Ce document propose une démarche expérimentale permettant de reproduire les écoulements pulsés, que l’on retrouve dans le collecteur d’échappement d’un moteur, sur les caractéristiques des performances d’un turbocompresseur de suralimentation. Une étude comparative des différents moyens d’essais existants, permettant de reproduire les effets pulsés en entrée de la turbine d’un turbocompresseur, est présentée. Elle permet d’évaluer les avantages et les inconvénients de chacun pour définir un cahier des charges de fonctionnalité d’un nouveau banc d’essai Les travaux permettant la mise en oeuvre de l’instrumentation spécifique propre à répondre aux besoins de développement de ce moyen d’essai sont exposés. Le principal objectif est pouvoir obtenir une mesure du débit instantané ainsi que celle de la température instantanée. Les premiers résultats obtenus avec les conditions d’essais utilisant le système mis en place pour simuler le régime pulsé, complétés par une analyse des différentes procédures d’exploitation, montrent qu’il est possible de restituer des essais cohérents en régime d’écoulement stationnaire et pulsé afin de les comparer. Les possibilités d’exploiter d’autres résultats sont évoquées, compte tenu de la flexibilité du banc ; il est en effet possible faire varier de façon indépendantes plusieurs types de conditions d’écoulements pulsés pour simuler, par exemple, différents points de charge d’un moteur donné ou de simuler différentes valeurs du nombre de cylindres. / The document presents the results of an experimental work devoted to create pulse flows, independently from a real car engine, equivalent to the exhaust pipe engine flow characteristics, on the overall performances of a turbocharger. A comparative analysis on existing test stands that are able to perform such flow conditions is presented. This allows defining a new test stand which specific conditions that are not already covered by previous test stands. All steps concerning the ability to set up of the new test stand and more specifically instrumentation development and acquisition systems are detailed. First set of results obtained with the test stand, in pulse conditions, are presented with some analysis on performance comparisons between steady and pulse inlet conditions at the turbocharger inlet section. The new pulse test stand allows performing more flexible variations of inlet flow unsteady conditions, different thrust load values and number of motor cylinders as well

A numerical study was carried out for enhanced heat transfer from two heated blocks in a pulsating channel flow by porous heat sink. The flow over the fluid region is governed by the Navier-Stokes equation, and the flow through the porous medium is governed by the Darcy-Brinkman-Forchheimer equation. These two flows are coupled through the interface boundary conditions at the porous/fluid and porous/solid interfaces. After a stream function-vorticity transformation, solution of the coupled governing equations for fluid/porous/solid composite system is obtained using the control-volume-based procedure and hybrid scheme. Comprehensive time-dependent flow and temperature data obtained and averaged over a cycle of pulsation in a periodic steady state. In addition, this study details the effects of variation in the governing parameters, such as inertia parameter, Dracy number, Reynolds number, Strouhal number, pulsation amplitude and geometric parameters, to illustrate important fundamental and practical results. The results show that the periodic change of shape of interblock recirculation flow caused by porous-covering blocks has significant enhanced effect on flow pattern and heat transfer characteristics. This enhanced effect is found to increase with Reynolds number, Strouhal number and pulsation amplitude but decrease with Dracy number. In comparison with the non-porous heat sink case for a steady non-pulsating flow, significant increases in the average Nusselt number are predicted and the instantaneous maximum temperatures within the heated block array are reduced. Moreover, it is shown that specific choices in certain geometric parameters, such as interblock space, can make pronounded change in the cooling of heated block.

