Dissertations / Theses on the topic 'Vortex interactions'
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1
Affes, Habib. "Tip-vortex/airframe interactions /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487777170407828.
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Peng, Di. "Vortex Dynamics and Induced Pressure/Load Fluctuations During Blade-Vortex Interactions." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408967632.
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Wu, Junxiao. "Numerical studies of plume-vortex interactions." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/11906.
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Thom, Alasdair D. "Analysis of vortex-lifting surface interactions." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/3037/.
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The interaction of a vortex with a lifting surface occurs in many aerodynamic systems, and can induce significant airloads and radiate impulsive noise. Yet due to their complex nature, the ability to accurately model the important flow physics and noise radiation characteristics of these interactions in realistic situations has remained elusive. This work examines two cases of vortex-lifting surface interactions by enhancing the capabilities of a high fidelity flow solver. This flow solver utilises high spatial discretisation accuracy with a 5th order accurate WENO scheme, and overset meshes to accurately resolve the formation, evolution and interaction of a tip vortex using an inviscid approximation of the fluid. An existing computational infrastructure is further developed and applied to analyse blade-vortex interactions that occur on a helicopter rotor. An idealised interaction is studied, where an independently generated vortex interacts with a rotor. It is found that through the employment of adequate spatial and temporal resolution, the current methodology is capable of resolving the important details of the interaction over a range of vortex-blade miss distances. A careful study of the spatial and temporal resolution requirements is conducted to ensure that the computed results converge to the correct physical solution. It is also demonstrated that a linear acoustic analysis can accurately predict the acoustic energy propagated from these interactions to the far-field, provided the blade surface pressures are accurately computed. The methodology is then used to study an idealised propeller wake-wing interaction, which occur behind a tractor mounted turboprop. A computationally efficient method of modelling the wake-wing interaction is developed and the computed surface pressures of the interaction are confirmed to agree well with the experimental data. The analysis is coupled to an optimisation algorithm to determine a novel wing design, and it is found that significant drag reductions can be achieved with small changes in the twist distribution of the wing. This work confirms that by using a combination of strategies including efficient grids, high order accurate numerical discretisations and a flexible software infrastructure, high fidelity methods can indeed be used to accurately resolve practical cases of vortex-lifting surface interactions in detail while being feasible in a design setting. The airloads and aeroacoustics from these interactions can be accurately predicted, thus confirming that with the modern advances in computing and algorithms, high fidelity methodologies such as those presented in this thesis are in a position to be used to gain a deep understanding of the relevant flow physics and noise radiation patterns, and their impact on aircraft design.
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O'Reilly, Gerard Kieran Pullin Dale Ian. "Compressible vortices and shock-vortex interactions /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-05262004-145030.
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Pesce, Matthew M. "Unsteady pressure and vorticity fields in blade-vortex interactions." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040643/.
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Clough, Ray Charles 1950. "Vortex interactions in an axisymmetric water jet." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276978.
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An axially symmetric water jet was designed and constructed to complement an existing air jet facility. The water jet operates at Reynolds numbers, based on nozzle diameter, up to 50,000. The jet is forced at high levels by a reciprocating Scotch yoke mechanism. By using an output signal from the Scotch yoke as a phase reference, it is possible to obtain either phase-locked hot film data or phase-locked photographs of the dye-marked coherent vortical structures in the shear layer. By assuming zero azimuthal velocity, continuity allows reconstruction of the vorticity field from the data obtained traversing the jet using a single straight hot film probe. Thus the phase-locked photographs and the phase-locked data sets can be compared. The close agreement of the reconstructed vorticity with the photographs gives credence to the assumption of zero azimuthal velocity, and shows that the dye injection method of flow visualization accurately represents the vortical structure of this flow.
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鄧志剛 and Chi-kong Clief Tang. "The interactions of two perturbed vortex rings." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31241025.
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Tang, Chi-kong Clief. "The interactions of two perturbed vortex rings /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22050474.
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Blackhurst, Tyler D. "Numerical Investigation of Internal Wave-Vortex Dipole Interactions." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3133.
