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This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087419889429., [EN] Estimating correctly the turbine acoustics can be valuable during the engine design stage; in fact, it can lead to a more optimised design of the silencer and aftertreatment, as well as to better prediction of the scavenging effects. However, obtaining the sound and noise emissions of radial turbocharger turbines with low computational costs can be challenging. To consider these effects in a time-efficient manner, the acoustic response of single-entry radial turbines can be characterised by means of acoustic transfer matrices that change with the operating conditions. Exploiting the different time-scales of the acoustic phenomena and the change in the operating point of the turbine, lookup tables of acoustic transfer matrices can be computed. Then, the obtained characterisation can be used in mean-value engine models. This article presents a method for generating these lookup tables by means of fast one-dimensional simulations of thoroughly validated fidelity, in terms of both acoustics and extrapolation capabilities. Due to the inherent behaviour of radial turbines, the number of computations needed to fill the lookup tables is relatively small, so the method can be used as a simple preprocessing phase before mean-value simulation campaigns.

[EN] New compact engine architectures such as pressure gain combustion require ad hoc turbomachinery to ensure an adequate range of operation with high performance. A critical factor for supersonic turbines is to ensure the starting of the flow passages, which limits the flow turning and airfoil thickness. Radial outflow turbines inherently increase the cross section along the flow path, which holds great potential for high turning of supersonic flow with a low stage number and guarantees a compact design. First, the preliminary design space is described. Afterward a differential evolution multi-objective optimization with 12 geometrical design parameters is deducted. With the design tool autoblade 10.1, 768 geometries were generated and hub, shroud, and blade camber line were designed by means of Bezier curves. Outlet radius, passage height, and axial location of the outlet were design variables as well. Structured meshes with around 3.7 x 10(6) cells per passage were generated. Steady three-dimensional (3D) Reynolds-averaged Navier-Stokes (RANS) simulations, enclosed by the k-omega shear stress transport turbulence model were solved by the commercial solver CFD++. The geometry was optimized toward low entropy and high-power output. To prove the functionality of the new turbine concept and optimization, a full wheel unsteady RANS simulation of the optimized geometry exposed to a nozzled rotating detonation combustor (RDC) has been performed and the advantageous flow patterns of the optimization were also observed during transient operation.

[EN] Over the past few decades, the aerodynamic improvements of turbocharger turbines contributed significantly to the overall efficiency augmentation and the advancements in downsizing of internal combustion engines. Due to the compact size of automotive turbochargers, the experimental measurement of the complex internal aerodynamics has been insufficiently studied. Hence, turbine designs mostly rely on the results of numerical simulations and the validation of zero-dimensional parameters as efficiency and reduced mass flow. To push the aerodynamic development even further, a precise validation of three-dimensional flow patterns predicted by applied computational fluid dynamics (CFD) methods is in need. This paper presents the design of an up-scaled volute-stator model, which allows optical experimental measurement techniques. In a preliminary step, numerical results indicate that the enlarged geometry will be representative of the flow patterns and characteristic non-dimensional numbers at defined flow sections of the real size turbine. Limitations due to rotor-stator interactions are highlighted. Measurement sections of interest for available measurement techniques are predefined.

[EN] The characterization of tip leakage flow plays an important role for one-dimesional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional tip leakage momentum ratio, a novel correlation has been derived. This allows a consistent characterization for variable tip gap sizes over a wide range of operating conditions. The correlation has been validated by means of CFD data with high variety in reduced speed tip gap geometry and expansion ratios. Results of the novel number show significant improvements of quantitative and qualitative results over a wide range of running conditions in comparison to existing correlations. Furthermore, correlations for tip leakage velocities, that can easily be used in one-dimensional models, have been derived. Finally, it has been demonstrated, that the influence of inlet flow momentum on the tip leakage flow can be analyzed with presented correlations.

[EN] Pulsating flow in automotive turbocharger turbines makes it necessary to know performance characteristics in difficult to measure off-design conditions. Physically based extrapolation models can be used to extrapolate towards unmeasured map regions. However, for model parameter fittings common maps have low numbers of measurement points per speedline available. Measurements with different variable geometry turbine (VGT) openings amplify the available data and help to characterize the turbine in a wider aerodynamic range. Nevertheless, physical models able to fit the data of several speeds and VGT positions with the same set of fitting parameters are rare. Thus, a model that is capable of fitting all speeds and VGT positions simultaneously and with the capability of extrapolating reliably towards low pressure ratios, unmeasured speeds, and VGT openings has been developed. The model is based on novel and commonly used loss correlations combined in an innovative way and has been validated in a wide range of pressure ratios towards extreme off-design conditions. By deactivating stator passage effects, the model can also extrapolate efficiency maps of vaneless turbines. The set of loss models is able to reproduce the measured data in a good quality for tested turbines with a very reduced number of fitting coefficients. (C) 2019 Elsevier Ltd. All rights reserved.

