Horizontal Axis Machines Research Articles

NUMERICAL ANALYSES OF A STRAIGHT BLADED VERTICAL AXIS DARRIEUS WIND TURBINE: VERIFICATION OF DMS ALGORITHM AND QBLADE CODE

Wind energy is among the most cost-effective renewable energies. Till date, turbines with different configurations had been designed to harness wind power, each having unique superiorities. Darrieus turbines are one of the mostly investigated vertical axis wind turbines using either experimental or numerical methods. Experimental analyses are time consuming works which requires high amount of effort and expenses. Thus, computational fluid dynamics (CFD) methods have been commonly used by scientists and engineers in order of obtaining detailed performance and illustration of the fluid flow. Contrary to the horizontal axis machines, Darrieus turbines are difficult to be analyzed by CFD algorithms due to high pressure and velocity variations which arise from extreme changes in the angle of attack beyond the stall condition at different azimuthal position of the blades. Therefore, more simplified numerical models are generated employing double multiple streamtube (DMS) theory together with additional improvements. QBlade is one of the mostly used numerical methods based on the lifting line free vortex wake method developed for calculating rotor aerodynamics. The main objective of this study is to verify the double multiple streamtube theory and QBlade algorithm with the experimental and computational results reported in the scientific literature. Analysis results represented good agreement with the previous studies especially at lower TSR ranges. Compare to the experimental results, an overestimation in the power coefficient is obtained at low free stream speed and high TSR ranges after exceeding the peak point. Sensitivity of the model to the Re number variations have also been outlined.

Improving VAWT performance through parametric studies of rotor design configurations using computational fluid dynamics

Vertical axis wind turbines present several advantages over the horizontal axis machines that make them suitable to a variety of wind conditions. However, due to the complexity of vertical axis wind turbine (VAWT) aerodynamics, available literature on VAWT performance in steady and turbulent wind conditions is limited. This paper aims to numerically predict the performance of a 5 kW VAWT under steady wind conditions through computational fluid dynamics modeling by varying turbine configuration parameters. Two-dimensional VAWT models using a cambered blade (1.5%) were created with open field boundary extents. Turbine configuration parameters studied include blade mounting position, blade fixing angle, and rotor solidity. Baseline case with peak Cp of 0.31 at tip-speed ratio of 4 has the following parameters: mounting position at 0.5c, zero fixing angle, and three blades (solidity = 0.3). Independent parametric studies were carried out and results show that a blade mounting position of 0.7c from the leading edge produces the best performance with maximum Cp = 0.315 while the worst case is a mounting position of 0.15c with peak Cp = 0.273. Fixing angle study reveals a toe-out setting of −1° producing the best performance with peak Cp of 0.315 and the worst setting at toe-in of 1.5° with peak Cp of 0.287. The solidity study resulted in the best case of four blades (solidity = 0.4) with peak Cp = 0.316 and the worst case of two blades (solidity = 0.2) with peak Cp = 0.283.

Comparative assessment of the harmonic balance Navier–Stokes technology for horizontal and vertical axis wind turbine aerodynamics

Several important wind turbine unsteady flow regimes, such as those associated with the yawed wind condition of horizontal axis machines, and most operating conditions of all vertical axis machines, are predominantly periodic. The harmonic balance Reynolds-averaged Navier–Stokes technology for the rapid calculation of nonlinear periodic flow fields has been successfully used to greatly reduce runtimes of turbomachinery periodic flow analyses in the past fifteen years. This paper presents an objective comparative study of the performance and solution accuracy of this technology for aerodynamic analysis and design applications of horizontal and vertical axis wind turbines. The considered use cases are the periodic flow past the blade section of a utility-scale horizontal axis wind turbine rotor in yawed wind, and the periodic flow of a H-Darrieus rotor section working at a tip-speed ratio close to that of maximum power. The aforementioned comparative assessment is based on thorough parametric time-domain and harmonic balance analyses of both use cases. The paper also reports the main mathematical and numerical features of a new turbulent harmonic balance Navier–Stokes solver using Menter’s shear stress transport model for the turbulence closure. Presented results indicate that (a) typical multimegawatt horizontal axis wind turbine periodic flows can be computed by the harmonic balance solver about ten times more rapidly than by the conventional time-domain analysis, achieving the same temporal accuracy of the latter method, and (b) the harmonic balance acceleration for Darrieus rotor unsteady flow analysis is lower than for horizontal axis machines, and the harmonic balance solutions feature undesired oscillations caused by the wide harmonic content and the high-level of stall predisposition of this flow field type.

