Rotor Configuration Research Articles

Numerical investigation on the hydrodynamic performance of variable length blade tidal turbine: an attribute to enhance energy capture

In the marine industry, it is important to improve the performance of tida turbines to reduce power generation costs. Modification of existing tidal turbine models is necessary to boost performance. The main objective of the present study is to investigate the hydrodynamic performance of a model variable length blade tidal turbine by modifying the baseline rotor to improve the performance using blade element momentum theory (BEMT). The QBlade BEMT simulation results were validated with the available published data and are in good agreement. Furthermore, the key performance parameters (i.e. thrust, moment, and power coefficient) and power output were predicted using the BEMT code for different blade configurations of the model rotor. The simulation results were compared with a standard conventional fixed blade turbine model. Based on the results from the simulations, with the increase in the rotor blade lengths, the performance parameters, particularly peak power coefficients, were observed to be improved up to 10%. The power extraction was also enhanced up to 79% below-rated tidal velocities without any loss in performance at the rated condition. Hence, the model is more efficient compared to the conventional models.

Quasimodes instability analysis of uncertain asymmetric rotor system based on 3D solid element model

Uncertainties are considered in the equation of motion of an asymmetric rotor system. Based on Hill's determinant method, quasimodes stability analysis with uncertain parameters is used to get stochastic boundaries of unstable regions. Firstly, A 3D finite element rotor model was built in rotating frame with four parameterized coefficients, which is assumed as random parameters representing the uncertainties existing in the rotor system. Then the influences of uncertain coefficients on the distribution of the unstable region boundaries are analyzed. The results show that uncertain parameters have various influences on the size, boundary and number of unstable regions. At last, the statistic results of the minimum and maximum spin speeds of unstable regions were got by Monte Carlo simulation. The used method is suitable for real engineering rotor system, because arbitrary configuration of rotors can be modeled by 3D finite element.

Rotordynamic Performance of a Shaft With Large Overhung Mass Supported by Foil Bearings

This work presents the theoretical and experimental rotordynamic evaluations of a rotor–air foil bearing (AFB) system supporting a large overhung mass for high-speed application. The proposed system highlights the compact design of a single shaft rotor configuration with turbomachine components arranged on one side of the bearing span. In this work, low-speed tests up to 45 krpm are performed to measure lift-off speed and to check bearing manufacturing quality. Rotordynamic performance at high speeds is evaluated both analytically and experimentally. In the analytical approach, simulated imbalance responses are studied using both rigid and flexible shaft models with bearing forces calculated from the transient Reynolds equation along with the rotor motion. The simulation predicts that the system experiences small synchronous rigid mode vibration at 20 krpm and bending mode at 200 krpm. A high-speed test rig is designed to experimentally evaluate the rotor–air foil bearing system. The high-speed tests are operated up to 160 krpm. The vibration spectrum indicates that the rotor–air foil bearing system operates under stable conditions. The experimental waterfall plots also show very small subsynchronous vibrations with frequency locked to the system natural frequency. Overall, this work demonstrates potential capability of the air foil bearings in supporting a shaft with a large overhung mass at high speed.

Performance and design optimization of two model based wave energy permanent magnet linear generators

Linear generators are a quickly growing segment of renewable ocean wave energy converters. This paper presents the modeling, simulation and optimal design of two types of permanent magnet linear generators for generating 3-phase voltages based on finite element analysis and intelligent design optimization techniques. Each generator stator and rotor configurations are modeled by using Computer Aided Three Dimensional Interactive Application software and the magnetic field simulation studies are carried out by using finite element method software ANSYS. Two intelligent evolutionary methods, Scatter Search optimization and Particle Swarm Optimization techniques are employed on design analysis programs which are developed by using Visual C++ software to derive optimal design parameters of the linear generator models. Simulation results show the effective exploration of the design and analysis objectives.

