The implementation of a ported shroud casing treatment is often used to extend the operating range of a centrifugal compressor. This work utilizes the STAR-CCM+ CFD package to analyze steady-state, single-passage simulations of a centrifugal compressor with and without a ported shroud to better understand how a ported shroud affects compressor flow physics. Verification and validation of simulations were conducted by comparison of results with a time-accurate full-annulus simulation and experimental data. Four different ported shroud revisions were considered and modeled along the full range of their stable operation, with emphasis placed on the flow limits of choke and stall. A ported shroud is found to improve the choked mass flow limit by increasing the aerodynamic area of the compressor. Near-stall operation is improved through flow recirculation through the ported shroud. This flow, which is induced with a large component of tangential velocity from having passed the impeller blades' leading edge once, reduces the impeller incidence. The influence of a strut is found to restrict both limits of operation by reducing the aerodynamic area and obstruction of tangential velocity. The revisions considered demonstrate that facilitation of flow entering the ported shroud under either near-stall or choked conditions causes a noteworthy improvement in performance. Such alterations, in this application, demonstrate a 3.3% improvement in choked mass flow rate under choked conditions and an 1.3 degree reduction in impeller incidence under near-stall conditions, as compared to the initial ported shroud design. Understanding the effect that a ported shroud casing treatment has on compressor flow physics, especially near its limits of operation, suggests methods for improving centrifugal compressor design to increase its stable operating range.

Diploma thesis deals with calculations of a steam turbine with two uncontrolled extraction points according to the assignment, aerodynamics of the last two stages and operating range with respect to ventilation, range of performance and straining of the last blading under the large condensation pressure deviations. For the first three stages the calculation of prismatic action blades is executed. The fourth and the fifth stages are designed with inconstant reaction over the blades length and their calculation is executed with constant circulation method. For these stages, aerofoil design with respect to their aerodynamic qualities is carried out using Bézier curves. During the whole time verification process of aerofoils qualities, their energy losses and isoentropic Mach number distribution is executed in MISES program in cooperation with Doosan Škoda Power.

This research aims to assess the causes of inefficient and unstable operation of centrifugal compressors and turboexpanders in process gas applications in order to provide a solution for performance restoration and enhancement. It encompasses thermodynamic and flow evaluations to examine the efficiency and operating range improvement options of new units. Besides, this work is complemented by a technoeconomic analysis to provide a rounded outcome from these studies. In order to achieve the desired objectives, a novel integrated approach has been developed to assess the design and performance of multi-stage centrifugal compressors. The proposed systematic methodology involves five basic elements including evaluation of compressor selection, compressor sizing and casing structure, performance prediction at the design and off-design conditions, modelling of efficiency and head deterioration causes; and stage design evaluation. This will contribute towards evaluating the geometrical parameters of the new units’ designs at the early preliminary design phase, and thus, will be useful to identify the options for efficiency and operating range enhancements. For installed units, this approach can be implemented to assess the cause of inefficient and unstable operation by assessing the available operation data. A method was developed to predict the performance curve of multi-stage centrifugal compressor based on a stage stacking technique. This approach considers the advantages of Lüdtke and Casey-Robinson methods with an incorporation of a methodology for compressor selection and sizing to generate more accurate results. To emphasize the validity of the developed model, it has been evaluated for both low and high flow coefficient applications. The obtained results show a significant improvement in the estimated efficiency, pressure ratio, shaft power and operating range as compared with the existing methods. The centrifugal compressor is designed to run under various operating conditions and different gas compositions with the primary objective of high efficiency and reliability. Therefore, a new iterative method has been developed to predict the equivalent compressor performance at off-design conditions. This technique uses the performance parameters at design conditions as a reference point to derive the corresponding performance characteristics at numerous suction conditions with less dependency on the geometrical features. Through a case study on a gas transport centrifugal compressor, it was found that the developed approach can be applied for design evaluation on the expected variation of working conditions, and for the operation diagnosis of installed units as well. Furthermore, a