Rotor Geometry Research Articles

Synchronous Reluctance Machine Optimization for High-Speed Applications

The synchronous reluctance machines with transversally laminated rotor and multi flux barriers per pole reach a high torque density, so that they are proposed as a valid alternative to permanent magnet machines. Such machines have been analyzed for different applications, mainly home appliance, industrial tool, traction, up to low-speed high-power generators. On the contrary, the use of synchronous reluctance machines for high-speed applications remains almost unexplored yet. The aim of this paper is to investigate the potential of a high-speed synchronous reluctance machine. An optimization is carried out so as to maximize the machine performance (high power, proper power factor, low vibration) at a given speed. The machine size is fixed and the focus is on the rotor geometry, with the purpose of maximizing the electromagnetic torque, according to the necessary thickness of the ribs. It is shown that, even if the ribs are thick, it is possible to reach a proper torque density. It is shown that different solutions exist, which allow to reach high torque and minimum torque ripple. However, the optimal solutions are quite sensitive to the geometrical variations, so that a particular care is required in the manufacturing of the machine. Finally, the power limit of the synchronous reluctance motor with barrier rotor is found.

A Nonlinear Analytical Model for the Rapid Prediction of the Torque of Synchronous Reluctance Machines

The synchronous reluctance motor works under heavy saturation. This paper presents a nonlinear analytical model of the reluctance machine, which is used to derive both average and torque harmonics as a function of the rotor geometry. Maps showing the torque harmonics as a function of the rotor barrier angles are derived. These maps are useful tools for the machine designer to get a proper rotor geometry. The torque maps are compared with those obtained from both linear analytical and finite element models. The maps computed analytically show good agreement with those derived by means of finite element analysis, and they are obtained in a much smaller computing time.

Design and Multi-Objective Optimization of Fiber-Reinforced Polymer Composite Flywheel Rotors

A multi-objective optimization strategy to find optimal designs of composite multi-rim flywheel rotors is presented. Flywheel energy storage systems have been expanding into applications such as rail and automotive transportation, where the construction volume is limited. Common flywheel rotor optimization approaches for these applications are single-objective, aiming to increase the stored energy or stored energy density. The proposed multi-objective optimization offers more information for decision-makers optimizing three objectives separately: stored energy, cost and productivity. A novel approach to model the manufacturing of multi-rim composite rotors facilitates the consideration of manufacturing cost and time within the optimization. An analytical stress calculation for multi-rim rotors is used, which also takes interference fits and residual stresses into account. Constrained by a failure prediction based on the Maximum Strength, Maximum Strain and Tsai-Wu criterion, the discrete and nonlinear optimization was solved. A hybrid optimization strategy is presented that combines a genetic algorithm with a local improvement executed by a sequential quadratic program. The problem was solved for two rotor geometries used for light rail transit applications showing similar design results as in industry.

Advanced noise modeling for future propulsion systems

In order to meet noise specifications for future foreseen aircraft propulsion systems, such as for ultrahigh bypass ratio turbofans and contra-rotating open rotors, the dominant turbomachinery noise mechanisms need to be modeled accurately at an early design stage. Two novel methods are presented here, which could significantly improve the existing analytical noise models. For the high-solidity ultrahigh bypass ratio, a mode-matching technique based on a modal expansion of acoustic and vortical variables in each subdomain of a blade row is shown to accurately reproduce sound generation and propagation in two-dimensional bifurcated channels and in three-dimensional annular unstaggered flat-plate cascades. For the low solidity contra-rotating open rotors, several extensions to Amiet’s compressible isolated airfoil theory are coupled with Curle’s and Ffowcs Williams and Hawkings’ acoustic analogy in the frequency domain within a strip theory framework, to yield both far-field tonal and broadband noise. Including sweep in both tonal and broadband noise models is shown to significantly improve the comparison with experiments on a stationary swept airfoil in a uniform turbulent stream and on a realistic contra-rotating open rotor geometry at approach conditions.

