Master of Science / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / Continued regulatory pressure necessitates the use of precisely designed turbochargers to create the design trapped equivalence ratio within large-bore stationary engines used in the natural gas transmission industry. The upgraded turbochargers scavenge the exhaust gases from the cylinder, and create the air manifold pressure and back pressure on the engine necessary to achieve a specific trapped mass. This combination serves to achieve the emissions reduction required by regulatory agencies. Many engine owner/operators request that an upgraded turbocharger be tested and verified prior to re-installation on engine. Verification of the mechanical integrity and airflow performance prior to engine installation is necessary to prevent field hardware iterations. Confirming the as-built turbocharger design specification prior to transporting to the field can decrease downtime and installation costs. There are however, technical challenges to overcome for comparing test-cell data to field conditions. This thesis discusses the required corrections and testing methodology to verify turbocharger onsite performance from data collected in a precisely designed testing apparatus. As the litmus test of the testing system, test performance data is corrected to site conditions per the design air specification. Prior to field installation, the turbocharger is fitted with instrumentation to collect field operating data to authenticate the turbocharger testing system and correction methods. The correction method utilized herein is the ASME Performance Test Code 10 (PTC10) for Compressors and Exhausters version 1997.

L’étude effectuée au cours de cette thèse a permis la caractérisation expérimentale des instabilités aérodynamiques se développant dans un compresseur centrifuge et une première évaluation de l’efficacité d’une stratégie de contrôle par aspiration de couche limite. Le compresseur, développé par Safran Helicopter Engines et dénommé Turbocel, est composé d’une roue directrice d’entrée, d’un rouet centrifuge splitté, d’un diffuseur radial aubé et splitté et d’un redresseur axial. Des travaux numériques antérieurs réalisés au Laboratoire de Mécanique des Fluides et d’Acoustique ont montré, aux bas régimes de rotation, un comportement singulier caractérisé par une structure d’écoulement dite « alternée » impliquant deux canaux adjacents du diffuseur radial. L’étude stationnaire réalisée sur l’ensemble des régimes de rotation du compresseur a conduit à une ségrégation des vitesses de rotation suite à l’établissement d’une variable– le taux d’asymétrie - caractérisant l’asymétrie de l’aérodynamique du diffuseur. Ce taux, quasi nul à très basse vitesse de rotation, croît jusqu’à atteindre un maximum à vitesse de rotation intermédiaire, puis s’effondre pour ré-augmenter légèrement. Une analyse fine des données instationnaires acquises à bas régimes a permis la description de deux modes de fonctionnement du compresseur associés à des structures de décollements différentes dans le diffuseur. Le premier mode est caractérisé par l’oscillation à une fréquence de l’ordre de 42 Hz d’un décollement localisé sur la face en dépression des aubes principales du diffuseur. Le second mode, à 12Hz, associé au pompage modéré du compresseur, correspond à la mise en place d’un schéma alterné et à son oscillation sur deux canaux adjacents du diffuseur.Les origines probables de ces différents modes de fonctionnement sont discutées à partir de considérations • aérodynamiques -- la mise en place d’une recirculation en tête de rouet est suspectée d’influer sur le taux d’asymétrie en modifiant l’incidence en entrée de diffuseur,• géométriques -- le nombre et le calage des aubes du diffuseur radial ainsi que la distance inter-roue indiquent une prédisposition du diffuseur à fonctionner en régime alterné sous certaines conditions d’incidence,• aéro-acoustiques -- un accrochage des fréquences aérodynamiques avec les fréquences des ondes acoustiques du banc d’essai semble se produire. Enfin, les résultats sur le contrôle d’écoulement par aspiration de couche limite à régime partiel sont présentés. Une amélioration du rendement est observée à certains points de fonctionnement, mais aucune extension de la plage de fonctionnement du compresseur n’est mesurée. Sans l’atténuer, l’aspiration permet de contrôler sur quels canaux s’établit le régime alterné. / This thesis presents an experimental characterization of the evolution of aerodynamic instabilities in a centrifugal compressor, and a first evaluation of the effectiveness of boundary layer suction as a control strategy. The compressor used in this study is Turbocel, a centrifugal compressor developed by Safran Helicopter Engines, featuring inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes.Previous numerical work, conducted at the Laboratoire de Mécanique des Fluides et d’Acoustique de Lyon, revealed a unusual behaviour of the compressor at low rotational speeds characterized by a distinctive alternate flow structure in the radial diffuser that develops across two adjacent blade channels. The steady analysis, which was conducted over the full operating range of rotational speeds, led to the distinction of different operating zones, following the establishment of a new indicator variable - the asymmetry rate - characterizing the asymmetry of the diffuser aerodynamics. This rate, which is close to zero at very low rotation speed, increases until it reaches a maximum value at intermediate rotational speed, before collapsing and slightly increasing again near the nominal rotational speed.Analysis of the unsteady data acquired at low speeds allowed for the characterization of two compressor operating modes, associated with different flow phenomena in the stalled diffuser. The first mode is characterized by the oscillation of a separation at 42 Hz, on the suction side of the main blades in the diffuser. The second mode, at 12Hz, associated with mild surge of the compressor, corresponds to the emergence of an alternate pattern of unsteady flow separation that occurs across two adjacent channels of the diffuser.The probable causes for these different operating modes are discussed in the context of different considerations:• aerodynamic -- the formation of a recirculation near the tip of the impeller is suspected to affect the asymmetry rate by changing the incidence angle at the diffuser inlet.• geometric -- the number and the stagger angle of the radial diffuser blades as well as the distance between the impeller and the diffuser may result in a predisposition of the diffuser to operate in an alternating mode, under certain conditions of incidence.• aero-acoustic -- as there is evidence of a lock-in of the aerodynamic frequencies with the acoustic modes of the test rig.Finally, boundary layer suction is explored as a means of flow control at partial rotational speed. Improvements in performance were observed for some operating points, however no extension of the compressor operating range was measured. Although boundary layer suction did not allow for the intensity of the oscillating separation pattern in the diffuser to be reduced, it was found to be an effective means of controlling the location of the alternate flow structure in the diffuser.

