The ability of fish to deform their bodies in steady swimming action is gaining from robotic designers. While bound by the same physical laws, fish have evolved to move in ways that often outperform artificial systems in critical measures such as efficiency, agility, and stealth through thousands of years of natural selection. As we expand our presence in the ocean with deep-sea exploration or offshore drilling for petroleum and natural gas, the demand for prolonging underwater operations is growing significantly. Therefore, it is critical for robotic designers to understand the physics of pisciform (fish-like) locomotion and learn how to effectively implement the propulsive mechanisms into their designs to create the next generation of aquatic robots. Aiming to assist this process, this thesis presents an experimental apparatus called Towed Biolocomotion Emulator (TBE), which is capable of imitating the undulating action of different fish species in steady swimming and can be quickly adapted to different configurations with modular modules. Using the TBE device, an experiment is performed to test its hydrodynamic performance and evaluate the effectiveness of the bio-inspired locomotion implemented on such a mechanical system. The analysis of hydrodynamic data collected from the experiment shows that there exists a small range of kinematic parameters where the undulating motion of the device produces the optimal performance. This result confirms the benefits of utilizing pisciform locomotion for small-scale underwater vehicles. In addition, this thesis also proposes a reduced-order flow model using the unsteady vortex lattice method (UVLM) to predict the hydrodynamic performance of such a system. The proposed model is then validated with the experimental data collected earlier. The tool developed can be employed to quickly explore the possible design space early in the conceptual design stage for such a bio-mimetic vehicle. / Master of Science / It is no surprise that through thousands of years of natural evolution, marine species possess incredible ability to navigate through water. As we expand our presence in the sea, more and more tasks require underwater operations such as ocean exploration, oil-rig maintenance, etc. Yet, most of the underwater robotic vehicles still utilize propellers as the primary propulsive mechanism. In many cases, the bio-inspired propulsion system that mimics the swimming action of fish offers many advantages in agility, maneuverability, and stealth. With the rising interest in the field, the works presented in this thesis aim to expand our understanding of how to implement the bio-inspired propulsive mechanism to robotic design. To achieve this, a mechanical device is designed to mimic the swimming action of different fish species. Then, an experiment is performed to subject the device to different fish-like motions and test their effectiveness. In addition, a reduced-ordered model is also introduced as an alternative method to predict the hydrodynamic performance of this propulsive mechanism. The works presented in this thesis help to expand the toolbox available for the engineer to design the next generation of the underwater robotic vehicle.

Detailed surface pressure measurements have been made on a NACA 0015 immersed in two grid generated homogenous flows at Re = 1.17 x 10⁶ for a = 0°, 4°, 8°, 12°, 16°, and 20°. The goal of this measurement was to reveal and highlight mean loading and turbulence scale effects on surface pressure fluctuations resulting from turbulence/airfoil interaction. Also, measurements are compared with the theory of Amiet (1976a,b). The surface pressure response shows a dependance on angle of attack, the nature of which is related to the relative chord/turbulence scale. The dependance on turbulence scale appears to be non-monotonic at low reduced frequencies, wr = Pi*f*c/U with both an increase and decrease in unsteady pressure magnitude occurring with increasing mean load. A reduced frequency overlap region exists at wr > 10 where the two different scale flows begin to produce similar effects on the surface pressure with increasing angle of attack manifesting as a rise in unsteady surface pressure magnitude. Also, the interaction of the full 3-dimensional wavenumber spectrum affects the distance over which pressure fluctuations correlate and the extent of correlation is affected by angle of attack as demonstrated in the chordwise and spanwise pressure correlation. Amiet's theory is shown to agree favorably with measurements in the leading edge region although demonstrates insufficiencies in predicting unsteady pressure phasing. / Master of Science

Strong interactions between flow about an aircraft wing and the wing structure can result in aeroelastic phenomena which significantly impact aircraft performance. Time-accurate methods for solving the unsteady Navier-Stokes equations have matured to the point where reliable results can be obtained with reasonable computational costs for complex non-linear flows with shock waves, vortices and separations. The ability to combine such a flow solver with a general finite element structural model is key to an aeroelastic analysis in these flows. Earlier work involved time-accurate integration of modal structural models based on plate elements. A finite element model was developed to handle three-dimensional wing boxes, and incorporated into the flow solver without the need for modal analysis. Static condensation is performed on the structural model to reduce the structural degrees of freedom for the aeroelastic analysis. Direct incorporation of the finite element wing-box structural model with the flow solver requires finding adequate methods for transferring aerodynamic pressures to the structural grid and returning deflections to the aerodynamic grid. Several schemes were explored for handling the grid-to-grid transfer of information. The complex, built-up nature of the wing-box complicated this transfer. Aeroelastic calculations for a sample wing in transonic flow comparing various simple transfer schemes are presented and discussed. / M.S.