Automotive catalytic converters are used extensively in the automotive industry to reduce toxic pollutants from vehicle exhausts. The flow across automotive exhaust catalysts is distributed by a sudden expansion and has a significant effect on their conversion efficiency. The exhaust gas is pulsating and flow distribution is a function of engine operating condition, namely speed (frequency), load (flow rate) and pressure loss across the monolith. The aims of this study are to provide insight into the development of the pulsating flow field within the diffuser under isothermal conditions and to assess the steady-state computational fluid dynamics (CFD) predictions of flow maldistribution at high Reynolds numbers. Flow measurements were made across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser in the presence of pulsating flow. Cycle-resolved Particle Image Velocimetry (PIV) measurements were made in the diffuser and hot wire anemometry (HWA) downstream of the monoliths. The ratio of pulse period to residence time within the diffuser (J factor) characterises the flow distribution. During acceleration the flow remained attached to the diffuser walls for some distance before separating near the diffuser inlet later in the cycle. Two cases with J ~ 3.5 resulted in very similar flow fields with the flow able to reattach downstream of the separation bubbles. With J = 6.8 separation occurred earlier with the flow field resembling, at the time of deceleration, the steady flow field. Increasing J from 3.5 to 6.8 resulted in greater flow maldistribution within the monoliths; steady flow producing the highest maldistribution in all cases for the same Re. The oblique entry pressure loss of monoliths were measured using a one-dimensional steady flow rig over a range of approach Reynolds number (200 < Rea < 4090) and angles of incidence (0o < α < 70o). Losses increased with α and Re at low mass flow rates but were independent of Re at high flow rates being 20% higher than the transverse dynamic pressure. The flow distribution across axisymmetric ceramic 400 cpsi and perforated 600 cpsi monoliths were modelled using CFD and the porous medium approach. This requires knowledge of the axial and transverse monolith resistances; the latter being only applicable to the radially open structure. The axial resistances were measured by presenting uniform flow to the front face of the monolith. The transverse resistances were deduced by best matching CFD predictions to measurements of the radial flow profiles obtained downstream of the monolith when presented with non-uniform flow at its front face. CFD predictions of the flow maldistibution were performed by adding the oblique entry pressure loss to the axial resistance to simulate the monolith losses. The critical angle approach was used to improve the predictions, i.e. the oblique entry loss was limited such that the losses were assumed constant above a fixed critical angle, αc. The result showed that the perforated 600 cpsi monolith requires the entrance effect to be restricted above αc = 81o, while the losses were assumed constant above αc = 85o for the ceramic 400 cpsi monolith. This might be due to the separation bubble at the monolith entrance being restricted by the smaller hydraulic diameter of the perforated monolith thus limiting the oblique entry loss at the lower incidence angle.

The reduction of fuel consumption and the reduction of toxic emissions are the main goals of research and development in the area of internal combustion engines. The use of exhaust gas recirculation (EGR) to come further in that direction is today an established method for diesel engines. EGR reduces the emissions of nitrogen oxides with a low penalty in fuel consumption. The increasingly hard regulations on emissions put high pressure on the manufacturers to improve these systems. The present work aims at increasing the knowledge in the area of EGR. Two of the main challenges when applying EGR are addressed, efficiency and mixing. The efficiency of the EGR-system is analyzed, focusing on keeping the fuel penalty low for a given EGR-rate. Different layouts of the EGR system are studied and compared regarding their stationary and transient properties. Exergy analysis is used to show the potential for improvement in different system components. In the same time, exergy analysis as a tool is introduced and compared to energy analysis of a system. The usefulness of exergy analysis of the entire gas exchange is shown by the example of a heavy-duty diesel engine. The problem of EGR and air mixing is approached by a detailed study of the mixing process in a heavy-duty diesel engine. Different methods for the measurement of EGR distribution are presented and compared. Additionally, the possibility to predict the mixing effects by 1-D and 3-D simulation is assessed. It is shown that the mixing between air and EGR is highly dependent on the pulsating nature of the flow. The EGR is shown to be transported in packets in the air flow. This leads to the conclusion that mixing not only at the mixing point, but also mixing in flow direction needs to be optimized, as the distribution of EGR between the cylinders is dependent on the timing between the passage of the EGR packets and the valve opening time. / <p>QC 20140203</p>

