Dissertations / Theses on the topic 'Unsteady'
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Renick, Dirk H. "Unsteady propeller hydrodynamics." Thesis, Springfield, Va. : Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA393206.
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Majumdar, Sharanya Jyoti. "Unsteady distortion noise." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311216.
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Morgan, P. "Unsteady flow in collapsible tubes." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37791.
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Hwu, Tzong-Her. "Dispersion in unsteady deflected flows." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259980.
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Mohd, Yatim Yazariah. "Unsteady flows of thin films." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=14374.
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Hwang, Kuo-Lun. "Friction in unsteady pipe flows." Thesis, University of Dundee, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413174.
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Wu, Z. Y. "Studies in unsteady flame propagation." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38197.
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Keenan, David P. "Marine propellers in unsteady flow." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14348.
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Armstrong, Brian Jeffrey. "Unsteady flow over bluff bodies." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/11409.
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Craske, John. "Unsteady turbulent jets and plumes." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/44208.
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This thesis investigates the physics of statistically unsteady axisymmetric turbulent jets and plumes using theory and direct numerical simulation. The focus is on understanding and modelling the physics that govern the behaviour of radially integrated quantities, such as the integral scalar flux, momentum flux and buoyancy flux. To this end, a framework is developed that generalises previous approaches, making no assumption about the longitudinal velocity profile, turbulence transport or pressure. The framework is used to develop well-posed integral models that exhibit a good agreement with simulation data. In the case of passive scalar transport, shear-flow dispersion is observed to be dominant in comparison with longitudinal turbulent mixing. A dispersion closure for free-shear flows based on the classical work of Taylor (Proc. R. Soc. Lond. A, vol. 219 1954b, pp. 186-203) is therefore developed. In the analysis of jets whose source momentum flux undergoes an instantaneous step change, it is demonstrated that a momentum-energy framework, of the kind used by Priestley & Ball (Q. J. R. Meteorol. Soc., vol. 81 1955, pp. 144-157), is the natural choice for unsteady free-shear flows. The framework is used to demonstrate why existing top-hat models of unsteady jets and plumes are ill-posed and that jets and plumes with Gaussian velocity profiles remain approximately straight-sided and are insensitive to source perturbations. Contrary to the view that the unsteady jet and plume equations are parabolic, it is shown that the generalised system of equations is hyperbolic. In unsteady plumes, the relative orientation of three independent families of characteristic curves determines whether propagating waves are lazy, forced or pure. To relate findings that are based on the momentum-energy framework to the classical mass-momentum framework, an unsteady entrainment coefficient is defined that generalises the decomposition proposed by Kaminski et al. (2005, J. Fluid Mech., vol. 526, pp. 361-376).
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Unsworth, Christopher Adam. "River dunes in unsteady conditions." Thesis, University of Hull, 2015. http://hydra.hull.ac.uk/resources/hull:13096.
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This thesis explores the nature of river dunes in unsteady conditions. River dune research has two main philosophical approaches that are necessitated by the nature of dunes; they are individually dynamic features emergent from the interaction between flow and sediment transport, whilst this dynamism is restricted by a mixture of instantaneous and historical flow and sediment boundary conditions. This thesis has applied both philosophical approaches to the investigation of river dunes in unsteady conditions and highlights key areas where flow and sediment processes at the laboratory scale overlap that of the larger scale river, such as in the suspension of sediment, and importance of velocity profile shape on dune shape. Normalising the downstream velocity with shear velocity was repeatedly found to simplify and explain the fluid processes over dunes across a range of conditions and indicates that the dominant processes controlling dune shape and sediment mobility are hydraulically smooth, despite hydraulically rough grain sizes. The existence of a turbulent wave over dunes reduces the magnitude of flow velocity that reaches the bed and effectively changes the grain Reynolds number. This turbulent flow structure was extensively measured in this thesis, with detailed instantaneous flow velocity measurements, across a range of flow conditions over fixed bedforms with the use of Particle Imaging Velocimetry. This also revealed that the well-known equilibrium turbulent flow structure over dunes is dramatically altered when in transient flow-morphology conditions. It was found that the wake and stacked wake, changes location and intensity with flow depth and discharge, and that reattachment length is strongly related to U/u* as measured at the dune crest. This research provides descriptions of the causal mechanisms behind many bedform adaptions to flow unsteadiness, such as the formation of humpback dunes in high shear stress conditions. A second set of laboratory experiments explored the mean scaling of dunes with a mobile bed in a recirculating flume. The mean velocity profile shape was adjusted to move the point of maximum downstream velocity toward the bed, whilst keeping depth and depth averaged velocity- two variables used in almost all bedform stability diagrams, the same. It was found that dune height scaled with bed shear stress in a parabola, whilst dune wavelength scaled linearly. This indicates that dune height is primarily controlled via flow separation and dune wavelength scales most well is shear velocity and grain size (i.e. sediment transport lengths). Lastly, dunes were measured in the field during the falling leg of the monsoonal wet season floods on a section of the Mekong River in Cambodia. The river bed consisted of large dunes with superimposed bedforms. The geometry of the large dunes showed no relationship with the hydraulic conditions present; however the secondary dunes size responded to the variations in flow depth. All large dunes migrated at a constant rate, despite variation in height, and it was hypothesised that the superimposed bedforms provided any excess sediment for the host dune migration. Large dune height was half that predicted from empirical equations using flow depth. Variations in suspended sediment did not match those predicted via the Rouse number, instead, plotting U/u*, across variations in discharge and depth showed a good relationship with suspended sediment concentration. This relationship between flow structure and suspended sediment, with the concurrent variation secondary dune size indicated that the large dunes were depth limited. This is despite the consistent presence of secondary dunes at the crest of the host bedform or strong free surface interaction and suggests that dune height in rivers with superimposed bedforms is controlled by the existence of superimposed bedforms.
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Bergmeier, Gene Georg 1972. "Sonic booms from unsteady sources." Thesis, The University of Arizona, 1997. http://hdl.handle.net/10150/291664.