An axial turbine in an innovative oscillating water column (OWC) device for sea-wave energy conversion

Wells turbines, self-rectifying air-driven axial turbines, are typically used to convert pneumatic power available in the periodic reversed airflow in Oscillating Water Column (OWC) device into mechanical energy. However, such turbines suffer from low aerodynamic efficiency; low powers produced, and narrow operating range. The current work proposes the operating principle of using water as the working fluid rather than air by submerging the Wells turbine in the sea water to enhance its performance. This gives an advantage for the turbine operation with a fluid having specific weight higher fluid than air. The analysis is carried out for an innovative device proposed by Boccotti in which a vertical axis hydraulic Wells turbine installed inside a vertical duct and contained in a caisson below the sea water surface. The CFD simulations are performed depend on the steady 3D incompressible Reynolds Averaged Navier-Stokes (RANS) calculations on this type of axial turbine rotor with realizable k−ε turbulence model. A comparative analysis between the computational results and experimental results is carried out and a good agreement is found between both results. This paper proved that, the hydraulic (immersed) Wells turbine performance is better than that of the air (conventional) Wells turbine. A substantial improvement in the torque coefficient is achieved with the hydraulic turbine of about 1.4 times the torque of the conventional air turbine. Using water as a working fluid which is the proposed concept leads to a wider operating range unlike using air. In addition, the effects of blade profile and rotor solidity on the turbine performance were clarified computationally. In this work, two kinds of symmetric blade profiles have been used (NACA 0015 and S1046). The present computational investigation was carried out for three rotor solidities (0.64, 0.48 and 0.24) through changing the number of turbine blades (8, 6 and 3 blades). It is found that for a hydraulic Wells turbine operating under oscillating water flow, the rotor geometry preferred is the blade profile of S1046 for the investigated three values of rotor solidities.

Design methodology for high‐speed synchronous reluctance machines

This study presents two design methodologies for high-speed synchronous reluctance (REL) machines. The interest for high-speed drives comes from the request for compactness and high efficiency. The synchronous REL motors have been widely studied for several applications, but a coherent design procedure for high speed has not been proposed in the literature. The study proposes some analytical procedures to get an initial design. Then the rotor geometry optimisation through a differential evolution algorithm is described. Finally, a design example is given and thoroughly analysed using these two approaches.

Effect of Inlet Distortion Features on Transonic Fan Rotor Stall

The effect of inlet distortion from curved intake ducts on jet engine fan stability is an important consideration for next-generation passenger aircraft such as the boundary layer ingestion (BLI) “silent aircraft.” Highly complex inlet flows which occur can significantly affect fan stability. Future aircraft designs are likely to feature more severe inlet distortion, pressing the need to understand the important factors influencing design. This paper presents the findings from a large computational fluid dynamics (CFD) investigation into which aspects of inlet distortion cause the most significant reductions in stall margin and, therefore, which flow patterns should be targeted by mitigating technology. The study considers the following aspects of distortion commonly observed in intakes: steady vortical distortion due to secondary flow, unsteady vortical distortion due to vortex shedding and mixing, static pressure distortion due to curved streamlines, and low momentum endwall flow due to thickened boundary layers or separation. Unsteady CFD was used to determine the stall points of a multipassage transonic rotor geometry with each of the inlet distortion patterns applied. Interesting new evidence is provided, which suggests that low momentum flow in the tip region, rather than distortion in the main body of the flow, leads to damaging instability.

Location-Optimized Aerodynamic Rotor Design of Small Wind Turbines and Lightweight Implementation Using Additive Hybrid Material

Abstract Wind power plays a crucial role in supplying cities with renewable energy. Combined with short transport routes, it is essential to establish site-specific small wind turbines in the urban environment. An increasing interest in small, decentralized, vertical-axis wind turbines (VAWT) can be observed here. However, concepts with low visual and auditory effects and economic efficiencies are largely limited. The project part described in this paper enables a specially developed design software tool of rotor geometries optimized for such boundary conditions. By using fiber-reinforced structures in combination with selective laser sintering, it is theoretically possible to economically produce even the smallest quantities of these geometries for a typical service life of wind turbines. The results presented and discussed in this work can serve as a basis for a subsequent feasibility study.