La perturbation des écoulements au voisinage de la paroi artérielle équipée d'un stent joue un rôle prépondérant dans l'apparition et le développement des complications liées aux maladies cardiovasculaires (sténose, resténose, thrombose...). La topologie de l'écoulement dans ces régions est très complexe. En effet, au voisinage du stent, des zones de recirculation se forment en amont et aval de chaque branche et les contraintes pariétales y sont très faibles. Des études in vivo et in vitro ont mis en évidence le rôle de ces caractéristiques de l'écoulement intra-stent sur les maladies cardiovasculaires. Pour cela, la bonne estimation des contraintes pariétales et la compréhension du comportement de l'écoulement intra-stent et son rôle dans le transfert du principe actif devraient permettre d'optimiser les traitements (design de la prothèse, principe actif...). L'approche numérique est une voie très utile pour étudier ces phénomènes. Cependant, la bonne précision du calcul dépend du choix du modèle d'écoulement, des conditions aux limites, de la géométrie du stent et de l'artère pour réaliser une simulation pertinente.Nous étudions ici dans un premier temps l'effet du choix du modèle hémodynamique sur les caractéristiques de l'écoulement intra-stent. Trois modèles numériques décrivant l'écoulement coronaire ont été utilisés. Ces modèles sont : un modèle stationnaire "MP", le modèle pulsé simplifié "MPS" et le modèle pulsé complet "MPC" basé sur l'analyse de Womersley. Nous avons ainsi montré l'importance de la prise en compte de l'instationnarité de l'écoulement mais au dépens d'un temps de calcul très accru. Dans un second temps, nous étudions expérimentalement l'écoulement intra-stent en utilisant la technique de mesure "PIV". Cette étude expérimentale a permis de confirmer les résultats numériques précédents. Au final, nous examinons numériquement l'effet de la pulsatilitié de l'écoulement sur les flux massiques libérés par les faces d'une branche de stent actif. Cette étude numérique a mis en exergue l'importance du couplage entre les recirculations et le transfert de masse vers la paroi artérielle. / The disturbance of the flow in the vicinity of the arterial wall equipped with a stent plays a key role in the onset and development of complications related to cardiovascular diseases (stenosis, restenosis, thrombosis...). The topology of the flow field in the intra-stent zone is very complex. Indeed, in the vicinity of the stent, recirculation zones form upstream and downstream of the stent strut where wall shear stress is very low. In vivo and in vitro studies have demonstrated the role of the in-stent flow features on cardiovascular diseases.The correct estimation of the wall shear stress, the understanding of the behavior of the in-stent flow and its role in the transfer of the drug are expected to help optimize treatments (stent geometry, drug composition...). The numerical approach (CFD) is a useful and versatile way to study these phenomena. However, the accuracy and the relevance of the results depend on the choice of the flow model, the boundary conditions and the stent and artery geometry.Firstly we study in this work the impact of the hemodynamic model on the in-stent flow characteristics. Three numerical models describing the coronary flow are used. These models are: the steady model "MP", the simplified pulsatile model "MPS" and the complete pulsatile model "MPC" based on Womersley's analysis. We show the importance of the pulsatility of the flow but at the expense of a high increase in the computing time. Secondly we study experimentally the in-stent flow using measurement technique "PIV". This experimental study confirms the previous numerical results. Finally we examine numerically the effects of the flow pulsatility on the mass fluxes released by the faces of a drug eluting stent. This numerical study highlights the importance of the coupling between the recirculation zones and the mass transfer into the arterial wall.