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Three-dimensional linear ray theory is used to investigate internal waves interacting with a Lamb-Chaplygin pancake vortex dipole. These interactions involve waves propagating in the same (co-propagating) and opposite (counter-propagating) horizontal directions as the dipole translation. Co-propagating internal waves in the vertical symmetry plane between the vortices of the dipole can approach critical levels where the wave energy is absorbed by the dipole or where the waves are overturned and possibly break. As wave breaking cannot be simulated with this linear model, changes in wave steepness are calculated to aid in estimating the onset of breaking. Counter-propagating internal waves in the vertical symmetry plane can experience horizontal and vertical reflections, including turning points similar to waves in two-dimensional steady shear. Wave capture is also a possible effect of either type of interaction, depending on initial wave properties and positioning relative to the vortex dipole. Away from the vertical symmetry plane, a spanwise converging (focusing) and diverging (defocusing) of wave energy is observed in co- and counter-propagating interactions as symmetric off-center rays interact with the dipole's individual vortices. Some off-center rays experience multiple horizontal refractions similar to wave trapping.
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Chaluvadi, Venkata Siva Prasad. "Blade-vortex interactions in high pressure steam turbines." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621152.
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鄧兆強 and Shiu-keung Tang. "The aeroacoustics of free shear layers and vortex interactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31233235.
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Nilawar, R. S. "Effects of finite Rossby radius on vortex-boundary interactions." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348497/.
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The effect of the finite Rossby radius on vortex motion is examined in a two-dimensional inviscid incompressible fluid, assuming quasigeostrophic dynamics in a single layer of fluid with reduced gravity for two geophysically significant problems: a vortex near a gap in a wall and a pair of steady translating vortices. For the motion of a point vortex near a gap in an infinite barrier, a key parameter determining the behaviour of the vortex is a, the ratio of the Rossby radius of deformation and the half-width of the gap. For large a, depending on the location of the vortex, a vortex sheet is placed either over the gap (gap method) or over the two semi-infinite barriers (barrier method). When the vortex sheet is over the gap, numerical inaccuracies are encountered when the vortex is close to the gap, therefore the conjugate (barrier) method is used. Both integral equations contain singularities which can be de-singularised and solved iteratively using the known exact solution in rigid-lid limit, i.e. a → ∞. For large a, there is only slight deviation from the analytical (a → ∞) trajectories. For smaller a, the integral equation from the conjugate method is solved by numerically approximating the integral equation into a system of linear equations and solving using matrix inversion. The integral equation is further simplified by splitting into even and odd parts, thus reducing the problem to the half plane. It is also found that decreasing a, increases the tendency for vortices to pass through the gap. Background flows influence vortex trajectories and are incorporated by modifying the conjugate method integral equation. These equations are solved using the matrix method. Streamlines for uniform symmetric and anti-symmetric (which has no analogy in the rigid-lid limit) flow through the gap are computed and their effect on the vortex trajectories are found. The motion of finite area patches of constant vorticity near a gap in a wall is computed using the matrix method in conjunction with contour dynamics. For fixed a, vortex patches are normalised to travel at the same speed as a point vortex. The normalisation is non-trivial and depends nonlinearly on the patch area and a. In the rigid-lid limit, it reduces to the ‘usual’ normalisation based on the patch circulation. For near circular patches, the trajectory of the centroid of the patches also follows the trajectory of the point vortices. When the patch becomes distorted the agreement is not so close. The splitting and joining of contours is also computed using contour surgery and some examples showing this sudden change of behaviour is presented. The next problem determines the effect of the Rossby radius of deformation, on steady translating vortex pairs or, equivalently, a patch in steady translation near a wall. The velocities for the normalised vortex patch are compared to the velocity of a point vortex located at the centroid of the patch. It is found there is good agreement for a range of patch sizes. When the patches are sufficiently far from the wall, decreasing the Rossby radius makes the steadily translating shapes more circular. However, when close to the wall, the effect of the Rossby radii results in patches deforming greatly, forming long slug-like shapes. These are shown to be stable using a time dependent contour dynamics code. Background flows are also incorporated and give different vortical shapes for finite Rossby radii flows, ranging from slug-like to tear-drop in shape.
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Dunn, David Christopher. "Vortex interactions with topographic features in geophysical fluid dynamics." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395836.
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Tang, Shiu-keung. "The aeroacoustics of free shear layers and vortex interactions /." [Hong Kong] : University of Hong Kong, 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13311633.
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Fuller, Raymond Preston. "Fuel-vortex interactions for enhanced mixing in supersonic flow." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-154721/.
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Weiland, Christopher. "Modification of Blade-Vortex Interactions Using Leading Edge Blowing." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/31723.
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The interaction of an unsteady wake with a solid body can induce sizable loading of the structure, which has many detrimental side effects in both the structural and acoustic senses. These interactions are ubiquitous in nature and engineering. A flow control technique is sought to mitigate this interaction, thereby decreasing the level of structural vibration.