A handling qualities analysis tool for rotorcraft conceptual designs

ABSTRACTOver the past decade, NASA, under a succession of rotary-wing programs, has been moving towards coupling multiple discipline analyses to evaluate rotorcraft conceptual designs. Handling qualities is one of the component analyses to be included in such a future Multidisciplinary Analysis and Optimization framework for conceptual design of Vertical Take-Off and Landing (VTOL) aircraft. Similarly, the future vision for the capability of the Concept Design and Assessment Technology Area of the U.S Army Aviation Development Directorate also includes a handling qualities component. SIMPLI-FLYD is a tool jointly developed by NASA and the U.S. Army to perform modelling and analysis for the assessment of the handling qualities of rotorcraft conceptual designs. Illustrative scenarios of a tiltrotor in forward flight and a single-main rotor helicopter at hover are analysed using a combined process of SIMPLI-FLYD integrated with the conceptual design sizing tool NDARC. The effects of variations of input parameters such as horizontal tail and tail rotor geometry were evaluated in the form of margins to fixed- and rotary-wing handling qualities metrics and the computed vehicle empty weight. The handling qualities Design Margins are shown to vary across the flight envelope due to both changing flight dynamics and control characteristics and changing handling qualities specification requirements. The current SIMPLI-FLYD capability, lessons learned from its use and future developments are discussed.

Magic angle spinning NMR with metallized rotors as cylindrical microwave resonators.

We introduce a novel design for millimeter wave electromagnetic structures within magic angle spinning (MAS) rotors. In this demonstration, a copper coating is vacuum deposited onto the outside surface of a sapphire rotor at a thickness of 50nm. This thickness is sufficient to reflect 197-GHz microwaves, yet not too thick as to interfere with radiofrequency fields at 300MHz or prevent sample spinning due to eddy currents. Electromagnetic simulations of an idealized rotor geometry show a microwave quality factor of 148. MAS experiments with sample rotation frequencies of ωr /2π=5.4kHz demonstrate that the drag force due to eddy currents within the copper does not prevent sample spinning. Spectra of sodium acetate show resolved 13 C J-couplings of 60Hz and no appreciable broadening between coated and uncoated sapphire rotors, demonstrating that the copper coating does not prevent shimming and high-resolution nuclear magnetic resonance spectroscopy. Additionally, 13 C Rabi nutation curves of ω1 /2π=103kHz for both coated and uncoated rotors indicate no detrimental impact of the copper coating on radio frequency coupling of the nuclear spins to the sample coil. We present this metal coated rotor as a first step towards an MAS resonator. MAS resonators are expected to have a significant impact on developments in electron decoupling, pulsed dynamic nuclear polarization (DNP), room temperature DNP, DNP with low-power microwave sources, and electron paramagnetic resonance detection.

Mixing ability examination of three different rotor cross sections and rotor geometry quantification with pressurization coefficient

ABSTRACTThe geometry of rotor cross section would affect the velocity profile of circumferential flow in continues mixer, which further dominated the mixing ability of rotor. To reveal the relationship between the geometry and mixing ability of rotor cross section, three rotor cross sections with different geometries were chosen, and the POLYFLOW simulations were applied to analyze the velocity profile and the flow stretching. The distribution for three rotors was evaluated both numerically and experimentally with the particle tracking technology. Then, the rotor geometry was quantified with pressurization coefficient S, which is a geometric parameter considering the wedge angle α, width of wing tip e, tip clearance h and the maximum clearance H0 between rotor and chamber wall. The results showed that the mixing ability and S for three rotor cross‐sections would vary with the rotor geometry changing, furthermore, the rotor cross‐section with larger S would have stronger mixing ability. Decreasing α or e, as well as increasing the H0, would induce the increase of S, and further resulting in the improvement of the mixing ability. Rotor geometry quantification with S would intuitionally reveal the relationship between rotor geometry and the mixing ability, and would contribute to the rotor cross‐section design and optimization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46623.

Innovative Savonius rotors evolved by genetic algorithm based on 2D-DCT encoding

The Savonius rotor is mainly known by its design simplicity, low cost, easy installation, good starting ability, relatively low operating speed and independent to wind directions. Over the last few decades, although many investigations around the world have reported performance gains of the Savonius rotor, none of the available techniques is capable of automatic generating innovative Savonius rotor geometries other than predefined models such as semicircular or its variations. This study aims to investigate the geometry optimization ability of evolution algorithms based on two-dimensional discrete cosine transformation (2D-DCT) through numerical simulations. By considering the cross-sectional area of a Savonius rotor as a picture, 2D-DCT has been employed to compress and encode the cross-sectional geometry into genomes which will be evolved by Genetic Algorithms to maximize their average torque coefficient. According to numerical simulation, the proposed technique improved the efficiency by 13.77% at tip speed ratio (TSR) 1.0 and 21.11% at TSR 0.0838, which discovered impressive and thought promoting innovative geometries automatically.

