A horizontal axis wind turbine suffers fluctuating aerodynamic loads, which result in oscillations of the rotor blades. Since the blade oscillation has considerable effects on the blade fatigue life, the influence on the fatigue loads from the interaction between the aerodynamic loads and the structural oscillations should be considered in the design process of the wind turbine rotor. The objective of this work is to analyze the aerodynamic effects on the fatigue loads of rotor blade due to structural oscillation and inflow conditions, by using numerical calculation method. This paper explains a calculation model which can estimate the aerodynamic loads on the rotor blade of the horizontal axis wind turbine in the inflow conditions with the turbulence and yawed misalignment. The fluid-oscillation coupled calculation has been performed for the geometry of the NREL test turbine. The calculated results are compared with the experimental results to evaluate the validity of the calculation model.

Small vertical axis wind turbine (VAWT) is promising for the development of wind energy in the built environment due to its insensitivity to yaw. In general, computer codes based on the blade element and momentum (BEM) theory, which have much less calculation time than CFD codes, are used for design and performance prediction of wind turbines. However, the results on small VAWTs obtained by the BEM theory often do not accord with the experimental results due to the low Reynolds number, the dynamic stall effects, and so forth. The three-dimension nature of the flow field around the VAWT rotor may be one of the reasons for the discord. This study aims to elucidate the actual flow field around small VAWT. In this study, velocity field measurements were carried out in the wake of a small straight-bladed VAWT by using an ultrasonic anemometer. The measurements of the V and W velocity components showed the downwash and the blow-up, which proceeded toward the equator level and merged into the horizontal flow. Counter flow of the U component was also observed in the mainstream direction. The wake velocity profile simulated by using the Double-Multiple Streamtube (DMS) model based on the BEM theory showed a similar behavior to that of the measured wake. However, the high thrust coefficient estimated from the measured deficit in the U velocity component almost doubles the estimation by the BEM theory.

A Darrieus-type open hydro turbine with inlet nozzle has been proposed for utilization of extra-low head hydropower though a ducted type is in general used, consisting of an intake, runner section and draft tube. The open turbine means the simplified one, which has no runner casing and no draft tube. By installing inlet nozzle for the open turbine, the turbine efficiency is never deteriorated in comparison with the ducted one. The role of inlet nozzle is to increase generated torque with higher efficiency on the upstream path of the Darrieus blade passing and to decrease the torque with lower efficiency on the other path by removing the runner casing as the Darrieus turbine is cross flow type. In the present paper, the more simplified open turbine, consisting of only the inlet nozzle and the quarter covered upper casing to support the runner shaft, is experimentally examined. It is found that the depth of water level, covering or uncovering the runner in downstream pond, which might be changed by flow rate in practical use due to river-flow type turbine, influences on the turbine performance. When the depth of water level is kept deeper than the runner height of vertical axis turbine, the performance is almost the same as that of the case with whole covered upper casing. With decreasing the water level shallower than the runner height, the generated power and the efficiency become deteriorated due to making the wavy motion of the water surface at first. Then the stable operation at the maximum efficiency point in normal condition cannot be obtained. The cause on the mechanism of performance deterioration is considered with visualization of fluid behavior around Darrieus blades.

In the present study, the hydrodynamic characteristics of underwater propulsors have been numerically investigated using a RANS flow solver based on pseudo-compressibility. A vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe’s FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. An unstructured overset mesh technique was adopted to treat the relative motion between multiple bodies. Calculations were made for the DTRC4119 marine propeller at several advancing ratios. Additional calculations were also made for multiple-blade-row underwater propulsors. Reasonable agreements were obtained between the present results and the experiment for the pressure coefficients on the blade surface and the integrated blade loadings. The interaction between multiple blade rows and the thrust and torque distributions were also analyzed to investigate the performance of underwater propulsors.

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio. Therefore, it is a good candidate for use as a self-starting turbine. Furthermore, it has low noise and excellent stability; therefore, it has attracted attention from the viewpoint of applications as a small wind turbine for an urban district. However, its maximum power coefficient is extremely low (10%) as compared to that of other small wind turbines. In order to improve the performance and the flow condition of the cross-flow rotor, symmetrical casing with a nozzle and a diffuser are proposed and experimental research with the symmetrical casing is conducted. The maximum power coefficient is obtained as C pmax = 0.17 for casing and C pmax = 0.098 in the case without the casing. In the present study, power characteristics of the cross-flow rotor and those of the symmetrical casing with the nozzle and the diffuser are investigated. Then, the performance and internal flow patterns of the cross-flow wind turbine with the symmetrical casings are clarified. After that, the effect of the side boards set on the symmetrical casing is discussed on the basis of the analysis results.

The Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) that it allows less chance to be degraded independent of wind direction and turbine can be operated even at the low wind speed. The objective of this study is to analyze aerodynamics of the VAWT airfoil and investigate the ideal shape of airfoil, more specifically cambers. The analysis of aerodynamic characteristics with various cambers has been performed using numerical simulation with CFD software. As the numerical simulation discloses local physical features around wind turbine, aerodynamic performance such as lift, drag and torque are computed for single airfoil rotation and multiple airfoil rotation cases. Through this study more effective airfoil shape is suggested based vortex-airfoil interaction studies.

Automatic reed valves are widely used to control refrigerant gas flow in reciprocating compressors for automotive air conditioners. The oil film in the clearance between the reed and the valve seat causes a delay in opening of the valve. This opening delay of the discharge valve leads to over compression, which increases losses such as friction in sliding components and gas overheating. Therefore it is important to understand the behavior both of the oil film and the elastic reed deformation in order to reduce losses due to the delay. This study aims to develop an experimental setup that enables simultaneous visualization of the oil film rupture and measurement of the reed deformation, and to observe this behavior during the valve opening process. The gas-compression stroke is simulated by controlling compressed air with an electromagnetic valve. The oil film rupture is visually observed using a high speed camera through a special valve seat made of glass. The total deformation of the cantilever reed is identified by multipoint strain measurement with 12 strain gauges. The experiment finds that the opening process is divided into four stages. In the first stage, the reed remains stuck to the seat and deforms while the bore pressure increases. In the second stage, cavitation occurs in the oil film and the film starts to rupture. In the third stage, the oil film ruptures and the bore pressure starts to decrease. Finally, in the fourth stage, the reed is separated from the seat and the gas flows through the valve. Reducing the reed/seat contact area changes the reed deformation in the first stage, thereby increasing the reed/seat distance and realizing an earlier oil film rupture and a shorter delay.

The performance characteristics of two cross-flow axis hydrokinetic turbines were evaluated in UNH’s tow and wave tank. A 1m diameter, 1.25m (nominal) height three-bladed Gorlov Helical Turbine (GHT) and a 1m diameter, four-bladed spherical-helical turbine (LST), both manufactured by Lucid Energy Technologies, LLP were tested at tow speeds up to 1.5 m/s. Relationships between tip speed ratio, solidity, power coefficient ( C p ), kinetic exergy efficiency, and overall streamwise drag coefficient ( C d ) are explored. As expected, the spherical-helical turbine is less effective at converting available kinetic energy in a relatively low blockage, free-surface flow. The GHT was then towed in waves to investigate the effects of a periodically unsteady inflow, and an increase in performance was observed along with an increase in minimum tip speed ratio at which power can be extracted. Regarding effects of turbulence, it was previously documented that an increase in free-stream homogenous isotropic turbulence increased static stall angles for airfoils. This phenomenon was first qualitatively investigated on a smaller scale with a NACA0012 hydrofoil in a UNH water tunnel, using an upstream grid turbulence generator and using high frame-rate PIV to measure the flow field. Since the angle of attack for a cross-flow axis turbine blade oscillates with higher amplitude as tip speed ratio decreases, any delay of stall should allow power extraction at lower tip speed ratios. This hypothesis was tested experimentally on a larger scale in the tow tank by creating grid turbulence upstream of the turbine. It is shown that the range of operable tip speed ratios is slightly expanded, with a possible improvement of power coefficient at lower tip speed ratios. Drag coefficients at higher tip speed ratios seem to increase more rapidly than in the non-turbulent case.