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The acoustical signatures as observed by an auditor on the ground are explored for various radiating bodies. Specifically, a theory that describes the origin of sonic booms of two unsteady point sources and of an airplane is developed. In 1968, Garrick and Maglieri conducted an experiment where a General Dynamics F-106 was subjected to sinusoidal pitch oscillations. At the time, the results of the observed sonic boom were not understood; they had expected a distorted sonic boom. The theory presented in the present study offers an explanation of the results. An essential point needed in order to understand their observations is the source distribution for an acoustically radiating body. This source distribution occupies a region of space many times the length of the airplane. Therefore, any attempts to distort a sonic boom must deal with the grand scale of the source distribution.
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Souza, Max Oliveira de. "Instabilities of rotating and unsteady flows." Thesis, University of Cambridge, 1998. https://www.repository.cam.ac.uk/handle/1810/251641.
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This dissertation is divided into two parts. The first part discusses the stability and breakdown of swirling flows. The second one deals with the stability of time periodic flows. Chapter 1 gives the background and reviews previous work in vortex breakdown. Chapter 2 deals with various aspects of axisymmetric breakdown. These include the study of basic states that do not support waves, and the role played by the downstream boundary conditions in steady solutions to the Euler equations. A description of the bifurcation diagram for pipes is presented, and we also show how the process of wave-steepening can lead to the formation of a highly oscillatory shock. In chapter 3, we study the weakly non-linear stability of trailing vortices. Following numerical calculations by Yang (1992), who found a viscous instability for arbitrary large values of the swirl at sufficiently large Reynolds number, we present an analysis for the steady states and their stability. We obtain fast-swirling, steady states, and study their linear stability to viscous centre-modes. For nearly neutral modes, we investigate their weakly nonlinear stability, accounting for non-parallel effects. Previous work on stability of time-periodic flows is reviewed in chapter 4. In chapter 5, we extend the critical-layer analysis by Lin (1955) to unsteady flows, and use it to investigate the stability of several oscillatory flows. For slightly oscillatory Plane-Poiseuille flow, the method is able to recover periodic modes (asymptotic Floquet modes for large Reynolds numbers). Nevertheless, the method fails for the Stokes layer; the reasons for such failure are discussed. Finally, we present in chapter 6 some results on the completeness of Floquet modes in channels.
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Richardson, David. "Unsteady aerodynamics of high work turbines." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4498.
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One method aircraft engine manufactures use to minimize engine cost and weight is to reduce the number of parts. A significant reduction includes reducing the turbine blade count or combining two moderately loaded turbines into one high-work turbine. The risk of High Cycle Fatigue in these configurations is increased by the additional aerodynamic forcing generated by the high blade loading and the nozzle trailing edge shocks. A lot of research has been done into the efficiency implications of supersonic shocks in these configurations. However what is less well understood is the resulting unsteady rotor forces. These unsteady aerodynamics aspects are the focus of this research.
The research investigates where manufacturers might concentrate their resources to reduce Direct Operating Costs (DOC). It compares the relative financial implications of disruption events to the cost of reducing DOC by further efficiency gains. The technical aspects of the research use computational aerodynamic modelling of a high work turbine to explore the unsteady aerodynamics and the resulting rotor forces. Investigation of parametric models into the effect of reaction, axial spacing, pressure ratio, the nozzle wake profile and the significance of the rotor boundary layer in dissipating the high gradient shocks is also investigated. Data from an experimental test program was used to characterise sub- and super-critical shock boundary layer interactions to determine if they are a significant forcing function.
The primary conclusions from this research include the relative merits of targeting resources into reducing disruption events rather than the relatively small financial gains which might be gained through further efficiency improvement by researching advanced technologies. The computational method is validated against an experimental dataset from a high-speed turbine stage rig. Overall, good agreement is found between the measurements and the predictions for both the detailed unsteady aerodynamics as well as the important rotor forces. The effect of different computational modelling standards is also explored.
The relative significance of the primary aerodynamic forcing functions such as the nozzle wake and trailing edge shock system is evaluated. Generally the rotor forces are found to increase with lower reaction, reduced axial spacing and higher pressure ratio. However the phasing of the forcing functions is found to be a critical aspect in determining the resultant net unsteady forces. The sub-critical shock boundary layer interaction is determined to be a second order effect in relation to the other primary forcing mechanisms, however the supercritical shock boundary layer interaction is shown to be a potential contributory factor in rotor forcing.
Finally, several recommendations are proposed which turbine designers should apply in the event that rotor forcing is considered to be a significant concern.
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Neculita, Catalin Silviu. "Unsteady compressible flows past oscillating airfoils." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99002.
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This thesis presents new and efficient analytical solutions for the unsteady subsonic compressible flows past rigid and flexible airfoils executing low frequency oscillations. These solutions are obtained using an especially developed method based on velocity singularities associated with the airfoil leading edge and ridges, which define the changes in the airfoil boundary conditions. The velocity singularity method has been initially developed by Mateescu.Closed form solutions are presented for the unsteady lift and pitching moment coefficients and for the chordwise distribution of the unsteady pressure difference coefficient in the general case of rigid airfoils executing oscillatory pitching rotations and translations, as well as for flexible airfoils executing flexural oscillations.
For the case of incompressible flows, the present solutions were found in excellent agreement with the previous incompressible flow results obtained by Theodorsen, Postel & Leppert and by Mateescu & Abdo.
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He, Li. "Unsteady flows around oscillating turbomachinery blades." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385407.
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Barker, Adam. "Heat transfer in unsteady pipe flow." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428390.
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Harris, Owen John. "Unsteady flows of dilute polymer solutions." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319993.
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Wang, Bo. "Unsteady wind effects on natural ventilation." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11653/.
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Ventilation stacks are becoming increasingly common in the design of naturally ventilated buildings. The overall aim of the work described is ultimately to improve design procedures for such buildings. This thesis presents the experimental and theoretical investigation of unsteady wind effects on natural ventilation of a single envelope with multiple openings for both wind alone, and wind and buoyancy combined cases. There are two types of openings: namely the sharp-edged orifice and the long opening (stacks being treated as long openings). Two methods are adopted: 1) direct wind tunnel measurements using the hot-wire technique; 2) theoretical analysis using steady and unsteady envelope flow models. For the wind alone experiments, the influences of wind speed, wind direction and opening configuration on flow patterns are studied. For the wind and buoyancy combined tests, the transitional process between wind dominated and buoyancy dominated states are investigated. The direct velocity measurements provide the criteria for testing the validity of the theoretical models, and ways to improve them. Additionally, improvements are made to the experimental techniques: e.g. a precise unsteady calibration method of the hot-wire is developed; improvements of pressure measurements are also investigated. The experimental technique works well with multiple stacks. Even though small openings are used, some dependence of the mean pressure coefficient on opening configuration is observed. The theoretical models also work reasonably well with multiple stacks, yet it is observed that the accuracy of the theoretical models decrease with the increasing number of openings, and is sensitive to the chosen discharge coefficient which defines the characteristics of ventilation openings.
