Helical Turbine Research Articles

Effects of end plates with various shapes and sizes on helical Savonius wind turbines

We experimentally studied the effects of end plates with various shapes and sizes on the aerodynamic performance of helical Savonius wind turbines with twist angles of 180° and two semicircular buckets. To apply the blockage correction method and investigate the effect of end plate, four different helical Savonius wind turbines were tested at a subsonic open-circuit type wind tunnel. The adapted Maskell's blockage correction method suggested by Alexander was adopted for the wind turbine model installed in a closed test section of the subsonic wind tunnel. In order to clarify the end plate effect, power and torque coefficients were measured with various end plate shapes and areas. The use of both upper and lower end plates significantly increases the power coefficient by 36% compared with no end plates. We found that the Maskell's blockage correction method for straight Savonius wind turbines is applicable to helical Savonius wind turbines for small blockage ratios ranging from 3 to 8.3%. It was also observed that the power coefficient increases linearly in proportion to the area of the end plate.

Performance measurements of cylindrical- and spherical-helical cross-flow marine hydrokinetic turbines, with estimates of exergy efficiency

Power and drag (or thrust) measurements were performed in a towing tank for two different helical cross-flow marine hydrokinetic energy conversion devices—a cylindrical Gorlov Helical Turbine (GHT) and a Lucid Spherical Turbine (LST). The turbines are compared with respect to their various design parameters, with the GHT overall operating at higher power and drag coefficients. An estimate for the exergy efficiency of a turbine in free flow is formulated using momentum theory, and this quantity is computed for both devices. The GHT's exergy efficiency advantage over the LST was higher than that based on the power coefficient. Momentum theory-based blockage corrections were applied to the measurements and compared with the non-corrected data. The results presented here will help increase the amount of experimental data for helical devices in the literature, which is necessary for the development of more accurate engineering tools that take into account the unique three-dimensional nature of these devices.

수직축 조류 터빈 발전효율 평가를 위한 유동-터빈 연동 CFD 해석 (I)

CFD (computational fluid dynamics) analyses that considered the dynamic interaction effects between the flow and a turbine were performed to evaluate the power output characteristics of two representative vertical-axis tidal-current turbines: an H-type Darrieus turbine and Gorlov helical turbine (GHT). For this purpose, a commercial CFD code, Star- CCM+, was utilized, and the power output characteristic were investigated in relation to the scale ratio using the relation between the Reynolds number and the lift-to-drag ratio. It was found that the power coefficients were significantly reduced when the scaled model t urbine was used, especially when the Reynolds number was lower than 10 5 . The power output characteristics of GHT in relation to the twisting angle were also investigated using a three-dimensional CFD analysis, and it was found that the power coefficient was maximized for the case of a Darrieus turbine, i.e., a twisting angle of 0°, and the torque pulsation ratio was minimized when the blade covered 360° for the case of a turbine with a twisting angle of 120°.

Evaluation of vertical axis turbine characteristics for tidal current power plant based on in situ experiment

The Korean peninsula has a number of coastal sites where the rhythmic rising and lowering of the water surface owing to tides results in a strong tidal current. The kinetic energy of these currents can be efficiently exploited by using tidal current turbines. This study investigated the characteristics of a vertical axis turbine based on an in-field test. After 2.2 and 3.0m diameter helical turbines were installed in a fast narrow channel on the Korean coastline, the current velocity, torque, rotational speed, power, and other factors were measured. The efficiency of the 2.2m diameter helical turbine was about 30% at a current velocity of 1.5–1.9m/s, and the 3.0m diameter turbine had an efficiency of 33% at a current velocity of 2.0–3.4m/s. The average tip speed ratio (TSR) of the 2.2m diameter turbine was 2.41; the 3.0m diameter turbine showed a similar TSR of 2.39. The optimum TSR for helical turbines more than 2.2m in diameter seems to be 2.4. The efficiency of the entire power generating system was nearly constant at current velocities higher than 2.2m/s. Thus, a power generating system using tidal currents can produce electric power stably over appropriate current velocity.

