Rotor Size Research Articles

Optimal design for the free-stream water wheel: A two-dimensional study

Free-stream water wheels running on floating river installations may contribute to hydropower production as part of a decentralized network meeting the highest ecological standards. While such devices are certainly not novel, their dynamics are complex and a need exists for an optimization of their power-producing characteristics. In this work, a parametrized two-dimensional computational fluid dynamics simulation is coupled to a genetic optimizer seeking to maximize the generated shaft power within a large domain of design parameters. Two objectives are pursued simultaneously: maximize the hydraulic efficiency, and maximize the power density of the device. After nearly 2000 individuals are evaluated, a Pareto front is identified; a family of designs is created to cover the trade-off between the two objectives. The results indicate that compared to operators constrained by the flow-exposed area, operators constrained by the rotor size would trade a 40% reduction in hydraulic performance in order to gain a 50% increase in power per unit rotor area. This optimization of the free-stream water wheel, the first in published literature to our knowledge, allows for the quantification of this trade-off and the publication of broadly-applicable design guidelines for the corresponding optimal blade geometry, number of blades, radius, and depth.

Progressive structural scaling of a 20 MW two-bladed offshore wind turbine rotor blade examined by finite element analyses

Two-bladed turbines offer a promising opportunity for rotor cost savings, especially considering the ongoing growth trend in rotor size. An increased chord and airfoil thickness of a two-bladed turbine’s blade results in potential structural improvements caused by a rapidly growing second moment of area. Compared to a three-bladed turbine’s blade, the blade structure would theoretically require less material, while withstanding 50% higher flapwise loads. An analytical method of progressive structural scaling for three-dimensional rotor blade structures, based on equal material stresses, is introduced to calculate the modified structural thickness properties of the two-bladed turbine’s blade. It simplifies the airfoil-shaped structure to a thin-walled rectangle, utilizes a fixed initial flapwise load factor, and scales the edgewise loads proportionally to the required blade mass. To evaluate the validity of this analytical approach, a progressively scaled and an iterated 20 MW two-bladed turbine’s blade are examined with finite element analyses for static loads. The outcomes are then compared to corresponding analyses of a three-bladed turbine’s reference blade. Overall, the static stress comparisons at different blade positions show good agreement with the analytical results. Nevertheless, the buckling analyses performed reveal stability issues, which subsequently will lead to a readjustment of the blade mass.

Induction motor rotor bars type effects towards energy efficiency, economic and environment

<span lang="EN-MY">Nowadays, the rotating motor is the most demoralized machine for the global Motor industry. Comfort of practice, start-up, small, weightiness, Increased efficiency, low maintenance and inexpensive for each power rating that generally meets the necessary features for industries. Efficient improvements are inspected with copper for the rotor bars slot. Usually, the copper loss in the induction motor Rotor division contributes to the loss of energy. The research work was planned a new rotor design, by improved rotor bars type slot, size and design. These tasks were inspected using two approaches, in particular, MotorSolve (IM) and calculations in theory. One set of simulation has shown a significant increase in energy efficiency for a new rotor frame design. Calculations in theory are used MATLAB. As a result, these new designs have improved energy efficiency by 77% as compared to its 74% existing design. The results proved to be using MATLAB. For energy, cost savings and emission reduction (ER), new design rotor frame has been saved 154KWH/year, utility bill RM 60.20/Year and 0.113 CO<sub>2 </sub>tons/years intended for individually motor. Finally, the estimated cost aimed at 100,000 pieces of new rotor bars pattern induction motor and indicates this price was kept almost RM6 million.</span>

Wind tunnel testing of a wind turbine in complex terrain

The paper describes the development of a scaled model of complex terrain, suitable for terrain-wind turbine interaction wind tunnel studies, taking into account flow similarity criteria. The size and the geometry of the experimental model of the complex terrain were refined using results of CFD simulations in order to achieve the best possible flow similarity and avoid edge effects arising from the finite (relative to the rotor size) terrain geometry. Moreover, Particle Image Velocimetry was used to survey the flow field on a longitudinal plane along the terrain center line. Flow measurements with and without a wind turbine model enabled to quantitatively evaluate the speed up produced by the terrain in the region of the wind turbine and the effect of the terrain on the wake characteristics of the wind turbine model.