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[ES] Está fuera de toda duda que la industria del automóvil está viviendo una profunda transformación que, durante los últimos años, ha progresado a un ritmo acelerado. Debido a la crecientemente estricta regulación sobre emisiones contaminantes y la necesidad de satisfacer la siempre creciente demanda de movilidad sostenible, es necesario que los motores de combustión modernos reduzcan su consumo y emisiones manteniendo el rendimiento del motor. Para enfrentarse a este desafío, los ingenieros de investigación y desarrollo han redoblado sus esfuerzos a la hora de diseñar y mejorar los modelos unidimensionales, hasta el punto en el que el desarrollo de modelos 1D así como la simulación juegan un papel fundamental en los primeras etapas de diseño de nuevos motores y tecnologías. Al mismo tiempo, la tecnología de turbosobrealimentación se ha consolidado como una de las más efectivas a la hora de construir motores de alta eficiencia, lo que ha hecho evidente la importancia de comprender y modelar correctamente los efectos asociados a los turbogrupos. Particularmente, los fenómenos que ocurren en la turbina en condiciones de flujo fuertemente pulsante han demostrado ser complicadas de modelar y sin embargo decisivas, ya que los códigos de simulación son especialmente útiles cuando son diseñados para trabajar en condiciones realistas. Este trabajo se centra en mejorar los modelos unidimensionales actuales así como en desarrollar nuevas soluciones con el objetivo de contribuir a una mejor predicción del comportamiento de la turbina sometida a condiciones de flujo pulsante. Tanto los esfuerzos realizados en los trabajos experimentales como en los de modelado se han producido para poder proporcionar métodos que sean fáciles de adaptar a las diferentes configuraciones de turbogrupo usadas en la industria, por ello, pueden ser aplicados por ejemplo en turbinas de entrada simple y también en las cada vez más usadas turbinas de entrada doble. En cuanto al trabajo de modelado en la parte de turbina de entrada simple, el foco se ha puesto en presentar una versión mejorada de un código quasi-2D. La validación del modelo se basa en los datos experimentales que están disponibles de trabajos enteriores de la literatura, proporcionando una comparación completa entre los modelos quasi-2D y el clásico modelo 1D. La presión a la entrada y salida de la turbina se ha descompuesto en ondas que viajan hacia delante y hacia atrás por medio de la descomposición de presiones, empleando la componente reflejada y transmitida para verificar la bondad del modelo. El trabajo experimental de esta tesis se centra en desarrollar un nuevo método para ensayar cualquier turbina de doble entrada sometida a condiciones de flujo fuertemente pulsante. La configuración del banco de gas se ha diseñado para ser suficientemente flexible como para realizar pulsos en las dos ramas de entrada por separado, así como para usar condiciones de flujo caliente o condiciones ambiente con mínimos cambios en la instalación. La campaña experimental se usa para validar un modelo integrado unidimensional de turbina tipo twin scroll con especial foco en las componentes reflejada y transmitida para analizar el desempeño del modelo su capacidad de predicción de la acústica no lineal. Finalmente, después de desarrollar el trabajo experimental y de modelado, se presenta un procedimiento para caracterizar el sonido y ruido de la turbina por medio de matrices de transferencia acústica que es comparado con el código unidimensional completo. En este sentido, el método proporciona una herramienta útil y fácil de implementar para simulaciones en tiempo real que aplica de una manera práctica el trabajo de modelado expuesto a lo largo de esta tesis. / [CA] Està fora de tot dubte que la indústria de l'automòbil està vivint una profunda transformació que, durant els últims anys, ha progressat a un ritme accelerat. A causa de la creixentment estricta regulació sobre emissions contaminants i la necessitat de satisfer la sempre creixent demanda de mobilitat sostenible, és necessari que els motors de combustió moderns reduïsquen el seu consum i emissions mantenint el rendiment del motor. Per a enfrontar-se a aquest desafiament, els enginyers de recerca i desenvolupament han redoblat els seus esforços a l'hora de dissenyar i millorar els models unidimensionals, fins al punt en el qual el desenvolupament de models 1D així com la simulació juguen un paper fonamental en les primeres etapes de disseny de nous motors i tecnologies. Al mateix temps, la tecnologia de turbosobrealimentación s'ha consolidat com una de les més efectives a l'hora de construir motors d'alta eficiència, la qual cosa ha fet evident la importància de comprendre i modelar correctament els efectes associats als turbogrupos. Particularment, els fenòmens que ocorren en la turbina en condicions de flux fortament polsant han demostrat ser complicades de modelar i no obstant això decisives, ja que els codis de simulació són especialment útils quan són dissenyats