복합재를 이용한 헬리컬 로터와 풍력터빈 나무 설계 및 구조해석

The objective of this paper is to analyze the structure of the wind power tree using a helical type wind turbine. The blades of a helical rotor is designed with a composite material. The structural analyses of a helical rotor have been implemented by finite element method. The structural analyses of the wind power tree which support four helical rotor, have been performed under a wind load, a rotational velocity of a rotor, and dead weight.

SIMULATION AND PIV EXPERIMENT OF THE DUCTED WATER CURRENT TURBINE AND EXTREMELY LOW HEAD HELICAL TURBINE

This research introduced for the Ducted Water Current Turbine Triple Helix with very low head less than 2m and water current at river or in the ocean, economical ecological use for small hydro power rating between 100 to 1000 kW still represent an unsolved problem. Unlike conventional hydro installation, water current turbine in open flow and generate power from flowing water with almost zero in environmental impact. Developments in water current turbine design are review and some potential advantages of duct or “diffuser augmented” current turbine and extremely low head turbine will be explored. For the output expected from the project is helical turbine with control flow on duct. The turbine design is based on the vertical turbine with helical blades. The basic idea of this research is optimized the helical turbine model, which is usually used in free stream (directly to the river stream line) can be apply with the situation inside the duct. And this research also tries to optimize the duct design. Therefore, get the better efficiency than the free stream flow turbine. The research aims to apply the helical turbine inside the duct to find the parameter of the power coefficient Cp against tip speed ratio λ. Parameters obtained from simulation in Fluent and through the experimental of the flow analysis by using PIV (Particle Image Velocimetry).

High Pressure Mixing Rheology of Drilling Fluids

Drilling fluids are multicomponent emulsions and/or suspensions, which normally show non-Newtonian behavior, i.e. yield stress, shear-thinning and thixotropy, and strong thermal and pressure dependence. The rheological characterization of drilling fluids using conventional geometries can be a difficult task due to the inherently heterogeneous nature of these systems. These problems may be overcome using nonconventional geometries, such as helical ribbons and blade turbines, which maintain the homogeneity of the system during the measurement. The overall objective of this work was to evaluate the use of mixing geometries, such as helical ribbons and blade turbines, for characterizing the flow behavior of drilling fluids as a function of pressure. From the experimental results it may be concluded that, using the Metzner-Otto approach, both four-blade and helical ribbon type-geometries are suitable for this purpose. This study shows that the Metzner-Otto constant, for a four blade turbine geometry, is practically independent of the flow index at atmospheric pressure, which shows a linear dependence at higher pressures. On the contrary, for the helical ribbon geometry, an exponential dependence of the Metzner-Otto constant on the flow index is observed independently of the measured pressure. From the experimental results obtained, it can be concluded that both nonconventional geometries can be used to measure the influence of pressure on the rheological parameters of non-Newtonian fluids. These tools extend the experimental shear-rate window covered by the coaxial cylinders conventional geometry to lower values, allowing the measurement of important engineering parameters, such as, for instance, yield stress.

Hydrofoil optimization and experimental validation in helical vertical axis turbine for power generation from marine current

A kind of hydrofoil, which is especially for use by helical vertical axis turbine for power generation from marine current, has been optimized by means of traditional genetic algorithms combined with hierarchical fair competition model. Bezier curve is used to parameterize the hydrofoils and numerical analysis is also introduced to evaluate hydrodynamic performance. Special fitness function as well as modified total lift–drag ratio is discussed in detail. Turbine performance tests and flow visualization experiments by PIV are conducted in order to draw a comparison between the optimized and two other competitive hydrofoils. The experimental results demonstrate that the optimized is more suitable to marine condition and beneficial to turbine efficiency improvement, and can be expected to act as a prospective hydrofoil for helical vertical axis turbine.

