Este trabalho propõe uma solução inovadora para o amortecimento de vibrações laterais indesejadas em máquinas rotativas através da conversão de energia cinética em energia elétrica por meio de um dispositivo eletromagnético passivo de colheita de energia, com o mínimo de geração de torque reativo. Para atingir estes objetivos, foram descritas e avaliadas as três principais técnicas de coleta de energia vibratória (piezelétrica, eletrostática e eletromagnética) juntamente com análises qualitativas das equações de eletromagnetismo e pelo Método dos Elementos Finitos. Um protótipo que consiste em um conjunto de ímãs permanentes anexos ao rotor e um conjunto de bobinas no estator demonstrou experimentalmente uma diminuição da amplitude de vibração em até 6,8%, na região de velocidades críticas, com geração não significativa de torque. Estes resultados foram obtidos experimentalmente mantendo-se os enrolamentos independentes entre si. / In this work, it is proposed a novel damping solution for undesired lateral vibrations in rotating machines by converting kinetic energy into electrical energy through a passive electromagnetic energy harvesting device, with minimal generation of reactive torque. In order to achieve these goals, it is described and evaluated the three main vibration energy harvesting techniques (piezoelectric, electrostatic and electromagnetic) along with qualitative analysis of electromagnetic equations and nite element analysis (FEA). Furthermore, a prototype consisting of a set of permanent magnets attached to the rotor and a set of coils attached to the stator showed a decrease in the amplitude of vibration up to 6,8% in the range of critical velocities, with non-signicant torque generation. Such results were obtained experimentally with independent-circuit coils.

Orientador: Euclides de Mesquita Neto / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-15T00:21:00Z (GMT). No. of bitstreams: 1 Sousa_AmilcarDanielOgazde_M.pdf: 3046046 bytes, checksum: 289cbf406a5a9496df2d904d50f26fe8 (MD5) Previous issue date: 2007 / Resumo: A presente dissertação descreve a resposta de um sistema dinâmico constituído por um rotor, uma fundação rígida e um solo homogêneo. O rotor considerado é um modelo de Jeffcott (Laval) com amortecimento externo. O rotor está fixado em uma fundação rígida que, por sua vez, está assentada em um solo homogêneo modelado como um semi-espaço viscoelástico. O sistema é analisado no plano do rotor. Uma cuidadosa dedução das equações de movimento é apresentada. A resposta dinâmica do solo é sintetizada com auxílio do Método dos Elementos de Contorno. A análise é conduzida no domínio da freqüência, reproduzindo o comportamento estacionário do rotor e da fundação. A influência de diversos parâmetros do sistema, sobre a resposta dinâmica do rotor e fundação é estudada. Entre os parâmetros geométricos considerados estão a altura do centro geométrico da fundação em relação ao solo e a altura do rotor em relação à fundação. O papel das razões de inércia entre rotor e fundação é investigado. A influência do amortecimento interno e do amortecimento geométrico do solo é analisada. O tipo de contato entre a fundação rígida e o solo também á estudada. / Abstract: The present work describes the dynamic response of a system consisting of a rotor, a rigid foundation and a homogeneous soil profile. The rotor is considered a Jeffcott (Laval) model with external damping which is attached to a rigid foundation. The foundation is supported by a viscoelastic half-space. The analysis is conducted in the plane of the rotor. A detailed deduction of the system's equation of motion is presented. The soil response is synthesized by the Boundary Element Method. The analysis is conducted in the frequency domain, leading thus to the stationary response of rotor and foundation. The influence of distinct system parameters of the dynamic response of rotor and foundation is addressed. The geometric parameters include the distance of the foundation mass center to the soil-foundation interface and the height of the rotor with respect to the foundation. The effect of rotor to foundation inertia ratio is investigated. The role of soil internal and geometric damping on the system response is also addressed. The influence of the contact type at the soil foundation interface, bonded or smooth, is also considered. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