A GEAR-SHIFTING MECHANISM WITH A ROTARY CONFIGURATION FOR APPLICATIONS IN A 16-SPEED BICYCLE TRANSMISSION HUB

A multi-speed bicycle transmission hub includes a geared speed-changing mechanism for providing different speed ratios and a gear-shifting mechanism for controlling the gear stage. This paper focuses on the embodiment design of a mechanical gear-shifting mechanism with a rotary configuration used in a 16-speed transmission hub for bicycles. A 16-link, five-degrees of freedom (DOF) split-power epicyclic gear mechanism, which consists of a gear differential and four sets of parallel-connected basic planetary gear trains, is introduced. Based on the clutching sequence table, a systematic design process is developed to come up with the embodiment design of the gear-shifting mechanism. A feasible and compact 16-speed rear transmission hub for bicycles is presented.

An Empirical Study of Overlapping Rotor Interference for a Small Unmanned Aircraft Propulsion System

The majority of research into full-sized helicopter overlapping propulsion systems involves co-axial setups (fully overlapped). Partially overlapping rotor setups (tandem, multirotor) have received less attention, and empirical data produced over the years is limited. The increase in demand for compact small unmanned aircraft has exposed the need for empirical investigations of overlapping propulsion systems at a small scale (Reynolds Number < 250,000). Rotor-to-rotor interference at the static state in various overlapping propulsion system configurations was empirically measured using off the shelf T-Motor 16 inch × 5.4 inch rotors. A purpose-built test rig was manufactured allowing various overlapping rotor configurations to be tested. First, single rotor data was gathered, then performance measurements were taken at different thrust and tip speeds on a range of overlap configurations. The studies were conducted in a system torque balance mode. Overlapping rotor performance was compared to an isolated dual rotor propulsion system revealing interference factors which were compared to the momentum theory. Tests revealed that in the co-axial torque-balanced propulsion system the upper rotor outperforms the lower rotor at axial separation ratios between 0.05 and 0.85. Additionally, in the same region, thrust sharing between the two rotors changed by 21%; the upper rotor produced more thrust than the lower rotor at all times. Peak performance was recorded as a 22% efficiency loss when the axial separation ratio was greater than 0.25. The performance of a co-axial torque-balanced system reached a 27% efficiency loss when the axial separation ratio was equal to 0.05. The co-axial system swirl recovery effect was recorded to have a 4% efficiency gain in the axial separation ratio region between 0.05 and 0.85. The smallest efficiency loss (3%) was recorded when the rotor separation ratio was between 0.95 and 1 (axial separation ratio was kept at 0.05). Tests conducted at a rotor separation ratio of 0.85 showed that the efficiency loss decreased when the axial separation ratio was greater than 0.25. The lower rotor outperformed the upper rotor in the rotor separation ratio region from 0.95 to 1 (axial separation ratio was kept at 0.05) at an overall system thrust of 8 N, and matched the upper rotor performance at the tested overall thrust of 15 N.

Primary study of a new permanent magnet flux switching machine over straight and spanned rotor configurations

Purpose The purpose of this paper is to address a fundamental study and performance analysis of a proposed 6Slots-10Poles permanent magnet flux switching machine (PMFSM) using straight rotor (StR) and 6Slots-8Poles PMFSM with spanned rotor (SpR) structure. Design/methodology/approach Design configuration of the proposed machine was developed using commercial finite element analysis package and JMAG-Designer V.14 software, which provides two-dimensional finite element solver throughout the investigation. An electromagnetic performance analysis is carried out and compared over the two proposed topologies which consist of machines no-load and under-load conditions. Findings This paper demonstrates the finding of the proposed StR structure which consist of more favorable three-phase sinusoidal feature, lower cogging torque and higher output torque. Flux density attributes reveal higher established magnetizing flux concentration in StR compared with SpR. Consequently, the StR structure requires low armature current before it may start to rotate and provides better robust construction with less material consumption and cost. Originality/value This paper describes the novel design of a new PMFSM configuration pertinent for high-speed applications.