parametric study has been conducted to investigate the effect of gas properties on the stage efficiency, surge margin, and compressor structure. The obtained results support the need for considering the gas properties variation when the off-design performance is derived. To evaluate the impact of internal blockage on the performance parameters, this study proposed an approach to model the effect of non-reactive deposits, which has been qualified using four operation cases and the obtained results are compared with the internal inspection findings from the stage overhauling process. This also covers the influential aspects of flow blockage on the technical and economic values. Since the main challenge here is to analyze the process gas composition in real time, the influences of the non-reactive deposits have been compared with the effect of the unanticipated gas composition change. Subsequently, it has turned out that the pressureratio parameter is not enough to assess the possibility of flow blockage and unexpected gas properties change. Moreover, it was observed that the stage discharge pressure was more sensitive to the fouled aftercooler comparing with suction and internal blockage. However, the effect of contaminated aftercooler on the surge point and discharge pressure and temperature of the upstream stage was found greater than its impact on the shaft power. Thus, a substantial surge margin reduction was detected when the first stage was operating with a fouled aftercooler comparing with the measured reduction as a result of unanticipated gas properties change. Furthermore, a larger pressure ratio drop was measured in the case of liquid carryover which revealed a more significant impact of the two phases densities difference comparing with the gas volume fraction (GVF) effect. The possibility of hydrate formation has been assessed using hydrate formation temperature (HFT) criteria. Additionally, this research highlights a number of challenges facing the selection of typical centrifugal stage design by assessing the contribution of design characteristics on the operating efficiency and stable flow range. Besides, an empirical-based-model was established to select the optimum impeller and diffuser configurations in order to make a compromise decision based on technical and economic perspective. It was concluded that there is no absolute answer to the question of optimum rotor and stator configuration. The preliminary aerothermodynamic evaluation exposed that the selection of the optimum impeller structure is governed by several variables: stage efficiency, pressure loss coefficient, manufacturing cost, required power cost, resonance frequency and stable operating range. Hence, an evaluation is required to compromise between these parameters to ensure better performance. Furthermore, it was argued throughout this study that the decision-making process of the typical stage geometrical features has to be based upon the long-term economic performance optimization. Thus, for higher long-term economic performance, it is not sufficient to select the characteristics of the impeller and diffuser geometry based on the low manufacturing cost or efficiency improvement criterion only. For turboexpanders, a simple and low cost tool has been developed to determine the optimum turboexpander characteristics by analysing the generated design alternatives. This approach was used in designing a turboexpander for hydrocarbon liquefaction process. Moreover, since the turboexpanders are expected to run continuously at severe gas conditions, the performance of the selected turboexpander was evaluated at different inlet flow rates and gas temperatures. It has turned out that designing a turboexpander with the maximum isentropic efficiency is not always possible due to the limitations of the aerodynamic parameters for each component. Therefore, it is necessary to assess the stage geometrical features prior the construction process to compromise between the high capital cost and the high energetic efficiency.

Previous studies have used accelerometers with various operating ranges (ORs) when measuring biomechanical parameters. However, it is still unclear whether ORs influence the accuracy of running parameters, and whether the different stiffnesses of footwear midsoles influence this accuracy. The purpose of the present study was to systematically investigate the influence of OR on the accuracy of stride length, running velocity, and on peak tibial acceleration. Twenty-one recreational heel strike runners ran on a 15-m indoor track at self-selected running speeds in three footwear conditions (low to high midsole stiffness). Runners were equipped with an inertial measurement unit (IMU) affixed to the heel cup of the right shoe and with a uniaxial accelerometer at the right tibia. Accelerometers (at the tibia and included in the IMU) with a high OR of ±70 g were used as the reference and the data were cut at ±32, ±16, and at ±8 g in post-processing, before calculating parameters. The results show that the OR influenced the outcomes of all investigated parameters, which were not influenced by tested footwear conditions. The lower ORs were associated with an underestimation error for all biomechanical parameters, which increased noticeably with a decreasing OR. It can be concluded that accelerometers with a minimum OR of ±32 g should be used to avoid inaccurate measurements.