Design of Compact Bearingless Disc Drive Systems

Inflating costs and emerging applications are spawning interests toward smaller and faster electric drives. The challenges of miniaturization make magnetic bearings more appealing, as they provide intrinsic high-speed capability and need virtually zero-maintenance. These advantages come at the cost of more sensors, which require a seamless integration especially at small geometrical scale. In the magnetic levitation domain, slice drives are particularly interesting, given their stabilizing passive characteristics that simplify the control of levitation and render the system simpler. These drives are already suitable for compressor applications, where control of all degrees of freedom is not necessary. In this article, the design process for a bearingless disc drive with a high degree of system integration is proposed. Two motor topologies, namely slotted and slotless drives, are rated by their passive stability, active properties, and power losses. Two sensor systems, fundamental for magnetic bearing commissioning, are proposed. They are simple to industrialize and offer a low footprint, thus not interfering with the drive design process. Ultimately, an optimization example is presented. For the presented scenario, drives with intermediate rotor size are the optimal contenders. Specifically among them, the slotless variant proves the best, given lower electrical losses and lighter mass compared to the slotted variant. However, the slotted becomes interesting if a stiffer magnetic bearing is needed.

Ship Airwakes in Waves and Motions and Effects on Helicopter Operation

Insight into the effects of motions and waves on a ship airwake can be used to provide information regarding safe conditions for at sea flight operations and pilot training. We present a study on the effects of waves and motions on a ship's airwake and a helicopter operating above the flight deck using full scale computational fluid dynamics simulations. The ONR Tumblehome Ship (ONRT) geometry is analyzed in wind and regular head waves corresponding to nominal sea states 3 and 6. In order to separate the effects of waves and motions, simulations are conducted for both sea states with combinations of: waves and motions, waves and no motions, no waves with motions, and no motions or waves. A triple velocity decomposition is conducted in order to quantify changes in the airwake due to motions and waves. The aerodynamic loads on a helicopter hovering in the airwake are studied with one-way and two-way coupling approaches. The one-way coupled analysis uses the velocity field data from the full scale airwake simulations along with disk actuator theory to calculate thrust fluctuations for three different rotor sizes operating above the flight deck. In the two-way coupled study a helicopter loosely based on the Sikorsky SH-60 Seahawk hovering above the flight deck of the ONRT is simulated, including dynamic overset grids of the main rotor, tail rotor and fuselage. This approach captures the interaction between the rotor downwash and the ONRT airwake. The study shows that for the lower sea state 3 the motions and waves have little effect on the airwake behavior, exhibiting little change with respect to the baseline case without motions and waves. At sea state 6 the flow field is modified significantly, which also affects the forces on the helicopter. Force fluctuations show main peaks at the wave encounter frequency and the blade passage frequency, as well as higher harmonics. The one-way coupling approach shows that larger rotors effectively filter out small scale fluctuations while smaller diameter rotors are affected by smaller flow structures.

Validation and accommodation of vortex wake codes for wind turbine design load calculations

Abstract. The computational effort for wind turbine design load calculations is more extreme than it is for other applications (e.g., aerospace), which necessitates the use of efficient but low-fidelity models. Traditionally the blade element momentum (BEM) method is used to resolve the rotor aerodynamic loads for this purpose, as this method is fast and robust. With the current trend of increasing rotor size, and consequently large and flexible blades, a need has risen for a more accurate prediction of rotor aerodynamics. Previous work has demonstrated large improvement potential in terms of fatigue load predictions using vortex wake models together with a manageable penalty in computational effort. The present publication has contributed towards making vortex wake models ready for application to certification load calculations. The observed reduction in flapwise blade root moment fatigue loading using vortex wake models instead of the blade element momentum (BEM) method from previous publications has been verified using computational fluid dynamics (CFD) simulations. A validation effort against a long-term field measurement campaign featuring 2.5 MW turbines has also confirmed the improved prediction of unsteady load characteristics by vortex wake models against BEM-based models in terms of fatigue loading. New light has been shed on the cause for the observed differences and several model improvements have been developed, both to reduce the computational effort of vortex wake simulations and to make BEM models more accurate. Scoping analyses for an entire fatigue load set have revealed the overall fatigue reduction may be up to 5 % for the AVATAR 10 MW rotor using a vortex wake rather than a BEM-based code.