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Harwood, Robin John. "Unsteady aerodynamic forces on parachute canopies." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/9153.
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A research programme has been conducted, the objective of which has been the determination of unsteady force coefficients for a range of parachute canopy models. These coefficients are required for prediction of the aerodynamic stability of full scale parachutes under conditions of unsteady motion during descent. The method of obtaining these coefficients required the collection of force and acceleration data for parachute canopy models which were tested in unsteady conditions. This was achieved by imposing oscillatory motion on individual canopies during towing tests, which were conducted under water in a ship testing tank. Two modes of unsteady motion were imposed on a canopy under test; one in which it was oscillated along its axis, and one in which it was oscillated laterally. A mathematical model describing such modes of motion consists of a general equation for the unsteady force developed on a bluff body. In this model the force F(t) is expressed using two components; a velocity dependent force component, and an acceleration dependent force component. Each component of the aerodynamic force contains an unknown parameter denoted by the terms ‘a’ and ‘b’ in the equation, which is shown below; F( t ) = a( t ) • V²( t ) + b( t ) • V( t ). An identification technique is used to determine the mean values per cycle of each parameter by substitution of the data obtained from these tests as functional variables in the mathematical model. Mean values of the velocity dependent force and stability coefficients; CT and ∂CN/∂α, and the added mass coefficients k11 and k33 are then obtained from these parameters. The results of this programme indicate a strong dependence in oscillatory motion of the mean value per cycle for the axial added mass coefficient k11 on the unsteady force parameter called the Keulegan-Carpenter number KC; KC = Û • T/DO. Where; Û = the velocity amplitude of the oscillation, T = the period of an oscillation, and DO = a typical canopy dimension. The velocity dependent axial force coefficient CT exhibits a similar, although not as substantial dependency. Good agreement has been obtained between steady-state test results from this programme and results from other independent work. The effects of values obtained in this investigation are considered in the linearised dynamic stability model developed by Doherr and Saliaris (1), and their influence on the descent characteristics of full-scale parachutes is assesed.
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Fincham, James Henry Sun-Ming. "Unsteady shockwave motion in supersonic intakes." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658855.
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Rocket engines have low specific impulse (Isp) compared to jet propulsion. Over the last few decades, a number of space launch vehicles that utilise airbreathing propulsion to aid their ascent have been proposed, though none have been flown. High-speed airbreathing engines such as ramjets, scramjets, and others, may significantly improve the performance of launch vehicles, potentially allowing for single-stage-to-orbit vehicles to become possible. Such vehicles should have better reliability and shorter down-time between missions than their multi-stage counterparts. A crucial component in high-speed air-breathing engines is the air intake, which must capture sufficient air-flow, and compress it to the conditions required by the engine. The compression occurs through one or more shockwaves. The performance of the intake is strongly dependent upon the positioning of these shockwaves. Unfortunately, the optimum positioning for these shockwaves in terms of performance is usually an unsafe position for engine operation. Furthermore, these shockwaves will move from their nominal locations during atmospheric disturbances such as gusts. A margin on their nominal position must be employed, to ensure that they do not move to unsafe locations within the intake during these disturbances. Calculation of the necessary size of this margin is not trivial; full CFD models can be used, but take a prohibitively long time to complete for an entire flight envelope and varying weather conditions. Since the performance of the intake is directly tied to the positioning of these shockwaves, it is important to develop a low-order model of shockwave motion during disturbances that can be solved much more rapidly than higher fidelity CFD techniques. This model could then be used to solve for shod;wave motion over a wide range of flight, weather, and design conditions. The work presented here uses the example of the Reaction Engines Ltd. SABRE engine to first demonstrate that shockwave motion during gusts can be significant, and then goes on to develop a low-order model to predict this motion. The accuracy of the model is demonstrated against inviscid CFD for a range of frequencies and lengths of discrete gusts.
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Ning, Wei. "Computation of unsteady flow in turbomachinery." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4819/.
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Unsteady flow analysis has been gradually introduced in turbomachinery design systems to improve machine performance and structural integrity. A project on computation of unsteady flows in turbomachinery has been carried out. A quasi 3-D time-linearized Euler/Navier-Stokes method has been developed for unsteady flows induced by the blade oscillation and unsteady incoming wakes, hi this method, the unsteady flow is decomposed into a steady flow plus a harmonically varying unsteady perturbation. The coefficients of the linear perturbation equation are formed from steady flow solutions. A pseudo-time is introduced to make both the steady flow equation and the linear unsteady perturbation equation time-independent. The 4-stage Runge-Kutta time-marching scheme is implemented for the temporal integration and a cell-vertex scheme is used for the spatial discretization. A 1-D/2-D nonreflecting boundary condition is applied to prevent spurious reflections of outgoing waves when solving the perturbation equations. The viscosity in the unsteady Navier- Stokes perturbation equation is frozen to its steady value. The present time-linearized Euler/Navier-Stokes method has been extensively validated against other well- developed linear methods, nonlinear time-marching methods and experimental data. Based upon the time-linearized method, a novel quasi 3-D nonlinear harmonic Euler/Navier-Stokes method has been developed. In this method, the unsteady flow is divided into a time-averaged flow plus an unsteady perturbation. Time-averaging produces extra nonlinear "unsteady stress" terras in the time-averaged equations and these extra terras are evaluated from unsteady perturbations. Unsteady perturbations are obtained by solving a first order harraonic perturbation equation, while the coefficients of the perturbation equation are forraed from time-averaged solutions. A strong coupling procedure is applied to solve the time-averaged equation and the unsteady perturbation equation simultaneously in a pseudo-time domain. An approximate approach is used to linearize the pressure sensors in artificial smoothing
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Forristal, Richard Michael. "Unsteady flow over a rectangular cavity." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343054.