A model for cross-flow axis hydrokinetic turbines based on blade element theory (BET) was developed. The model combines an extensive experimental and numerical high Reynolds number data set for symmetric airfoils with governing equations to predict performance characteristics of the turbines. The model allows for any number of turbine blades and for variable hydrofoil sweep angles; both straight blade (H-Darrieus) and helical blade (Gorlov) cross-flow axis turbines are modeled. In this model the free stream velocity and the turbine’s rate of rotation are not coupled hydrodynamically, and experimental calibration of the model for a specific turbine design is necessary. The calibrated model is then used with real inflow data from an actual tidal energy site to predict instantaneous power and energy yield over a period of time. Investigation of tip speed ratios allows for predictions of unsteady loadings, optimal performance and power outputs. The model provides the versatility to predict characteristics of many different shapes and sizes of cross-flow axis turbines. Through investigation of turbine stall characteristics predicted by the model, two, turbine-specific tip speed ratios of interest were determined: the critical and optimal tip speed ratios. The “critical tip speed ratio” is defined as the tip speed ratio above which there are no longer regions of negative torque during the turbine rotation. The “optimal tip speed ratio” is defined as the tip speed ratio for which the coefficient of torque, averaged over one rotation, is maximized. It is hypothesized that these tip speed ratios correspond to specific turbine operating points: A turbine operating under no load conditions will spin near the optimal tip speed ratio, and a turbine operating at peak power conditions will spin near the critical tip speed ratio.

When a Francis hydraulic turbine operates under different working heads at small flow condition, the fluid in the flow passage will generate vortex shedding near the blade leading-edge and form the channel vortex in the blade passages due to the mismatch between the outlet angle of guide vane and the inlet angle of runner blade. The severity of channel vortex will trigger high-frequency vibration or generate unit resonant vibration, affecting the operational stability of the turbines. In this paper some typical operation points were chosen out for the steady simulation of a model turbine according to a unit hill-chart. The computational domain was chosen as the whole flow passage from the inlet of the volute to the outlet of the draft tube. Based on RNG k–ε turbulence model, the internal flows was simulated, and the occurrence of vortex between the turbine runner blades was discussed. The numerical results show that the vortex motion near the development-line (IVDL) is stronger than that near the channel vortex inception-line (IVIL) in channel vortex zone marked in the hill-chart. The velocity triangle is used to explain the reasons that channel vortex occur in the suction side at high working head while in the pressure side at the low working head, and two different forms and formation mechanism of the channel vortex were analyzed.

To cope with warming global environments, authors have proposed the counter-rotating type hydroelectric unit, which is composed of tandem runners and the peculiar generator with double rotational armatures. The unit can be provided for various water circumstances at not only the onshore but also the offshore. This paper discusses effects of setting angle and the number of runner blades on turbine performances and then optimum blade setting angles giving the maximum output and/or the maximum efficiency, namely the on-cam operation, are presented at various discharges/heads.

This paper presents the unique ocean wave power station, which is composed of the floating type platform with a pair of the floats lined up at the interval of one wave length and the counter-rotating type power unit submerged in the seawater at the middle position of the platform. Such profiles make the flow velocity through the turbines two times faster than that of the traditional OWC types, and make the turbine diameter large as possible because the rotational moment hardly acts on the platform. The previous paper verified that the station is effective to get the power from the ocean wave at the normally oscillating motion. Continuously, this paper discusses the effect of the wave length on the motion of the platform and present the flow conditions around Wells type hydraulic turbine in CFD. The platform in which the floats are at the symmetrical position to the anti-node oscillates normally irrespective of the stationary wave length. On the contrary, the platform with the floats the asymmetrically arranged or being at the progressive wave plays in the dutch-roll condition and does not get the fruitful power.

High amplitude of pressure fluctuation is observed in a draft tube, for the case of partial load operation. Several methods had been reported to decrease the amplitude so far, such as, air or water injection to the draft tube, fins on the draft tube surface, or runner replacement with optimized velocity profile at runner exit. However, several problems for each method can be considered, such as, negative influence on efficiency, high cost, technical difficulties for installation, and so on. To solve these problems and satisfy the demand for decreasing the amplitude of pressure fluctuation simultaneously, a new runner cone with grooves on the surface was developed. As for the case with reversible pump turbine, grooved runner cone was developed with unsteady draft tube calculation based on Design of Experiment (DOE) method, and confirmed by model tests. Finally, developed runner cone was installed to the prototype pump turbine, and predicted performance was confirmed by on-site tests. Using this result, development of a new runner cone for hydraulic turbine had been started. For this case, meridian shape of the runner cone was also selected as a design parameter. Finally, we obtained the optimized shape, “diverged runner cone with spiral groove”, and the performance is confirmed by the model test. In this paper, details of development, especially for the case of hydraulic turbine and considerations of the mechanism are treated.