The dynamic response of turbine flowmeters in low pressure gas flows (i. e. where the rotational inertia of the fluid is negligible) is well understood and methods for correcting meter signals for a lack of response are available. For liquid flows there has been a limited amount of experimental work on the response of meters to step changes but no reports have been found of the response of meters to sinusoidally pulsating flows. "Small" turbine meters are expected to behave differently from "large" meters for a number of reasons: a smaller meter would generally have: (1) a larger percentage of tip clearance leakage flow; (2) less fluid momentum between the meter blading; and, (3) less fluid friction forces on the effective surface area. In this research, arbitrarily, meters up to size 25 mm were defined as small; and within this study, meters of size 6 mm to 25 mm were investigated. The aim of the research was to investigate and to understand the response of small turbine meters to pulsating liquid flows and to provide methods for correction. Three approaches were used: (1) application of an existing theoretical model of turbine meter behaviour; (2) an experimental investigation of meter performance in pulsating flows; and (3) simulation of flow behaviour through one selected meter using CFD and extending the simulation to predict the rotor dynamics and, hence, the response of this meter to specified cases of pulsating flow. A theoretical model developed by Dijstelbergen (1966) assumes frictionless behaviour and that flow is perfectly guided by meter blading through the rotor and that fluid within the rotor envelope rotates as a "solid body". Results from this theoretical model applied for pulsating flows showed that there was likely to be positive error in predicted mean flow rate (over-registration) and negative error for predicted values of the amplitude of the pulsations (amplitude attenuation). This behaviour is due to the fundamental asymmetry between flows with increasing and decreasing angle of attack relative to the meter blades, throughout a pulsation cycle. This qualitative behaviour was confirmed by experimental work with meters up to size 25mm working with pulsation frequencies up to 300 Hz. For low frequency pulsations (below 10 Hz), the over-registration errors were within the limits of specified meter accuracy. At higher frequencies and larger pulsation amplitudes, the largest over-registration observed was 5.5 % and amplitude attenuation could be as large as 90 %. The dependence of these errors on both the flow pulsation amplitude and frequency were investigated. The theoretical model was also used as a basis for generating correction procedures, to be applied to both the mean flow and the pulsation amplitude measurements. The results from the CFD simulation showed qualitative good agreement with the experimental data. The same kind of meter error trends were observed and it was shown to provide a better correlation with the experimental trends than the theoretical model derived from Dijstelbergen. From the CFD simulation, the causes of over-registration and amplitude attenuation in turbine flowmetering were understood through the investigation of rotor dynamics coupled with fluid behaviour around meter blading within the pulsation cycle. The CFD results were used to evaluate fluid angular momentum flux and to review the validity of the assumption that fluid within the rotor "envelope" rotated as a solid body. For the case investigated, whilst the assumption that flow is perfectly guided is not inappropriate, the volume of fluid assumed to rotate as a "solid body" was found to be significantly less than the rotor envelope volume.

The concept of added hydrodynamic properties such as added mass is of importance in modern hydropower development, mainly for rotor dynamic calculations. Added mass could result in reduced natural frequencies and altered mode compared to existing simulation models. It is of importance to quantify added mass but also added damping to make the simulation models more accurate. Experiments are conducted on a model Kaplan turbine, D = 0,5 m, and a steel cube, S = 0,2 m, for linear vibrations in still water confined in a cylindrical tank. The experiments are conducted in air and water for evaluation of added forces. The vibrations are generated with an electrodynamic vibration exciter with a frequency range of approximately 1-10 Hz with amplitudes 0,5-3 mm. The experiments were repeated to check test rig reliability. Each individual working point [frequency, amplitude] were in total tested 40 times in 15 s intervals. The added mass was found to be function of acceleration for the model Kaplan with an increase in added mass from 10 % at 4 m/s2 to 35 % at 0,5 m/s2. The damping forces was at best measured at ±30 %, making added damping calculations unreliable. The cube experiments resulted in small differences between water and air. Cube results must be interpreted with caution due to test rig uncertainties.