The marine electrical power industry with the use of renewable energy carriers. Part 2. Axial multipole synchronous generators with permanent magnets for wind and wave offshore power plants

The paper deals with problems of selection of structures and optimum design of multipole permanent magnet synchronous machines (PMSMs) for operation in offshore wind- and wave-power plants under severe conditions for maintenance service. It is shown that multipole PMSMs are a new and very suitable electrical machine for direct connected turbogenerators in power plants and, at the same time, multipole PMSMs meet a number of other important demands, including high reliability, contactless construction, high efficiency, minimum mass and dimensions, and cost effectiveness. With the aim of systematization, an integrated classification scheme of PMSMs is presented to describe the variety of designs of stator and rotor configurations. With the help of a theoretical analysis based on a geometrical approach, analytical expressions for PMSM comparison are derived using the relationship between the criterion of optimization (maximum power density) and the main geometric parameters of PMSMs. Comparative analysis of the PMSMs with radial and axial magnetic fluxes for the case of various numbers of poles and different diameters of rotors has confirmed that axial multipole PMSMs are synchronous machines with maximum power density and an optimum variant for direct connected turbogenerator structures for offshore wind- and wave-power plants. It is noted that the advantage of axial PMSMs over radial PMSMs is monotonic growth in accordance with increasing number of poles p. Under the condition that p ≥ 20, which is strictly necessary for designing direct connected turbogenerators in offshore wind- and wave-power plants, we have more than doubled the power density at axial PMSMs as compared with radial ones.

Simulation and wake analysis of a single vertical axis wind turbine

AbstractBecause of several design advantages and operational characteristics, particularly in offshore farms, vertical axis wind turbines (VAWTs) are being reconsidered as a complementary technology to horizontal axial turbines. However, considerable gaps remain in our understanding of VAWT performance since cross‐flow rotor configurations have been significantly less studied than axial turbines. This study examines the wakes of VAWTs and how their evolution is influenced by turbine design parameters. An actuator line model is implemented in an atmospheric boundary layer large eddy simulation code, with offline coupling to a high‐resolution blade‐scale unsteady Reynolds‐averaged Navier–Stokes model. The large eddy simulation captures the turbine‐to‐farm scale dynamics, while the unsteady Reynolds‐averaged Navier–Stokes captures the blade‐to‐turbine scale flow. The simulation results are found to be in good agreement with three existing experimental datasets. Subsequently, a parametric study of the flow over an isolated VAWT, carried out by varying solidities, height‐to‐diameter aspect ratios and tip speed ratios, is conducted. The analyses of the wake area and velocity and power deficits yield an improved understanding of the downstream evolution of VAWT wakes, which in turn enables a more informed selection of turbine designs for wind farms. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of the far wake behind dual rotor and dual disk configurations

There is an increasing interest in studying the development of far wakes behind two or more interacting wind turbines in order to determine the influence of wake interaction in relation to the design of wind farms. The focus of this experimental study is to understand and describe the resulting wake features for two rotors subjected to different operating and spatial conditions. As a part of this, a comparison with the wake development behind two disks replacing the rotor models was performed to determine the difference between the two wake systems.LDA and Stereo PIV experiments were carried out to study the development of far wakes behind configurations of dual HAWT wind turbine rotors and dual circular disks. The setups were placed in the middle of a water flume. The initial flow in the flume is subjected to a very low turbulence level, limiting the influence of all external disturbances in order to focus the study to the inherent wake instability.As a result of the investigation, we obtained decays of profiles for the velocity deficit and turbulent pulsations in the far wakes behind both dual rotor and dual disk configurations. By using regression techniques to fit the obtained velocity profiles the experimental data were approximated by identical analytical models and compared to each other. An identical rational dependence with the same powers, but with different coefficients, was found for the two configurations.

Flow interaction of diffuser augmented wind turbines

Up-scaling of wind turbines has been a major trend in order to reduce the cost of energy generation from the wind. Recent studies however show that for a given technology, the cost always rises with upscaling, notably due to the increased mass of the system. To reach capacities beyond 10 MW, multi-rotor systems (MRS) have promising advantages. On the other hand, diffuser augmented wind turbines (DAWTs) can significantly increase the performance of the rotor. Up to now, diffuser augmentation has only been applied to single small wind turbines. In the present research, DAWTs are used in a multi-rotor system. In wind tunnel experiments, the aerodynamics of two and three DAWTs, spaced in close vicinity in the same plane normal to a uniform flow, have been analysed. Power increases of up to 5% and 9% for the two and three rotor configurations are respectively achieved in comparison to a stand-alone turbine. The physical dynamics of the flows are analysed on the basis of the results obtained with a stand-alone turbine.

