This study is concerned with the numerical simulation of the flow through an open type cross-flow runner of a nano-hydraulic turbine driven by rapid and shallow stream. It employs the two-dimensional particle method, ...This study is concerned with the numerical simulation of the flow through an open type cross-flow runner of a nano-hydraulic turbine driven by rapid and shallow stream. It employs the two-dimensional particle method, which was used for the flow simulation of a small-scale hydraulic turbine of impulse-type in the prior study. The tip speed ratio 2, defined as the ratio of the runner tip speed to the water stream velocity upstream of the runner, ranges from 0.1 to 0.8. The simulated flow at 2 = 0.5 is confirmed to agree well with the experimentally visualized one. The effect of 2 on the flows inside the rotating cascade as well as around the runner is clarified. The turbine performance, calculated by using the simulated flow, is also highlighted to agree almost with the measurement. These demonstrate that the present simulation method is indeed applicable to the development of open type cross-flow runner of nano-hydraulic turbine utilizing rapid and shallow stream.展开更多
Direct numerical simulation of a jet issuing from a nozzle having a rectangular cross-section is conducted. The vortex in cell (VIC) method, of which computational accuracy was heightened by the authors in a prior stu...Direct numerical simulation of a jet issuing from a nozzle having a rectangular cross-section is conducted. The vortex in cell (VIC) method, of which computational accuracy was heightened by the authors in a prior study, is used for the DNS. The aspect ratio of the nozzle cross-section is 15, and the Reynolds number based on the shorter side length of the nozzle exit is 6700. The turbulence statics, such as the mean velocity and the turbulence intensity, are favorably compared with the experimentally measured results. The behavior of the large-scale eddies as well as the development of the turbulent flow is also confirmed to agree with the measurement. These indicate that the authors’ VIC method is successfully employed for the DNS of rectangular jet.展开更多
The dynamics of flapping motion of a rectangular jet under acoustic excitation is studied experimentally by means of hot-wire measurement and flow visualization with smoke method. The excitation sufficiently enables“...The dynamics of flapping motion of a rectangular jet under acoustic excitation is studied experimentally by means of hot-wire measurement and flow visualization with smoke method. The excitation sufficiently enables“phase-lock”, which permitted us to extract the organized wave motion from a background field of finite turbulent fluctuations. The mean and fluctuation velocity are investigated and focused on the excitation frequency and the Reynolds number. As the excitation frequency decreases, it was found that the jet flapping and the jet spread were enhanced. The excitation with sub-harmonic frequency has significant effects on the rectangular jet behavior. The maximum value of the periodic velocity fluctuation strongly depends on the excitation frequency.展开更多
Flows through an open cross-flow-type nano-hydraulic turbine are numerically simulated to investigate the effects of the clearance Hc between the rotor and the ground on the turbine performance. A two-dimensional part...Flows through an open cross-flow-type nano-hydraulic turbine are numerically simulated to investigate the effects of the clearance Hc between the rotor and the ground on the turbine performance. A two-dimensional particle method is employed, which was successfully used for flow simulations of impulse-type and open cross-flow-type nano-hydraulic turbines in the authors＇ previous works. When the clearance Hc is smaller than a critical value, the simulated turbine performance decreases with decreasing Hc, in good agreement with the experiment. The simulations make it clear that such a reduction of turbine performance is attributable to an increase in the circumferential component of the water velocity at the rotor outlet. The simulations also demonstrate that the effect of the tip speed ratio of the rotor on the relation between Hc and turbine performance can be analyzed.展开更多
