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Volume 37, Issue 2
Displaying 1-5 of 5 articles from this issue
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Technical Papers
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Kunihiko YOSHITAKE, Hidenobu SHOUJI, Kazuo MATSUUCHI2009 Volume 37 Issue 2 Pages 78-84
Published: 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe movement of the wing of the cycloidal propeller can be described as combination of in-phase pitching and heaving oscillation. Under consideration of this, characteristics of the propeller are analyzed with unsteady airfoil theory by Karman and Sears. Reduced frequency of the wing in this case is decided by the ratio of half chord length to rotational radius and is unrelated to rotational speed. It can be clarified that reduced thrust depends on the amplitude of the oscillation and the moving velocity of the propeller. Results of quasi-steady and unsteady analyses are shown in the vector diagrams, and unsteady flow effect by wake vortices generation is inferred by comparing both results. Calculated results of the power for generating thrust and the thrust efficiency are also discussed.View full abstractDownload PDF (439K) -
Junsuke MURATA, Yutaka HASEGAWA, Koichi NARITA, Kota TANAKA, Hiroshi I ...2009 Volume 37 Issue 2 Pages 85-93
Published: 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe gust events frequently bring about the breakdown and fatigue damage of the wind turbine generator system (WTGS). Therefore load calculation using gust model should be performed during the design process of WTGS. The present paper describes averaged shapes, i.e. temporal and spatial velocity variations of the gust events for several wind conditions, which have been derived from the time-series of the simultaneous wind measurements at multiple points. The extracted temporal mean gust shapes have been compared to those from 'NewGust model', which is a kind of theoretical model, and the validity of the model is evaluated. In addition, the aerodynamic loads on the rotor blades due to the gust events are analyzed by using mean gust shapes from NewGust model and a numerical calculation method.View full abstractDownload PDF (1422K) -
Donghyuk KANG, Koichi YONEZAWA, Tatsuya UEDA, Nobuhiro YAMANISHI, Chis ...2009 Volume 37 Issue 2 Pages 94-103
Published: 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA large eddy simulation (LES) of flow in an inducer is carried out under flow rate oscillations. The present study focuses on characteristics of dynamic responses of the backflow and the pressure performance to the flow rate fluctuations under non-cavitation conditions. Results show that the backflow response delays behind the flow rate fluctuation. The pressure performance curve exhibits a closed curve caused by the effect of inertia associated with the flow rate fluctuations. Comparing with one dimensional evaluation of the inertia effects, it was found that the inertial effects obtained by the LES are smaller. Additionally, the averaged negative slope of the performance curve becomes larger under unsteady conditions. From the conservations of angular momentum and energy, an expression useful for the evaluation of unsteady pressure rise was obtained. The examination of each term of this expression shows that the apparent decrease of inertia effects is caused by the response delay of Euler head and that the increase of negative slope is caused by the inertial term associated with the delay of backflow response.View full abstractDownload PDF (1789K) -
Jun-Ho KIM, Takashi ATONO, Koichi ISHIZAKA, Satoshi WATANABE, Akinori ...2009 Volume 37 Issue 2 Pages 104-111
Published: 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. In operating condition at partial flow rate and extremely low suction pressure, however, cavitation surge oscillation occurs. As the cavitation surge oscillation with low frequency occurs in a close relation between the inlet back-flow cavitation and the growth of blade cavity into the throat section of blade passage, one method of installing an axi-asymmetrical plate upstream of inducer has been proposed to suppress the oscillation. The inlet flow distortion due to the axi-asymmetrical plate makes different elongation of cavity on all blades, which prevents the flow from becoming simultaneously unstable at all throat sections. In the present study, changes of the suppression effects with the axial distance between the inducer inlet and the plate and the changes with the blockage ratios of plate area to the cross-sectional area of inducer inlet are investigated for helical inducers with tip blade angles of 8° and 14°.Then a conceivable application will be proposed to suppress the cavitation surge oscillation by installing axi-asymmetrical inlet plate.View full abstractDownload PDF (1120K) -
Shoichi YAMATO, Shogo NAKAMURA, Akinori FURUKAWA2009 Volume 37 Issue 2 Pages 112-122
Published: 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSReviewing and analyzing the field test results carried out in 65 hydroelectric power stations in Japan, low head power station tends to have low velocity of wave propagation and it exceeds 1,000 m/s in power station of more than 100 m of net head. This is influenced by slight volume of air in the river flow because bubbly flow continues under low head, namely,low pressure. On the other hand,increase of pressure reduces the void fraction, that is no influence by the air, thus the wave propagation velocity is defined by only the rigidity of penstock. The wave propagation velocity for low head power station exceeds l,000 m/s in case means for vortex elimination is provided at the intake.View full abstractDownload PDF (826K)
Review
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