Modeling Vertical-Axis Wind-Turbine Performance: Blade-Element Method Versus Finite Volume Approach

Vertical-axis wind turbines offer an inherently simpler design than horizontal-axis machines, and their lower blade speed mitigates safety and noise concerns. Although vertical-axis turbines do offer significant operational advantages, development has been hampered by the difficulty of modeling the aerodynamics involved, along with their rotating geometry. This paper presents results from a simulation of a baseline vertical-axis wind turbine computed using Star-CCM+, a commercial finite volume code, and compares them with data obtained from a multiple-streamtube model. Emphasis was placed on the dynamic stall characteristics and wake production, which have the greatest influence on turbine performance. A model was developed to replicate the blade–wake interactions common at higher tip-speed ratios and was found to greatly improve the accuracy of the blade-element momentum model.

The aerodynamics of a camber-bladed vertical axis wind turbine in unsteady wind

VAWT (Vertical axis wind turbines) pose several advantages over the horizontal axis machines that make them more suitable for applications where wind conditions are inherently turbulent. However, due to the complexity of VAWT aerodynamics, technical literature on the subject is very limited with research on VAWT performance mostly focused on steady wind analysis. This paper aims to numerically predict the performance of a 5 kW VAWT under fluctuating wind conditions through computational fluid dynamics modeling. Two dimensional VAWT models using symmetric and cambered blades were created with open field boundary extents. Fluctuating wind speed was imposed on the inlet with average magnitude of 5 m/s, amplitude of fluctuation of 10%, and frequency of fluctuation of 1 Hz. Results revealed that fluctuating wind imposes a detrimental effect on VAWT performance. A VAWT blade with 1.5% camber shows the best performance with the cycle-averaged unsteady power coefficient at 0.31 versus the optimum steady power coefficient of 0.34. In spite of increased available wind power due to the fluctuating wind at 233.13 Watts in one wind cycle compared to 229.69 Watts for the steady 5 m/s wind case, power generated by the camber bladed VAWT drops to 74.96 Watts from the steady wind rotor power of 78.32 Watts.

Actual Usage Conditions, Energy Savings and Associated Emission Reductions of Washing Machines

About 19% of the total electricity production is consumed in the residential sector and this fraction is expected to grow in future. Air conditioners, refrigerators, washing machines and other appliances are major energy users in this sector. In this paper, the energy consumption of 50 real-houses domestic clothes washers have been monitored to give an overview of the usage pattern of this appliance in Malaysian households. A questionnaire was designed to get relevant information regarding the usage of this appliance in the actual environment as well. This information is paramount in shaping or implementing a program that would get more support from users. Finally, energy savings, bill savings and CO2 reductions associated with energy savings have been calculated and presented in this paper for using horizontal axis machines rather than vertical axis using actual monitored data.

A Feasibility Study for Floating Offshore Windfarms in Japanese Waters

This paper reports the results of technical and economic feasibility studies of floating offshore wind farms under typical environmental conditions in Japanese Waters. Outline designs are considered, with economic assessments. Both horizontal and vertical axis wind turbines are considered, although it is realised that horizontal axis machines now dominate.

Energy-Efficient Appliances

Washing machines and other household devices are being redesigned for greater efficiency. Key to creating an energy-efficient washer is to cut the use of water, because 85 to 90 percent of the energy used in washers goes to heating the water. This is typically accomplished by a front-loading unit with a tub that rotates around a horizontal axis. Studies by Electric Power Research Institute (EPRI), Palo Aldo, CA, show that horizontal-axis machines use about one-third less water and two-thirds less energy than the vertical-axis machines that have captured almost the entire U.S. market. Maytag Laundry Appliances Research and Development’s new front-loading Neptune washer features a horizontal-axis tub that is angled up 15 degrees to improve visibility and access. Rather than agitating wash loads in a full tub of water like standard top loaders, the Neptune washer substitutes a clothes-dryer-like tumbling action that dunks fabrics in a smaller volume of water.