A methodology for multirotor aircraft power budget analysis

Purpose The primary purpose of this study is to analyse the performance of multirotor unmanned aircraft system platforms for passenger transport and compare them with an ordinary helicopter solution. This study aims to define a standard procedure for power budget analysis of unconventional vehicles recently proposed in the aerospace industry, providing guidelines on rotor sizing in terms of required power and the total number of rotors. The ultimate purpose of the proposed work is to describe a methodology for power estimation with regard to emerging electric vertical takeoff and landing (EVTOL) vehicles. Design/methodology/approach In the context of urban mobility, short-range passenger transport between critical hubs in cities is taken into account and innovative aircraft and traditional helicopters are compared according to a common mission profile. The power budget equations used in the helicopter literature are revisited to consider different multirotor configurations (up to 20 rotors) and evaluate the feasibility of innovative aerospace vehicle design. Findings The paper includes insights into the maximum number of rotors that ensure a significative, relative power reduction compared to helicopter platforms (the power-to-cruise over power-to-hover ratio appears to be improved). Based on this preliminary analysis, the results suggest the benefit of reducing the installed rotors to avoid excessive power loss in forward flight. Practical implications The proposed study provides guidelines for further design considerations and the future development of EVTOL multirotor aircraft. Originality/value This paper fulfils the identified need for a systematic approach on performance analysis for innovative vehicles involved in commercial applications.

Mechanical strength analysis and optimization of metallic sleeve in high-speed permanent magnet synchronous machines

Metallic sleeves are widely used to ensure the mechanical integrity of rotors in high-speed permanent magnet (PM) synchronous machines (HSPMSM). However, in traditional high-speed rotors, the PMs which are very weak in tensile stress cannot be well protected by sleeves. Furthermore, the material properties of both the sleeves and PMs cannot be fully used. As a result, the high-speed running range of the machines are limited by the mechanical strength for a given rotor size. In this paper, taking a 230-kW 35-kr/min prototype as an example, the mechanical strength issues of the rotor are investigated by analytical method and finite element analysis (FEA). In order to overcome the unbalanced protective effect of the sleeve and make fully use of the materials, an optimal sleeve, as well as an improved rotor structure, is presented. The comparison results show that the optimized sleeve has well balanced protective effect to the PM as well as good utilization of materials, with a resultant increase in maximum speed of nearly 40% with respect to the prototype.

Fast Frequency Response of a Doubly-Fed Induction Generator for System Inertia Support

Converter-interfaced doubly-fed induction generators (DFIGs) can provide short-term frequency support (STFS) capability by releasing rotating kinetic energy. After arresting the frequency decrease, the rotor speed should return to its initial operating condition. During the rotor speed recovery process, special attention should paid to the performance of the rotor speed restoration duration and size of the second frequency drop (SFD). This paper suggests an enhanced STFS method of DFIGs to preserve better performance of the frequency nadir with less released rotating kinetic energy and accelerate the rotor speed restoration. To this end, a rotor speed-varying incremental power is proposed and is added to the maximum power tracking (MPT) operation reference during STFS, thereby releasing less rotating kinetic energy from DFIGs; afterward, the power reference smoothly decreases to the reference for MPT operation during the preset period. Test results clearly demonstrate that since even less rotating kinetic energy is utilized, the proposed method can preserve better performance of heightening the frequency nadir; furthermore, the proposed method accelerates the rotor speed restoration when the proposed strategy produces the same SFD as the conventional method, thereby improving the power grid resilience.

Editorial on Special Issue “Wind Turbine Power Optimization Technology”

This Special Issue collects innovative contributions in the field of wind turbine optimization technology. The general motivation of the present Special Issue is given by the fact that there has recently been a considerable boost of the quest for wind turbine efficiency optimization in the academia and in the wind energy practitioners communities. The optimization can be focused on technology and operation of single turbine or a group of machines within a wind farm. This perspective is evidently multi-faced and the seven papers composing this Special Issue provide a representative picture of the most ground-breaking state of the art about the subject. Wind turbine power optimization means scientific research about the design of innovative aerodynamic solutions for wind turbine blades and of wind turbine single or collective control, especially for increasing rotor size and exploitation in offshore environment. It should be noticed that some recently developed aerodynamic and control solutions have become available in the industry practice and therefore an interesting line of development is the assessment of the actual impact of optimization technology for wind turbines operating in field: this calls for non-trivial data analysis and statistical methods. The optimization approach must be 360 degrees; for this reason also offshore resource should be addressed with the most up to date technologies such as floating wind turbines, in particular as regards support structures and platforms to be employed in ocean environment. Finally, wind turbine power optimization means as well improving wind farm efficiency through innovative uses of pre-existent control techniques: this is employed, for example, for active control of wake interactions in order to maximize the energy yield and minimize the fatigue loads.