This dissertation applies a commercial flow simulation software package together with common signal processing techniques to the task of accurately detecting leakage in a large commercial gas pipeline. The techniques developed significantly improved the ability to produce accurate, reliable and stable leak detection predictions for the gas transmission pipeline studied and can be applied generally to other pipelines as well. Recommendations for minimum pipeline requirements to implement successful leak detection are also detailed. There are several commercial software packages available that perform some form of leak detection via system modelling. However, due to the commercial aspects of these products, vendors do not publish the detailed methods of leak detection. This thesis identifies the fundamental techniques required to have accurate and reliable leak detection on a gas transmission pipeline, whilst taking into account the lack of measurement data typically encountered on most gas pipelines. The investigation confirmed that a mass balance technique could be successfully used to produce stable leak detection results for compressible flow in gas transmission pipelines. This leak detection [using mass balance] can be achieved without flow measurement along the pipeline, instead, using only pressure and temperature measurements. Although it is recognized that flow measurement data will greatly improve the ability to detect leaks, the focus of this work is on pipelines where this flow measurement data at intermediate points along the pipeline is not available. It was also demonstrated the reliability of the leak detection was improved by the application of on-line signal processing techniques at various stages of the data processing. / It was clear early into the investigation that the majority of the errors within the leak detection model were created by random errors from the input field data. These non-systematic errors from the measurement data that included pressure and temperature, produced interference with model output. This interference resembled random “white” noise that was removed by a combination of well established data filtering techniques. The most appropriate process of calculating leak detection flow was determined after analysing the results of different techniques applied to large quantities of actual pipeline operating data. The validation of the on-line techniques developed provides a valuable resource for those wishing to implement similar leak detection schemes elsewhere. Furthermore a software environment was chosen which incorporated an open input and output platform for data that could be interfaced with any operating system. Therefore these techniques can be applied to the numerous Supervisory Control and Data Acquisition (SCADA) systems in operation throughout the gas transmission industry, to provide a low cost solution to leak monitoring.

This thesis contributes to the knowledge and the characterization of scroll machines and their systems. It is based on experimental and modeling works carried out on: a) A hermetic scroll compressor used inside an air-cooled water chiller. b) An oil-free open-drive scroll expander integrated into an Organic Rankine Cycle (ORC) power system. c) Open-drive scroll compressor and expander used in a Liquid Flooded Ericsson Cycle Cooler (LFEC). Such a system uses the liquid flooding of the compressor and of the expander to approach isothermal compression and expansion processes. New semi-empirical models of the scroll compressor and expander were proposed and existing models improved. A deterministic model of the scroll expander was established. The model associates a geometrical description of the machine with a thermodynamic description of the expansion process. This model was validated for the two expanders investigated experimentally. The model validation revealed that the performance of the expanders is mainly affected by the supply pressure drop and by the internal leakages. Using the validated model, parametric studies were carried out to investigate the variation of the performance of both expanders with modification of their design and with the operating parameters. The thesis also investigated the scroll machines from the point of view of their integration into thermal systems. A first experimental investigation was carried out on an air-cooled chiller. The scroll compressor semi-empirical model, with its parameters identified on the basis of published manufacturer data, was used as a refrigerant flow meter. The analysis of the experimental data allowed a better understanding of the chiller operation and a better identification of its model parameters (such as the fan and the hot gas bypass control models). A second experimental investigation was carried out on an ORC power system, working with R123. In order to select the most appropriate fluid, the performances achieved with four different fluids were compared by simulation. The experimental study confirmed that the scroll expander is a good candidate for an ORC system: the tested prototype presented a good performance (the maximum global isentropic effectiveness achieved was 68%). Using an ORC simulation model, parametric studies were carried out to investigate the effects of the expander characteristics and operating conditions on the cycle performance. The latter is mainly affected by the expander internal leakage and by the liquid subcooling at the condenser exhaust. A third experimental investigation was performed on a LFEC working with nitrogen as refrigerant and alkyl-benzene oil as flooding liquid. Experimental data was used to identify the parameters of the scroll compressor and expander semi-empirical models. Parametric studies were performed to identify the different factors affecting their performance. One of the undesirable features of the machines is the increase of the supply and exhaust pressure drops with the increase of oil quantity.

