Simulation Of Rotor Research Articles

Integration of Hydraulic Lag-Damper Models with Helicopter Rotor Simulations

This paper describes the design and integration of a generic hydraulic lag-damper model into an industrial helicopter rotor simulation code. The paper explains the details of an implementation of a computational platform integrating the rotor simulation code with a damper model. A parametric physical damper model is developed here in order to allow physically consistent improvements to helicopter performance studies. Further, this model enables investigating novel uses of lag dampers, such as for vibration reduction. The physical consistency of this work is demonstrated in two case studies. In the first instance, the damper laboratory experimental data are used for a correlation and validation study illustrating the capability of the modeling methodology to generate the model with refined response predictions. The second case study considers a physics-based lag-damper model with an active flow restrictor based on a modified version of the validated passive damper model. This realistic model is shown to be able to induce physically consistent changes in the nonrotating rotor-hub responses. A parametric study with harmonic three-per-revolution flow-restrictor activity suggests that significant load changes are possible in the nonrotating in-plane hub forces and moment. The study also shows possible tradeoffs such as high damper peak forces corresponding to the reduced in-plane forces. Therefore, the presence of these tradeoffs will require the use of constrained optimization formulation to address more complex problem configurations.

Laboratory experiments on mountain‐induced rotors

AbstractIn this article we present some laboratory experiments on stratified flows over isolated obstacles which were aimed at the simulation of atmospheric rotors as induced by the interaction of mountain waves and the boundary layer. For this purpose we modified the classical tank experiments on mountain waves performed with constant density gradients by introducing an elevated density inversion above the obstacle height. This kind of inversion seems to favour very much the development of mountain‐induced rotors as was shown in recent numerical simulations. In fact our experimental set‐up was guided by the simulations of Vosper, which provided systematically the upstream conditions under which mountain rotors are expected. We were able to confirm the results from these numerical simulations over a wide range of parameters. Detailed analyses of flow structures for some selected cases, as obtained by particle image velocimeter analysis, are presented. Copyright © 2010 Royal Meteorological Society

4A16 Model-Based Condition Monitoring of an Auxiliary Bearing following Contact Events

Auxiliary bearings are used in many rotor systems, e.g. those with active magnetic bearings. In a case of a contact with the auxiliary bearing, high impact forces and wear are possible. Therefore the auxiliary bearings have to be replaced after a certain number of contact events. This is very costly and often needs complete dismantling of the rotor system. In this paper a concept for model based condition monitoring of an auxiliary bearing is developed. The rotor system is modeled in a multibody simulation environment, including the contact to the auxiliary bearing and various fault parameters. After contact (drop or bouncing contact) occurs in the real rotor system, an identification algorithm analyses the measuremental data of the contact event and determines the fault which occurred. Based on the results of the identification algorithm, an optimization tool aligns the rotor simulation with the measurement by varying the fault parameters. After the alignment of the simulation, the simulation results are evaluated. The contact forces are evaluated against location on the surface of the auxiliary bearing and are stored. This procedure is performed after each contact event. Hence, a weighting of the load over the surface of the auxiliary bearing is gained. Depending on the material and structure, these data can be used for a life-time estimation of the auxiliary bearing. Using an active magnetic bearing test facility, the monitoring system has been successfully tested.

Design for Motor Controller in Hybrid Electric Vehicle Based on Vector Frequency Conversion Technology

Motor and its control technology are one of the main components of Hybrid Electric Vehicle (HEV). To meet HEV′s fast torque response, vector control algorithm based on rotor flux‐oriented and simulation model is concerned and modular designs for controller′s hardware and software are presented in the paper in order to build a platform to achieve the vector control of asynchronous induction motor. Analyze the controller′s electromagnetic compatibility, introduce the corresponding antijamming measures to assure the normal operation of the electromagnetic sensitive devices such as CAN bus; experiment proves that the measure is practical and feasible. On the basis of the control logic correct, such as improving CAN bus communication reliability, assuring power‐on sequence and fault treatment, carry on the motor bench experiment, test its static properties, and adjust the controller parameters. The experimental results show that the designed driving system has the performance of low speed and high torque, a wide range of variable speed and high comprehensive efficiency.