Experiments and Design Criteria for a High-Speed Permanent Magnet Synchronous Generator With Magnetic Bearing Considering Mechanical Aspects

In this work, the design and experimental analysis of a high-speed permanent magnet (PM) synchronous generator (PMSG) with a magnetic bearing without mechanical friction were performed. The rotor size was derived using the torque per rotor volume method and an analytical method. Rotor structure analysis was performed to verify the validity of the selected sleeve and PM thickness. The magnetic bearing was designed considering the input aerodynamic force and DN-factor. Then, the validity of the proposed design method was verified through the electromagnetic and mechanical analysis, design, and comparison with the experimental results of a high-speed PMSG (124 kW and 36 krpm).

Effect of rotor length on generating power in horizontal axis wind turbines

The benefits of the rotor design are optimizing power generation and reducing cost of build in wind turbines. In this study, a performance comparison of horizontal axis wind turbines in terms of their rotor diameter is made using Qblade software. The airfoil selected is the National Advisory Committee for Aeronautics (NACA 0012) for all models, and the wind turbines have three blades. From simulations, the optimal rpm for each rotor diameter was calculated, and the generated power for different wind speeds.The results found show that the operation of wind turbines consider need operated with tip speed ratios of between 4 to 7 to give optimal power output. Maximum power was produced for a blade diameter of 170 metres and the highest power coefficient found was for a diameter of 30 metres and for this case also had the highest tip speed ratio of 6.68. Overall results can suggest which diameter range is used for choosing a rotor size that is the most cost-effective.

Introduction to Coupled Vane compressor: Mathematical modelling with validation

A new rotary compressor known as Coupled Vane compressor (CVC) is introduced. The unique feature of CVC is that a set of two vanes are coupled together and they cut through the rotor diametrically. Theoretically, any rotor size which can accommodate the vanes will work with this design. This design removes most of the geometrical constraints imposed on the size of the rotor, as what are in most of the rotary compressors. The ability to accommodate a significantly small rotor in this new design, makes it substantially more compact which, also reduces material wastage, cost of machining and fabrication. This new design is intended to be used in refrigeration, household cooling and heating applications. In this paper, the mathematical models of the CVC were formulated to study its operational characteristics. The results of the simulation model were validated using measured data from a CVC prototype. This CVC prototype, with a volumetric displacement of 44 cm3, was operated in an open-type configuration using air as the working fluid. The predicted results were generally found to be within 15% of the measured data.

Optimal relationship between power and design-driving loads for wind turbine rotors using 1-D models

Abstract. We investigate the optimal relationship between the aerodynamic power, thrust loading and size of a wind turbine rotor when its design is constrained by a static aerodynamic load. Based on 1-D axial momentum theory, the captured power P̃ for a uniformly loaded rotor can be expressed in terms of the rotor radius R and the rotor thrust coefficient CT. Common types of static design-driving load constraints (DDLCs), e.g., limits on the permissible root-bending moment or tip deflection, may be generalized into a form that also depends on CT and R. The developed model is based on simple relations and makes explorations of overall parameters possible in the early stage of the rotor design process. Using these relationships to maximize P̃ subject to a DDLC shows that operating the rotor at the Betz limit (maximum CP) does not lead to the highest power capture. Rather, it is possible to improve performance with a larger rotor radius and lower CT without violating the DDLC. As an example, a rotor design driven by a tip-deflection constraint may achieve 1.9 % extra power capture P̃ compared to the baseline (Betz limit) rotor. This method is extended to the optimization of rotors with respect to annual energy production (AEP), in which the thrust characteristics CT(V) need to be determined together with R. This results in a much higher relative potential for improvement since the constraint limit can be met over a larger range of wind speeds. For example, a relative gain in AEP of +5.7 % is possible for a rotor design constrained by tip deflections, compared to a rotor designed for optimal CP. The optimal solution for AEP leads to a thrust curve with three distinct operational regimes and so-called thrust clipping.

Output wind power curve optimization based on design wind speed concept

The output wind power curve versus wind speed is the most important characterization parameter of wind turbines. It allows quantifying and analyzing the design performances of wind turbines, monitoring its database, and controlling the operation modes and manufacturing products. Wind power curve can be used to select the proper rotor size to estimate the potential of wind energy at candidate wind sites and to assess the control device of the operating conditions. Developing model strategies for wind farms has the basic objectives such as the optimization of wind power produced and the minimization of dynamic loads to provide the best quality of output wind power at reasonable cost. Optimal design of wind turbines requires maximum-closing to the cubical output wind power curve despite technical and economic considerations. This study aims to determine the design wind speed of a wind turbine based on modeling-optimization of the output wind power curve under certain working conditions. The procedure is applied to a unit wind turbine in Gamesa wind farm (G52/850, 10.2 MW, http://www.thewindpower.net ) connected to an electrical grid located in south-west Algeria and extrapolated for other windy sites in Algeria. From simulation results, the design wind speed to inlet wind speed ratio [Formula: see text] increased from 0.35 to 7.68 once [Formula: see text] increased from 0.001 to 2.9999. Consequently, the output wind power predicted an increase of about 17.7% and an annual specific wind energy factor of about 2.55%–4% than nominal value given by the manufacturer, reducing the unit average cost of the electricity, generated by wind farms, by about 18.75%.