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Roberts, Richard Peter. "Rational function approximations to unsteady aerodynamics." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361136.
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Green, Henry Gregory. "Characteristics of steady and unsteady jets." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38338.
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Stevens, Patrick Robert Robbie James. "Unsteady low Reynolds number aerodynamic forces." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709135.
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Wright, Stewart Andrew. "Aspects of unsteady fluid-structure interaction." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621939.
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McNae, Duncan Murray. "Unsteady hydrodynamics of tidal stream turbines." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24138.
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The unsteady hydrodynamics of tidal stream turbines have been investigated using numerical methods and experiments. Dynamic inflow, which represents the change in backflow induced by the circulation present in the wake due to variations in rotor loading, is the particular focus of this work. An implementation of an unsteady vortex lattice method has been developed for modelling tidal stream turbines in a variety of flow conditions. The vortex lattice method is an inviscid potential flow solver, with the blades represented as surfaces on the camber line. The vortex lattice method is used to analyse the difference between a sudden collective change in blade pitch, compared with a sudden change in mean flow. The observed differences are explained with the examination of several simulation properties, such as the wake induced flow field. The vortex lattice method is also used to model a tidal turbine in an oscillatory flow environment. Additionally, experiments have been conducted in a recirculating water flume. A scale turbine model is mounted on a controllable carriage, which can move arbitrarily along the flow direction. Strain gauges are place at the root of one turbine blade, and on the mounting strut of the turbine. This thesis examines the loading response of the turbine due to oscillation of the carriage and turbine system, over a range of Keulegan-Carpenter numbers and current numbers. The conclusions drawn from the experimental and numerical work describe the degree of importance of dynamic inflow, and will show that it can be responsible for overshoots in turbine thrust loads, and lag in the load response when the turbine is subjected to oscillating flow. Dynamic inflow is shown to have significant influence on the turbine thrust in unsteady flows. Added mass, the inertial force that arises when accelerating a body through a fluid is also investigated with two-dimensional unsteady airfoil theory, and is estimated to have an important role in the unsteady loading of tidal stream turbines. A two-bladed device is the main point of interest in this thesis, however the concepts can be extended for many rotor designs.
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Jaffa, Nicholas Andrew. "Unsteady measurement techniques for turbomachinery flows." Thesis, University of Notre Dame, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3732212.
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Accurate unsteady measurements are required for studying the flows in high speed turbomachines, which rely on the interaction between rotating and stationary components. Using statistics of phase locked ensembles simplifies the problem, but accurate frequency response in the 10-100 kHz range significantly limits the applicable techniques. This research advances the state of the art for phase resolved measurement techniques using for high speed turbomachinery flows focusing on the following areas: development, validation, and uncertainty quantification. Four methods were developed and implemented: an unsteady total pressure probe, the multiple overheat hot-wire method, the slanted hot-wire method, and the phase peak yaw hot-wire method. These methods allow for the entire phase locked average flow field to be measured (temperature, pressure, and velocity components, swirl angle, etc.). No trusted reference measurement or representative canonical flow exists for comparison of the phase resolved quantities, making validation challenging. Five different validation exercises were performed to increase the confidence and explore the range of applicability. These exercises relied on checking for consistency with expected flow features, comparing independent measurements, and cross validation with CFD. The combined uncertainties for the measurements were quantified using uncertainty estimates from investigations into the elemental error sources. The frequency response uncertainty of constant temperature hot-wire system was investigated using a novel method of illuminating the wire with a laser pulse. The uncertainty analysis provided estimates for the uncertainty in the measurements as well as showing the sensitivity to various sources of error.
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Bissessur, Prithiraj. "Unsteady aerodynamics using high-order methods." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/49924/.
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Unsteady flows occur in many applications of engineering interest. One category of unsteady flows occur as self-sustaining oscillatory fluid motion, such as the flow over rectangular cavities. There has been a significant amount of research performed on this topic over the years, both experimentally and numerically. The unsteady flow over rectangular cavities is the case study in this research. In this work, a generic numerical solver is developed and written to predict the near-field aerodynamics of unsteady fluid motions at low Mach numbers. High order numerical schemes are employed to this effect. The Detached Eddy Simulation (DES) method is considered for the turbulence modelling part. At the start of this project, the combination of high order Computational Aeroacoustics (CAA) numerical schemes, non-reflecting boundary conditions and DES constituted a state of the art approach to the simulation of unsteady compressible flow phenomena at low Mach numbers. In the numerical study of 2D cavities, a number of cases with different length-to depth (L/D) ratios were considered. Under the same flow conditions, the relation of the L/D to the radiated sound in the farfield is sought. It is found that the nature of the flow interaction with the downstream corner, which changes with L/D, dictates the directivity and amplitude of the sound field observed at a far distance from the source. To gain more insight into the topology of 3D cavity flows, an experimental study using non-intrusive measurement techniques is outlined. This explains the work performed on 3D cavities with different spanwise dimensions. A detailed flow visualisation of the meanflow patterns in various measurements planes describes the presence of strong 3D features. In particular, the symmetrical flow behaviours at relatively large width-to-depth (W/D) ratios of 3 and 2 are highlighted. This provides the justification to employ a symmetry condition in the 3D DES study. Therefore, the final case study is based on the numerical simulation of a 3D cavity geometry where only half of the cavity is simulated. The observations from the 2D simulations and the experimental work provided a basis of the expectations of this test case. Again, a correlation between the near-field aerodynamics and the farfield sound is sought. The 3D cavity showed (as in the 2D cases) a preferred directivity in the farfield.
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Muchatibaya, Gift. "Mathematical modelling of unsteady contact melting." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4912.
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Includes abstract.Includes bibliographical references (leaves 115-122).
The work in this thesis deals with the heat transfer and fluid flow problem encountered in the analysis of an unsteady contact melting process. Chapters 2 and 3 deal with only the heat transfer problem without fluid flow. In Chapter 2 the pre-melting problem is treated. The focus is to obtain the best approximate analytical solution to be used in the melting phase where there are no known exact solutions. The approximate solutions are constructed using the heat balance integral method.
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Walker, William Paul. "Unsteady Aerodynamics of Deformable Thin Airfoils." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34620.