Lagwise Loads Analysis of a Rotor Blade with an Embedded Chordwise Absorber

An aeroelastic simulation of a stiff in-plane hingeless rotor in forward flight is conducted to evaluate the feasibility of reducing lagwise root loads via an embedded absorber within the blade. A finite element analysis based on a moderate deflection beam model is employed to capture the flap, lag, and torsion deflections of the rotor blade. The mass-spring-damper absorber system is simulated as a one-degree-of-freedom rigid body with chordwise motion. By using the Hamilton principle, system equations of motion are derived based on the generalized force formulation. Dynamic responses are calculated to investigate the potential of the absorber for in-plane loads reduction. Parametric studies are conducted to explore the influence of the absorber on the dynamic characteristics of the rotor blade. From the aeroelastic analysis of the blade-absorber system, results indicate that placing an embedded absorber in the blade chordwise direction can decrease the 1 and 2/rev lagwise root bending moments by about 50 and 90%, respectively, under large load states. The effects of absorber frequency, absorber damping, chordwise position of the absorber, rotor thrust, forward speed, and trim condition are also studied.

Modeling and simulation of wind turbine Savonius rotors using artificial neural networks for estimation of the power ratio and torque

The power factor and torque of wind turbines are predicted using artificial neural networks (ANNs) based on experimental data which have been collected for seven prototype vertical Savonius rotors tested in a wind tunnel. In this research, the rotors with different configurations were located in the wind tunnel and the tests were repeated 4–6 times in order to reduce errors. Since the Reynolds number has a negligible effect on power ratio, therefore tip speed ratio (TSR) is the main input parameter to be predicted in neural network. Also, the rotor’s power factor and torque were simulated for different tip speed ratios and different blade angles. The simulated results show a strong capability for providing reasonable predictions and estimations of the maximum power of rotors and maximizing the efficiency of Savonius turbines. According to artificial neural nets simulations and the experimental results, increasing tip speed ratio leads to a higher power ratio and torque. For all the tested rotors, a maximum and minimum amount of torque has happened at angle of 60 o and 120 o, respectively.

Simulation and prediction of main rotor, tail rotor, and engine parameters from flight tests

In the framework of this research project, the main rotor torque, tail rotor torque, engine torque, and main rotor speed of a helicopter in forward flight are estimated by using a state-space model from flight tests data. The state-space model inputs are non-linear terms made of combinations of pilot controls and helicopter states. The model simulates the helicopter outputs while knowing the states and controls at all times. It was also implemented as a prediction tool, for possible use in an envelope protection flight control system in which the states, controls, and outputs are known at the present time, and predict the future helicopter states and controls following to pilot controls time history. The state-space model parameters are identified by using the subspace identification method, a relatively recent non-iterative algorithm, which constructs an observability matrix from input and output data and uses this matrix to obtain the state-space matrices. The obtained parameters are then optimized with the Levenberg—Marquardt output-error method. A comparison of the results with and without optimization is also conducted. The results show that the subspace method provides a good estimate of the outputs within the FAA tolerance bands and that these results can further be improved by use of the minimization algorithm. The generated model using the subspace method is found to be very good for prediction applications, which makes it a promising model for flight control simulator applications.