Previous studies have used accelerometers with various operating ranges (ORs) when measuring biomechanical parameters. However, it is still unclear whether ORs influence the accuracy of running parameters, and whether the different stiffnesses of footwear midsoles influence this accuracy. The purpose of the present study was to systematically investigate the influence of OR on the accuracy of stride length, running velocity, and on peak tibial acceleration. Twenty-one recreational heel strike runners ran on a 15-m indoor track at self-selected running speeds in three footwear conditions (low to high midsole stiffness). Runners were equipped with an inertial measurement unit (IMU) affixed to the heel cup of the right shoe and with a uniaxial accelerometer at the right tibia. Accelerometers (at the tibia and included in the IMU) with a high OR of ±70 g were used as the reference and the data were cut at ±32, ±16, and at ±8 g in post-processing, before calculating parameters. The results show that the OR influenced the outcomes of all investigated parameters, which were not influenced by tested footwear conditions. The lower ORs were associated with an underestimation error for all biomechanical parameters, which increased noticeably with a decreasing OR. It can be concluded that accelerometers with a minimum OR of ±32 g should be used to avoid inaccurate measurements.

La conception optimale de turbomachines repose usuellement sur des méthodes itératives avec des évaluations soit expérimentales, soit numériques qui peuvent conduire à des coûts élevés en raison des nombreuses manipulations ou de l’utilisation intensive de CPU. Afin de limiter ces coûts et de raccourcir les temps de développement, le présent travail propose d’intégrer une méthode de paramétrisation et de métamodélisation dans un cycle de conception d’une turbomachine axiale basse vitesse. La paramétrisation, réalisée par l’étude de sensibilité d’ordre élevé des équations de Navier-Stokes, permet de construire une base de données paramétrée qui contient non seulement les résultats d’évaluations, mais aussi les dérivées simples et les dérivées croisées des objectifs en fonction des paramètres. La plus grande quantité d’informations apportée par les dérivées est avantageusement utilisée lors de la construction de métamodèles, en particulier avec une méthode de Co-Krigeage employée pour coupler plusieurs bases de données. L’intérêt économique de la méthode par rapport à une méthode classique sans dérivée réside dans l’utilisation d’un nombre réduit de points d’évaluation. Lorsque ce nombre de points est véritablement faible, il peut arriver qu’une seule valeur de référence soit disponible pour une ou plusieurs dimensions, et nécessite une hypothèse de répartition d’erreur. Pour ces dimensions, le Co-Krigeage fonctionne comme une extrapolation de Taylor à partir d’un point et de ses dérivées. Cette approche a été expérimentée avec la construction d’un méta-modèle pour une hélice présentant un moyeu conique. La méthodologie fait appel à un couplage de bases de données issues de deux géométries et deux points de fonctionnement. La précision de la surface de réponse a permis de conduire une optimisation avec un algorithme génétique NSGA-2, et les deux optima sélectionnés répondent pour l’un à une maximisation du rendement, et pour l’autre à un élargissement de la plage de fonctionnement. Les résultats d’optimisation sont finalement validés par des simulations numériques supplémentaires. / The turbomachinery optimal design usually relies on some iterative methods with either experimental or numerical evaluations that can lead to high cost due to numerous manipulations and intensive usage of CPU. In order to limit the cost and shorten the development time, the present thesis work proposes to integrate a parameterization method and the meta-modelization method in an optimal design cycle of an axial low speed turbomachine. The parameterization, realized by the high order sensitivity study of Navier-Stokes equations, allows to construct a parameterized database that contains not only the evaluations results, but also the simple and cross derivatives of objectives as a function of parameters. Enriched information brought by the derivatives are utilized during the meta-model construction, particularly by the Co-Kriging method employed to couple several databases. Compared to classical methods that are without derivatives, the economic benefit of the proposed method lies in the use of less reference points. Provided the number of reference points is small, chances are a unique point presenting at one or several dimensions, which requires a hypothesis on the error distribution. For those dimensions, the Co-Kriging works like a Taylor extrapolation from the reference point making the most of its derivatives. This approach has been experimented on the construction of a meta-model for a conic hub fan. The methodology recalls the coupling of databases based on two fan geometries and two operating points. The precision of the meta-model allows to perform an optimization with help of NSGA-2, one of the optima selected reaches the maximum efficiency, and another covers a large operating range. The optimization results are eventually validated by further numerical simulations.