The aim of this investigation was to improve power performance of Savonius hydraulic turbine utilizing small stream for electric generation.An attempt was made to increase the power coefficient of runner by the use of...The aim of this investigation was to improve power performance of Savonius hydraulic turbine utilizing small stream for electric generation.An attempt was made to increase the power coefficient of runner by the use of flat shield plate placed upstream of the runner.The difference of the power coefficient is discussed in relation to clearance between the runner and the bottom wall and the rotation direction of the runner.The flow field around the runner was also examined visually to clarify influences of setting conditions on the power performance.From this study it was found that the power coefficient is achieved for 0.47 by only using a flat shield plate,the increase is up to 80% over the runner without the plate.Moreover,it is the proper condition that clearance ratio is 0.73 in this study.展开更多
文摘This study is concerned with the numerical simulation of the flow through an open type cross-flow runner of a nano-hydraulic turbine driven by rapid and shallow stream. It employs the two-dimensional particle method, which was used for the flow simulation of a small-scale hydraulic turbine of impulse-type in the prior study. The tip speed ratio 2, defined as the ratio of the runner tip speed to the water stream velocity upstream of the runner, ranges from 0.1 to 0.8. The simulated flow at 2 = 0.5 is confirmed to agree well with the experimentally visualized one. The effect of 2 on the flows inside the rotating cascade as well as around the runner is clarified. The turbine performance, calculated by using the simulated flow, is also highlighted to agree almost with the measurement. These demonstrate that the present simulation method is indeed applicable to the development of open type cross-flow runner of nano-hydraulic turbine utilizing rapid and shallow stream.
文摘Direct numerical simulation of a jet issuing from a nozzle having a rectangular cross-section is conducted. The vortex in cell (VIC) method, of which computational accuracy was heightened by the authors in a prior study, is used for the DNS. The aspect ratio of the nozzle cross-section is 15, and the Reynolds number based on the shorter side length of the nozzle exit is 6700. The turbulence statics, such as the mean velocity and the turbulence intensity, are favorably compared with the experimentally measured results. The behavior of the large-scale eddies as well as the development of the turbulent flow is also confirmed to agree with the measurement. These indicate that the authors’ VIC method is successfully employed for the DNS of rectangular jet.
文摘The dynamics of flapping motion of a rectangular jet under acoustic excitation is studied experimentally by means of hot-wire measurement and flow visualization with smoke method. The excitation sufficiently enables“phase-lock”, which permitted us to extract the organized wave motion from a background field of finite turbulent fluctuations. The mean and fluctuation velocity are investigated and focused on the excitation frequency and the Reynolds number. As the excitation frequency decreases, it was found that the jet flapping and the jet spread were enhanced. The excitation with sub-harmonic frequency has significant effects on the rectangular jet behavior. The maximum value of the periodic velocity fluctuation strongly depends on the excitation frequency.
文摘Flows through an open cross-flow-type nano-hydraulic turbine are numerically simulated to investigate the effects of the clearance Hc between the rotor and the ground on the turbine performance. A two-dimensional particle method is employed, which was successfully used for flow simulations of impulse-type and open cross-flow-type nano-hydraulic turbines in the authors＇ previous works. When the clearance Hc is smaller than a critical value, the simulated turbine performance decreases with decreasing Hc, in good agreement with the experiment. The simulations make it clear that such a reduction of turbine performance is attributable to an increase in the circumferential component of the water velocity at the rotor outlet. The simulations also demonstrate that the effect of the tip speed ratio of the rotor on the relation between Hc and turbine performance can be analyzed.
基金supported by KAKENHI No.2231004 and Ministry of Environment
文摘The aim of this investigation was to improve power performance of Savonius hydraulic turbine utilizing small stream for electric generation.An attempt was made to increase the power coefficient of runner by the use of flat shield plate placed upstream of the runner.The difference of the power coefficient is discussed in relation to clearance between the runner and the bottom wall and the rotation direction of the runner.The flow field around the runner was also examined visually to clarify influences of setting conditions on the power performance.From this study it was found that the power coefficient is achieved for 0.47 by only using a flat shield plate,the increase is up to 80% over the runner without the plate.Moreover,it is the proper condition that clearance ratio is 0.73 in this study.
