Behavior Of Rotor Research Articles

Experimental and numerical investigation of the unbalance behavior of rigid rotors supported by spiral-grooved gas journal bearings

The forced response of rigid rotors, supported by herringbone-grooved gas journal bearings are investigated numerically and experimentally. The rotor configurations are varied by using end cylinders, attached at both sides of the shaft. Three rotors with different center of mass positions relative to the bearing locations are investigated for a variation of unbalance conditions. The numerical predictions by a quasi-linear unbalance approach and a full transient analysis are compared with experimentally obtained data. Different unbalance configurations are tested for validating the numerical models at orbital motions larger than 50% of the clearance and for bearing compressibility numbers of up to Λ=42. The investigation shows a maximum difference of 19.5% between nominal model predictions and experimental data at maximum orbital motions. The influence of the center of mass position on the rotor motion is proven to be significant and agrees with the numerical predictions. Further, the test unit is operated at different tilt angles, allowing to investigate the influence of static loading due to gravitational force on the forced response. It is found, that under different static loading, the rotor orbital motion remains unaltered and its influence can be neglected in the unbalance analysis.

Transient analysis of H-type Vertical Axis Wind Turbines using CFD

In this study, the effect of various parameters on the start-up and transient behavior of Darrieus straight-bladed Vertical Axis Wind Turbine (VAWT) was analyzed. Airfoil profile, angle-of-attack, and chord length were varied, yielding two optimal turbines, one for transient and another for steady performance. This optimization revealed that the chord length (solidity) has the most significant impact on the performance of the turbine undergoing both transient and steady operations. An examination of the contribution of drag and lift forces to the startup of these two optimized turbines shows that the drag has a positive contribution to the performance of the transient optimized turbine especially at high TSRs. The performance of the optimized turbines when subject to four different wind profiles: a real wind profile, and three distinct sinusoidal profiles was also assessed. At low average wind speeds, a high frequency of the incoming wind is favorable for allowing both optimized turbines to produce more power. The rotor behavior under dynamic loads was also investigated, demonstrating that the transient optimized turbine is more responsive and therefore easier to control. In addition, minimizing the inertia of the steady-optimized turbine significantly improves its startup characteristics, making it superior to its steady-optimized counterpart.

Experimental and Numerical Modal Analysis of a Bladed Rotor

The behavior of an asymmetric bladed rotor was investigated in this study. The bladed rotor which performs solid-solid, liquid-liquid, liquid-solid separation processes is part of the decanter machine and named as screw conveyor. The purpose of this study is to determine the dynamics of the rotor on the free conditions for future development of the asymmetric and blade assembled rotors. It is important for the designer to determine the natural frequencies of the bladed asymmetric rotor so that some precautions can be taken during the design of the machine and in the operating conditions of the machine. This study consisted of two parts. In the experimental one, the modal test of the bladed rotor was performed and in the numerical part, the modal analysis of the rotor was carried out under free-free boundary conditions using a simulation program based on the finite-element method. The natural frequencies of the blades and the rotor were obtained experimentally and numerically. It was found that the experimental results and numerical results were in good agreement. Besides, it was concluded that the two mode shape was equal to the transverse mode frequency of the rotor and blades and the following mode shapes correspond to the bending and torsion mode frequencies of the blades. Since the shape properties of the rotor and blades are different, it has been observed experimentally and numerically that their natural frequencies also differ.

Dynamic behavior of aluminium matrix composite rotor on bearing vibration

Aluminium composite drive shafts have been used in pickup trucks by various companies from many years. In this work, the effect of damping behavior of aluminium composite rotor is experimentally studied on bearing vibration. Three different types of Aluminium composite rotors manufactured by a stir casting method where molten metal is stirred for a particular time to mix reinforcements are examined in present work. The primary objective of this work is to determine the optimal composition of Aluminium composites out of 6 wt% Al2O3/Al 6061, 12 wt% Al2O3/Al 6061 and 18 wt% Al2O3/Al 6061. Experiments have been carried out on a customized rotor bearing test rig, and the captured data is analyzed using the OROS NV-Gate data collecting system through MATLAB code. It is observed that the 18 wt% % Al2O3/Al 6061 composite damped more vibration.

