The main objective of this Master´s thesis is the appropriate calculation proposal of pressure and discharge conditions in extensive ducts in unsteady flow. The calculation proposal was aimed at the conenction of two commercial programmes. Exacly the programme Ansis Fluent and Matlab, which deals with the connection of onedimensional (1D) calculation in Matlab and multidimensional (2D) calculation in Ansys Fluent programme. This Mastr’s thesis also deals with creation of the independent 1D model (Matlab, method of characteristic) and independent 2D model flow (Ansys Fluent, Inviscid model).

In this Master thesis are mentioned the most used constructions of non-return valves. Further consist of operation principles, fields of application, properties and diffi-culties connected to non-return valves. Motion plug of check valve in liquid is described based on CFD Software simulation.

Die Abgasturboaufladung erweist sich als sinnvolles Hilfsmittel den Kraftstoffverbrauch eines Hubkolbenverbrennungsmotors bei gleichbleibender Fahrdynamik zu verringern und somit die Effizienz des Motors zu erhöhen. Zur optimalen Nutzung der im Abgas enthaltenen Energie werden Abgassysteme moderner Pkw – Motoren äußerst kompakt ausgeführt, um der Abgasturboladerturbine ein möglichst hohes Enthalpiegefälle zur Verfügung zu stellen. Diese Umstände, sowie zunehmend kleinere Zylinderzahlen mit großen Zündabständen führen dazu, dass sich die Eintrittsbedingungen von Radialturbinen von Abgasturboladern heutiger Motoren periodisch ändern. Die Strömungsmaschine kann aufgrund ihrer Trägheit dem Druckanstieg nicht unverzögert folgen und wird vorwiegend bei niedrigen Schnelllaufzahlen betrieben. Die Entwicklung von Abgasturboladern und deren Anpassung an den Verbrennungsmotor erfolgen überwiegend auf Grundlage von messtechnisch ermittelten Kennfeldern von Verdichter und Turbine. Diese werden an stationär betriebenen Heißgasprüfständen ermittelt. Aufgrund der stationären Leistungsbilanz zwischen beiden Strömungsmaschinen an diesen Prüfständen beschreiben stationär gemessene Turbinenkennfelder nicht den gesamten motorrelevanten Betriebsbereich der Turbine. Für die Entwicklung innovativer Turboladerturbinen sind Untersuchungen der Turbinenwirkungsgrade und Durchsatzkennzahlen in diesen Betriebspunkten essentiell. Zur Untersuchung von Wechselwirkungen zwischen aufgeladenen Verbrennungsmotoren und Aufladesystemen stellt die Motorprozessrechnung eine wichtige Technologie dar. Die numerische Beschreibung des Turboladerverhaltens im Motorbetrieb erfolgt ebenfalls auf Basis von gemessenen Turboladerkennfeldern. Aufgrund des eingeschränkten Messbereichs der Turbinenkennfelder werden diese stark extrapoliert und beschreiben das thermodynamische Verhalten der Turboladerturbine fragwürdig. Die vorliegende Arbeit stellt ein neues Verfahren an einem erweiterten Heißgasprüfstand zur Vermessung und Untersuchung von Turboladerturbinen in motorrelevanten Betriebszuständen vor. Parallel wird ein Berechnungsmodell entwickelt, um Messergebnisse zu plausibilisieren und die numerische Beschreibung instationärer Turbinenströmungen zu untersuchen. Die Methode basiert auf der Ausnutzung zusätzlicher Beschleunigungsleistung zur Erhöhung der Aufnahme der Turbinenleistung, um niedrigere Schnelllaufzahlen unter motorrealistischen Randbedingungen untersuchen zu können. Mit Hilfe eines geeigneten Druckverlaufes werden temporär stationäre Strömungszustände erzeugt, sodass thermodynamische Zustände in der Turbine zuverlässig beschrieben werden können. Ferner werden Betriebsbedingungen der Turbinenuntersuchung denen der Turboladerturbine im Motorbetrieb angepasst. Kurzzeitig stellen sich quasi-stationäre Zustände ein, woraufhin phasenkorrigierte Messgrößen die Strömung in den Schaufelkanälen der Turbine belastbar beschreiben. Durch Variation der pulsierenden Strömung können Wirkungsgrad- und Massendurchsatzkennfelder mit hoher Abtastrate erweitert werden, wodurch verlässliche Interpolationen der Turbinenkennfelder bei niedrigen Laufzahlen möglich sind. Am Heißgasprüfstand lassen sich Turbineneintrittstemperatur, Druckamplitude und mittleres Druckverhältnis mit speziellen Impulsgeneratoren einstellen. Auch eine instationäre Massenstrommessung und Temperaturmessung ist möglich. Die instationäre Messmethode bildet eine Synthese mit stationären Turbinenvermessungen und deckt einen Großteil des Turbinenbetriebes aufgeladener Hubkolbenverbrennungsmotoren ab. Damit hat dieses Verfahren das Potential Turboladerkennfelder die am stationären Heißgasprüfstand ermittelt wurden sinnvoll zu ergänzen. Ergebnisse der neuen Messmethode werden mit Resultaten äquivalenter Simulationsrechnungen auf Grundlage stationär und instationär ermittelter Kennfelder verglichen. Auf Basis erweiterter Turbinenkennfelder können Wechselwirkungen zwischen dem Verbrennungsmotor und dem Aufladeaggregat mit Hilfe der Motorprozessrechnung genauer untersucht werden. Dies ermöglicht eine ideale Anpassung des Abgasturboladers an den Motor, wodurch Effizienz und Dynamik verbessert sowie Abgasemissionswerte des Antriebes reduziert werden können.