Tip Vortex Conservation on a Helicopter Main Rotor Using Vortex-Adapted Chimera Grids

This paper presents a method to improve the tip vortex conservation in a computational fluid dynamics simulation of a helicopter main rotor. Our approach uses vortex-adapted Chimera child grids to achieve a local refinement of the grid in the vicinity of the vortex and thus reduce the numerical dissipation of the vortex. The method is applied to the higher-harmonic-control aeroacoustic rotor test case to evaluate its potential with respect to the prediction of blade-vortex interaction airloads. To allow a meaningful comparison with the experimental data, the rotor is trimmed for thrust, as well as for longitudinal and lateral mast moments, using weak fluid-structure coupling with a flight mechanics code. We obtained a good overall agreement with the experimental data for both aerodynamics and blade dynamics. The effect of the improvement in tip vortex conservation is demonstrated by comparison with simulations without Chimera refinement and with the experimental results. It turned out that a very fine grid resolution in the vicinity of the vortex is necessary to capture the blade-vortex interaction airloads. The required grid resolution was provided by a refinement of the vortex-adapted grids, allowing for a very good reproduction of the blade-vortex interaction airloads, especially on the retreating blade side.

Dynamic simulation of a flexible rotor during drop on retainer bearings

Active magnetic bearings (AMBs) present a technology which has many advantages compared to traditional bearing concepts. However, they require retainer bearings in order to prevent damages in the event of a system failure. In the drop-down when the rotor falls from the magnetic field on the retainer bearings, the design of the retainer bearings has a significant influence on the dynamic behavior of the rotor. In this study, the dynamics of an active magnetic bearing supported rotor during the drop on retainer bearings is studied employing a detailed simulation model. The retainer bearings are modeled using an accurate ball bearing model which takes into account damping and stiffness properties, oil film, inertia of rolling elements and friction between races and rolling elements. The model of a flexible rotor system accounts for unbalances as well as stiffness and damping properties of the support. In this study, the flexibility of the rotor is described using the finite element approach with the component mode synthesis. This study sheds light on the effects of a number of modes used in the component mode synthesis on the accuracy of simulated responses during the drop-down. In addition, the effect of different friction models on the behavior of the rotor is examined.

Shock wave strength reduction by passive control using perforated plates

Strong, normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a source of a high-speed impulsive helicopter noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes an extended validation against the experimental data for relatively simple geometries of transonic nozzles. It is a first step towards a full simulation of a helicopter rotor equipped with a noise reducing passive control device in hover and in forward flight conditions.

Design and sensitivity analysis of a reduced-order rotor flux optimal observer for induction motor control

This paper aims to give simple and effective design criteria of rotor flux reduced-order observers for motion control systems with induction motors. While the observer is optimized for rotor and stator resistance variations, a sensitivity analysis is carried out in the presence of variations of all the motor parameters by means of either transfer function from true to observed rotor flux or simulation in a MATLAB-SIMULINK environment, assuming the voltages supplying the motor to be different from those supplying the observer. The sensitivity analysis makes it possible to establish design criteria for the observer in question. The behaviour of the proposed reduced order observer is compared with current model and voltage model observers. Experimental results are also given, with the dual aim of confirming the validity of this design method and showing that the observer can be implemented on microprocessor-based devices.

Application of a parallel rotor CFD code on HPCx

Aspects of parallel simulation of rotor flows are considered. These flows can be extremely expensive for a compressible finite-volume CFD code, and parallelisation can be essential. The award of HPCx time through the UK Applied Aerodynamics Consortium has allowed large rotor simulations to be performed and wake grid dependence to be investigated. However, there are several issues that need to be investigated when considering very large simulations, including the grid generation process, the parallel flow-solver, including an effective mesh motion approach, and visualisation options. Details of these are presented here, with particular emphasis on the flow-solver parallel performance. A detailed performance analysis of the unsteady flow-solver has been undertaken and the code optimised to improve parallel performance, and details of the parallel scaling performance are presented. The parallel scaling of the code is very good on all the HPC architectures tested here, and this has been recognised by an HPCx Gold Star Capability Incentive award. Results of simulation of a fourbladed lifting rotor in forward flight are also presented, for two mesh densities. It is shown that the solution computed on the serial limit on mesh size, around four million cells, exhibits excessive diffusion, and is of limited use in terms of detailed flow features. The results on a very fine mesh, 32 million cells, have shown a much better solution resolution, and it is also demonstrated that the λ2 vortex core visualisation option is extremely useful.

