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The deflections of screw rotors under machining forces cause mismatch between the male and female rotors and, consequently, accelerated wear and suboptimal efficiency in their performance. Optimizing the machining process to minimize the generated forces and accounting for the resulting mismatch in the design of the rotor profile requires accurately computing the machining forces in computer simulations. Virtual machining systems combine graphics-based computation of the Cutter-Workpiece Engagement (CWE) with the physics-based models of machining mechanics to simulate the forces during complex machining processes. However, because of the high computational load of graphical simulations, virtual machining is not suitable for the repetitive force simulations that are required for optimizing the design and manufacturing of rotors. In this work, we present a new method that simulates screw milling forces based on the process kinematics instead of graphical simulations. Utilizing mathematical equations that describe the process kinematics, the theoretical rotor profile is determined for feasible combinations of cutting tool profile, setup angle, and centre distance. Subsequently, to find the milling forces, the cutting edge is discretized into multiple small edge segments and a mechanistic cutting force model is used to determine the local cutting forces at each segment. After geometric and kinematic transformations of these local forces, the screw milling forces are obtained for each roughing and finishing pass. Instead of graphics-based methods, the engagement conditions between the cutter and workpiece are determined by the ensemble of 2D rotor and tool profiles; as a result, the computational efficiency is increased substantially. The semi-analytical nature of the presented method allows for computing the forces with arbitrary resolution within a reasonable time. The accuracy and efficiency of the presented method is verified by comparing the simulated forces against a dexel-based virtual machining system. / Graduate

This work treats dual-plane automatic ball balancing of elastically-mounted cylindrical rotors. The application is primarily to systems with a vertically-oriented single-bearing support, but extension is also made to horizontally-oriented single-bearing support as typically found in a vehicle wheel. The rotor elastic mounting includes three translational degrees of freedom for the body geometric center and three rotational degrees of freedom. Damping is included for each of these six degrees of freedom. The model for the automatic ball balancer consists of up to two arbitrarily-located hollow circumferential races, each of which contains up to two sliding particles. The friction model for the particles includes both viscous and Coulomb friction forces. Of considerable complexity is the logic path for the individual particles being either in motion or stationary relative to the rotor. The exact equations of motion for the overall system are derived via a Newtonian approach. Numerical-integration results show that the balancer performance depends strongly on the friction levels as well as the operating speed of the body. Simulations conducted with a pure static imbalance show that ideal automatic balancing is possible only for vertical-axis rotors that have zero Coulomb friction levels between the balancing particles and the races. Simulations with a horizontal-axis statically-imbalanced rotor show that an automatic balancer can improve performance for certain operating speeds and non-zero Coulomb friction levels in the presence of gravitational forces. Simulations conducted with a pure dynamic imbalance show that there is no inherent mechanism to counteract rotational displacements of the rotor about its geometric center. As a result, the balancing particles exhibit several phenomena described in previous works such as synchronous motion and oscillatory behaviors within their respective races. Simulations for an arbitrarily located imbalance show that rotor performance can be improved using dual-plane balancing techniques for certain operating speeds and Coulomb friction levels. Due to the inherent complexity in eliminating an arbitrarily located mass imbalance, the system is generally unable to reach a perfectly balanced configuration, but performance can be improved for carefully-selected initial conditions. / Ph. D.

The internal voltage angle of a generator is an important parameter that indicates the stability, both transient and steady-state, of the generator. This paper proposes a method of measuring and synchronizing the internal angle using a microprocessor and an optical encoder installed on the shaft of a generator. With a synchronized angle measurement, accurate stability studies and wide-area controls can be implemented. The experimental setup for measuring the rotor angle of a generator is explained in this work. A wide-area power system stabilizer implementing the synchronized angle measurement is then investigated using a four machine, two-area system. A synchronized remote feedback rotor angle signal is included in a traditional stabilizer design. It is shown that this remote signal helps increase the stability of the system while also having the benefit of being able to be predicted accurately. This capability makes bad data detection and communication delay compensation possible. / Master of Science