The history and trajectory of the human race is inseparable from our innate need to explore the unknown. As human exploration drives boundless new insights into the universe, characterization and accurate modeling methods are required to develop the next generation of exploratory vehicles to map and analyze foreign lands. As such the presented work looks to provide characterization and modeling approaches for unsteady aerodynamic phenomena in the extraterrestrial environments of Mars and Titan. Specifically, unsteady aerodynamic loads including dynamic stall are characterized using high-fidelity numerical experiments to better understand the effects of low Reynolds number and high Mach number flows on the process. Additionally, modeling of unsteady aerodynamic behavior at low Reynolds numbers similar to those observed when designing the Mars ingenuity rotorcraft are developed and extensively evaluated. Lastly, the characterization and multi-fidelity modeling of unsteady aerodynamic effects under Titan atmospheric conditions is conducted for a coaxial rotor system.

Aerodynamic flow control using internal acoustic excitation holds promise as it combines the simplicity of passive flow control techniques (in terms of added weight and operational complexity) with the control authority of active flow control methods. While previous studies have analyzed the effects of acoustic excitation on steady wing aerodynamics, the effect of excitation on the unsteady aerodynamics is not known, which is the aim of the current effort. Internally mounted speakers on a symmetric National Advisory Committee for Aeronautics (NACA) 0012 wing are used to excite the unsteady boundary layer at the wing’s leading edge as it executes linear pitch motions ranging from quasi-steady (trailing-edge driven stall) to vortex dominated (mixed leading- and trailing-edge driven stall) motions at freestream Reynolds numbers (����) of 120, 000 and 180, 000. Experimental results show that, while acoustic excitation delays stall for quasi-steady motions, it enhances lift in the linear region and increases leading-edge vortex strength for vortex -dominated motions. The degree of change was observed to be a function of the excitation frequency. The current work establishes the effects of acoustic flow excitation in unsteady, low-���� wing aerodynamics and provides insights on the path forward to effectively implement the method for active flow control.

<p align="justify">This work deals with the development of numerical methods for compressible flow simulation with application to the interaction of fluid flows and structural bodies.</p> <p align="justify">First, we develop numerical methods based on multidimensional upwind residual distribution (RD) schemes. Theoretical results for the stability and accuracy of the methods are given. Then, the RD schemes for unsteady problems are extended for computations on moving meshes. As a second approach, cell centered and vertex centered finite volume (FV) schemes are considered. The RD schemes are compared to FV schemes by means of the 1D modified equation and by the comparison of the numerical results for scalar problems and system of Euler equations. We present a number of two and three dimensional steady and unsteady test cases, illustrating properties of the numerical methods. The results are compared with the theoretical solution and experimental data.</p> <p align="justify">In the second part, a numerical method for fluid-structure interaction problems is developed. The problem is divided into three distinct sub-problems: Computational Fluid Dynamics, Computational Solid Mechanics and the problem of fluid mesh movement. The problem of Computational Solid Mechanics is formulated as a system of partial differential equations for an anisotropic elastic continuum and solved by the finite element method. The mesh movement is determined using the pseudo-elastic continuum approach and solved again by the finite element method. The coupling of the problems is achieved by a simple sub-iterative approach. Capabilities of the methods are demonstrated on computations of 2D supersonic panel flutter and 3D transonic flutter of the AGARD 445.6 wing. In the first case, the results are compared with the theoretical solution and the numerical computations given in the references. In the second case the comparison with experimental data is presented.</p>

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.

