Simulation Of Rotor Research Articles

Analyzing the use of pins in safety bearings

A new concept for safety bearings is analyzed: useful in emergency situations, it shall protect the bearing from destruction by the use of pins which impact with a disc, both capable of good energy dissipation. Results of work in progress are presented by validating partial stages of the development. Starting with a disc without shaft impacting on pins, the second stage being a vertical rotor with a clamped-free shaft that is limited by pins to a final stage where the gap due to the pins is controlled by step motors. In the first stage, a numerical simulation performed by the Runge–Kutta method is validated with experimental results. Simulations of rotor orbits due to the impact condition are analyzed and compared to data obtained from the experiment giving a good perspective on the use of pins. The contact interaction between rotor and pins uses an elastic-dissipative model. In addition, the variation of energy content of the disc after each contact is considered. Actually, the validation of the clamped-free rotor is done. The main goal is to design an automatic system with the capability of changing the gap when necessary in order to avoid the rotor colliding with the inner part of the bearing.

An actuator line method with novel blade flow field coupling based on potential flow equivalence

AbstractA Reynolds‐averaged Navier–Stokes‐embedded actuator line model for wind and tidal turbine simulation has been implemented and validated using the National Renewable Energy Laboratory Phase VI wind tunnel experimental results. Actuator line models, first introduced by Sørensen and Shen, represent the blades virtually, enabling time‐resolved rotor simulations without requiring blade boundary layer discretization. This results in a lower computational cost than blade‐resolved simulations while preserving the predominant features of the rotor flow. The present method introduces a novel technique, based on potential flow equivalence, to determine the local flow velocity at the blade, and a method of projecting the resulting momentum sources to the flow field. These methods circumvent the requirement for smearing techniques used in other actuator line models. In addition, the model is adapted for use with an unstructured mesh, thereby enabling turbine components such as the tower and nacelle to be explicitly included in the domain. The model is validated through comparison of computed integrated loads and local force coefficients with the National Renewable Energy Laboratory Phase VI experimental results. Results for local force coefficients indicate general agreement with experiment, although discrepancies associated with three‐dimensional flow effects are observed at the tips. Copyright © 2014 John Wiley & Sons, Ltd.

Real-time simulation of aeroelastic rotor loads for horizontal axis wind turbines

Wind turbine drivetrain research and test facilities with hardware-in-the-loop capabilities require a robust and accurate aeroelastic real-time rotor simulation environment. Recent simulation environments do not guarantee a computational response at real-time. Which is why a novel simulation tool has been developed. It resolves the physical time domain of the turbulent wind spectra and the operational response of the turbine at real-time conditions. Therefore, there is a trade-off between accuracy of the physical models and the computational costs. However, the study shows the possibility to preserve the necessary computational accuracy while simultaneously granting dynamic interaction with the aeroelastic rotor simulation environment. The achieved computational costs allow a complete aeroelastic rotor simulation at a resolution frequency of 100 Hz on standard computer platforms. Results obtained for the 5-MW reference wind turbine by the National Renewable Energy Laboratory (NREL) are discussed and compared to NREL's fatigue, aerodynamics, structures, and turbulence (FAST)- Code. The rotor loads show a convincing match. The novel simulation tool is applied to the wind turbine drivetrain test facility at the Center for Wind Power Drives (CWD), RWTH Aachen University to show the real-time hardware-in-the-loop capabilities.

Aerodynamic Thrust Modelling in Wave Tank Tests of Offshore Floating Wind Turbines Using a Ducted Fan