The Morton Effect in the rotor - bearing systems may lead to an unstable operation. Up to the present, most of the established research efforts have been focused on the overhung rotor systems. In this dissertation, a systematic study on the Morton Effect induced instability in mid-span rotor systems is presented. First, the mechanism study is conducted. The simplified rotor models with isotropic linear bearing supports are adopted for the derivation of analytical expressions. The threshold speeds of instability in simple forms are obtained for the systems with the thermal imbalance acting concurrent with or perpendicular to the direction of the response displacement. For a perspective view of the system stability, a stability map for the damped rigid mid-span rotors with the thermal imbalance having arbitrary phase difference has been generated. It shows that the stable operating regions of the system are bounded by two curves of threshold of instability. The results show that the Morton Effect induced instability thresholds are actually affected by both the magnitude and relative phase of the thermal imbalance. The mechanism of the Morton Effect induced thermal instability of mid-span rotors supported by linear isotropic bearings can be explained through the fact that the Morton Effect introduces either negative stiffness or negative cross-coupled stiffness. Next, the steady-state response performance under the influence of the Morton Effect is discussed. The results show that the Morton Effect has a comprehensive impact on both the amplitude and phase lag of the steady-state unbalance response. It may shift both curves in a manner dependent on the relative magnitude and direction of the thermal imbalance. Then, the mid-span rotors supported by the hydrodynamic journal bearings are analyzed. The models to calculate the thermal bending of the shaft and the temperature distribution across the journal surface are established. The calculations of the temperature difference and its equivalent thermal imbalance are conducted and discussed with the comparison to the analytical results. It shows that the thermal imbalance may increase to the level of the mechanical imbalance and its influence on the system stability should be then included. The suggested thermal bending model also explains that the mid-span rotors are less liable to be influenced by the Morton Effect than are the overhung configurations, because of the restraining effect between the two supports. The simulation results of a symmetric mid-span rotor - hydrodynamic journal bearing system show that the inclusion of the Morton Effect may lead to an unstable operation of the system. Considering the existence of the oil film self-induced vibration due to the dynamic characteristics of fluid film bearings, the Morton Effect may make a further negative impact on the instabilities of the rotor system under some working conditions. Finally, the predictive solution method for the general mid-span rotors is discussed. The computer code, VT-MAP, is developed for the predictions of the Morton Effect induced instability of rotor systems in either mid-span and overhung configurations. / Ph. D.

This work assesses the feasibility of designing and implementing the wave rotor (WR), the pulse detonation engine (PDE) and the internal combustion wave rotor (ICWR) as part of novel Brayton cycles able to reduce emissions of future aircraft. The design and evaluation processes are performed using the simplified analytical solution of the devices as well as 1D-CFD models. A code based on the finite volume method is built to predict the position and dimensions of the slots for the WR and ICWR. The mass and momentum equations are coupled through a modified SIMPLE algorithm to model compressible flow. The code includes a novel tracking technique to ensure the global mass balance. A code based on the method of characteristics is built to predict the profiles of temperature, pressure and velocity at the discharge of the PDE and the effect of the PDEs array when it operates as combustion chamber of gas turbines. The detonation is modelled by using the NASA-CEA code as a subroutine whilst the method of characteristics incorporates a model to capture the throttling and non-throttling conditions obtained at the PDE's open end during the transient process. A medium-sized engine for business jets is selected to perform the evaluation that includes parameters such as specific thrust, specific fuel consumption and efficiency of energy conversion. The ICWR offers the best performance followed by the PDE; both options operate with a low specific fuel consumption and higher specific thrust. The detonation in an ICWR does not require an external source of energy, but the PDE array designed is simple. The WR produced an increase in the turbine performance, but not as high as the other two devices. These results enable the statement that a pressure rise combustion process behaves better than pressure exchangers for this size of gas turbine. Further attention must be given to the NOx emission, since the detonation process is able to cause temperatures above 2000 K while dilution air could be an important source of oxygen.

Aviation industry has a crucial impact on society on the grounds that it offers wider social and economic benefits. The demand of transportation is increasing and it is expected that the worldwide fleet of aircraft and rotorcraft will increase accordingly. This growth will introduce an increased environmental impact which can be controlled with the introduction and the implementation of new and greener technologies which can provide both a reduced carbon foot-print and increased efficiency. Therefore, the simulation of new designs with tools that can capture the flow physics accurately is crucial, on the grounds that an accurate simulation could provide novel designs and new ways in order to design from scratch new vehicles as well as providing a better appreciation of the physics that are involved. This work has a central aim to propose a methodology which combines CFD simulations and the method of performance mapping. It focuses on the application of a ducted tail rotor which can offer significant performance benefits compared to a conventional tail rotor. The developed methodology was tested against the results of an in-house rotorcraft comprehensive code and provided a reasonable qualitative correlation. In principle, this methodology can work for all helicopter flight phases such as hover, climb, cruise, descend but due to the complexity of the investigations, together with the lack of experimental data that can be used to refine the CFD model, only the hover and forward flight were considered. Although CFD studies of a ducted tail rotor currently exist in the literature (though scarce), this work can be considered, to the best knowledge of the author as a first attempt in investigating the performance of the configuration, from low to high forward flight speed, by combining CFD and performance mapping.