The fundamentals of wind-driven water pumpers

Basic theory aerodynamic theory wind characteristics types and performances of horizontal-axis turbine rotors major factors influencing the design of horizontal-axis machines furling systems for horizontal-axis machines pumps variable delivery pumps flapping vane, savonius and drag type machines structural design.

Review of wind turbine control

The literature on the design of control sysems for medium- and large-scale wind turbine generators is reviewed. The vast majority of relevant literature is concerned with the control of horizontal-axis machines. Emphasis is given to public-utility service machines with power outputs in the range hundreds to thousands of kilowatts. This work was prompted by the need to determine specific objectives for the turbine control system. The control system is an integral part of the wind turbine; it is stochastic and non-linear and the different wind-turbine configurations pose a variety of design goals. The review highlights the lack of a clear consensus on the role of the control system and an inadequate treatment of dynamic and stochastic issues. Wind-turbine control is an application area with an interesting set of problems for control engineering. These problems have not been adequately solved and continue to pose challenges to the control community. Wind-turbine control issues are therefore important, since ...

Broadband sound from wind turbine generators

Sound spectra are characterized for the various types of wind turbine generators. Emphasis is placed on the broadband sound because it is an important component for upwind and downwind horizontal axis machines as well as for vertical axis machines. The various sources of broadband sound are identified and are rank ordered for the MOD-2 machine which has 300-ft-diam blades and is rated at 2.5-MW power output. The main sound sources for the MOD-2 rotor are noted to be the inflow turbulence (30 to 50 Hz) and the interactions of the turbulent boundary layers with the blade trailing edges (800 to 1300 Hz). The MOD-2 rotor radiates in all directions but the distant sound level contours are elongated in the downwind direction due to refraction effects of the wind. [Work supported by the NASA Lewis Research Center and the Department of Energy.]

Indirect utilization of solar energy

The atmosphere can be regarded as a heat engine converting solar heat into the mechanical energy of wind, which in turn generates waves on the surface of the sea, so that both wind and wave energy can readily be traced back to the solar input. Wind energy used to be a major source of power, but gave way to the much cheaper and more reliable source presented by coal. Looking to the future, we can certainly make much better windmills (15 % efficiency was perhaps the best in the past) but the improvement in size/cost ratio with increasing size drives one to large structures. A preference for disaggregated supply is needed to put even medium sized aerogenerators into the running, and a house-by-house supply would require quite sizeable structures. Really big structures, especially on the favoured hill top sites, would raise environmental questions that might drive one to off-shore locations, though of course these may well involve increased costs. Vertical axis as well as horizontal axis machines are being studied. Isolated locations, where the competition is less severe, might offer the first chance of economic viability without going to very large sizes. Wave energy has the great merit of being dependent on a non-local supply. In particular, the longer waves with their high energy content may originate hundreds or even thousands of miles from the scene of exploitation, and so the system has a steadiness much greater than might be expected. Indeed, the U.K. is located in one of the World’s most favourable positions. Engineering exploitation is made difficult by the need for the apparatus to survive the wildest conditions and by the fact that, in many devices, the input is a large force with small displacement, a form of power for which there is little practical experience in its utilization. A variety of devices are being supported so as to establish where we should concentrate our effort. The potential size of the resource and its seasonal phasing in line with demand make this a most essential field of renewable development.

An inverse problem of vertical-axis wind turbines

Vertical-axis turbines drag and lift coefficients were studied and it was determined that vertical-axis turbines cannot equal horizontal-axis machines in efficiency because the angle of attack of the horizontal-axis turbine can be varied to suit conditions. The best hope for vertical-axis wind turbines lies in concentrating on the regions where complete extraction is theoretically possible and looking for a blade profile that will most nearly match the lift and drag curves. (FS)