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Unsteady aerodynamic theories are essential in the analysis of bird and insect flight. The study of these types of locomotion is vital in the development of flapping wing aircraft. This paper uses potential flow aerodynamics to extend the unsteady aerodynamic theory of Theodorsen and Garrick (which is restricted to rigid airfoil motion) to deformable thin airfoils. Frequency-domain lift, pitching moment and thrust expressions are derived for an airfoil undergoing harmonic oscillations and deformation in the form of Chebychev polynomials. The results are validated against the time-domain unsteady aerodynamic theory of Peters. A case study is presented which analyzes several combinations of airfoil motion at different phases and identifies various possibilities for thrust generation using a deformable airfoil.Master of Science
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Zakaria, Mohamed Yehia. "Unsteady Nonlinear Aerodynamic Modeling and Applications." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79909.
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Unsteady aerodynamic modeling is indispensable in the design process of rotary air vehicles, flapping flight and agile unmanned aerial vehicles. Undesirable vibrations can cause high-frequency variations in motion variables whose effects cannot be well predicted using quasi-steady aerodynamics. Furthermore, one may exploit the lift enhancement that can be generated through an unsteady motion for optimum design of flapping vehicles. Additionally, undesirable phenomena like the flutter of fixed wings and ensuing limit cycle oscillations can be exploited for harvesting energy. In this dissertation, we focus on modeling the unsteady nonlinear aerodynamic response and present various applications where unsteady aerodynamics are very relevant.
The dissertation starts with experiments for measuring unsteady loads on an NACA-0012 airfoil undergoing a plunging motion under various operating conditions. We supplement these measurements with flow visualization to obtain better insight into phenomena causing enhanced lift. For the model, we present the frequency response function for the airfoil at various angles of attack. Experiments were performed at reduced frequencies between 0.1 and 0.95 and angles of attack up to 65 degrees. Then, we formulate an optimization problem to unify the transfer function coefficients for each regime independently to obtain one model that represents the global dynamics. An optimization-based finite-dimensional (fourth-order) approximation for the frequency responses is developed. Converting these models to state-space form and writing the entries of the matrices as polynomials in the mean angle of attack, a unified unsteady model was developed. In the second set of experiments, we measured the unsteady plunging forces on the same airfoil at zero forward velocity. The aim is to investigate variations of the added forces associated with the oscillation frequency of the wing section for various angles of attack. Data of the measured forces are presented and compared with predicted forces from potential flow approximations. The results show a significant departure from those estimates, especially at high frequencies indicating that viscous effects play a major role in determining these forces.
In the second part of this dissertation, we consider different applications where unsteady loads and nonlinear effects play an important role. We perform a multi-objective aerodynamic optimization problem of the wing kinematics and planform shape of a Pterosaur replica ornithopter. The objective functions included minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. The results show that there is an optimum kinematic parameter as well as planform shape to fulfill the two objectives. Furthermore, the effects of preset angle of attack, wind speed and load resistance on the levels of harvested power from a composite beam bonded with the piezoelectric patch are determined experimentally. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations as well as the level of power harvested. This is followed by testing of a centimeter scale micro wind turbine that has been proposed to power small devices and to work as a micro energy harvester. The experimental measurements are compared to predicted values from a numerical model.
The methods developed in this dissertation provide a systematic approach to identifying unsteady aerodynamic models from numerical or experimental data that may work within different regimes. The resulting reduced-order models are expressed in a state-space form, and they are, therefore, both simple and efficient. These models are low-dimensional linear systems of ordinary differential equations so that they are compatible with modern flight dynamic models. The specific form of the obtained added force model, which defines the added forces as a function of plunging velocity and drag forces, guarantees that the resulting model is accurate over a range of high frequencies. Moreover, presented applications give a sense of the broad range of application of unsteady aerodynamics.Ph. D.
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Sanders, Darius Demetri. "An Investigation of Controlled Oscillations in a Plasma Torch for Combustion Enhancement." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/35700.
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The oscillating plasma torch is proposed as a potential device that will produce an oscillating shock and resulting control of the supersonic combustion process. This research will capitalize on previous results [Gallimore, 1998] which indicate that the plasma torch oscillations originate from the inherent oscillations of the voltage applied to the torch. The aim of this research is to thoroughly investigate the oscillation behavior of the plasma torch with the plan of ultimately controlling the oscillation at chosen frequencies. A modulating power system used for dynamic control of the plasma torch oscillation was designed and tested in quiescent conditions (no flow), Mach 2.4 cold supersonic flow, and Mach 2 heated supersonic flow conditions. The oscillating plasma torch used nitrogen feedstock and was operated over a frequency range of 2Hz- 4kHz. A dynamic torch model using the hybrid Mayr-Cassie electric arc model was developed to predict the plasma torch electric arc response at appropriate frequencies for interaction with supersonic combustion.
In quiescent conditions, the dynamic response of the plasma torch power system and plasma jet were characterized using signal processing techniques and high speed video imaging. High speed Schlieren images were used to determine the behavior of the oscillating plasma jet in Mach 2.4 cross flow and its influence on the induced shock structure. The unsteady nitrogen-fed torch was integrated with the flush walled 4-hole aerodynamic ramp injector using hydrogen and hydrocarbon fuels at the University of Virginia Aerospace Research Lab (ARL) heated Mach 2 supersonic flow. Unsteady pressure variations from the oscillating shock produced by the plasma torch were recorded using recess-mounted Kulite pressure transducers. Also, measurements of the static pressure of the combustion produced by the oscillating plasma torch were obtained.
The oscillating torch system performed well over a range of different flow conditions. It will enable active control input to the combustion process. The controllable unsteady blockage might provide a type shock interaction needed to increase turbulence and mixing augmentation [Kumar, et al. 1987].Master of Science
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Gerhardt, Frederik C. "Unsteady aerodynamics of upwind-sailing and tacking." Thesis, University of Auckland, 2011. http://hdl.handle.net/2292/6599.