<p dir="ltr">Gas turbines are widely used to provide propulsion, electrical-power, and mechanical power. Though tremendous advances have been made since Frank Whittle’s patent of a turbojet in 1930 and Hans von Ohain’s patent of the first operational turbojet in 1936, industry still has aggressive goals on improvements in efficiency and service life. One area where further advances are needed is better control of the flow across the gap between the blade tip and the shroud, referred to as tip-leakage flow (TLF). This is because TLF accounts for up to one-third of the aerodynamic losses in a turbine stage.</p><p dir="ltr">In this study, hybrid LES-RANS based on IDDES and steady RANS based on the SST turbulence model were used to study the compressible flow in a 1.5-stage turbine with geometry and operating conditions that are relevant to power-generation gas turbines. The focus is on the flow in the tip-gap region that account for the flow features created by the upstream stator vanes, stator-rotor interactions, and downstream stator vanes. Results obtained reveal the flow structures about the tip-gap region and the flow mechanisms that create them. Results obtained also show where steady RANS with mixing plane could predict correctly when compared with results from IDDES that resolve the unsteadiness of the turbulence and the motion of the rotor blades passing the stator vanes. Turbulent statistics from the IDDES were generated to guide the development of better RANS models. Results were also obtained by using RANS to examine the effects of blade loading, where mass flow rate through the 1.5 stage turbine was varied with the rotor’s rotational speed fixed at 3,600 RPM – the speed at which power-generation gas turbines operate in the U.S.</p><p dir="ltr">Key findings are as follows: In the first-stage stator, horseshoe, passage, and corner vortices were found to be confined within 10 to 15% span from the hub and shroud, and both steady RANS and IDDES generated similar results. Steady RANS and IDDES, however, differed considerably in how they predicted the wake downstream of the vane’s trailing edge. This coupled with the use of mixing plane, steady RANS was unable to account for effects of stator-rotor interactions and their effects on the tip-leakage flow. In the rotor, steady RANS predicted passage vortices that extended up to 50% span from the hub and 25% span from the shroud. The flow through the tip gap was found to induce a separation bubble on the blade tip and one large and two small vortical structures on the suction side of the blade and a vortical structure next to the shroud. These structures were found to grow along the axial chord of the blade. Steady RANS also predicted the large tip leakage vortex that contained the fluid from the tip-leakage flow to breakdown. IDDES did not predict the vortex breakdown because all of the coherent vortical structures identified including the separated region on the blade tip were unsteady and constantly shedding. As a result, IDDES predicted much smaller mean passage vortices – albeit the instantaneous structures were nearly as large as those predicted by steady RANS.</p>