per a treballar en condicions realistes. Aquest treball se centra en millorar els models unidimensionals actuals així com a desenvolupar noves solucions amb l'objectiu de contribuir a una millor predicció del comportament de la turbina sotmesa a condicions de flux polsant. Tant els esforços realitzats en els treballs experimentals com en els de modelatge s'han produït per a poder proporcionar mètodes que siguen fàcils d'adaptar a les diferents configuracions de turbogrupo usades en l'indústria, per això, poden ser aplicats per exemple en turbines d'entrada simple i també en les cada vegada més usades turbines d'entrada doble. Pel que fa al treball de modelatge en la part de turbina d'entrada simple, el focus s'ha posat a presentar una versió millorada d'un codi quasi-2D. La validació del model es basa en les dades experimentals que estan disponibles de treballs anteriors de la literatura, proporcionant una comparació completa entre els models quasi-2D i el clàssic model 1D. La pressió a l'entrada i eixida de la turbina s'ha descompost en ones que viatgen cap avant i cap enrere per mitjà de la descomposició de pressions, emprant la component reflectida i transmesa per a verificar la bondat del model. El treball experimental d'aquesta tesi se centra en desenvolupar un nou mètode per a assajar qualsevol turbina de doble entrada sotmesa a condicions de flux fortament pulsante. La configuració del banc de gas s'ha dissenyat per a ser prou flexible com per a realitzar polsos en les dues branques d'entrada per separat, així com per a usar condicions de flux calent o condicions ambient amb mínims canvis en la instal·lació. La campanya experimental s'usa per a validar un model integrat unidimensional de turbina tipus twin-scroll amb especial focus en les components reflectida i transmesa per a analitzar l'acompliment del model la seua capacitat de predicció de l'acústica no lineal. Finalment, després de desenvolupar el treball experimental i de modelatge, es presenta un procediment per a caracteritzar el so i soroll de la turbina per mitjà de matrius de transferència acústica que és comparat amb el codi unidimensional complet. En aquest sentit, el mètode proporciona una eina útil i fàcil d'implementar per a simulacions en temps real que aplica d'una manera pràctica el treball de modelatge exposat al llarg d'aquesta tesi. / [EN] It is beyond all doubt that the automotive industry is living a deep transformation that, during the last years, has progressed at an ever accelerating rate. Due to the increasingly stringent pollutant emission regulations and the necessity to fulfil an ever growing demand for sustainable mobility, the modern internal combustion engines are required to strongly reduce the fuel consumption and emissions, while keeping the engine performance. In order to confront this challenge, engine research and development engineers have redoubled their efforts in designing and improving one-dimensional codes, to the point that the development of 1D models and simulation campaigns play a major role in the early steps of designing new engines or technologies. At the same time as the turbocharging technology has arisen as one of the most effective and extended solutions for building high efficient engines, the importance of understanding and modelling correctly the turbocharger effects has become evident. In particular, the phenomena that occurs in the turbine under highly pulsating conditions have proven to be challenging to model and yet decisive, as simulation codes are especially useful when they are designed to work under realistic conditions. This work focusses on the improvement of current one-dimensional models as well as in the development of new solutions with the aim of contributing to a better prediction of the turbine performance under pulsating conditions. Both experimental and modelling efforts have been made in order to provide methods that are easily adaptable to different turbocharger configurations used in the industry, so they can be applied for example in single turbines and also in the increasingly used two-scroll turbine technology. Regarding the modelling work of the single entry turbine part, the work has been focused in presenting an improved version of a quasi-2D code. The validation of the model is based on the experimental data available from previous works of the literature, providing a complete comparison between the quasi-2D and a classic 1D model. By means of a pressure decomposition, the pressure at the turbine inlet and outlet has been split into forward and backward travelling waves, employing the reflected and transmitted components to verify the goodness of the model. The experimental work of the thesis is centred in developing a new method in order to test any two-scroll turbine under highly pulsating flow conditions. The gas stand setup has been designed to be flexible enough to perform pulses in both inlet branches separately as well as to use hot or ambient conditions with minimal changes in the installation. The experimental campaign is used to fully validate