Effect of Blade Inclination Angle on a Darrieus Wind Turbine

This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall rotor torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.

헬리컬 터빈의 설계인자에 따른 성능 연구

조류발전용 다리우스 터빈의 변형된 형태인 헬리컬 터빈의 설계 인자 변화에 따른 성능을 수치해석으로 살펴보았다. 헬리컬 터빈은 수직축 다리우스 터빈을 회전축을 중심으로 상부와 하부를 비틀리게 함으로써 다리우스 터빈의 일반적인 취약점인 초기구동불량과 진동문제를 개선하기 위해 고안된 형태이다. 본 논문에서는 헬리컬 터빈의 비틀림각(Twisting Angle)과 직경대비 높이를 변화시키며 수치해석을 수행하였고, 결과를 바탕으로 최적의 구조를 제안하였다. 3차원 비정상 난류유동해석을 위하여 FLUENT의 RANS방정식과 k-ω SST 난류모델을, 격자계 모델링을 위하여 GAMBIT을 이용하였다. 헬리컬 터빈은 적절한 비틀림각에서 양호한 발전효율을 보장하면서 진동을 유발하는 회전력 변화의 진폭을 최소화 할 수 있음을 확인하였고, 효율의 최대가 확보되는 터빈의 최소 높이를 발견하였다.

Tests on ducted and bare helical and straight blade Darrieus hydrokinetic turbines

Despite much optimistic language on commercial websites, little data is available on actual performance of hydrokinetic turbines. This paper summarises the findings of a series of tests on several Darrieus type cross flow hydrokinetic turbines (HKTs). Although this type of hydrokinetic turbine (HKT) has some advantages over axial flow turbines, fixed pitch Darrieus HKTs also have some drawbacks, including inability to self-start under load, low efficiency and shaking. Variable pitch has been suggested to increase starting torque and efficiency, ducts to increase power output and helical blades to produce smooth torque. To assess each of these modifications, tests were conducted in Australia and Canada on HKTs with fixed and variable pitch straight blades, fixed helical blades, with and without a slatted diffuser, by mounting each turbine in front of a barge and motoring through still water at speeds ranging from less than 1 m/s up to 5 m/s. The diffuser increased the power output by a factor of 3 in one configuration but considerably less in others. A reason for this finding is suggested. The maximum coefficient of performance Cp of the fixed pitch straight blade and helical turbines without a diffuser ranged from about 0.25 at 1.5 m/s down to less than 0.1 at 5 m/s, while Cp for those with a diffuser ranged from about 0.45 down to about 0.3. Fixed blade turbines, both straight and helical, exhibited low starting torque, while variable pitch turbines started easily. Considerable differences in Cp were observed for the same turbine configuration at different speeds. The turbine with fixed pitch, straight blades was found to shake violently due to cyclical hydrodynamic forces on blades, while the helical and variable pitch turbines did not shake excessively. These findings suggest that variable pitch cross flow HKTs should be further investigated.

Effect of impeller type and stirring frequency on the behavior of an AnSBBR in the treatment of low-strength wastewater

The influence of impeller type and stirring frequency on the performance of a mechanically stirred anaerobic sequencing batch reactor containing immobilized biomass on an inert support (AnSBBR--Anaerobic Sequencing Batch Biofilm Reactor) was evaluated. The biomass was immobilized on polyurethane foam cubes placed in a stainless-steel basket inside a glass cylinder. Each 8-h batch run consisted of three stages: feed (10 min), reaction (460 min) and discharge (10 min) at 30 °C. Experiments were performed with four impeller types, i.e., helical, flat-blade, inclined-blade and curved-blade turbines, at stirring frequencies ranging from 100 to 1100 rpm. Synthetic wastewater was used in all experiments with an organic-matter concentration of 530±37 mg/L measured as chemical oxygen demand (COD). The reactor achieved an organic-matter removal efficiency of around 87% under all investigated conditions. Analysis of the four impeller types and the investigated stirring frequencies showed that mass transfer in the liquid phase was affected not only by the applied stirring frequency but also by the agitation mode imposed by each impeller type. The best reactor performance at all stirring frequencies was obtained when agitation was provided by the flat-blade turbine impeller.