These thesis review some recent results on the construction of very high order multidimensional upwind schemes for the solution of steady and unsteady conservation laws on unstructured triangular grids.<p>We also consider the extension to the approximation of solutions to conservation laws containing second order dissipative terms. To build this high order schemes we use a subtriangulation of the triangular Pk elements where we apply the distribution used for a P1 element.<p>This manuscript is divided in two parts. The first part is dedicated to the design of the high order schemes for scalar equations and focus more on the theoretical design of the schemes. The second part deals with the extension to system of equations, in particular we will compare the performances of 2nd, 3rd and 4th order schemes.<p><p>The first part is subdivided in four chapters:<p>The aim of the second chapter is to present the multidimensional upwind residual distributive schemes and to explain what was the status of their development at the beginning of this work.<p>The third chapter is dedicated to the first contribution: the design of 3rd and 4th order quasi non-oscillatory schemes.<p>The fourth chapter is composed of two parts: we start by understanding the non-uniformity of the accuracy of the 2nd order schemes for advection-diffusion problem. To solve this issue we use a Finite Element hybridisation.<p>This deep study of the 2nd order scheme is used as a basis to design a 3rd order scheme for advection-diffusion.<p>Finally, in the fifth chapter we extend the high order quasi non-oscillatory schemes to unsteady problems.<p>In the second part, we extend the schemes of the first part to systems of equations as follows:<p>The sixth chapter deals with the extension to steady systems of hyperbolic equations. In particular, we discuss how to solve some issues such as boundary conditions and the discretisation of curved geometries.<p>Then, we look at the performance of 2nd and 3rd order schemes on viscous flow.<p>Finally, we test the space-time schemes on several test cases. In particular, we will test the monotonicity of the space-time non-oscillatory schemes and we apply residual distributive schemes to acoustic problems. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The present thesis involves the study of introducing passive exit flexibility in a two dimensional starting jet. This is relevant to various biological flows like propulsion of aquatic creatures (jellyfish, squid etc.) and flow in the human heart. In the present study we introduce exit flexibility in two ways. The first method was by hinging rigid plates at the channel exit and the second was by attaching deformable flaps at the exit. In the hinged flaps cases, the experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia; these limiting structural properties permitting the largest flap openings. In the deformable flaps cases, the flap’s stiffness (or its flexural rigidity EI) becomes an important parameter. In both cases, the initial condition was such that the flaps were parallel to the channel walls. With this, a piston was pushed in a controlled manner to form the starting jet. Using this arrangement, we start the flow and visualize the flap kinematics and make flow field measurements. A number of parameters were varied which include the piston speed, the flap length and the flap stiffness (in case of the deformable flaps). In the hinged rigid flaps cases, the typical motion of the flaps involves a rapid opening with flow initiation and a subsequent more gradual return to its initial position, which occurs while the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, additional pairs of vortices are formed because of the motion of the flaps and a complete redistribution of vorticity is observed. The length of the flaps is found to significantly affect flap kinematics when plotted using the conventional time scale L/d. However, with a newly defined time-scale based on the flap length (L/Lf ), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15 degrees. Even though the flap kinematics collapses well with L/Lf , there are differences in the distribution of the ejected vorticity even for the same L/Lf . In the deformable flap cases, the initial excess pressure in the flap region causes the flaps to bulge outwards. The size of the bulge grows in size, as well as moves outwards as the flow develops and the flaps open out to reach their maximum opening. Thereafter, the flaps start returning to their initial straight position and remain there as long as the piston is in motion. Once the piston stops, the flaps collapse inwards and the two flap tips touch each other. It was found that the flap’s flexural rigidity played an important role in the kinematics. We define a new time scale (t ) based on the flexural rigidity of the flaps (EI) and the flap length (Lf ). Using this new time scale, we find that the time taken to reach the maximum bulge (t* 0.03) and the time taken to reach the maximum opening (t* 0.1) were approximately similar across various flap stiffness and flap length cases. The motion of the flaps results in the formation of additional pairs of vortices. Interestingly, the total final circulation remains almost the same as that of a rigid exit case, for all the flap stiffness and flap lengths studied. However, the final fluid impulse (after all the fluid had come out of the flap region) was always higher in the flap cases as compared to the rigid exit case because of vorticity redistribution. The rate at which the impulse increases was also higher in most flap cases. The final impulse values were as large as 1.8 times the rigid exit case. Since the time rate of change of impulse is linked with force, the measurements suggest that introduction of flexible flaps at the exit could result in better propulsion performances for a system using starting jets. The work carried out in this thesis has shown that by attaching flexible flaps at the exit of an unsteady starting jet, dramatic changes can be made to the flow field. The coupled kinematics of the flaps with the flow dynamics led to desirable changes in the flow. Although the flaps introduced in this work are idealized and may not represent the kind of flexibility we encounter in biological systems, it gives us a better understanding of the importance of exit flexibility in these kinds of flows.

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.