Rotor Geometry Design of Saliency-Based Sensorless Controlled Distributed-Winding IPMSM for Hybrid Electric Vehicles

This paper presents the design process of a sensorless-oriented interior permanent magnet synchronous motor (IPMSM). The motor uses spatial saliency for the position-sensorless traction drive in a hybrid electric vehicle (HEV). The sensorless control consists of two signal-injection techniques to achieve wide-torque-range operation at low speed. Realization of a stable sensorless drive necessitates a design capable of expanding the transition region between the two techniques. This paper describes our proposed design methods that can achieve the self-sensing capability while retaining the required torque-speed capability. Finite element analysis is used to evaluate both the self-sensing capability and the torque-speed capability. Under the restricted specifications of dimensions and requirements, the 350 N·m-36 kW IPMSM is optimally designed for HEV applications. The validity of the proposed design method and the expected drive characteristics are experimentally verified by using the prototype.

Numerical studies on two turbulence models and a laminar model for aerodynamics of a vertical-axis wind turbine

The purpose of this study is the analysis of flow around a one-bladed Darrieus-type wind turbine using computational fluid dynamics (CFD). The rotor geometry consists of a NACA 0015 airfoil with chord length of 0.15 m. Numerical simulations are performed using ANSYS Fluent, employing laminar model and two turbulence models: SST k-ω and RNG k-e. The obtained numerical results of unsteady aerodynamic blade loads are compared with available experimental results from literature. Computed aerodynamic characteristics of normal and tangential forces comply with the experiment results. The RNG k-e turbulence model has a good accuracy in determining aerodynamic blade loads for the upwind and downwind parts of the rotor. The laminar model and the SST k-ω turbulence model slightly overestimate the tangential aerodynamic blade loads at the downwind part of the rotor. An averaged wind turbine velocity profile computed at one rotor radius downstream of the rotor has a Gaussian shape. The steady-state airfoil characteristics are computed for the Reynolds number comparable to the Reynolds number of a moving blade employing the SST k-ω and RNG k-e turbulence models and using the same computational grid as for unsteady simulations of the rotor.

Design and Analysis of Multi-Phase BLDC Motors for Electric Vehicles

This paper presents a design and analysis of multi-phase brushless direct current (BLDC) motor for electric vehicles (EV). In this work, hub-wheels having 110Nm, 900rpm rated values have been designed for the proposed EV. This EV can produce 440 Nm without using transmission, differential and other mechanical components which have very high losses due to the mechanical fraction. The motors to be used in the EV have been designed as 3-, 5- and 7-phase by Infolytica/Motor Solve Software to compare their performances at the same load conditions. The same rotor geometry has been utilized for the motors. However, slot numbers and dimensions of the stator have been determined by considering the motor phase number. Performance curves of phase-currents, output powers, torques, efficiencies and power factors have been presented for these motors at the same operating conditions. It can be possible to use lower power switches in motor drive system thanks to the phase current reduction since the phase currents decrease proportionally to motor phase number. This work shows that the multi-phase BLDC motors are a good alternative in order to obtain lower torque and lower power inverter structure than the 3-phase BLDC motors which are used as standard.

Design and Analysis of Multi-Phase BLDC Motors for Electric Vehicles

This paper presents a design and analysis of multi-phase brushless direct current (BLDC) motor for electric vehicles (EV). In this work, hub-wheels having 110Nm, 900rpm rated values have been designed for the proposed EV. This EV can produce 440 Nm without using transmission, differential and other mechanical components which have very high losses due to the mechanical fraction. The motors to be used in the EV have been designed as 3-, 5- and 7-phase by Infolytica/Motor Solve Software to compare their performances at the same load conditions. The same rotor geometry has been utilized for the motors. However, slot numbers and dimensions of the stator have been determined by considering the motor phase number. Performance curves of phase-currents, output powers, torques, efficiencies and power factors have been presented for these motors at the same operating conditions. It can be possible to use lower power switches in motor drive system thanks to the phase current reduction since the phase currents decrease proportionally to motor phase number. This work shows that the multi-phase BLDC motors are a good alternative in order to obtain lower torque and lower power inverter structure than the 3-phase BLDC motors which are used as standard.