L’écoulement dans les turbomachines est tri-dimensionnel et instationnaire. Actuellement, les concepteurs de moteurs cherchent à réduire l’encombrement et le poids des machines. En conséquence, les interactions entre les roues, appelées interactions rotor-stator, sont renforcées. Parmi elles, l’effet potentiel remontant n’est désormais plus négligeable malgré sa rapide atténuation spatiale. Dans cette étude, cet effet potentiel remontant a été analysé sur une configuration spécialement conçue : une grille linéaire d’aubes de turbine, suivie de barreaux défilants en aval à une distance de 20% de corde axiale, simulant des aubes de rotor en aval. La grande échelle du banc d’essais facilite l’étude du comportement de la couche limite des aubes de la grille. Des mesures de pression et d’anémométrie laser à deux composantes, synchronisées avec le défilement des barreaux aval sont réalisées. Le nombre de Reynolds, basé sur la corde, est 1.6 × 105. Une grille de turbulence placée en amont de la grille d’Aube afin de pouvoir augmenter le taux de turbulence amont a été utilisée. Des résultats de mesures en absence de cette grille (faible taux de turbulence amont) sont également présentés et analysés. Une modélisation numérique, basée sur un calcul laminaire avec un préconditionnement basse vitesse pour la même configuration, a montré la déformation des lignes de courant de l’écoulement dans le canal inter-aubes, en fonction de la position du barreau aval. La distribution de pression autour de l’aube est également périodiquement modifiée. Les résultats stationnaires expérimentaux, en absence de tout barreau aval, ont révélé un décollement de la couche limite à l’extrados de l’aube à bas taux de turbulence amont(Tu−am = 1.2%) qui est supprimé à haut taux de turbulence amont (Tu−am = 4.2%) ; la couche limite commence alors sa transition par un mode by-pass. Aucun effet instationnaire dans la couche limite n’a été observé à l’intrados, quel que soit le taux de turbulence amont. L’étude instationnaire, avec le défilement des barreaux en aval, a permis de mettre en évidence un décollement périodique de la couche limite à l’extrados à bas taux de turbulence amont (Tu−am = 1.8%). Dans ce cas, la couche limite suit deux modes de transition au cours d’une période : une transition par décollement et une transition bypass. Au contraire, dans le cas à fort taux de turbulence amont (Tu−am = 4.0%), aucun décollement de la couche limite n’a été décelé. La couche limite est sujette à l’effet instationnaire à l’extrados. Elle est devenue turbulente au bord de fuite à tout instant par un mode by-pass. Cette étude a montré que l’effet potentiel issu d’un roue en aval est du même ordre de grandeur que les effets de sillage et doit être pris en compte dans l’analyse des phénomènes. Par des méthodes d’indexation de roues, le décollement de la couche limite pourrait être supprimé. / Turbomachinery designers wish to reduce the size and weight of engines. One way of achieving this is by reducing the distance between rotor and stator elements. In doing so, the rotor-stator interaction becomes more significant. In particular, the long-range influence of pressure potential is no longer negligible, and affects both upstream and downstream flow. Previously, only downstream interactions of blade wakes were considered important. Here we examine the upstream potential effect generated by downstream moving cylindrical rods on an upstream low pressure turbine blade. A large scale rectilinear blade cascade was constructed to improve access to the boundary layer. The Reynolds number, based on the chord, was 1.6 × 105. Pressure measurements and two-dimensional Laser Doppler Anemometry around the blade were performed to study the boundary layer behavior. Recorded data points are phase averaged with the downstream moving cylindrical rods. A grid is placed upstream of the blade cascade to increase the inlet turbulence intensity. A numerical investigation, based on a laminar simulation with low velocity preconditioning method was carried out on the same configuration. The flow streamlines and the pressure distribution around the blade were found to depend strongly on the downstream rod position. No unsteady effects in the boundary layer of the pressure side were observed, for the inlet turbulence intensities used in our study. Steady experimental results revealed a boundary layer separation bubble on the blade suction side at a low turbulence intensity (Tu−in = 1.2%), whereas the boundary layer became turbulent via by-pass transition at a higher turbulence intensity (Tu−in = 4.2%).It is seen that, in the unsteady configuration, at a low turbulence intensity (Tu−in =1.8%), the laminar boundary layer experiences separation once per rod period. Two transition modes were identified that alternate during a rod period : a separation transition mode and a by-pass mode, which were conditioned by the downstream rod position. Ata higher turbulence intensity (Tu−in = 4.0%), no boundary layer separation occurred thereby following a bypass transition mode during an entire rod period. The experimental results presented here demonstrate the large influence of the downstream potential effect generated by a downstream row on the upstream blade boundary layer behavior. In order to improve the efficiency of engines, this effect and its interaction with the wake effect must be taken into account in turbomachinery design.