Opportunities for and challenges to further reductions in the “specific power” rating of wind turbines installed in the United States

A wind turbine’s “specific power” rating relates its capacity to the swept area of its rotor in terms of Watt per square meter. For a given generator capacity, specific power declines as rotor size increases. In land-rich but capacity-constrained wind power markets, such as the United States, developers have an economic incentive to maximize megawatt-hours per constrained megawatt, and so have favored turbines with ever-lower specific power. To date, this trend toward lower specific power has pushed capacity factors higher while reducing the levelized cost of energy. We employ geospatial levelized cost of energy analysis across the United States to explore whether this trend is likely to continue. We find that under reasonable cost scenarios (i.e. presuming that logistical challenges from very large blades are surmountable), low-specific-power turbines could continue to be in demand going forward. Beyond levelized cost of energy, the boost in market value that low-specific-power turbines provide could become increasingly important as wind penetration grows.

Making a case for a Non-standard frequency axial-flux permanent-magnet generator in an ultra-low speed direct-drive hydrokinetic turbine system

This research project investigates the impacts of the rotor and generator sizes on rotational speed and voltage output of a direct-drive hydrokinetic turbine system. It searches for a possibility of reducing the generator size while possessing the capability to produce sufficient voltage at an ultra-low RPM. The system has a Darrieus rotor that directly drives an axial-flux permanent-magnet generator, hence the friction loss from the transmission system is eliminated. However, the direct-drive system possesses a very low rotational speed, which adversely affects the generator. In particular, the output voltage is not sufficient for regular applications or the generator diameter needs to be enlarged. Numerical models of the rotor and generator were constructed in MATLAB. The rotor and generator sizes were varied under several design conditions. The models delivered design parameters for the system and their relationships. It was found that designing the generator with 50/60 Hz electrical frequency limits the number of slot/phase and hence the maximum output voltage. The study makes a case for designing a generator with electrical frequency other than the standard frequency, where it would be novel to be able to produce a higher voltage when a location with high water velocity is available, in addition to an improved power production. It would allow the generator to produce higher voltage at a given water velocity and rotational speed or have a smaller diameter at a given output voltage.

Computational characterization of a Gurney flap on a DU91(2)W250 airfoil

The considerable increase of wind turbine rotor size and weight in the last years has made impossible to control as they were controlled 20 years ago. The cost of energy is an essential role to maintain this type of energy as a viable alternative in economic terms with traditional or other renewable energies. Through the last decades many different flow control devices have been developed. Most of them were shaped for aeronautical issues and this was its first research application. Currently researchers are working to optimize and introduce these types of devices in multi megawatt wind turbines. Gurney flap (GF) is a vane perpendicular to the airfoil surface with a size between 0.1 and 3% of the airfoil chord length, placed in the lower or upper side of the airfoil close to the trailing edge of the airfoil. When GFs are appropriately designed, they increase the total lift of the airfoil while reducing the drag. Thanks to the implementation of the of this flow control device the efficiency of a wind turbine improves, which results on an increase in the power generation.

Design criteria and experiments considering the mechanical characteristics of high-speed permanent magnet synchronous generator of 8kW and 40krpm class

In this study, we designed, analyzed, and tested a permanent magnet synchronous generator by considering the mechanical characteristics of the rotor and the stator of an unmanned aerial vehicle (UAV) system operating at high-speed (40krpm). The size of the generator rotor was determined using the torque per rotor volume (TRV) analytical method. The designed generator uses a sleeve to prevent damage to the magnet during high-speed operation, and this sleeve must be designed to take into account the relationship between its mechanical characteristics and thickness, which affects electromagnetic behavior. Hence, the permanent magnet and the thickness of the sleeve and were selected by analyzing the rotor structure and considering the mechanical characteristics at the rated rotation speed. The characteristics of the designed generator were analyzed using the finite elements method and verified by experimental testing.