Benchmarking aerodynamic prediction of unsteady rotor aerodynamics of active flaps on wind turbine blades using ranging fidelity tools

Simulations of a stiff rotor configuration of the DTU 10MW Reference Wind Turbine are performed in order to assess the impact of prescribed flap motion on the aerodynamic loads on a blade sectional and rotor integral level. Results of the engineering models used by DTU (HAWC2), TUDelft (Bladed) and NTUA (hGAST) are compared to the CFD predictions of USTUTT-IAG (FLOWer). Results show fairly good comparison in terms of axial loading, while alignment of tangential and drag-related forces across the numerical codes needs to be improved, together with unsteady corrections associated with rotor wake dynamics. The use of a new wake model in HAWC2 shows considerable accuracy improvements.

Open Access Wind Tunnel Measurements of a Downwind Free Yawing Wind Turbine

A series of free yawing wind tunnel experiments was held in the Open Jet Facility (OJF) of the TU Delft. The ≈ 300 W turbine has three blades in a downwind configuration and is optionally free to yaw. Different 1.6m diameter rotor configurations are tested such as blade flexibility and sweep. This paper gives a brief overview of the measurement setup and challenges, and continues with presenting some key results. This wind tunnel campaign has shown that a three bladed downwind wind turbine can operate in a stable fashion under a minimal yaw error. Finally, a description of how to obtain this open access dataset, including the post-processing scripts and procedures, is made available via a publicly accessible website.

Influence of Honeycomb Rubbing on the Labyrinth Seal Performance

The aircraft engine operates in various conditions. In consequence, the design of seals must take account of the seal clearance changes and the risk of rubbing. A small radial clearance of the rotor tip seal leads to the honeycomb rubbing in take-off conditions, and the leakage flow may increase in cruise conditions. The aim of this study is to compare two honeycomb seal configurations of the low-pressure gas turbine rotor. In the first configuration, the clearance is small and rubbing occurs. In the second,—the fins of the seal are shorter to eliminate rubbing. It is assumed that the real clearance in both configurations is the same. A study of the honeycomb geometrical model is performed to reduce the computational effort. The problem is investigated numerically using the RANS equations and the two-equation k–ω SST turbulence model. The honeycomb full structure is taken into consideration to show details of the fluid flow. Main parameters of the clearance and leakage flows are compared and discussed for the rotor different axial positions. An assessment of the leakage flow through the seal variants could support the design process.

Experimental and numerical investigation of the effect of turbulent inflow on a Horizontal Axis Wind Turbine (Part I: Power performance)

This study aimed to analyze the effect of turbulence intensity and wind shear on the power characteristics of a Horizontal Axis Wind Turbine (HAWT). For this purpose, the blade pitch angle and yaw were compared by using a two-bladed HAWT in the wind tunnel experiments. In this study, the turbulence intensities were generated by active turbulence grids and wind shears were obtained by an atmospheric boundary layer generation device. Through measurement of the power and thrust coefficients for each rotor configuration, the aerodynamic feasibility of this wind turbine was discussed. As a result, it was clarified that the power coefficient was strongly dependent on the blade pitch angle and yaw angle. The optimum power coefficients were 0.308, 0.321, 0.298 at the blade pitch angle of β = 4°, for the turbulence intensities of TI = 1.4%, 8.0% and 13.5%. Moreover, thrust coefficient decreased with the increase of pitch angle. For the optimum pitch angle, the maximum power and thrust coefficients obtained at as = 0.0558, showing smaller values than the results of wind shear as = 0.1447. From this study, these results were very important for developing HAWT suitable for turbulence environment.

