characteristics have been clarified in the study.
Journal of Fluid Science and Technology 01/2008; 3(3):450-457. DOI:10.1299/jfst.3.450
[Show abstract][Hide abstract] ABSTRACT: In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plate on the turbine characteristics has been investigated experimentally by model testing. As a result, it is found that the characteristics of the Wells turbine with end plates are superior to those of the original Wells turbine, i.e., the turbine without end plate and the characteristics are dependent on the size and position of end plate. Furthermore, by using a computational fluid dynamics (CFD), reason of the performance improvement of the turbine has been clarified and the effectiveness of the end plate has been demonstrated.
[Show abstract][Hide abstract] ABSTRACT: In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plates on the turbine
characteristics has been investigated experimentally by model testing under steady flow conditions. The end plate attached
to the tip of the original rotor blade is slightly larger than the original blade profile. The characteristics of the Wells
turbine with end plates have been compared with those of the original Wells turbine, i.e., the turbine without end plate.
As a result, it has been concluded that the characteristics of the Wells turbine with end plates are superior to those of
the original Wells turbine and the characteristics are dependent on the size and position of end plate. Furthermore, the effect
of annular plate on the turbine performance, which encircles the turbine and is attached to the tip, was investigated as an
additional experiment. However, its device was not effective in improving the turbine characteristics.
[Show abstract][Hide abstract] ABSTRACT: In this study, in order to achieve further improvement of the performance of an impulse turbine with fixed guide vanes for
wave energy conversion, the effect of guide vane shape on the performance was investigated by experiment. The investigation
was performed by model testing under steady flow condition. As a result, it was found that the efficiency of the turbine with
3D guide vanes are slightly superior to that of the turbine with 2D guide vanes because of the increase of torque by means
of 3D guide vane, though pressure drop across the turbine for the 3D case is slightly higher than that for the 2D case.
[Show abstract][Hide abstract] ABSTRACT: The three-dimensional separation in a decelerating channel flow generated by the suction through a porous side wall had been investigated experimentally. Unsteady characteristics of two corner separations were especially focused on. The profiles of time averaged static pressure are two-dimensional in the height direction even in the case with large regions of corner separation. The contour of the turbulence level of the mainstream velocity shows two peak values which correspond to two corner separations. The value of cross-correlation gets large negative values without any lag and the value of coherence gets peak value at around 0.5–2 Hz. The corner separations near the top wall and near the bottom wall are not independent and keep coherent structure both with negative value of cross correlation function and with the frequency of around 0.5–2 Hz.
ASME Turbo Expo 2006: Power for Land, Sea, and Air; 01/2006
[Show abstract][Hide abstract] ABSTRACT: An experimental investigation was made into three-dimensional separated flow and the vortices within the flow separation in
a decelerating channel flow generated by the suction from a porous side wall. The flows along the side and bottom walls were
visualized by the surface tuft method. The turbulent internal flow was measured by the split-film probe to investigate the
turbulent flow including the reverse flow. In the flow visualization for the strong decelerating flow (the suction flow ratio:0.8),
two typical flow patterns appear alternatively. One is that the flow near the bottom wall separates more upstream than the
flow near the top wall and a clockwise vortex can be seen in the separation region. Another is the reversal flow pattern with
a counterclockwise vortex. By the turbulent flow measurement using the split-film probe, two peaks of turbulence level are
observed for the strong decelerating flow case. These peaks can be related with two flow patterns mentioned above.
[Show abstract][Hide abstract] ABSTRACT: An experimental study was carried out to develop a new type of two-way diffuser suitable for a fluid flow energy conversion system. It is known that the power available from the fluid flow is proportional to the cube of the free stream velocity of the flow. Therefore, in order to take higher power output from the fluid flow, it is very important to construct a suitable system to increase the flow velocity. For a wind turbine, it has been reported that the speed of wind passing through it is dramatically increased by the use of a diffuser with a brim around the turbine. In this study, a new type of two-way diffuser suitable for a flow periodically changing its direction, such as a tidal current, was developed, applying the system to accelerate the wind speed for the wind turbine. The effects of the brim height and the outside body shape on the diffuser performance were experimentally investigated by measurement of the pressure and the velocity distributions along the center axis of the diffuser and around the diffuser. The present study is the first one to clarify the effect of these on diffuser performance.
Renewable Energy 08/2004; 29(10):1757-1771. DOI:10.1016/j.renene.2004.02.007 · 3.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Monoplane and biplane Wells turbines for wave power conversion have hysteretic characteristics in a reciprocating flow. In this paper, the mechanisms of the hysteretic behaviors were elucidated based on unsteady 3 dimensional Navier–Stokes numerical simulations. For the monoplane Wells turbine, the hysteretic loop is opposite to the well known dynamic stall of an airfoil. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the suction surface. For the biplane Wells turbine, the hysteretic behavior was similar to that of the monoplane at lower attack angles, but the hysteretic loop similar to the dynamic stall was observed at higher attack angles, which was attributed to unsteady flow separation near the hub and the trailing edge of the suction surface of the upstream blade.
Energy Conversion and Management 06/2004; 45(9-45):1617-1629. DOI:10.1016/j.enconman.2003.08.021 · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal-flow fan. The test fan was a high–specific-speed (ns=1620) type of diagonal-flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot-wire surveys were performed using a single-slant hotwire probe. The data obtained by these surveys were processed by means of a double phase-locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time-dependent ensemble averages of the three-dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated.
International Journal of Rotating Machinery 09/2003; 9(5). DOI:10.1155/S1023621X03000319
[Show abstract][Hide abstract] ABSTRACT: When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In
the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion
of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the
additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted
in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally.
The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination
between non-equilibrium condensation and the position of porous wall.
[Show abstract][Hide abstract] ABSTRACT: An experimental apparatus was developed to study the three dimensional separated flow with spiral-foci. The internal decelerating
flow was generated by the air suction from a side wall to produce the separation on an opposite-side wall. The relation between
the upstream boundary layer and the generation of spiral-foci in the separation region was observed by a tuft method. As a
result, it was clarified that the spiral-focus type separation could be produced on the side wall and its behavior was closely
related to the vortices supplied into the separation region from the boundary layer developing along top wall or bottom one.