[ES] Para lograr una correspondencia óptima entre el turbocompresor y el motor de combustión interna en un amplio rango del mapa de operación del motor, su compleja interacción se analiza comúnmente por medio de modelos transitorios unidimensionales. El flujo pulsante de los gases de escape del motor causa altas variaciones de caudal, presión total y temperatura total en la entrada de la turbina. Esto lleva a la turbina del turbocompresor hacia condiciones extremadamente fuera de diseño. Por lo tanto, se requieren amplios mapas de operación de turbina como entrada para estos modelos unidimensionales. La medida de los mapas de turbinas suele estar restringida por el choque y el bombeo del compresor. En esta tesis, el compresor del turbocompresor se convirtió en una turbina centrífuga para ayudar a la rotación del eje cuando la turbina produce o incluso consume baja potencia. Para aumentar la potencia de salida de la rueda del compresor, se colocó una IGV aguas arriba de la entrada del compresor. Para reducir el esfuerzo de adiabatización de la significativa transferencia de calor interna en estas condiciones de operación, se desarrolló una correlación simple que solo depende de las medidas de temperatura de fluidos. Con los datos obtenidos fuera del diseño, se validó una configuración de CFD para el logro de resultados convergentes en condiciones extremadamente fuera del diseño. Para reducir la problemática de los elevados ángulos de flujo en la salida de la turbina, cuando se opera con bajos caudales másicos, el conducto de salida se extendió y se tuvo que colocar un conducto cónico justo antes de la salida del dominio. Por medio de los resultados de CFD bien validados, se analizaron los efectos tridimensionales del flujo. Operando en condiciones fuera del diseño, el remolino de salida, y por lo tanto, el gradiente de presión estática es tan alto que el flujo colapsa y se produce un flujo reverso. Esta reversión del flujo regresa al interior del rotor y se mezcla nu, [CA] Per aconseguir una correspondència òptima entre el turbocompressor i el motor de combustió interna en una amplia zona del mapa d'operació del motor, la seva complexa interacció s'analitza comunament per mitjà de models transitoris unidimensionals. El flux polsant dels gasos d'escapament del motor causa altes variacions de cabal, pressió total i temperatura total a l'entrada de la turbina. Això porta a la turbina del turbocompressor cap a condicions extremadament fora de disseny. Per tant, es requereixen amplis mapes d'operació de turbina com a entrada per a aquests models unidimensionals. La mesura dels mapes de turbines sol estar restringida pel choke i el surge del compressor. En aquesta tesi, el compressor del turbocompressor va esdevenir una turbina centrífuga per ajudar a la rotació de l'eix quan la turbina produeix o fins i tot consumeix baixa potència. Per augmentar la potència de sortida de la roda del compressor, es va col·locar una IGV aigües amunt de l'entrada del compressor. Per reduir l'esforç de adiabatización de la significativa transferència de calor interna en aquestes condicions d'operació, es va desenvolupar una correlació simple que només depèn de les mesures de temperatura del fluids. Amb les dades obtingudes fora del disseny, es va validar una configuració de CFD per a l'assoliment de resultats convergents en condicions extremadament fora del disseny. Per reduir la problemàtica dels elevats angles de flux a la sortida de la turbina, quan s'opera amb baixos cabals màssics, el conducte de sortida es va estendre i es va haver de posar un conducte cònic just abans de la sortida del domini. Per mitjà dels resultats de CFD ben validats, es van analitzar els efectes tridimensionals del flux. Operant en condicions fora del disseny, el remolí de sortida, i per tant, el gradient de pressió estàtica és tan alt que el flux col·lapsa i es produeix un flux revers. Aquesta reversió del flux torna a l'interior del rotor i es barreja novament amb el flux p, [EN] To achieve an optimal matching between the turbocharger and internal combustion engine over a wide range of the engine operation map, their complex interaction is commonly analyzed by means of transient one-dimensional modeling. The pulsating flow of the engine exhaust gases causes high variations of turbine inlet mass flow, total pressure, and total temperature. This pushes the turbocharger turbine operation towards extreme off-design conditions. Hence, wide turbine operation maps are required as input for the one-dimensional models. The measurement of turbine maps is typically restricted by compressor choke and surge. At the same time, only minor geometrical changes are required to maintain the important thermal characteristics of the turbocharger. In this thesis the turbocharger compressor was converted into a centrifugal turbine to assist the axis rotation when the turbine produces or even consumes low power. For enhancing the power output from the compressor wheel, an IGV was placed upstream of the compressor inlet. To reduce the effort for adiabatizing, a simple correlation only dependent on fluid temperature measurements was developed. Further test monitoring strategies were documented that can assist the measurement of off-design conditions. With the obtained off-design data a CFD setup for the achievement of convergent results in extreme off-design conditions was validated. To reduce the problem of high swirl angles in the turbine outlet when operating with low mass flows, the outlet duct was extended and a tapered duct had to be attached just before the domain outlet. By means of the well validated CFD results, three-dimensional flow effects were analyzed. Operating in high off-design conditions the outlet swirl and thus, the static pressure gradient was so high that the flow collapses and a reverse flow develops. This reverse flow reenters the rotor and mixes again with the main flow. On one hand this effect produces pressure losses and locally negat