Mixing Time in Rheologically Evolving Model Fluids by Hybrid Dual Mixing Systems

Mixing time experiments were performed using a hybrid dual mixing system, which included a helical ribbon impeller (HR) and either a Smith (ST) or Rushton turbine (RT). Xanthan gum solutions were used as rheologically evolving fluids to evaluate changes in mixing time under non-aerated and aerated conditions. The helical ribbon agitator and turbine of the hybrid dual mixing system was kept at a constant rotational speed ratio, N T /N HR =10. Experiments showed that performance of the hybrid mixing system was superior to that of the individual impellers. Flow properties and gassing conditions played an important role in mixing time. While mixing time was practically identical under non-gassed conditions for both the ST-HR and RT-HR mixing systems in low-viscosity fluids, differences up to 1000% were observed in high shear-thinning fluids. In these fluids, the RT-HR combination exhibited better performance than the ST-HR. In high-viscosity fluids, gassing enhanced mixing time particularly when the ST-HR hybrid system was used. Both mixing systems showed similar mixing times under the highest gassed condition evaluated in this work.

Gas Dispersion in Rheologically-Evolving Model Fluids by Hybrid Dual Mixing Systems

Gas dispersion experiments (0.18≤Fr≤0.71, 0.02≤Fl≤0.09) were carried out using a hybrid dual mixing system, which included a helical ribbon impeller and either a Smith or a Rushton turbine. Newtonian and non-Newtonian model fluids were used as rheologically-evolving fluids to evaluate changes in gas dispersion performance. A motionless helical ribbon agitator was used as a baffle in low-viscosity Newtonian fluids. Both Smith and Rushton turbines produced a vortex, which was eliminated by the motionless helical ribbon impeller. Gas dispersion in low-viscosity fluids was enhanced when the helical ribbon agitator and turbine of the dual hybrid mixing system was kept at a rotational speed ratio of 10 (N T /N HR =10), which allowed dispersion at a lower Fr than the turbine alone. For moderate-viscosity Newtonian fluids, gas dispersion was achieved at Fr≤0.71 and Fl≤0.05. Flow properties of non-Newtonian fluids played an important role in gas dispersion; transition from dispersing to flooding stages was observed for the fluids that were more shear-thinning (n≤0.38).

혼합탱크 내의 임펠라 형태에 따른 유동 특성에 관한 수치해석

The present study is concerned with the flow patterns induced by various impellers in a rectangular tank. Impellers are FBT (Flat blade turbine), PBT (Pitched blade turbine), Shroud turbine, Rushton turbine, and Helical ribbon turbine types. The solutions of flows in moving reference frames require the use of

Limits of the Turbine Efficiency for Free Fluid Flow

An accurate estimate of the theoretical power limit of turbines in free fluid flows is important because of growing interest in the development of wind power and zero-head water power resources. The latter includes the huge kinetic energy of ocean currents, tidal streams, and rivers without dams. Knowledge of turbine efficiency limits helps to optimize design of hydro and wind power farms. An explicitly solvable new mathematical model for estimating the maximum efficiency of turbines in a free (nonducted) fluid is presented. This result can be used for hydropower turbines where construction of dams is impossible (in oceans) or undesirable (in rivers), as well as for wind power farms. The model deals with a finite two-dimensional, partially penetrable plate in an incompressible fluid. It is nearly ideal for two-dimensional propellers and less suitable for three-dimensional cross-flow Darrieus and helical turbines. The most interesting finding of our analysis is that the maximum efficiency of the plane propeller is about 30 percent for free fluids. This is in a sharp contrast to the 60 percent given by the Betz limit, commonly used now for decades. It is shown that the Betz overestimate results from neglecting the curvature of the fluid streams. We also show that the three-dimensional helical turbine is more efficient than the two-dimensional propeller, at least in water applications. Moreover, well-documented tests have shown that the helical turbine has an efficiency of 35 percent, making it preferable for use in free water currents.

