Hysteretic characteristics of Wells turbine for wave power conversion

A Wells turbine blade for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. And also the effects of solidity, setting angle and blade thickness on the hysteretic characteristics of the Wells turbine have been discussed.     

Features of Rotating Stall Cell in a Diagonal Flow Fan（in Case of Mid-loading Rotor）

The structure and behavior of rotating stall cell were experimentally clarified in a diagonal flow fan. The specific-speed of the fan was 1140 (r/min, m3/min, m), and the total pressure-rise coefficient at design flow-rate was 0.345. The static pressure on outer casing wall and the total pressure at rotor inlet and outlet were measured using a high response pressure transducer. The measured data were processed by the use of DPLA technique, and the structure and behavior of rotating stall cell were obtained. As a result, the stall cell extent for circumferential and spanwise direction and the pressure distributions inside stall cell were clarified. The details of stall cell propagation were also shown.     

Three Dimensional Separation with Spiral—Focus in a Decelerating Duct Flow （Effect of Asymmetric Inlet Boundary Layer Thickness）

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.     

Effects of Hub-To-Tip Ratio and Tip Clearance on Hysteretic Characteristics of Wells Turbine for Wave Power Conversion

A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.     

Performance of an impulse turbine with fixed guide vanes for wave power conversion

A simple fixed geometry impulse turbine has been studied as a suitable power converter in Oscillating Water Column based wave power plants. Comparison with the Wells turbine, which is the commonly used self-rectifying turbine in such applications, shows it to be superior in performance under irregular flow conditions. Optimum guide vane angle for maximum efficiency has been arrived at based on the five angles tested.     

Flow fields with vortex in a small semi-open axial fan

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.     

Effects of blade geometry on performance of wells turbine for wave power conversion

IntroductionThe fossil fuel energy with the problem of airpollution might run out by the middle of the 21stcentury. So many researchers have studied forscores of years on alternative, renewable energysources11] such as tidal, wave, salinity gradient,current, wind and solar energy.The energy density level of waves is higherthan the other energy sources stated above. Thereare various techniques for extraction of energyfrom waves[2]. Several of the wave energydevices using the principle of an os…     

Vortices within the Separation Region in a Decelerating Channel Flow （Effect of Inlet Velocity Gradient）

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.     

Effect of End Plates on the Performence of a Wells Turbine for Wave Energy Conversion

In order to improve the performance of the Wells turbine for wave energy conversion,the effect of end plates onthe 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.Thecharacteristics 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 turbinewith end plates are superior to those of the original Wells turbine and the characteristics are dependent on the sizeand position of end plate. Furthermore, the effect of annular plate on the turbine performance,which encircles theturbine and is attached to the tip,was investigated as an additional experiment.However,its device was not effec-tive in improving the turbine characteristics.     

Comparison of Performances of Turbines for Wave Energy Conversion

The Wells turbine for a wave power generator is a self-rectifying air turbine that is available for an energy conversion in an oscillating water-air column without any rectifying valve. The objective of this paper is to compare the performances of the Wells turbines in which the profile of blade are NACA0020, NACA0015, CA9 and HSIM15-262123-1576 in the small-scale model testing. The running characteristics in the steady flow, the start and running characteristics in the sinusoidal flow and the hysteretic characteristics in the sinusoidal flow were investigated for four kinds of turbine. As a conclusion, the turbine in which the profile of blade is NACA0020 has the best performances among 4 turbines for the running and starting characteristics in the small-scale model testing.