Wave tank testing of scaled models is standard practice during the development of floating wind turbine platforms for the validation of the dynamics of conceptual designs. Reliable recreation of the dynamics of a full scale floating wind turbine by a scaled model in a basin requires the precise scaling of the masses and inertias and also the relevant forces and its frequencies acting on the system. The scaling of floating wind turbines based on the Froude number is customary for basin experiments. This method preserves the hydrodynamic similitude, but the resulting Reynolds number is much lower than in full scale. The aerodynamic loads on the rotor are therefore out of scale. Several approaches have been taken to deal with this issue, like using a tuned drag disk or redesigning the scaled rotor.This paper describes the implementation of an alternative method based on the use of a ducted fan located at the model tower top in the place of the rotor. The fan can introduce a variable force that represents the total wind thrust by the rotor. A system controls this force by varying the rpm, and a computer simulation of the full scale rotor provides the desired thrust to be introduced by the fan. This simulation considers the wind turbine control, gusts, turbulent wind, etc. The simulation is performed in synchronicity with the test and it is fed in real time by the displacements and velocities of the platform captured by the acquisition system. Thus, the simulation considers the displacements of the rotor within the wind field and the calculated thrust models the effect of the aerodynamic damping. The system is not able currently to match the effect of gyroscopic momentum.The method has been applied during a test campaign of a semisubmersible platform with full catenary mooring lines for a 6MW wind turbine in scale 1/40 at Ecole Centrale de Nantes. Several tests including pitch free decay under constant wind and combined wave and wind cases have been performed. Data from the experiments are compared with aero-servo-hydro-elastic computations with good agreement showing the validity of the method for the representation of the scaled aerodynamics. The new method for the aerodynamic thrust scaling in basin tests is very promising considering its performance, versatility and lower cost in comparison with other methods.

Comparison of two LES codes for wind turbine wake studies

For the third time a blind test comparison in Norway 2013, was conducted comparing numerical simulations for the rotor Cp and Ct and wake profiles with the experimental results. As the only large eddy simulation study among participants, results of the Technical University of Denmark (DTU) using their in-house CFD solver, EllipSys3D, proved to be more reliable among the other models for capturing the wake profiles and the turbulence intensities downstream the turbine. It was therefore remarked in the workshop to investigate other LES codes to compare their performance with EllipSys3D. The aim of this paper is to investigate on two CFD solvers, the DTU's in-house code, EllipSys3D and the open-sourse toolbox, OpenFoam, for a set of actuator line based LES computations. Two types of simulations are performed: the wake behind a signle rotor and the wake behind a cluster of three inline rotors. Results are compared in terms of velocity deficit, turbulence kinetic energy and eddy viscosity. It is seen that both codes predict similar near-wake flow structures with the exception of OpenFoam's simulations without the subgrid-scale model. The differences begin to increase with increasing the distance from the upstream rotor. From the single rotor simulations, EllipSys3D is found to predict a slower wake recovery in the case of uniform laminar flow. From the 3-rotor computations, it is seen that the difference between the codes is smaller as the disturbance created by the downstream rotors causes break down of the wake structures and more homogenuous flow structures. It is finally observed that OpenFoam computations are more sensitive to the SGS models.

Flow-driven rotor simulation of vertical axis tidal turbines: A comparison of helical and straight blades

In this study, flow-driven rotor simulations with a given load are conducted to analyze the operational characteristics of a vertical-axis Darrieus turbine, specifically its self-starting capability and fluctuations in its torque as well as the RPM. These characteristics are typically observed in experiments, though they cannot be acquired in simulations with a given tip speed ratio (TSR). First, it is shown that a flow-driven rotor simulation with a two-dimensional (2D) turbine model obtains power coefficients with curves similar to those obtained in a simulation with a given TSR. 3D flowdriven rotor simulations with an optimal geometry then show that a helical-bladed turbine has the following prominent advantages over a straight-bladed turbine of the same size: an improvement of its self-starting capabilities and reduced fluctuations in its torque and RPM curves as well as an increase in its power coefficient from 33% to 42%. Therefore, it is clear that a flow-driven rotor simulation provides more information for the design of a Darrieus turbine than a simulation with a given TSR before experiments.

A similitude method and the corresponding blade design of a low-speed large-scale axial compressor rotor

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper. The first step of this method is the derivation of similarity criteria for tip clearance flow, on the basis of an inviscid model of tip clearance flow. The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor. According to the aerodynamic and geometric parameters of the target compressor rotor, a large-scale low-speed rotor blade is designed with an inverse blade design program. In order to validate the similitude method, the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points. It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model. These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.

Effects of Tip Clearance Size on Flowfield in a Low-Speed Axial Compressor Rotor

The simulations of a low-speed axial compressor rotor with two tip clearance sizes, 0.5% chord and 1.5% chord, were performed in the study. Overall performance and detailed flow fields at near stall condition are analyzed. The results show that the rotor stall occurs at higher mass flow condition with large tip clearance. For the small tip clearance the tip leakage vortex and the corner vortex both contribute significantly to the rotor stall, and the interaction between the vortices promotes the stall generation. While for the large tip clearance the tip leakage vortex plays a primary role, and the vortices interaction is ignorable.