Influence of rotor’s radial rub-impact on imbalance responses

Abstract The response of rotor’s mass imbalance is synchronous vibration proportional to mass, mass eccentricity, and the square of rotating speed. But in the presence of rotor’s radial rub-impact, it does not keep this property. It is observed from numerical simulations of rotor’s radial rub-impact that the magnitude of imbalance response in power spectrum is affected by rotor’s radial rub-impact. In the absence of radial rub-impact, the magnitudes of both lateral and torsional responses maintain constant. But in the presence of radial rub-impact, the magnitude of lateral response goes down all the way to a bottom while that of torsional response goes up all the way to a roof, as radial rub-impact grows strong. These properties can be used for the diagnostics of rotor’s radial rub-impacts.

Simulation of rotor’s axial rub-impact in full degrees of freedom

Abstract Axial rub-impact problem scarcely discussed in the previous literature is investigated based on a full-degree-of-freedom Jeffcott rotor. An axial rub-impact force model corresponding to all the six degrees of freedom is developed according to Coulomb’s friction law. A rotordynamic model of a rotor with unbalances and axial rub-impact is established using Lagrangian equation, with the integration of the axial rub-impact force model into it. The dynamic responses are obtained using ODE solvers in MATLAB. The dynamic behaviors of the rotor are demonstrated by means of waveforms, frequency spectrums, orbit trails, Poincare maps, and bifurcation diagrams. It is concluded that the dynamic behaviors of axial rub-impact are quite distinct from those of radial ones, and that the dynamic behaviors of axial vibration are essential to the diagnostics of axial rub-impact. In addition, an internal bending–torsion coupling phenomenon is disclosed.

Closed-form analysis of adjustable-speed drive performance under input-voltage unbalance and sag conditions

Voltage unbalance or sag conditions generated by the line excitation can cause the input rectifier stage of an adjustable-speed drive (ASD) to enter single-phase rectifier operation. This degradation of the input power quality can have a significant negative impact on the induction-machine performance characteristics. This paper provides an approximate closed-form analysis of the impact of line-voltage sags and unbalance on the induction-machine phase voltages, currents, and torque pulsations for a general-purpose ASD consisting of a three-phase diode bridge rectifier, a dc link, and a pulsewidth modulation (PWM) inverter delivering constant volts-per-hertz excitation. Attention is focused on the impact of the dominant second harmonic of the line frequency, which appears in the dc link voltage during the sag/unbalance conditions, neglecting the impact of the other higher order harmonics. In addition to the closed-form analytical results that assume constant rotor speed, both simulation and experimental results are presented, which confirm the key analytical results, including the dominance of the second harmonic in the resulting torque pulsations. The analytical results can be used as a valuable design tool to rapidly evaluate the approximate impact of unbalance/sag conditions on ASD machine performance.

Three-dimensional unsteady investigation of HP turbine stages

This article deals with a three-dimensional unsteady numerical simulation of the unsteady rotor—stator interaction in a HP turbine stage. The numerical approach consists of a computational fluid dynamics (CFD) parallel code, based on an upwind total variation diminishing finite volume approach. The computation has been carried out using a sliding plane approach with hybrid unstructured meshes and a two-equation turbulent closure. The turbine rig under investigation is representative of the first stage of aeronautic gas turbine engines. A brief description of the cascade, the experimental setup, and the measuring technique is provided. Time accurate CFD computations of pressure fluctuations and Nusselt number are discussed against the experimental data.

Helicoidal vortex model for steady and unsteady flows

A helicoidal vortex model is used to predict the flow past the blades of a wind turbine. As the tip speed ratio (TSR) varies, the environment in which the blades operate varies, and for low enough TSR, the local angle of attack α will be larger than ( α) Clmax, the incidence of maximum lift. The problem becomes highly nonlinear and it is shown that adding an artificial viscosity term to the equation allows the iterative algorithm to converge toward a smooth solution that is physically acceptable. The introduction of unsteady effects is useful to understand the cyclic forces and moments due to yaw or tower interaction, both for the design of blades to account for fatigue and for power output prediction. The 2-D impulsively plunging plate problem is solved with a semi-implicit scheme and the integral and numerical solutions compared and shown to be in excellent agreement. A 2-D test case to study the convection of a periodic shedding of vorticity downstream of a blade element is analyzed using the same semi-implicit algorithm and a stretched mesh similar to that used to model a turbine vortex sheet. The scheme captures accurately the vorticity distribution in the wake. Finally, the scheme is applied to the simulation of the NREL two-bladed rotor in yaw to assess the validity of the approach.