This thesis investigates the effectiveness of steady leading-edge blowing (LEB) flow control for modifying the vortex induced vibrations on an airfoil in the wake of a circular cylinder. The airfoil was allowed to oscillate perpendicular to the fluid flow direction in response to the impinging Von-Karman vortex street. The flow field and airfoil vibrations were simultaneously captured using Digital Particle Image Velocimetry (DPIV) and accelerometer measurements in a time-resolved sense. The results indicate that LEB can significantly reduce the degree of unsteady loading due to the blade vortex interaction (BVI). In some cases, the LEB jet appears to break the coherency of a vortex incident on the airfoil, and in other cases the jet increase the mean stand-off distance of the vortex as it convects over the airfoil surface. It was also found that, for large circular cylinders, if the airfoil is within the mean closure point of the circular cylinder wake, the LEB can increase the level of BVI.
The Proper Orthogonal Decomposition (POD) was also used to analyze the DPIV data. POD is mathematically superior for reducing a data rich field into fundamental modes; a suitable basis function for the reduction is chosen mathematically and it is not left to the researcher to pick the basis function. A comparison of the energy in these modes is useful in ascertaining the dynamics of the BVI. For one of the two cases examined with POD, it was found for no LEB the fundamental (i.e. most energetic) mode is given by the vortex shedding of the circular cylinder upstream. The addition of LEB reduces the energy contained in this fundamental mode. Thus the LEB jet has the effect of reducing the flow field coherency; the structure of the large vortices is broken up into smaller vortices. For the other case, the LEB jet has the opposite effect: the jet has the ability to organize the circular cylinder wake into coherent structures. This acts to increase the coherency of the circular cylinder wake and increases the level of BVI.Master of Science
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Edström, Alexander. "Non-Pairwise Vortex Interactions in Ginzburg-Landau Theory of Superconductivity." Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95350.
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Roberts, Douglas A. "Experimental study of loadings during high-incidence airfoil-vortex interactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/MQ42254.pdf.
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Vasudeo, Nikhil Baburam. "The Regime Diagram for Premixed Flame Kernel-Vortex Interactions - Revisited." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-10302009-145332/.
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Regimes of flame kernel-vortex (KV) interactions are investigated numerically using a detailed mechanism for hydrogen chemistry. The parametric simulations explore a wide range of conditions that are representative of conditions encountered at various degrees of turbulence intensity. The results show that KV interactions can be classified into five different regimes, which include 1) the laminar kernel regime, 2) the wrinkled kernel regime, 3) the breakthrough regime, 4) the global extinction regime, and 5) the regeneration after global extinction (RGE) regime. With the exception of the last regime, the transition from one regime to another in the order listed corresponds to increasing the vortex size and strength. Operation at the RGE regime reveals interesting dynamics of the flame front that results in reignition or mending of combustion regimes after most of the original kernel has extinguished due to intense straining. Two different types of combustion zones are observed, which correspond to a flamelet structure as well as to more diffuse structures of merged flame segments. A revised regime diagram of the KV interactions is proposed that includes the broader range of KV interactions and incorporate the new RGE regime.
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Maestri, Joseph. "Vortex-wave interactions and exact coherent structures in shear flows." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/51109.
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Recent studies of transition to turbulence in linearly stable shear flows have been dominated by finding, and characterising, so-called exact coherent structures which exist as either equilibrium or travelling wave solutions of the governing Navier-Stokes equations. These structures have been shown to act as either edge states between laminar and turbulent flow or become associated with attractors for turbulent flows, making the quest to understand these structures equally as mathematically interesting as it is industrially relevant. In this thesis, vortex-wave interaction theory, an asymptotic approach based on the assumption of large Reynolds number, is used as a means of finding such structures in plane Couette flow. A new, iterative, numerical method will be developed to solve the governing interaction equations that will allow us to circumvent many of the difficulties in calculating such structures (in particular at high Reynolds numbers) and perform analyses into the state-space of solutions, as well as explore their stability properties. A number of previously found exact coherent structures will be shown to be vortex-wave interaction states, including the so-called upper branch sinuous mode and the class of solutions called mirror-symmetric modes. A number of receptivity type problems will also be considered. Namely, the use of periodic blowing/suction on the channel walls and the introduction of variations in the wall shape. The effect of these two techniques on the skin friction drag and the wave amplitude will be discussed in the context of whether they are beneficial in terms of laminar flow control. Further, it will be shown that the use of periodic blowing/suction leads to a new class of synchronous mirror-symmetric modes and variations in the wall shape lead to a new class of inhomogeneous vortex-wave interaction states.