Steady and Unsteady Flow inside a Centrifugal Pump for Two Different Impellers

Various parameters affect the pump performance. The impeller outlet diameter, the blade angle, the blade number and casing are the most critical. In this study, experimental and numerical investigations are carried out for two impellers different in diameter with the same casing. Numerical simulation of the whole machine (impeller, vaneless diffuser and volute) is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady state calculations and the rotor/stator model is used for the unsteady one. The model pump has a design rotation speed 2800 rpm and two impellers with 7 blades (70 mm and 105 mm outer diameters). For each pump, the performance measurements are measured and CFD analyses are carried out for different flow rates for steady and unsteady calculations. Finally, a comparison between the CFD and performance measurement is fairly good.

Vibration quenching in a large scale rotor-bearing system using journal bearings with variable geometry

Abstract In large scale rotating machinery the resonance amplitude during the passage through resonance is a matter of consideration because of its influence in the surrounding environment of the rotational system and foundation. In this paper, a variable geometry journal bearing (VGJB), recently patented, is applied for the mounting of a large scale rotor bearing system operating at the range of medium speed. The simulation of the rotor-bearing system incorporates a recent method for simulation of a multi-segment continuous rotor in combination with nonlinear bearing forces. The use of the current bearing gives results that encourage the use of such a bearing in rotating machinery since the vibration amplitude during the passage through the critical speed can be reduced up to 60–70%. In the presented study, the developed amplitude and the rotor stresses are severely reduced compared to those of the system with normal cylindrical journal bearings during a virtual start up of the system.

Rotor Fault Diagnosis and Simulation Based on LabVIEW

A fault diagnosis system based on LabVIEW is researched to analyze the rotating machinery fault. By developing data acquisition, signal analysis, processing and simulation, pattern recognition and fault diagnosis modules, this system can automatically measure and identify the shaft orbit of a rotor and get fault results. A pattern recognition method on the basis of the invariant moment algorithm is studied with LabVIEW and used to recognize shaft orbit shapes. The experimental results show that the shaft orbit of a rotor can be identified through invariant moment calculation. Because the shape of the shaft orbit of the rotor is close to the ellipse the main fault is imbalance. The fault result is proved to be correct by spectrum analysis. This study is helpful to develop a online fault diagnosis system based on LabVIEW.

BEM Simulation and Performance Analysis of a Small Wind Turbine Rotor

The blade element momentum (BEM) method is a popular tool for predicting the performance of wind turbine rotors. This study investigated the impact of including factors such as tip loss, hub loss and drag coefficients in BEM simulations of a Bergey XL.1 small wind turbine. The Bergey XL.1 has constant chord, untwisted blades that are challenging to simulate owing to the large variation in angle of attack along the blade during operation. Methods of including post-stall airfoil characteristics, and three wake approaches (Buhl, Glauert and Wilson-Walker) were also examined. BEM simulations were consistent with test data from a Bergey XL.1 collected using a vehicle-based platform. Including tip losses, drag coefficients and wake effects in the BEM simulation had a significant impact on predicted performance, while the effect of including hub loss was negligible. The results illustrate that BEM methods can predict the performance of small wind turbine rotors.

Numerical analysis of flow field around NREL Phase II wind turbine by a hybrid CFD/BEM method

In this study, a mixed CFD (Computational Fluid Dynamics) and BEM (Blade Element Momentum Method) analysis is implemented for simulating the flow field around a wind turbine rotor to predict the aerodynamic performance such as the Power Curve diagram and the forces and moments imposed on the rotor blades that are essential in structure and/or aeroelastic design. The present approach requires considerable less computational time and memory than three-dimensional simulation of a wind turbine rotor by merely CFD methods, while retains the desirable accuracy. This work consists of two parts: 1—calculating 2D aerodynamic coefficients of several spanwise sections of the blades by CFD methods, using Fluent commercial software. 2—Simulating 3D-flow field through the wind turbine rotor using the BEM technique. To validate the current approach, the Combined Experiment Phase II Horizontal Axis Wind Turbine known as NREL Phase II Rotor is used. The comparison indicates that the combination of CFD and BEM methods is much faster than merely CFD approaches while accurate enough to be used for engineering purposes.