L'objet de cette étude est de mieux formaliser et modéliser de façon générique le processus de structuration d'un produit par le procédé de foisonnement, en reliant les paramètres opératoires aux propriétés des mousses formées et de contribuer ainsi à un meilleur pilotage de l'opération. Une ligne de foisonnement par battage en continu a été instrumentée et l'évolution du diamètre des bulles en fonction des paramètres du produit et du procédé a été suivie pour des milieux modèles newtoniens et rhéofluidifiants. L'analyse dimensionnelle à l'échelle du procédé a permis d'aboutir à un modèle physique de l'opération, et donc d'avoir une compréhension des phénomènes en présence. Elle a aussi permis d'intégrer les paramètres du produit et du procédé et de simplifier la représentation des résultats expérimentaux. Enfin, la cohérence de ce modèle avec d'autres issus de la littérature et une première approche de validation avec un produit réel, semble justifier son caractère générique. / The aim of this study is to better formalize and model in a generic way the structuring of a product by the foaming operation process, by linking the operating parameters to the foams properties and contribute to a better steering of the operation. A continuous whipping line was instrumented and the evolution of bubble diameter depending on both product and process parameters was characterized for Newtonian and shear-thinning model fluids. Dimensional analysis of the process has lead to a physical model of the operation, and therefore makes possible the understanding of the phenomena involved. It also helped to integrate the product and the process parameters and simplify the representation of experimental results. Finally, the consistency of this model with others from the literature and a first validation with a real product seems to justify his relevance.

Le bruit généré par l'impact du sillage de la soufflante avec les aubes du redresseur est une source prédominante des turboréacteurs en conditions d'approche, et la composante à large bande contribue fortement au niveau sonore global. Une méthode numérique basée sur un code CAA résolvant les équations d Euler est développée dans cette thèse afin d'estimer le bruit d'interaction entre un sillage turbulent et un aubage de géométrie quelconque. Le sillage amont est modélisé à l'aide d'une méthode stochastique supposant un spectre de turbulence homogène isotrope et une représentation spatiale simplifiée du champ de vitesse. Ces fluctuations de vitesse sont injectées dans le code CAA via des conditions aux limites adéquates. La méthode ainsi mise en place est validée dans un premier temps sur des cas d'interaction avec une plaque plane en comparant les résultats numériques aux solutions du modèle d'Amiet. Un chaınage avec une méthode intégrale est aussi réalisé pour estimer le rayonnement acoustique. La méthode numérique est ensuite mise en œuvre pour simuler la réponse acoustique d'un profil isolé avec un bord d'attaque ondulé conçu et testé dans la soufflerie de l'ISVR dans le cadre du projet européen FLOCON. Enfin, la méthodologie est étendue à des configurations de grilles d'aubes annulaires en conduit. Après une étape de validation sur des cas monofréquentiels issus d'un benchmark CAA, des simulations large bande sont réalisées, tout d'abord sur une configuration de grille d'aubes sans incidence (écoulement axial uniforme) testée en soufflerie au LMFA, puis sur une configuration plus complexe de grille d'aubes non chargée en écoulement tournant proposée par Atassi / Noise generation due to the rotor wakes impinging the stator vanes is a dominant turbofan source at approach conditions, and the broadband noise component is significantly contributing to the overall level. A numerical method based on a CAA code solving the Euler equations is developped in this thesis in order to simulate the interaction noise between a turbulent wake and a vane row without geometry restrictions. The upstream turbulent flow is synthesized using a stochastic approach by considering an homogeneous isotropic turbulence spectrum model and a simplified spatial representation of the velocity field. These velocity gusts are injected in the CAA code by implementing a suited boundary condition. The present methodology is first va- lidated against turbulence-flat plate interaction cases, by comparing the numerical predictions to Amiet model solutions. A chaining with an integral formulation is also performed to assess the acoustic far-field. Then, the method is used to estimate the acoustic response of an isolated airfoil with a wavy leading egde, designed and tested in ISVR wind tunnel in the framework of European FLOCON project. Finally, the computations are extended to ducted annular grid configurations. After a validation step on single-frequency cases described in a CAA benchmark, broadband noise simulations are performed, firstly on a flat-plate annular grid in a uniform axial flow tested in the LMFA wind tunnel, and then on a more complex configuration related to an unloaded grid in a swirling mean flow proposed by Atassi