Helical Turbines for the Gulf Stream: Conceptual Approach to Design of a Large-Scale Floating Power Farm

This paper describes the helical turbine as an efficient new instrument for converting the kinetic energy of hydro streams into electric or other mechanical energy. A multi-megawatt project is proposed, conceived as an ocean power farm equipped with a number of helical turbines, along with a floating factory for in situ production of hydrogen fuel by means of electrolyzing ocean waters. Besides mega hydro-power farms, mini-power stations with helical turbines of a few kilowatts each are also proposed as possibilities for small communities or even individual households located near tidal shorelines or river banks with strong water currents. No construction of hydro dams is necessary for such applications.

Application of the theory of naturally curved and twisted bars to designing Gorlov's helical turbine 1. System of governing equations

The method of designing a new type of turbine used in flows of various kinds is discussed. Static, kinematic, and constitutive equations for transversely isotropic naturally curved and twisted bars are given, and the hypotheses used are discussed. The statement of the problem is linear and corresponds to small displacements. A method for solving the statically indeterminate problem is proposed. The objectives of numerical calculations, which will comprise the content of the second part of the investigation, are formulated.

Measurement of rheological properties of filamentous fermentation broths

It is well established that fermentation broths of filamentous microorganisms possess viscous non-Newtonian rheological properties. Despite the industrial significance of these broths and their fermentation products, the correct application of rheological measurement methodologies to filamentous broths and the influence of broth rheology on transport phenomena in bioreactors is poorly understood. In this work, the rheological properties of broths of the filamentous microorganisms Aspergillus niger, Penicillium chrysogenum and Streptomyces levoris grown on soluble substrates were studied. Three different types of viscometers were used: (1) three on-line pipeline viscometers (5.8, 11.6 and 15.4 mm i.d.); (2) two rotating cylinder viscometers (Haake model RV12, MV2 and MV3 sensors), and (3) helical ribbon and turbine impeller viscometers. Results obtained with all three viscometer types showed increasing pseudoplastic behaviour (power law parameters from MV2 viscometer data: 0.3 ⩽ n⩽1; 0.001 ⩽ K ⩽5 Pa.s n ) and yield stress (0⩽ t y ⩽16 Pa) with increasing biomass concentration(up to 20 g dw/1). Comparison of measurements at equivalent shear rates revealed lower measured apparent viscosities for the smallest pipeline viscometer, thus indicating the presence of wall “slip”. In contrast, higher apparent viscosities were observed with the turbine impeller, leading to the conclusion that the commonly made assumption that the average shear rate in this type of viscometer is independent of fluid rheology is not valid. Reasonable agreement was obtained among rheological measurements made on the large (≳ 11.6 mm i.d..) pipelines, the helical ribbon impeller and two different diameter rotating cylinder viscometers (provided the yield stress was exceeded inside the cup/bob gap); this suggests that “slip” effects were not significant in these viscometers. Based on these results,recommendations are provided to assist in the selection of appropriate viscometers for application to heterogeneous, non-Newtonian fermentation broths.

Analytical Modeling of Helical Screw Turbines for Performance Prediction

An analysis is first performed to determine the exposed frontal area and effective volume as a function of rotor angle for circular lobed helical screw turbines. It is shown that once the female to male lobe ratio is set, the entire design is determined with respect to the male rotor pitch radius. These volume and area functions are then used in an overall dynamic model of the turbine. The model includes inlet and exhaust dynamics, leakage throughout the turbine, and the thermodynamics within the lobes. “Start up” of the system can be tested which is particularly important in determining critical speeds. The principal intended use of the model is for comparative parametric studies.