Experimental analysis on the effect of ring and rotor spun yarns for comfort characteristics of weft knitted fabric structures

This research study experimentally analyzed the effect of ring and rotor yarns which are 100% cotton spun yarn with 30s Ne count on the physical and comfort characteristics of single jersey, rib, and interlock knitted fabrics. The physical characteristics such as fabric Thickness, Tightness factor, Bursting strength, Abrasion resistance, and Pilling behavior were studied according to the ASTM Standard and statistically analyzed using Minitab software with ANOVA analysis. The Comfort characteristics were Thermal Insulation behavior (TIV), Water Vapor Permeability, and Air permeability; they were experimentally studied and reported. The results revealed that rotor spun yarn knitted fabrics demonstrated higher Thermal insulation behavior in the knitted structures when compared to ring spun yarn knitted fabrics. Ring spun yarn has better Abrasion resistance than rotor spun yarn, but the air permeability of the knitted fabric made from rotor spun yarn has better air permeability than ring spun yarn. The low stress mechanical properties are shear and compression behavior of ring and rotor spun yarn knitted fabrics were also critically analyzed. The results show that in a few cases the differences between regular fabric properties and the rotor and ring yarn fabric properties are quite significant, while marginal in other cases. However, the surface roughness values showed some interesting features of the knitted fabric structures.

Unsteady Aerodynamic Modeling and Analysis of Load Distribution for Helicopter Rotor Blades

The complexity of the kinematics and aerodynamics of rotors is a challenging problem for achieving accurate modeling for prediction of rotor loads. The present paper describes an unsteady aerodynamic model based on strip theory for the prediction of local aerodynamic loads on helicopter blades in translational flights. The proposed model accounts aerodynamically for unsteady behavior, poststall, leading-edge suction, and, structurally, local elastic torsion. Also, the local pitching moment coefficient is calculated according to the local parameters of both aerodynamic characteristics and unsteady angle of attack. A case study with published experimental data is selected to validate the model for the same operating conditions. The case is the 7A rotor high-speed test (point 312) performed in the French Space Lab’s (ONERA) S1MA wind tunnel in Modane-Avrieux, France. The proposed model is capable of predicting, qualitatively, the variation in both local normal force and pitching moment coefficients. Computational solver results are compared with experimental results to qualitatively clarify the physical differences between them. The main conclusion is that the proposed model calculations generally reflect the same trends as the test data, providing confidence in the ability to increase the model’s fidelity in calculating the aerodynamic behavior of rotors.

Reliable crack detection in a rotor system with uncertainties via advanced simulation models based on kriging and Polynomial Chaos Expansion

In this study the authors propose to take into account the nonlinear effects induced by the presence of a transverse crack to carry out vibratory monitoring and detect transverse cracks in rotating systems subject to model uncertainties. More precisely, we focus more particularly on the global complexity of the nonlinear dynamic behaviour of cracked rotors and the evolution of their harmonic components as a function of the parameters of a transverse breathing crack (its position and depth) when numerous uncertainties are considered. These random uncertainties correspond to random geometric imperfections (two disc thicknesses), random material properties (Young modulus and material density) and boundary conditions uncertainty (two bearing stiffnesses). The objective of the present work is to identify robust indicators capable of determining the presence of a crack and its status even though numerous uncertainties are present.To conduct such a study, an advanced surrogate modelling technique based on kriging and Polynomial Chaos Expansion (PCE) is proposed for the prediction of both the critical speeds and the harmonic components n× during passage through sub-critical resonances. An extensive study to ensure the validation of the surrogate models and a relevant choice of both the parametric and random Design of Experiments (i.e. kriging DoE and PCE DoE) is proposed. The proposed methodology is applied on a flexible rotor with a transverse breathing crack and subjected to random geometric imperfections and fluctuations in material properties of the rotor system.