Reduction of Cogging Torque and Torque Ripple in Interior PM Machines With Asymmetrical V-Type Rotor Design

High cogging torque is a common drawback of the interior permanent magnet machine. In this paper, a novel technique is adopted to reduce cogging torque and torque ripple by using an asymmetrical V-type rotor configuration. First, the analysis modes are presented, and the proposed rotor is optimized by the hybrid design of experiment. A satisfactory set of parameters is determined. Next, the cogging torque and the torque ripple of the proposed model are compared with those of the basic model. The results demonstrate that the cogging torque and the torque ripple are reduced significantly by the adoption of the proposed rotor. Then, the performance of the proposed model rotating clockwise is compared that of the proposed model rotating counterclockwise to evaluate the effectiveness of the proposed rotor. Finally, the validity of the proposed method is confirmed by experiment.

A Mathematical and FEM Design of Novel Axial Field Switched Reluctance Motor for Electrical Vehicle (EV) Application

Switch reluctance (SR) motors attract attention as a motor that does not use permanent magnet material. So it is a strong candidate for electrical vehicle (EV) application. In EV application axial flux machines are preferred over radial flux machines due to high power density. In this Article novel axial field switched reluctance motor (AFSRM) design is presented which intend to improve the output torque by single flux path distribution in C- core stator. Unlike conventional radial field SRMs, the windings of the C-core stator can be individually wound without complex winding equipment. This topology has an 8/6 pole dual air gap single rotor and single C-core stator configuration without overlapping winding arrangement. Computer Aided Design (CAD) is used to calculate the phase inductance and average torque for a novel AFSRM topology. The two and three-dimensional Finite element (FE) analyses is carried out to validate obtained CAD results.

Dynamic Mesh Analyses of Helicopter Rotor–Fuselage Flow Interaction in Forward Flight

AbstractUnsteady compressible flow analyses of helicopter rotor–fuselage interaction in hover and forward flight conditions are carried out using commercially available computational fluid dynamics (CFD) solver FLUENT. The individual effects of each component on the flow are investigated by simulating the isolated fuselage and the isolated rotor configurations. Then, the rotor-fuselage interaction problem is analyzed. Azimuthal variations of the flap and pitch motions of the blades are prescribed a priori as a first-order Fourier series through a user-defined function feature of the code. The prescribed blade motion may result in meshes with undesirable grid qualities, which may lead to unphysical solutions. A non-overset dynamic mesh motion method that applies volume mesh deformation and cell remeshing within a priori organized block mesh structure is used to accommodate the rigid blade motion. The remeshing is performed when the grid deformation is more than a predefined skewness value of 0.95. The near...

Design, analysis, and implementation of extra low air-gap single-phase axial-flux induction motors for low-cost applications

Summary In this paper, design and prototyping of two-speed capacitor-run single-phase axial-flux induction motor (AFIM) for direct-drive applications is presented. The proposed structure has single stator-single rotor configuration with high magnetic pull between the stator and rotor, which may compel rotor to lock. Although the most efficient method to overcome this problem is using a second rotor or stator in the mirror with the first one, it is not applicable in low-cost applications. So, in this paper, two new and fast construction techniques are proposed to fabricate an AFIM with extra low air-gap length and minimum cost. Beside design and optimization process, a thermal equivalent circuit considering radial and lateral heat transfers is proposed. Then different losses and thermal resistances are exactly calculated to estimate the temperature rise of different motor parts and the maximum specific magnetic and electric loadings. Then, motor performance is evaluated using three-dimensional time-stepping finite-element analysis. Finally, a comprehensive fabrication algorithm for AFIMs is presented, and a prototype of the studied motor is fabricated and tested. The experimental results validate the design, optimization, thermal model, and finite element simulations. Copyright © 2016 John Wiley & Sons, Ltd.

Saturation Effects on the Parameters of Interior Permanent Magnet Synchronous Motors with Different Rotor Configuration

The paper presents an investigation of the saturation and cross-saturation effects on the d-axis and q-axis reactance of the permanent magnet synchronous motors. Three configurations of the rotor are analyzed. It is shown that the magnetic flux distribution in the q-axis is greatly influenced by the saturation with the increase of the load and this changes the value of the torque load angle at a given output power.