Sliding Mode Control of Flexible Rotor Based on Estimated Model of Magnetorheological Squeeze Film Damper

By using magnetorheological (MR) fluid as the lubricating oil in a traditional squeeze film damper (SFD), one can build a variable-damping SFD, thereby controlling the vibration of a rotor by controlling the magnetic field. This study aims to control the vibration of a flexible rotor system using a magnetorheological squeeze film damper (MR-SFD). In order to evaluate the performance of the damper, the Bingham plastic model is used for the MR fluid and the hydrodynamic equation of MR-SFD is presented. Usually, the numerical methods are necessary for solving this equation. These methods are too costly and time consuming, especially in the simulation of complex rotors and the implementation of model-based controllers. To fix this issue, an innovative estimated equation for pressure distribution in MR-SFD is presented in this paper. By integration of this explicit expression, the hydrodynamic forces of MR-SFD are easily calculated as an algebraic equation. It is shown that the pressure and forces, which are calculated from the introduced expression, are consistent with the corresponding results of the original equations. Furthermore, considering the structural and parametric uncertainties of the system, proportional-integral-furthermore controller (PID) and sliding mode controllers are chosen for reducing the vibration level of the flexible rotor system, which is modeled by the finite element method. The time and frequency responses of a flexible rotor in the presence of these controllers show a good performance in reducing vibration of the shaft's midpoint, although near the rotor's critical speed the results of the sliding mode controller (SMC) are better than the corresponding results of the PID controller. The last part of this article is devoted to an analysis of the system's uncertainties. The results of the open loop system indicate that changes in the stiffness coefficient of the elastic foundation and the temperature of the MR fluid (two uncertainties of the system) strongly affects the outputs while using the controllers well increases the robustness of the system. The obtained results indicate that both the PID and sliding mode controllers have good performance against the uncertainty of the stiffness coefficient, but for changes in the MR fluid's temperature, the SMC presents better outputs compared to the PID controller, especially for high rotational speeds.

UAV Mathematical Modeling, Analysis and Fuzzy Controller Design

The objective of this work is to introduce the design, simulation and control of a quad rotor, equipped with Inertial Sensors, as an example of unmanned aerial vehicle. To fulfill this objective a mathematical model of the quad rotor has been developed, using Newton-Euler Formulation. The simulation of the model and controller design is developed in MATLAB/Simulink environment. It is intended to make the model flexible and easily modified to be used with any similar model. In order to evaluate the real model mass and mass moment of inertia, a solid model had been built using Autodesk Inventor software package. To validate the proposed model output results, a comparison with published research has been carried out which showed a good agreement. Finally, a fuzzy controller is designed to control the quad rotor altitude and the three Euler angles of roll, pitch and yaw. The controller showed a good controllability within a certain range of the controlled parameter.

Lagwise dynamic analysis of a variable speed rotor

An aeroelastic simulation of a variable speed rotor in forward flight is conducted to investigate its dynamic characteristics in steady and transient states. The system equations of motion are derived based on the generalized force formulation by using Hamiltonʼs principle. The periodic and transient aeroelastic responses of a four bladed stiff in-plane rotor are analyzed to investigate the loads transfer phenomenon in the lagwise direction. The transient lagwise moment increases sharply during the 2/rev resonance crossing. This high transient load in rotating frame is not transferred to the fixed frame. Flap motion has vital contribution to the periodic and transient lagwise loads. The 1/rev flapping motion in the rotating frame can excite the 4/rev rotor torque in the fixed frame due to the Coriolis force. The faster the blade crosses the resonance area, the smaller the transient lagwise loads and the higher the rotor torque. For the dissimilar rotor with 5% reduction of one blade mass at 60% to 70% rotor radius, the unbalanced 2/rev lag moment in the rotating frame is transferred to the fixed frame as the 2/rev rotor torque. Increasing blade lag critical damping from 1% to 5% can reduce the peak–peak lagwise root bending moment by 64.9%, and the rotor torque is reduced to the level without dissimilarity. The dynamics of a stiffer rotor during the 4/rev resonance crossing is also addressed.

Higher harmonic pitch link loads reduction using fluidlastic isolators

Fluidlastic isolators are proposed for higher harmonic pitch link loads reduction in helicopter rotors. An aeroelastic simulation of a soft in-plane rotor in high forward flight is conducted to investigate the dynamic characteristics of the coupled rotor and fluidlastic isolators. Using Hamilton’s principle, the system equations of motion are derived based on the generalized force formulation. The results indicate that the application of the fluidlastic isolator can reduce the 4/rev pitch link load by 98.9% in high forward flight with small variations in the other harmonic loads. The isolator has significant influence on the higher harmonic torsional rotation of the blade tip. Increasing the tuning port area ratio can significantly reduce the tuning mass with little variation of the isolation ability. Within 5% variation of the normal rotor speed, the 4/rev isolator can reduce more than 80% of the 4/rev pitch link load. The effects of isolator’s damping, forward speed, and thrust on the performance of the isolator are also studied. The ability to isolate other higher harmonic pitch link loads is also investigated.