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Predicting unsteady sailing yacht performance is of significant current interest to racing syndicates and yacht designers alike because it is anticipated that optimising boats for dynamic conditions will lead to large performance gains. Such optimisations are usually carried out with the aid of Dynamic Velocity Prediction Programs (DVPPs). These programs require knowledge about the behaviour of the sails in unsteady flow. To this end Part A of this work looks at the simplified unsteady aerodynamics of a yacht that sails upwind in waves. Unsteady thin aerofoil theory is extended to the case of two interacting aerofoils representing the headsail and mainsail. The developed novel method is analytical in nature and is based on representing the sail bound vorticity distributions and the unsteady vortex wakes by planar vortex sheets. The theory is successfully validated against data from the literature and pressure distributions from wind tunnel tests. An application of the theory to the case of an International America's Cup Class yacht that pitches in waves reveals that the time-varying components of the aerodynamic forces are small and that only very little energy can be extracted from the unsteady flow about the sails and converted into thrust. Part B looks at the aerodynamics of a yacht that tacks. Since today's DVPPs usually suffer from a lack of available data on the behaviour of the sail forces at very low apparent wind angles a series of quasi-steady experiments was carried out. Test results for different tacking scenarios (headsail flogging or backed) are presented in a form that facilitates incorporation into a DVPP. The quasi-steady approach used in the wind tunnel tests does not account for unsteady effects like the aerodynamic inertia due to the 'added mass' of the sails. The added inertia of a sail can, however, be estimated by 'strip theory'. Using expressions from the literature and experimental results it is found that such a strip theory over-estimates the added inertia of a mainsail by about 20% because it neglects the three-dimensional flow around the head and the foot of the sails. Using the DVPP FS Equilibrium the influence of added sail inertia on the tacking behaviour of a yacht is studied and it is found that added sail inertia has a small but noticeable influence on tacking performance.
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Akay, Busra. "Unsteady Aerodynamic Calculations Of Flapping Wing Motion." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608773/index.pdf.
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The present thesis aims at shedding some light for future applications of μ
AVs by investigating the hovering mode of flight by flapping motion. In this study, a detailed numerical investigation is performed to investigate the effect of some geometrical parameters, such as the airfoil profile shapes, thickness and camber distributions and as well as the flapping motion kinematics on the aerodynamic force coefficients and vortex formation mechanisms at low Reynolds number. The numerical analysis tool is a DNS code using the moving grid option. Laminar Navier-Stokes computations are done for flapping motion using the prescribed kinematics in the Reynolds number range of 101-103. The flow field for flapping hover flight is investigated for elliptic profiles having thicknesses of 12%, 9% and 1% of their chord lengths and compared with those of NACA 0009, NACA 0012 and SD 7003 airfoil profiles all having chord lengths of 0.01m for numerical computations. Computed aerodynamic force coefficients are compared for these profiles having different centers of rotation and angles of attack. NACA profiles have slightly higher lift coefficients than the ellipses of the same t/c ratio. And one of the most important conclusions is that the use of elliptic and NACA profiles with 9% and 12% thicknesses do not differ much as far as the aerodynamic force coefficients is concerned for this Re number regime. Also, two different sinusoidal flapping motions are analyzed. Force coefficients and vorticity contours obtained from the experiments in the literature and present study are compared. The validation of the present computational results with the experimental results available in the literature encourages us to conclude that present numerical method can be a reliable alternative to experimental techniques.
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Mata, Bueso Enrique. "Unsteady Aerodynamic Vortex Lattice of Moving Aircraft." Thesis, KTH, Aerodynamik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48928.
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It is aim of this thesis to develop a potential ow solver for unsteady aerodynamics in MATLAB environment. In order to achieve this target a vortex lattice method based has been developed. The validation of this program involves two dierent stages. Initially, it is compared with classical experiments and a well tested code. In a second step, the program is compared with wind tunnel experiments for two dierent aircraft's con gurations, classical and with canard. In the end it will be demonstrated that the present method achieves good agreement in both stages.
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Polpitiye, Sisira J. "Unsteady fluid flow around certain bluff bodies." Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/34813.
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It is shown in this thesis that fluid dynamic forces on unsteadily moving bluff bodies depend on the history of motion as much as on the velocity and acceleration of motion. An empirical relationship between the motion of the body and the resulting force is obtained by analysing the effect of the history of motion on the fluid dynamic force at any instant. The fluid dynamic force, velocity and acceleration are obtained as functions of time, by oscillating test models in water while they are being towed at constant speed. The test models used are: 1. a two-dimensional circular cylinder, 2. a rectangular block with square frontal area and fineness ratio of 3:1, 3. a cruciform parachute canopy with arm ratio of 4:1, and 4. a ring-slot parachute canopy. The functions by which the history of flow affects the future forces, are evaluated by using the Convolution Integral. The results show that the effects due to history of both velocity and acceleration are by no means negligible, that is the velocity and the acceleration at a specific time prior to any instant is so domineering that the fluid dynamic force can approximately be expressed as being delayed by this period of time. This 'time-delay', or time lag (as opposed to phase-lag) in the part of the measured force is found to be independent of the frequency of excitation. In the light of this evidence, a prediction model is suggested for estimating unsteady fluid forces. The data required for the application of this prediction model are obtained experimentally. Chapter One of this thesis gives a brief explanation of the historical background of unsteady fluid dynamics. The effects of acceleration on the fluid dynamic force, in both ideal and real fluids, are discussed in Chapter Two. Explained in Chapter Three are the techniques used for building the force prediction model, and data acquisition. The experimental procedure is explained in Chapter Four. Chapter Five gives the empirical form of the prediction model, and some data that are used in association with this model.
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Ly, Eddie, and Eddie Ly@rmit edu au. "Numerical schemes for unsteady transonic flow calculation." RMIT University. Mathematics and Geospacial Sciences, 1999. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20081212.163408.