In this study, loss and loading characteristics of compressor tandem blades are evaluated. Whole study was focused on change of the total camber so called turning angle. Effects of camber change were investigated in terms of loss and loading characteristics. Methodology was increasing overall camber first by aligning angular positions of blades and second, if required, using more cambered airfoils. 2-dimensional cascade flow CFD analyses were performed to obtain loss-loading information of different tandem blade combinations. Acquired results were compared with the classical axial compressor blades&rsquo / loading and loss characteristics which were obtained from literature. Results showed that most of the time tandem blade configuration performed better than the single blade counterpart in 2-dimensional cascade flow. Lastly, to clarify the benefit of the study and present the gained performance in numbers, only one cascade flow CFD analysis was performed for a classical single compressor blade. Loss and loading results were compared with the tandem blade counterpart where single and tandem configurations both having the same degree of camber. It was clearly seen that tandem blade performed better again.

Conversion of a scroll compressor to an expander for organic Rankine Cycle: modeling and analysis / UOIT

This paper discussed a way of applied stress to control the photonic crystal fiber dispersion curve, so that it can act on the anomalous dispersion or normal dispersion region area. By this way, we can design the pulse compressor and pulse stretcher for higher peak power laser system. Recently, high-power shortpulse laser has become an indispensable tool in many field, using short-pulse laser oscillator, combined with chirped-frequency amplification technology to produce high-power short-pulse laser system can be used for industrial or medical applications. The all-fiber laser system not only provide better pulse quality and also increased pulse laser system on the stability of the environment.

This paper proposes a sensorless control construction adapting to different speed with DSP2407 as the signal processing control core for rotation compressor. The sensorless control method obtains the rotor position by detecting the back electromotive force signals directly, then obtains better communications and the speed estimation by using digital signal which controlling power switches. Finally ,it carries out speed feedback control and current feedback control to improvt efficiency. Comparing adaptive-step control with traditional-step control and six-step control , the experiment result shows that adaptive-step control has better efficiency and lower vibration.

The DSP is used as the control kernel in this thesis, proposing a method of sensorless and variable speed driving with current feedback for the DC compressor. By detecting the back electromotive force signals directly, the information of rotor position can be obtained, the commutation process and the speed estimation can also be achieved. Combining the current feedback method, the sinusoidal commutation with sensorless control makes the motor lower speed ripple and higher rotating efficiency. The results show that the sinusoidal commutation approach has the advantages of higher efficiency and less speed ripple as compared to the approaches of traditional-step commutation and six-step with current feedback by experimental setting.

Among the major deterioration problems a gas turbine encountered while in operation is compressor blade fouling. This is the accumulation and adhesion of dirt and sediment on the compressor blade which contributes between 70 to 85% of gas turbine performance loss. Fouling reduces turbine air mass flow capacity, compressor pressure ratio and overall gas turbine efficiency. In most cases, its effect does not manifest immediately in gas turbine power output and efficiency since they are not measured directly. However, it is apparent on the gradual increase in Turbine Entry temperature (TET) and Exhaust Gas Temperature (EGT). More fuel is burnt in the combustion chamber to maintain turbine power output which leads to high combustion flame temperature and thus reduces creep life of hot components. This research seeks to analyse the technical and economic consequences of compressor fouling in overall gas turbine performance. The work begins with simulation of TS3000 engine and examination of its design and off design performance. Subsequently, medium size gas turbine engine was modelled, simulated and its performance at different condition was examined to validate the outcome of field data analysis. Three months field operating data of Hitachi H-25 gas turbine generator used for power generation at bonny oil and gas terminal in Nigeria was collected and corrected to international standard ambient condition, using thermodynamic calculations. These data were analysed to determine the effect of fouling on the engine fuel consumption, power output in order to determine the plant profitability. The above analysis gives an estimation of fuel cost saving benefit of $41,000 over the period of one year plant operation due to regular two weekly compressor online water wash which is a good indication of the engine efficiency.