Bipolar Electrogram Shannon Entropy at Sites of Rotational Activation

Background— The pivot is critical to rotors postulated to maintain atrial fibrillation (AF). We reasoned that wavefronts circling the pivot should broaden the amplitude distribution of bipolar electrograms because of directional information encoded in these signals. We aimed to determine whether Shannon entropy (ShEn), a measure of signal amplitude distribution, could differentiate the pivot from surrounding peripheral regions and thereby assist clinical rotor mapping. Methods and Results— Bipolar electrogram recordings were studied in 4 systems: (1) computer simulations of rotors in a 2-dimensional atrial sheet; (2) isolated rat atria recorded with a multi-electrode array (n=12); (3) epicardial plaque recordings of induced AF in hypertensive sheep (n=11); and (4) persistent AF patients (n=10). In the model systems, rotation episodes were identified, and ShEn calculated as an index of amplitude distribution. In humans, ShEn distribution was analyzed at AF termination sites and with respect to complex fractionated electrogram mean. We analyzed rotation episodes in simulations (4 cycles) and animals (rats: 14 rotors, duration 80±81 cycles; sheep: 13 rotors, 4.2±1.5 cycles). The maximum ShEn bipole was consistently colocated with the pivot zone. ShEn was negatively associated with distance from the pivot zone in simulated spiral waves, rats, and sheep. ShEn was modestly inversely associated with complex fractionated electrogram; however, there was no relationship at the sites of highest ShEn. Conclusions— ShEn is a mechanistically based tool that may assist AF rotor mapping.

Simulating 3D Flows Passing Wind Turbine Rotors with a Domain Decomposition Method on a Moving Domain

Accurate numerical simulations of flows around wind turbines play an important role in rotor blades design and operation control. The computation is very challenging because of the large size of the blades, the large fluids domain, the complex moving geometry, and the high Reynolds number. A popular method is the blade element momentum method which is relatively easy to implement, but has low fidelity. More recently, some high fidelity methods have been developed for the wind turbine simulations, such as Reynolds averaged Navier-Stokes methods, large-eddy simulations and direct numerical simulations (DNS). In this paper, we study DNS for flows passing 3D wind turbine rotors. The flow in the moving domain is modeled by the 3D unsteady incompressible Navier-Stokes equations in the arbitrary Lagrangian-Eulerian form. A stabilized bi-linear moving mesh finite element method, based on the unstructured tetrahedron mesh, is introduced to discretize the problem in space, and an implicit scheme is used to discretize the temporal variable. A parallel Newton-Krylov method with a domain decomposition type preconditioner is applied to solve the fully coupled nonlinear algebraic system at each timestep. We mainly focus on the performance of the domain decomposition preconditioner. To understand the efficiency of the algorithm, we test the software on a supercomputer for the simulation of a NREL 5MW wind turbine rotor. The numerical results show that the newly developed algorithm is scalable with thousands of processors for problems with tens of millions of unknowns.

Online Adaptive Fuzzy Neural Identification of a Piezoelectric Tube Actuator System

A coupled actuator-flap-circuit system model and its online identification are presented. The coupled system consists of a piezoelectric tube actuator, a trailing-edge flap, and a series R-L-C circuit. The properties of the coupled system are examined using a Mach-scaled rotor simulation on hovering state. According to the high nonlinear hysteretic characteristics of the coupled system, the generalized dynamic fuzzy neural networks (GD-FNN) implementing Takagi-Sugeno-Kang (TSK) fuzzy systems based on extended ellipsoidal radial basis function (EBF) neural network is used to identify the coupled system. The structures and parameters are adaptive adjusted during the learning process, and don’t need too much expert experiences. Simulation studies show that the piezoelectric tube actuator has high authority with a broad frequency bandwidth, satisfies the requirements for helicopter vibration reduction; GD-FNN has a high learning speed, the final networks have a parsimonious network structure and generalize well, possessing broad application prospects in the helicopter vibration reduction.