This master´s thesis provides an overview of all designs of check valves, their usage and typical features. Main purpose of this work is to clear up the phenomenon of check valve slam and the other problems that occur during transients. The check valve slam was measured at the test rig in the hydraulic laboratory. For unsteady flow evaluation after pump shut down was used Gibson method. The dynamic characteristic was possible to create by results from this method. It was achieved without impact of the speed of sound in the fluid. This work also contains 2D transient CFD calculations, which was used for evaluation of the hydrodynamic torque acting on the hinge pin. This approach provides an option to calculate wide range of cases at the expense of not entirely exact geometry. The main contribution of the theoretical study at the beginning of this thesis is its entireness. It might give an important clue when right valve is selecting. For good choice of valve might be helpful to use dynamic characteristics in this thesis presented. Mentioned characteristics were created by new way and its background is in measurements and simplified CFD calculations.

Indiana University-Purdue University Indianapolis (IUPUI) / We numerically investigate the underlying physics of two peculiar phenomena, which are axis-switching and saddle-back velocity profile, in both laminar and turbulent rectangular jets using lattice Boltzmann method (LBM). Previously developed computation protocols based on single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann equations are utilized to perform direct numerical simulation (DNS) and large eddy simulation (LES) respectively. In the first study, we systematically study the axis-switching behavior in low aspect-ratio (AR), defined as the ratio of width over height, laminar rectangular jets with <italic>AR=1</italic> (square jet), 1.5, 2, 2.5, and 3. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the streamwise velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. The <italic>45&deg</italic> and <italic>90&deg</italic> axis-switching occur in characteristic decay (CD) region consecutively at the early and late stage. The half-width contour (HWC) reveals that <italic>45&deg</italic> axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when <italic>45&deg</italic> axis-switching occurs. The close examinations of flow pattern and vorticity contour, as well as the correlation between streamwise velocity and vorticity, indicate that <italic>90&deg</italic> axis-switching results from boundary effect. Specific flow patterns for <italic>45&deg</italic> and <italic>90&deg</italic> axis-switching reveal the mechanism of the two types of axis-switching respectively. In the second study we develop an algorithm to generate a turbulent velocity field for the boundary condition at jet inlet. The turbulent velocity field satisfies incompressible continuity equation with prescribed energy spectrum in wave space. Application study of the turbulent velocity profile is on two turbulent jets with <italic>Re=25900</italic>. In the jets with <italic>AR=1.5</italic>, axis-switching phenomenon driven by the turbulent inlet velocity is more profound and in better agreement with experimental examination over the laminar counterpart. Characteristic jet development driven by both laminar and turbulent inlet velocity profile in square jet (<italic>AR=1</italic>) is also examined. Overall agreement of selected jet features is good, while quantitative match for the turbulence intensity profiles is yet to be obtained in future study. In the third study, we analyze the saddle-back velocity profile phenomenon in turbulent rectangular jets with AR ranging from 2 to 6 driven by the developed turbulent inlet velocity profiles with different turbulence intensity (<italic>I</italic>). Saddle-back velocity profile is observed in all jets. It has been noted that the saddle-back's peak velocities are resulted from the local minimum mixing intensity. Peak-center difference <italic>&Delta_pc</italic> and profound saddle-back (PSB) range are defined to quantify the saddle-back level and the effects of AR and <italic>I</italic> on saddle-back profile. It is found that saddle-back is more profound with larger AR or slimmer rectangular jets, while its relation with <italic>I</italic> is to be further determined.

Indiana University-Purdue University Indianapolis (IUPUI) / A constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.