[EN] Due to the power consumption restriction of the turbocharger compressor, common turbine maps are rather narrow. To extrapolate them, reliable physical submodels are needed that are valid for broad ranges. Plenty of research has been done referring to tip leakage losses in axial and traditional radial turbomachinery. However, less effort has been put into the tip leakage analysis of radial turbocharger turbines, whose characteristics including high rotational speed and geometry are rather different. Commonly developed tip leakage loss models in radial turbines are mainly based on correlations with the rotational speed, while in axial turbomachinery they are mainly based on blade loading assumptions. Wide range computational fluid dynamics (CFD) data of a medium sized automotive turbine have been used to analyze tip leakage mass flow under extremely diverse running conditions. To be able to fit a model in a broad range of the map, blade loading and rotational speed have to be considered. A novel tip clearance model has been derived from the Navier Stokes Equations. The model owns a dependency on the rotational speed and the blade loading. With this approach CFD data have been fitted in a very good quality to model the tip leakage mass flow rate and tip leakage losses.

[EN] During automotive urban driving conditions and future homologation cycles, automotive radial turbines experience transient conditions, whereby the same operate at very high blade speed ratios and, thus, at very low power outputs. Under those conditions, the turbine power output might not be enough to feed the mechanical power needs of the compressor. Typical fast one-dimensional full engine simulations rely on steady-state performance maps to characterize the turbocharger. Due to the restricting compressor braking power, extreme off-design measurements cannot be obtained in standard gas stands without using an external brake instead of the compressor or without using a motor attached to the turbocharger shaft. Such turbocharger assemblies cause shaft balancing issues inherent to the connection to a brake operating at high rotational speeds or need basic changes of the turbocharger geometry. This paper presents a novel approach for turbine performance map measurements at very low expansion ratio and very low mass flow without the aforementioned issues. The method uses the turbocharger compressor as a centrifugal turbine, providing mechanical power to the shaft and enabling turbine performance measurements from points of very high expansion ratio up to very low pressure ratio. It is even possible to measure at almost zero flow rate in the turbine when it consumes shaft power instead of producing it. This experimental procedure that can be applied to whatever turbocharger produces valuable information for the development and validation of turbine performance models aiming to extrapolate its behaviour at off-design conditions.

[EN] Due to the acceleration and the deceleration in automotive urban driving cycles, turbochargers experience unusual flow conditions for thermal turbomachinery. The knowledge of the right flow behavior at such off-design conditions can improve the matching of engines and turbochargers, whereby a reduction in the fuel consumption can be achieved. To analyze the flow field the CFD software StarCCM+ will be used. For obtaining reliable results the solution method of the CFD calculation has to be validated in advance., [ES] Debido a la aceleración y la desaceleración en ciclos de conducción urbana de automoción, los turbocompresores experimentan condiciones de flujo inusuales para la turbomaquinaria térmica. El conocimiento del comportamiento de flujo fuera de diseño puede mejorar la adecuación de los motores y turbocompresores, por lo que una reducción en el consumo de combustible se puede lograr. Para analizar el campo de flujo se utilizará el software CFD StarCCM+. Para la obtención de resultados fiables el método de solución del cálculo CFD tiene que ser validado por adelantado y esta será una tarea del presente TFG.