This degree project in applied physics studies the tip gap flows over the rotor blades of a high-pressure turbine. The rotor blade used in the study has an improved design that utilizes both a cavity tip and an uneven profiling to reduce turbine loss. The designed rotor blade is shown to admit a 21% lower leakage mass flow rate across the tip gap than a reference rotor blade with a flat tip. By studying the designed rotor blade using transient CFD, the flow field of the tip gap region has been studied through one blade passage. The flow field characteristics of particular interest are the leakage mass flow rate across the tip gap region, which is proportional to turbine loss, and the characteristic vortices that reside within the cavity tip. By using post-processing scripts, the leakage mass flow rate has been calculated for every time step across one blade passage, showing a strong time dependence. The characteristic vortices are found using two different vortex detection algorithms, and their respective vorticity magnitude is shown to depend on the leakage mass flow rate. The simulation shows that the vorticity magnitude is increasing above a threshold of leakage mass flow rate, and that it is decreasing under this threshold. This effect is shown to destabilize the leakage mass flow rate, increasing its amplitude over its period of one blade passage.

No description available.

Typical aero-engine assemblies have at least two nested rotors mounted within a flexible casing via squeeze-film damper (SFD) bearings. As a result, the flexible casing structures become highly sensitive to the vibration excitation arising from the High and Low pressure rotors. Lowering vibrations at the aircraft engine casing can reduce harmful effects on the aircraft engine. Inverse problem techniques provide a means toward solving the unbalance identification problem for a rotordynamic system supported by nonlinear SFD bearings, requiring prior knowledge of the structure and measurements of vibrations at the casing. This thesis presents two inverse solution techniques for the nonlinear rotordynamic inverse problem, which are focused on applications where the rotor is inaccessible under operating conditions, e.g. high pressure rotors. Numerical and experimental validations under hitherto unconsidered conditions have been conducted to test the robustness of each technique. The main contributions of this thesis are:• The development of a non-invasive inverse procedure for unbalance identification and balancing of a nonlinear SFD rotordynamic system. This method requires at least a linear connection to ensure a well-conditioned explicit relationship between the casing vibration and the rotor unbalance via frequency response functions. The method makes no simplifying assumptions made in previous research e.g. neglect of gyroscopic effects; assumption of structural isotropy; restriction to one SFD; circular centred orbits (CCOs) of the SFD. • The identification and validation of the inverse dynamic model of the nonlinear SFD element, based on recurrent neural networks (RNNs) that are trained to reproduce the Cartesian displacements of the journal relative to the bearing housing, when presented with given input time histories of the Cartesian SFD bearing forces.• The empirical validation of an entirely novel approach towards the solution of a nonlinear inverse rotor-bearing problem, one involving an identified empirical inverse SFD bearing model. This method is suitable for applications where there is no adequate linear connection between rotor and casing. Both inverse solutions are formulated using the Receptance Harmonic Balance Method (RHBM) as the underpinning theory. The first inverse solution uses the RHBM to generate the backwards operator, where a linear connection is required to guarantee an explicit inverse solution. A least-squares solution yields the equivalent unbalance distribution in prescribed planes of the rotor, which is consequently used to balance it. This method is successfully validated on distinct rotordynamic systems, using simulated data considering different practical scenarios of error sources, such as noisy data, model uncertainty and balancing errors. Focus is then shifted to the second inverse solution, which is experimentally-based. In contrast to the explicit inverse solution, the second alternative uses the inverse SFD model as an implicit inverse solution. Details of the SFD test rig and its set up for empirical identification are presented. The empirical RNN training process for the inverse function of an SFD is presented and validated as a part of a nonlinear inverse problem. Finally, it is proved that the RNN could thus serve as reliable virtual instrumentation for use within an inverse rotor-bearing problem.

Accurately predicting fan performance, including bounds of operation, is an important function of any Computational Fluid Dynamics (CFD) package. The presented research uses a CFD code developed as part of the Computational Research and Engineering Acquisition Tools and Environment (CREATE), known as Kestrel, to evaluate a single stage compressor at various operating conditions. Steady-state, single-passage simulations are carried out to validate capabilities recently added to Kestrel. The analysis includes generating speedlines of total pressure ratio and efficiency, as well as radial total temperature and total pressure profiles at two axial locations in the compressor at various operating conditions and fan speeds, and simulation data from the single-passage runs is compared to experimental data. Time-accurate, full annulus simulations are also carried out to capture and analyze the processes leading to stall inception for both uniform and distorted inlet conditions. The distortion profile used contains a 90 degree sector of lower total pressure at the inlet. The observed fan behavior at stall inception is compared to previous research, and it is concluded that the inlet distortion significantly changes the behavior of the part-span stall cells that develop after stall inception. Understanding the physical processes that lead to stall inception allows fan designers to design more robust fans that can safely take advantage of the better performance associated with operating closer to stall.

No description available.