IRFOC induction motor with rotor time constant estimation modelling and simulation

PurposeTo provide a new and simple inverse rotor time constant identification method which can be used to update an indirect rotor field oriented controlled (IRFOC) induction motor algorithm.Design/methodology/approachTwo different equations are used to estimate the rotor flux in the stator reference frame. One of the equations is a function of the rotor time constant, rotor angular velocity and the stator currents. The other equation is a function of measured stator currents and voltages. The equation that uses the voltage and the current signals of the stator serves as reference model, however, the other equation works as an adjustable model with respect to the variation of the rotor time constant. Voltage signals used in the reference model equation are obtained from the measured DC bus voltage and the inverter gating signals. The proposed scheme is verified using a MATLAB/SIMULINK model for two different motors and experimentally using a DSP development tool (MCK 243) supplied by Technosoft S.A.FindingsThe proposed estimator was able to successfully track the actual value of the inverse rotor time constant for different load torque and speed operating conditions. Increased oscillations in the estimated inverse rotor time constant appeared at lower speeds (below 10 per cent of rated speed) due to drift in a PI regulator (used at the estimator side), which was tuned under rated operating conditions and using parameters nominal values.Research limitations/implicationsThis estimation scheme is limited when near zero speed operation is demanded; otherwise it gives a simple and practical solution. A suggested way out of this, is to provide a self‐tuning controller that can automatically adjust even for zero speed operation, or to automatically disconnect the estimator and take the most updated value as long as the operating speed is below a predetermined value.Originality/valueThis paper presented a new inverse rotor time constant estimator for an IRFOC induction motor application and in conjunction rotor flux was estimated without voltage phase sensors.

Numerical simulations of rotors, hydraulic jumps and eddy shedding in the Falkland Islands

AbstractHigh‐resolution three‐dimensional simulations of flows over East Falkland, South Atlantic, are presented. With a temperature inversion upwind, lee waves, rotors and hydraulic jumps are found to occur, giving rise to highly unsteady phenomena such as wakes and eddy shedding. Such flows are known to represent a significant hazard to aviation. Copyright © 2006 Royal Meteorological Society

Evidence for new bands in the 3ν1 and 4ν1 regions of propyne

Vibrationally mediated photodissociation and room-temperature photoacoustic (PA) spectroscopy have been used for obtaining action (monitoring the yield of H photofragments) and absorption spectra of the second (3nu(1)) and third (4nu(1)) C-H acetylenic stretches overtone regions in propyne. The band contours appearing in these regions seem mostly regular even though they are perturbed, as expressed by the origin shifts in different K components, splitting of the K structure, and splitting due to resonances between neighboring states. Symmetric rotor simulations of the band contours of the PA and action spectra allowed extraction of the molecular parameters and rough estimates for the homogeneous broadening arising from energy flow to the bath vibrational states. We particularly benefited from the reduced congestion in the jet-cooled action spectra and their simulations, which enabled observation of yet unknown features in the vicinity of the 3nu(1) and 4nu(1) states. Particularly, the emergence of the new state in the 3nu(1) region was confirmed by the action spectra monitored at several differing jet temperatures, suggesting that it is a dark state in IR vibrational excitation that becomes brighter in UV excitation to the upper electronic state. The monitored and Gaussian-fitted Doppler profiles point to the release of H photofragments with low average translational energies, attributed to an indirect dissociation process occurring after internal conversion to the ground electronic state and isomerization to allene.