REVIEW OF STUDIES ON THE CFD-BEM APPROACH FOR ESTIMATING POWER LOSSES OF ICED-UP WIND TURBINES

The application of computational fluid dynamics (CFD) in wind turbine design and analysis is becoming increasingly common in research on wind energy, resulting in a better knowledge of the aerodynamic behaviour of rotors. Due to the deformation of blade airfoils on account of icing, a significant drop in aerodynamic performance brings wind turbines to lose considerable portions of their productivity. Estimating power degradation due to icing via 3D simulation, although it is essential to capture the three-dimensional turbulence effects, is very costly in computational resources despite technological development it then becomes unfeasible when it comes to different operation scenarios to estimate icing originated power losses. The Quasi-3D simulation based on the CFD-BEM method is a practical alternative for generating wind turbines power curves. It showed effectiveness in predicting performance up to a certain level. More than few studies in the literature have adopted this approach to generate the power curve for both clean (un-iced) and iced-up wind turbines. However, the methodology was not adequately presented and discussed for wind turbine icing. This paper reviews the results of almost all the up-to-date published papers that approached this method, summarizing the findings and federates the research in that field to conclude with concrete facts and details that advance research in this domain.

Rotor Behavior and Friction Torque Characteristics of a Gerotor Pump Used for Automatic Transmissions

Abstract Rotor behavior may affect the torque characteristics of gerotor pumps, but the measurement of the behavior has received little attention. Thus, in this study, we measure the rotor behavior of a gerotor pump used for automatic transmissions under various operating conditions. The experiments revealed that the inner rotor rotated near the middle of the cover wall and casing sidewall, slightly tilted with respect to them. The outer rotor rotated in the vicinity of the casing sidewall and came closer to the sidewall with decreases in the dimensionless parameter μN/ΔP (where μ [Pa·s] is the oil viscosity, N [s−1] is the rotational speed, and ΔP [Pa] is the pressure difference). In addition, the eccentricity of the outer rotor was observed to increase with decreases in μN/ΔP. The inclination of the inner rotor and the approximation of the outer rotor to the casing sidewall may increase the driving torque of the pump. Taking the measured results on rotor behavior into account, a clear physical meaning is given to an existing mathematical model of viscous friction torque.

Quantifying impacts of shell augmentation on power output of airborne wind energy system at elevated heights

This work presents an in-depth design analysis of full-scale airborne wind energy systems. The prime focus is to quantify the impact of an airfoil-based shell carrying a 3-bladed rotor tailored to airborne needs. A high-fidelity numerical approach is used to gain insights into the design's performance by solving the numerical model of the resulting system. Three-dimensional simulations are carried out for a range of wind speeds and tip speed ratios to evaluate the aerodynamic behavior of the shell rotor by lifting the complete shell rotor assembly at elevated heights. The sensitiveness of the performance is rigorously analyzed in terms of the power coefficient (Cp,s), thrust coefficient, blockage effect, swallowed mass flow and bound circulation. An important finding highlights that the shell configuration is more efficient under optimal flow conditions in augmenting the power output. Besides, the augmented effects of the shell significantly contribute to the resulting Cp,s to outperform the Betz limit. Meanwhile, the net extracted power of the proposed design is 66% higher than that of the bare rotor. Finally, the simulation results suggest that the shell rotor operating close to the higher tip speed ratios behaves quite similar to that of the bare rotor configuration.

Numerical Study of Non-Linear Dynamic Behavior of an Asymmetric Rotor for Wave Energy Converter in Regular Waves

This study conducted a numerical investigation on the non-linear motion problems between a Salter duck-type rotor and large waves using CFD simulations. Regular waves of five different wave heights were generated. First, the linear motion of the rotor from the CFD simulation was verified by comparing it with the existing experimental and frequency domain analysis results. Then, a series of CFD simulations were performed to investigate the non-linear motions of the rotor. In the case of a lower wave height, the CFD simulation results were in good agreement with the experimental and frequency domain analysis results. However, as the wave height increased, the resonance periods were different in each other. In addition, the magnitudes of normalized pitch motions by the wave heights decreased as the wave heights increased. To investigate the aforementioned phenomena, the pitch motion equation was examined using separate CFD simulations. The results showed that changing the restoring moments induced changes in the maximum pitch motions and magnitudes of the normalized pitch motions. In the case of a higher wave height, non-linear phenomena and the changing restoring moments induced non-linear motion.