an integrated 1D twin-scroll turbine model with special focus in the reflected and transmitted components for analysing the performance of the model and its non-linear acoustics prediction capabilities. Finally, after the experiment and modelling work is developed, a procedure to characterise the turbine sound and noise by means of acoustic transfer matrices is presented and tested against the fully one-dimensional code. In this sense, this method provides a useful and easily-implementable tool for fast and real time simulations that applies in a practical way the modelling work exposed along this thesis. / Soler Blanco, P. (2020). Simulation and modelling of the performance of radial turbochargers under unsteady flow [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/141609

This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a strongly pulsatile motion is superposed on the already complex flow field. Nonetheless, gas flow meters are commonly applied in such environments, e.g. in the measurement of the air flow to the engine or the amount of exhaust gas recirculation. The aim of the present thesis is therefore to understand and assess, and if possible to improve the performance of various flow meters under highly pulsatile conditions as well as demonstrating the use of a new type of flow meter for measurements of the pulsating mass flow upstream and downstream the turbine of a turbocharger. The thesis can be subdivided into three parts. The first one assesses the flow quality of a newly developed flow rig, designed for measurements of steady and pulsating air flow at flow rates and pulse frequencies typically found in the gas exchange system of cars and smaller trucks. Flow rates and pulsation frequencies achieved and measured range up to about 200 g/s and 80 Hz, respectively. The time-resolved mass flux and stagnation temperature under both steady and pulsating conditions were characterized by means of a combined hot/cold-wire probe which is part of a newly developed automated measurement module. This rig and measurement module were used to create a unique data base with well-defined boundary conditions to be used for the validation of numerical simulations, but in particular, to assess the performance of various flow meters. In the second part a novel vortex flow meter that can measure the timedependent flow rate using wavelet analysis has been invented, verified and extensively tested under various industrially relevant conditions. The newly developed technique was used to provide unique turbine maps under pulsatile conditions through time-resolved and simultaneous measurements of mass flow, temperature and pressure upstream and downstream the turbine. Results confirm that the quasi-steady assumption is invalid for the turbine considered as a whole. In the third and last part of the thesis, two basic fundamental questions that arose during the course of hot/cold-wire measurements in the aforementioned high speed flows have been addressed, namely to assess which temperature a cold-wire measures or to which a hot-wire is exposed to in high speed flows as well as whether the hot-wire measures the product of velocity and density or total density. Hot/cold-wire measurements in a nozzle have been performed to test various hypothesis and results show that the recovery temperature as well as the product of velocity and stagnation density are measured. / QC 20120510

Šiame darbe tiriama švarių paviršių paruošimo sūkuriniu pulsuojančiu srautu galimybė. Darbo tikslas: išsiaiškinti švarių paviršių paruošimo galimybę, naudojant vandens srautą, kuriame turbulencijos lėtėjimo dėka sukeliama kavitacija. Darbas sudarytas iš keturių dalių. Pradžioje apibūdinami švarūs paviršiai, jų klasifikacija. Toliau apžvelgiami švarių paviršių paruošimo metodai, problemos. Po to, skaitmeninės simuliacijos būdu, tiriamos sūkurinį pulsuojantį srautą generuojančių purkštukų konstrukcijos. Eksperimentinėje dalyje pateikiami bandymo rezultatai, kuomet iš aliumininės plokštelės šalinamos abrazyvo liekanos, įstrigusios paviršiuje šlifavimo metu. Darbo pabaigoje pateikiamos išvados. Darbo apimtis – 51 psl. teksto be priedų, 36 iliustracijos, 3 lentelės, 13 bibliografinių šaltinių. Atskirai pridedami darbo priedai. / This study investigates the preparation of clean surfaces with pulsating vortex flow option. The aim of work: to determine the possibility of clean surface preparation using a water flow with generated cavitation. The work consists of four parts. At the start of the work characterized clean surfaces and their classification. The following provides an overview of clean surface preparation methods, problems. After that, the digital simulation method investigated vortex-generating jets pulsating flow structures. In the experimental part are presented the test results, when the aluminum plate is disposed abrasive residues trapped on the surface of the grinding time. At the end of the work there are given conclusions. Work size - 51 text pages without appendixes, 36 figures, 3 tables, 13 bibliographical sources.