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An obvious reason for studying unsteady flows is the prediction of the effect of unsteady aerodynamic forces on a flight vehicle, since these effects tend to increase the likelihood of aeroelastic instabilities. This is a major concern in aerodynamic design of aircraft that operate in transonic regime, where the flows are characterised by the presence of adjacent regions of subsonic and supersonic flow, usually accompanied by weak shocks. It has been a common expectation that the numerical approach as an alternative to wind tunnel experiments would become more economical as computers became less expensive and more powerful. However even with all the expected future advances in computer technology, the cost of a numerical flutter analysis (computational aeroelasticity) for a transonic flight remains prohibitively high. Hence it is vitally important to develop an efficient, cheaper (in the sense of computational cost) and physically accurate flutter simulation tech nique which is capable of reproducing the data, which would otherwise be obtained from wind tunnel tests, at least to some acceptable engineering accuracy, and that it is essentially appropriate for industrial applications. This need motivated the present research work on exploring and developing efficient and physically accurate computational techniques for steady, unsteady and time-linearised calculations of transonic flows over an aircraft wing with moving shocks. This dissertation is subdivided into eight chapters, seven appendices and a bibliography listing all the reference materials used in the research work. The research work initially starts with a literature survey in unsteady transonic flow theory and calculations, in which emphasis is placed upon the developments in these areas in the last three decades. Chapter 3 presents the small disturbance theory for potential flows in the subsonic, transonic and supersonic regimes, including the required boundary conditions and shock jump conditions. The flow is assumed irrotational and inviscid, so that the equation of state, continuity equation and Bernoulli's equation formulated in Appendices A and B can be employed to formulate the governing fluid equation in terms of total velocity potential. Furthermore for transonic flow with free-stream Mach number close to unity, we show in Appendix C that the shocks that appear are weak enough to allow us to neglect the flow rotationality. The formulations are based on the main assumption that aerofoil slopes are everywhere small, and the flow quantities are small perturbations about their free-stream values. In Chapter 4, we developed an improved approximate factorisation algorithm that solves the two-dimensional steady subsonic small disturbance equation with nonreflecting far-field boundary conditions. The finite difference formulation for the improved algorithm is presented in Appendix D, with the description of the solver used for solving the system of difference equations described in Appendix E. The calculation of steady and unsteady nonlinear transonic flows over a realistic aerofoil are considered in Chapter 5. Numerical solution methods, based on the finite difference approach, for solving the two-dimensional steady and unsteady, general-frequency transonic small disturbance equations are presented, with the corresponding finite difference formulation described in Appendix F. The theories and solution methods for the time-linearised calculations, in the frequency and time domains, for the problem of unsteady transonic flow over a thin planar wing undergoing harmonic oscillation are presented in Chapters 6 and 7, respectively. The time-linearised calculations include the periodic shock motion via the shock jump correction procedure. This procedure corrects the solution values behind the shock, to accommodate the effect of shock motion, and consequently, the solution method will produce a more accurate time-linearised solution for supercritical flow. Appendix G presents the finite difference formulation of these time-linearised solution methods. The aim is to develop an efficient computational method for calculating oscillatory transonic aerodynamic quantities efficiently for use in flutter analyses of both two- and three-dimensional wings with lifting surfaces. Chapter 8 closes the dissertation with concluding remarks and future prospects on the current research work.
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DeBruhl, Christopher Dwayne. "NOx Formation in Unsteady Counterflow Diffusion Flames." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-07062003-115155/.
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The formation of NO and NO2 are sensitive indicators of both temperature and residence time. In this work, the NOx emission index is measured in an unsteady counterflow diffusion flame for methane, propane and ethylene, as a function of average strain rate and amplitude and frequency of imposed sinusoidal oscillation. The flames studied vary from non-sooting to high soot loading, and from low average strain rate to near extinction. Due to the relatively long time scales associated with NOx formation, the effect of unsteadiness on emission index is weaker than on either temperature or soot volume fraction. Time average global measurements were taken using a California Analytical Instruments Model 400 HCLD NO/NOx analyzer. Results are compared with unsteady calculations using a modified OPPDIF code included in the Chemkin package.
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Smith, Thomas M. "Unsteady simulations of turbulent premixed reacting flows." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13097.
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Huang, Chih-Wei 1974. "Analysis of unsteady flows past oscillating wings." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79233.
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This thesis presents a more accurate and efficient method for the study of finite span wings in steady and unsteady supersonic flows with more computing efficiency.For steady flows, the boundary conditions are expressed in terms of the source distributions over wing surfaces. Specific theoretical solutions are derived for the calculations of pressure coefficient distribution and the lift, pitching moment, and rolling moment coefficients. The present solutions have been validated for delta and trapezoidal wings by comparison with high order conical flow results based on the theory developed by Carafoli, Mateescu, and Nastase. An excellent agreement was found between these results.
For unsteady flows, the boundary conditions of finite span wings are modeled by using pulsating sources distributing over the wing surface. The present method leads to more accurate solutions for rigid wings executing harmonic oscillations in translation, pitching rotation, and rolling rotation of various oscillating frequencies. These solutions were found in very good agreement with the available high order conical flow solutions obtained by Carafoli, Mateescu, and Nastase.
Then the method has been used to obtain solutions for the flexible wings executing flexural oscillations, which are of interest for the aeroelastic studies in the aeronautical applications.
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Stallard, Timothy J. "Simulation of unsteady viscous flow-structure interaction." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418130.
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The design of slender structures such as longspan bridges, masts, offshore risers and cables is strongly influenced by their response behaviour when subjected to unsteady loads due to wind, waves and current. Simulation of the behaviour of a viscous flow past a structural cross section is of great importance to engineers concerned with the design of such structures. Offshore engineers are concerned with estimating the magnitude of structural forces induced by the most severe storm-induced wave events. Numerous studies have been conducted in an effort to estimate the structural forces induced by both regular and irregular waves. However, estimation of the maximum extreme wave-induced structural forces, particularly for relatively small diameter horizontal components, has received less attention. Since the most widely used method for estimating the force experienced by a bluff body subjected to wave loading is the empirical drag-inertia equation developed by Morison, O’ Brien, Johnson, and Schaaf (1950), it is important to determine whether this equation is adequate to describe the forces imposed by extremely large ocean waves. A method is presented for the simulation of incompressible viscous flow past acylinder using a stream function vorticity-transport formulation discretised on a cutcell quadtree mesh. A cut-cell technique is employed to provide accurate boundary representation and to facilitate the simulation of flow past a moving boundary. The finite volume discretisation consists of second-order accurate central difference approximations within uncut flow cells and a polynomial reconstruction technique within the cut-cells that are intersected by the solid boundary. Several preliminary validation tests concerned with flow past a circular cylinder are presented to confirm the accuracy of the numerical model. Firstly, the cut-cell discretisation is applied to the solution of the Euler equations and is shown to be almost second order accurate. Comparisons of wake geometry and force coefficients for steady and oscillatory flows at low Reynolds number are then made with existing results, and show satisfactory agreement. Preliminary tests are presented to assess the accuracy of a cut-cell based method for simulating flow past a circular body that moves across a background mesh. A series of experiments is also presented concerned with the measurement of theforce experienced by a circular cylinder undergoing a pre-defined two-dimensionalmotion within a still fluid. The cylinder trajectory is representative of the motionof a fluid particle beneath an idealised large ocean wave as defined by the NewWave formulation (Tromans et al. 1991). It is observed that, whilst the magnitude of high frequency vortex induced force fluctuations varies with the ratio of wave amplitude to cylinder diameter (A=D) and the wave spectrum shape, the overall shape of both x- and y-direction force time histories is very similar for all wave groups for which the underlying spectrum has the same shape. For all of the two-dimensional cylinder motions considered, the spectrum of both measured forces closely approximates the spectrum of uq (where u is a component of the velocity vector and q the absolute velocity) and, as a result, the vector form of the well known equation developed by Morison et al. (1950) is shown to provide a satisfactory estimate of the cartesian force components. The high frequency component of the force that is not captured by the Morison et al. equation is clearly identified as a lift-type force in the radial direction. For design purposes, a reasonable estimate of the magnitude of the peak force is obtained by neglecting inertial forces and employing a drag coefficient CD = 1.0.