Dynamic Aeroelastic Response of Stall-Controlled Wind Turbine Rotors in Turbulent Wind Conditions

With the current global trend of the wind turbines to be commissioned, the next generation of state-of-the-art turbines will have a generating capacity of 20 MW with rotor diameters of 250 m or larger. This systematic increase in rotor size is prompted by economies-of-scale factors, thereby resulting in a continuously decreasing cost per kWh generated. However, such large rotors have larger masses associated with them and necessitate studies in order to better understand their dynamics. The present work regarding the aeroelastic behavior of stall-controlled rotors involves the study of the frequency content and time evolution of their oscillatory behavior. A wide range of experiments were conducted to assess the effects of rapid variations on the rotor’s operational conditions. Various gust conditions were tested at different wind speeds, which are represented by pulses of different intensities, occurring suddenly in an otherwise constant wind regime. This allowed us to observe the pure aero-elasto-inertial dynamics of the rotor’s response. A reduced-order characterization of the rotor’s dynamics as an oscillatory system was obtained on the basis of energy-transfer principles. This is of fundamental interest for researchers and engineers working on developing optimized control strategies for wind turbines. It allows for the critical elements of the rotor’s dynamic behavior to be described as a reduced-order model that can be solved in real time, an essential requirement for determining predictive control actions.

Adsorption and rotational barrier for a single azobenzene molecule on Au(111) surface* *Project supported by the National Natural Science Foundation of China (Grant Nos. 21961142021, 11774395, 91753136, and 11727902), the Beijing Natural Science Foundation, China (Grant No. 4181003), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant Nos. XDB30201000 and XDB28000000).

The orientation switching of a single azobenzene molecule on Au(111) surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments. Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory (DFT) calculation. The anchor phenyl ring prefers adsorption on top of the fcc hollow site, simulated by a benzene molecule on close packed atomic surface. The adsorption energy for an azobenzene molecule on Au(111) surface is calculated to be about 1.76 eV. The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site, illustrating a potential barrier about 50 meV. The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface.

Experimental Aerodynamic and Aeroelastic Investigation of a Transonic Compressor Rotor with Reduced Blade Count

This study investigates the aerodynamic and aeroelastic characteristics of a transonic axial compressor, focusing on blade count reduced rotor behavior. The analysis is based on experiments, conducted at the Transonic Compressor Darmstadt test rig at Technical University of Darmstadt and compulsory simulations. In order to obtain measurement data for the detailed aerodynamic and aeroelastic investigation, extensive steady and unsteady instrumentation was applied. Besides transient measurements at the stability limit to determine the operating range and limiting phenomena, performance measurements were performed, presenting promising results with respect to the capabilities of blade count reduced rotors. Close to the stability limit, aerodynamic disturbances like radial vortices were detected for both rotors, varying in size, count, speed and trajectory. Comparing the rotor configurations results in different stability limits along the compressor map as well as varying aeromechanical behavior. Those effects can partially be traced to the variation in blade pitch and associated aerodynamics.

Adjusting Rotational Behavior of Molecular Rotors by a Rational Tuning of Molecular Structure.

Many crystalline molecular rotors have been developed in the past decades. However, manipulating the rotational gesture that intrinsically controls the physical performance of materials remains a challenge. Herein, we report a series of crystalline rotors whose rotational gestures can be modulated by modifying the structures of molecular stators. In these dynamic crystals, the ox2- (ox2- = oxalate anion) behave as molecular rotators performing axial-free rotation in cavities composed of five complex cations, [MII(en)3]2+ (en = ethylenediamine). The structure of [MII(en)3]2+ that serves as a molecular stator can be tuned by varying the metal center with different ionic radii, consequently altering the chemical environment around the molecular rotator. Owing to the quasi-transverse isotropy of ox2- and multiple hydrogen-bond interactions around it, the molecular rotator exhibits unusual motional malleability, i.e., it can rotate either longitudinally in the compound of ZnII, or with a tilt angle of 42° in the compound of FeII, or even laterally in the compound of CdII. The atypical dynamic behavior demonstrated here provides a new chance for the development of exquisite crystalline molecular rotors with advanced tunable functionalities.