Im Fokus dieser kumulativ angefertigten Dissertation stehen vier methodenorientierte biomechanische Studien, in welchen die potentiellen Fehlerquellen analysiert werden, die beim Einsatz von Inertialsensoren in der biomechanischen Gang- und Laufanalyse auftreten können. In den einzelnen Beiträgen werden die Einflüsse der Inertialsensoraufnahmefrequenz (Studie I) und des Messbereichs der Beschleunigungssensoren (Studie II) auf die kinematischen, kinetischen und räumlich-zeitlichen Parameter systematisch untersucht. Des Weiteren wird sich kritisch mit der Genauigkeit verschiedener Detektionsmethoden des initialen Bodenkontaktes (Studie III) sowie mit der Aussagekraft der maximalen Eversionsgeschwindigkeit (Studie IV) auseinandergesetzt. Um ein umfassendes Bild der Einflussgrößen zu erhalten, wurde in den Studien II, III und IV untersucht, ob die Materialcharakteristik der Laufschuhsohle die Genauigkeit der biomechanischen Parameter beeinflusst. Zudem wurde in Studie III geprüft, welchen zusätzlichen Effekt der Laufstil (Vor- und Rückfußlaufen) auf die Genauigkeit der initialen Bodenkontaktbestimmung hat sowie welchen Einfluss die Bewegungsgeschwindigkeit (Gehen und Laufen) auf die maximale Eversionsgeschwindigkeit nehmen kann (Studie IV). Die Ergebnisse der vier Untersuchungen werden am Ende dieser Arbeit in einem gemeinsamen Kontext diskutiert. Auf Grundlage der Erkenntnisse konnte eine Übersicht erstellt werden, welche sowohl die Mindestanforderungen an Inertialsensoren als auch die Einflussgrößen auf die Genauigkeit der biomechanischen Parameter enthält. Mit diesem Überblick erhalten Nutzer von Inertialsensoren (z.B. Sportler, Trainer, Mediziner und Wissenschaftler) bei der Planung einer Bewegungsanalyse die Unterstützung, die Sensoren mit der passenden Sensorspezifikation in Kombination mit den präzisesten Auswertealgorithmen auszuwählen. Zudem können die Informationen aus dieser Dissertation dazu genutzt werden, Erkenntnisse bereits publizierter Studien kritisch zu hinterfragen. / In previous studies, inertial sensors were used to investigate kinematic, kinetic, and spatio-temporal parameters during walking and running. The present cumulative doctoral thesis consists of four methodological studies. Two of the studies examine the influence of inertial sensor sampling rate (study I) and accelerometer operating range (study II) on the accuracy of biomechanical parameters. Another study investigated whether different published foot strike detection methods can accurately detect the time of initial ground contact (study III). The final study examined whether a single gyroscope can be used to accurately determine peak eversion velocity (study IV). In order to obtain a comprehensive view of the influencing factors, studies II, III and IV also investigated whether the material characteristics of the running shoe sole also influence the accuracy of the biomechanical parameters. Additionally, the effect of running style (forefoot or rearfoot) on the accuracy of foot strike detection methods was investigated in study III, and the effect of locomotion speed (walking, running slow up to running fast) on the accuracy of peak eversion velocity was examined in study IV. The results of the four investigations will be summarized and discussed in a common context. Based on the findings, an overview was prepared which contains both the minimum requirements for inertial sensors and also the influencing variables on the accuracy of the biomechanical parameters. This overview may assist users of inertial sensors (e.g. athletes, trainers, physicians, or scientists) in planning gait and running analyses to select inertial sensors with the appropriate specification in combination with the most accurate algorithms. In addition, the information from this dissertation can be used to critically consider the findings of published studies.