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Pesiridis, Apostolos. "Turbocharger turbine unsteady aerodynamics with active control." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498148.
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Liu, Yan. "Numerical simulations of unsteady complex geometry flows." Thesis, University of Warwick, 2004. http://wrap.warwick.ac.uk/2360/.
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Numerical simulations have been here carried out for turbulent flows in geometries relevant to electronic systems. These include plane and ribbed channels and a central processor unit (CPU). Turbulent flows are random, three-dimensional and time-dependent. Their physics covers a wide range of time and space scales. When separation and reattachment occur, together with streamline curvature, modelling of these complex flows is further complicated. It is well known that, when simulating unsteady flows, the traditional, steady, linear Reynolds-averaged Navier-Stokes (RANS) models often do not give satisfactory predictions. By contrast, unsteady, non-linear RANS models may perform better. Hence the application of these models is considered here. The non-linear models studied involve explicit algebraic stress and cubic models. The Reynolds Stress Model (RSM) has been also evaluated. Modelling strategies more advanced than RANS, i.e. Large Eddy Simulation (LES) and zonal LES (ZLES), have also been tested. Validation results from URANS, LES and ZLES indicate that the level of agreement of predictions with benchmark data is generally consistent with that gained by the work of others. For the CPU case, flow field and heat transfer predictions from URANS, LES ; and ZLES are compared with measurements. Overall, for the flow field, ZLES and LES are more accurate than URANS. Zonal low Reynolds number URANS models (using a hear wall k-l model) perform better than high Reynolds number models. However, for heat transfer prediction, none of the low Reynolds number models investigated performed well.
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Yang, Hui. "3D unsteady flow in oscillating compressor cascade." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2835/.
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An experimental and computational study has been carried out to enhance current understanding of three dimensional (3D) cascade aeroelastic mechanisms. 3D unsteady pressure data produced during executing this project is the first-of-its-kind, which can be directly used for validation of advanced 3D numerical methods for the prediction of aeroelastic problems in turbomachines. A new, low speed flutter test rig with a linear compressor cascade consisting of seven Controlled-Diffusion Blades has been commissioned. The unsteady aerodynamics of the oscillating cascade is investigated using the Influence Coefficient Method, by which the middle blade is mechanically driven to oscillate in a 3D bending mode. Off-board pressure transducers are utilized to allow detailed measurement of the unsteady blade surface pressures in conjunction with a Tubing Transfer Function (TTF) method to correct tubing distortion errors. The linearity of the unsteady aerodynamic response is confirmed by tests with different oscillation amplitudes, which enables unsteady results of a tuned cascade to be constructed by using the Influence Coefficient Method at various inter-blade phase angles. An examination of the techniques adopted and experimental errors indicates a good level of accuracy and repeatability to be attained in the measurement of unsteady pressure. A detailed set of steady flow is obtained from the middle three blades, which demonstrates a reasonable blade-to-blade periodicity. At a nominal steady flow condition unsteady pressure measurements were performed at six spanwise sections between 20% and 98% span for three different reduced frequencies. The 2D laminar bubble-type separation around middle chord on the suction surface is identified to have a local effect on the unsteady flow. The measured results illustrate the fully 3D unsteady flow
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Caserta, Maurizio G. G. "Capacity utilisation, effective demand and unsteady growth." Thesis, University College London (University of London), 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247429.
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Spies, Peter-Jost. "The transport of sand in unsteady winds." Thesis, University of Aberdeen, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295798.
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This work is a study into the unsteady behaviour of aeolian sediment transport. A one-dimensional and a two-dimensional numerical model were developed in order to investigate the temporal behaviour of transport rate as well its spatial distribution. The numerical model of McEwan (1991) for steady state saltation served as a starting point in the development phase. Both models presented in this thesis are capable of simulating temporary varying winds. In addition, the two-dimensional model allows the relaxation of the assumption of streamwise homogeneous flow. The one-dimensional model was tested against results for steady state predicted by previous models. Further tests showed that the discretisation time step size Δt has an influence on the model's temporal behaviour. The reason for this is the better coupling of the wind-sand system when a smaller Δt is used. The implications of bed area choice on the statistical accuracy of predicted transport rate was demonstrated. In the one-dimensional case the grain cloud's total forward momentum equals transport rate, which is independent of model geometry. The initial over-shoot reported by previous investigators was found not to appear for simulation heights small than 50 to 60cm. This is due to the fast propagation of the grains' influence (momentum exchange) upward in the flow and the immediate deceleration of the wind. Confirmation of these findings comes from reports of experiments conducted in differently sized wind tunnels. Different types of wind velocity variations were investigated. The transport rate's response depends on the amplitude and frequency of the wind fluctuations. At frequencies higher than f ≈ 0.5Hz the transport rate was found not to respond to the wind changes.
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Peskett, Jonathan Paul. "The development of unsteady aerodynamic mathematical models." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299504.
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Roberts, E. P. L. "Unsteady flow and mixing in baffled channels." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385348.
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