Design methodology of a highly loaded tandem rotor and its performance analysis under clean and distorted inflows

Compact and efficient compressor design is one of the key challenges in aero-engine development. The flow through a compressor is exposed to adverse pressure gradients, which limits the maximum allowable flow turning in a compressor blade. Tandem blading is an interesting concept to achieve a higher total pressure rise by augmenting the flow turning angle. Variation in axial overlap and percentage pitch of the forward and aft blade elements largely influences the behavior of the tandem configuration. In the present study, the genetic algorithm is used to optimize the axial overlap and the percentage pitch for the tandem rotor. Results indicate that a lower axial overlap and higher percentage pitch results in optimum performance. The paper presents the parametric study of four tandem configurations with different axial overlaps and percentage pitches. A detailed experimental analysis of the four different tandem configurations is included in this paper. The behavior of the tandem rotor is examined under the clean and radially distorted inflow. Further, a comparison is drawn with a conventional single rotor in terms of aerodynamic parameters such as total pressure rise, axial velocity, and stall margin. The experimental analysis is supplemented by some interesting computational results, which are included to provide some insight into the complex flow field of the tandem rotor. Tandem rotor design is observed to have a higher sensitivity to radial tip inflow distortion. The upstream shift of the aft rotor blade adversely affects the total pressure rise and stall margin of the tandem rotor.

Stability analysis of rotating shaft under electromagnetic and bearing oil-film forces

The stability of the fixed pints of a flexible rotor supported by journal bearings is investigated through the Bifurcation diagrams. In this paper the effect of nonlinear electromagnetic harmonic force is added to the simultaneous consideration of the effects of the nonlinearity in curvature and inertia, mass eccentricity and hydrodynamic forces of the journal bearings. Solution of the Reynolds equation renders the pressure distribution in the bearings. The bearing forces are found from integrating the pressure distribution on the surface of bearings. Derivation of the equations is performed using the Hamilton's principle and the nonlinearity terms are related to the eccentricity and the curvature of shaft. Primary and combination resonances are imposed to the rotor-bearing system and steady state responses show the effects of magnetic and bearing forces on the stability of amplitudes. In combination resonance, frequency of the electromagnetic load is tuned as the average of the forward and backward natural frequencies of the rotor. Existence of unstable Hopf points demonstrates that periodic, quasi-periodic and chaotic motions may be arisen in the nonlinear behavior of rotor.

Establishment of a contact stiffness matrix and its effect on the dynamic behavior of rod-fastening rotor bearing system

Establishment of a contact stiffness matrix and its effect on the dynamic behavior of rod-fastening rotor bearing system

Reduction of the finite element model of a gas turbine engine rotor using CMS technique

This paper is devoted to the problems of modeling the vibration behavior of rotors of gas turbine engines. The necessity of modeling their dynamic behavior is caused by their strong influence on the strength characteristics of the engine and its resource. The complexity of solving this problem lies in the fact that the design of modern gas turbine engines has many features that do not allow the use of only one-dimensional models, and the application of three-dimensional models requires a lot of computing resources. Thus, it is suggested to use methods of reduction of finite element models for solving the problems in three-dimensional statement. This paper uses the mode component synthesis (CMS) method to reduce the dimensionality of the rotor model. It also compares the speed of solving modal analysis tasks and determining critical frequencies using complete and reduced models. The quality of reduction is determined. Conclusions about the efficiency of the reduction technique aimed at solving rotor dynamics problems are made.

Effects of bearing lubrication conditions on rotor dynamic behavior

Usually, rotor dynamic analyses do not consider the effects of the lubricant supply condition, although this is an important aspect of journal bearing performance. Therefore, this work has implemented a mass-conserving model to realistically describe the oil feeding condition and evaluate its influence on rotor dynamics. This analysis was carried out by varying feeding pressure and groove position and the results indicate that the oil supply conditions significantly influence the bearing performance and affect the dynamic behavior of the entire rotor. In general, lower flow rates lead to a bearing with a greater stability region, as observed mainly in the bearing with a groove at 270° and, on the other hand, the increase in feeding pressure reduces the instability threshold.