Optimization of using waste plastic fuel on diesel engine was observed. The investigation experimental project was comparison between using waste plastic fuel and diesel fuel. The engine experiment was conducted with YANMAR TF120 single cylinder four stroke diesel engine set-up at variable engine speed at 2100, 1900, 1700, 1500 and 1300 rpm. The data have been taken at each point of engine speed during the stabilized engine-operating regime. Measurement of emissions parameters at different engine speed conditions have generally indicated reduce in engine CO 2 , NO x and SO x emission when using plastic fuel compared to base diesel oil with good in fuel consumption.

A twin unidirectional impulse turbine has been proposed in order to enhance the performance of wave energy plant. This turbine system uses two unidirectional impulse turbines and their flow direction is different each other. However, the turbine characteristics have not been clarified to date. The performances of a unidirectional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study.

As gas prices rise and the green movement grows, more fluid power companies are working to develop hydraulic drive trains for large trucks to passenger cars and wind turbines. The hydraulic drive system is more effective and efficient than traditional hybrid systems because there is less energy lost between the engine and the wheels. Specially designed for stop-and-go vehicles, the system captures energy as the vehicle brakes. When the vehicle is restarted, the series hydraulic hybrid system puts the vehicle in motion. When the captured energy is depleted, then the engine kicks in. Here, the accumulator in the system is used to recover the kinetic energy without reversion of fluid flow. Variable displacement pump/motor unit is utilized for both driving and hydro-static regeneration mode. This paper gives an insight on dynamic simulation results obtained using LMS Amesim tool. The effect of various system parameters like pre-charge pressure and hydraulic pump/motor-pump maximum displacement on system output power is discussed. Varying pre-charge pressure of the accumulator shows significant improvement in the system output power. Maximizing the system output power indirectly leads to less fuel consumption and pollution reduction in hybrid vehicles.

Unsteady flow analysis in water power stations is one of the most important issues in order to predict undesirable pressure variations in waterways and also probable changes in rotor speed for the power plants safe operation. Installation of surge tank and relief valve is the two main methods for controlling of hydraulic transient. The relief valve is used in several medium and small hydropower stations instead of the surge tank and mounted on the penstock near the powerhouse. The recent generation of relief valves are reliable and beneficial and consist of fully control system that directly conducted by governor. This paper presents a numerical method for transient flow in hydropower stations using surge tank and relief valve. For this purpose the governing equations of transient flow in closed conduit are solved using the method of characteristics (MOC) using unsteady friction. Hydraulic turbine, surge tank and relief valve are considered as internal boundary conditions. The influence of surge tank and also relief valve on the maximum pressure in spiral case and turbine over speed has been studied for a real case. The results show that the transient condition is considerably improved by using a relief valve and this device can be mounted in lieu of an expensive surge tank.

A bidirectional (oscillating) air flow is central to energy conversion from wave to wire in an oscillating water column based wave energy plant. Several classes of bidirectional turbines, which operate with such an oscillating flow, have been designed and tested with limited efficiencies. A topology which uses fluidic diodes in conjunction with unidirectional turbines is shown to significantly improve the efficiency. The design and test results from several fluidic diodes for such an application are discussed. It is shown that a combination of a fluidic diode and the unidirectional turbine can achieve a very high impedance to reverse flow while having a high efficiency in the forward direction, over a wide range of flow coefficients.

The aim of this investigation is to develop an open type cross-flow runner for environmentally friendly nano-hydraulic turbine utilizing extremely low head waterfalls. The waterfall condition is strongly affected by weather, so flow rate changes frequently. It causes a decrease in runner performance because it does not have any flow adjusting mechanisms. It is, therefore, important to evaluate the runner performance against the change of flow condition for stable power generation. This study focused on the influence of waterfall flowing position and its thickness on the runner performance. An open type cross-flow runner was applied for waterfall generation. As a result, we found that the runner characteristic varied with the waterfall condition. In particular, the waterfall thickness has great influence on the runner performance. The value of C Pmax reaches the highest value of 0.61 at Q = 3.0×10 −3 m 3 /s.