Francis turbine draft tube parameterization and analysis of performance characteristics using CFD techniques

Abstract The present paper focuses on the parameterization of the draft tube elbow based on the initial geometry of the GAMM Francis turbine model. The goal was to obtain a draft tube geometry that improves the hydrodynamic performance. For this purpose, CFD analyzes were carried out, considering the GAMM Francis turbine pre-distributor, distributor and rotor geometry, and different parameterized draft tube geometries. Related to the draft tube parameterization methodology, it has modified the generatrix geometry of the elbow that defines its contour. Three types of curves were used to define the elbow contour geometry: logarithmic spiral format curve, circle arc format curve and denominated hyperbolic spiral curve. These curves and their combinations were used to define the elbow contour in the longitudinal plane, resulted in four draft tubes geometries. The numerical results were compared with experimental results, showing good conformity. The efficiency of the Francis turbine was higher for the four draft tubes of this work than the original draft tube GAMM Francis turbine. Therefore, it was found that the draft tube in hyperbolic-logarithmic spiral format has the highest efficiency and the draft tube in logarithmic spiral format has the lowest loss coefficient. Consequently the hydrodynamic performance have been discussed in this work.

RANS-based design optimization of dual-rotor wind turbines

PurposeAn improvement in the energy efficiency of wind turbines can be achieved using dual rotors. Because of complex flow physics, the design of dual-rotor wind turbines (DRWTs) requires repetitive evaluations of computationally expensive partial differential equation (PDE) simulation models. Approaches for solving design optimization of DRWTs constrained by PDE simulations are investigated. The purpose of this study is to determine design optimization algorithms which can find optimal designs at a low computational cost.Design/methodology/approachSeveral optimization approaches and algorithms are compared and contrasted for the design of DRWTs. More specifically, parametric sweeps, direct optimization using pattern search, surrogate-based optimization (SBO) using approximation-based models and SBO using kriging interpolation models with infill criteria are investigated for the DRWT design problem.FindingsThe approaches are applied to two example design cases where the DRWT fluid flow is simulated using the Reynolds-averaged Navier−Stokes (RANS) equations with a two-equation turbulence model on an axisymmetric computational grid. The main rotor geometry is kept fixed and the secondary rotor characteristics, using up to three variables, are optimized. The results show that the automated numerical optimization techniques were able to accurately find the optimal designs at a low cost. In particular, SBO algorithm with infill criteria configured for design space exploitation required the least computational cost. The widely adopted parametric sweep approach required more model evaluations than the optimization algorithms, as well as not being able to accurately find the optimal designs.Originality/valueFor low-dimensional PDE-constrained design of DRWTs, automated optimization algorithms are essential to find accurately and efficiently the optimal designs. More specifically, surrogate-based approaches seem to offer a computationally efficient way of solving such problems.

Improving rotor geometry to strengthen anti-demagnetization ability of PM

Improving rotor geometry to strengthen anti-demagnetization ability of PM

Power generation of small wind turbine: Under high-speed operation

Mechanical energy is produced through the rotation of wind turbine blades by air that converts mechanical energy into electrical energy. Wind turbines are usually designed for particular applications, and design characteristics may vary depending on the area of use. The variety of applications is reflected on the size of turbines and their infrastructures. Wind turbine performance may be enhanced by analyzing the small horizontal axis wind turbine (SHAWT) under high-wind-speed operation. This work analyzes the implementation of the SHAWT and investigates its performance in simulation and real life. The power performance of the SHAWT, which largely depends on the real structure of the rotor geometry and aerodynamic test, was simulated using ANSYS Fluent software at different wind speeds of up to 33.33 m/s (120 km/h) to numerically investigate actual turbine operation. Dynamic mesh and user-defined function (UDF) were used to revolve the rotor turbine via wind. Simulation results were further validated by experimental data, and good matching was achieved. A car alternator was formed and used as a small horizontal wind turbine to reduce energy production cost. Consequently, the alternator-based turbine system was found to be a low-cost solution for the exploitation of wind energy.