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Barnes, Caleb J. "Unsteady Physics and Aeroelastic Response of Streamwise Vortex-Surface Interactions." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1431937866.
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鄭世有 and Sai-yau Vincent Cheng. "Interactions of flows over two unequal circular cylinders." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31236686.
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Cheng, Sai-yau Vincent. "Interactions of flows over two unequal circular cylinders /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19161402.
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Saunders, Daniel Curtis. "Wind Turbine Wake Interactions - Characterization of Unsteady Blade Forces and the Role of Wake Interactions in Power Variability Control." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/745.
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Growing concerns about the environmental impact of fossil fuel energy and
improvements in both the cost and performance of wind turbine technologies has spurred
a sharp expansion in wind energy generation. However, both the increasing size of wind
farms and the increased contribution of wind energy to the overall electricity generation
market has created new challenges. As wind farms grow in size and power density, the
aerodynamic wake interactions that occur between neighboring turbines become
increasingly important in characterizing the unsteady turbine loads and power output of
the farm. Turbine wake interactions also impact variability of farm power generation,
acting either to increase variability or decrease variability depending on the wind farm
control algorithm. In this dissertation, both the unsteady vortex wake loading and the
effect of wake interaction on farm power variability are investigated in order to better
understand the fundamental physics that govern these processes and to better control
wind farm operations to mitigate negative effects of wake interaction.
The first part of the dissertation examines the effect of wake interactions between
neighboring turbines on the variability in power output of a wind farm, demonstrating
that turbine wake interactions can have a beneficial effect on reducing wind farm
variability if the farm is properly controlled. In order to balance multiple objectives, such
as maximizing farm power generation while reducing power variability, a model
predictive control (MPC) technique with a novel farm power variability minimization
objective function is utilized. The controller operation is influenced by a number of
different time scales, including the MPC time horizon, the delay time between turbines,
and the fluctuation time scales inherent in the incident wind. In the current research, a
non-linear MPC technique is developed and used to investigate the effect of three time
scales on wind farm operation and on variability in farm power output. The goal of the
proposed controller is to explore the behavior of an "ideal" farm-level MPC controller
with different wind, delay and horizon time scales and to examine the reduction of
system power variability that is possible in such a controller by effective use of wake
interactions.
The second part of the dissertation addresses the unsteady vortex loading on a
downstream turbine caused by the interaction of the turbine blades with coherent vortex
structures found within the upstream turbine wake. Periodic, stochastic, and transient
loads all have an impact on the lifetime of the wind turbine blades and drivetrain. Vortex
cutting (or vortex chopping) is a type of stochastic load that is commonly observed when
a propeller or blade passes through a vortex structure and the blade width is of the same
order of magnitude as the vortex core diameter. A series of Navier-Stokes simulations of
vortex cutting with and without axial flow are presented. The goal of this research is to
better understand the challenging physics of vortex cutting by the blade rotor, as well as
to develop a simple, physics-based, validated expression to characterize the unsteady
force induced by vortex
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Crocker, Elspeth Louise. "Vortex interactions and the significance of balance in two dimensional flows." Thesis, University of Reading, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398292.
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趙遠宏 and Yuen-wang Alex Chiu. "Near wake flow interactions of two square cylinders." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31238348.
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Chiu, Yuen-wang Alex. "Near wake flow interactions of two square cylinders /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20297099.
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Weiler, Justin D. "Numerical Simulation of Flame-Vortex Interactions in Natural and Synthetic Gas Mixtures." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4774.
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The interactions between laminar premixed flames and counter-rotating vortex pairs in natural and synthetic gas mixtures have been computationally investigated through the use of Direct Numerical Simulations and parallel processing. Using a computational model for premixed combustion, laminar flames are simulated for single- and two-component fuel mixtures of methane, carbon monoxide, and hydrogen. These laminar flames are forced to interact with superimposed laminar vortex pairs, which mimic the effects of a pulsed, two-dimensional slot-injection. The premixed flames are parameterized by their unstretched laminar flame speed, heat release, and flame thickness. The simulated vortices are of a fixed size (relative to the flame thickness) and are parameterized, solely, by their rotational velocity (relative to the flame speed). Strain rate and surface curvature measurements are made along the stretched flame surfaces to study the effects of additive syngas species (CO and H2) on lean methane-air flames. For flames that share the same unstretched laminar flame speed, heat release, and flame thickness, it is observed that the effects of carbon monoxide on methane-air mixtures are essentially negigible while the effects of hydrogen are quite substantial. The dynamics of stretched CH4/Air and CH4/CO/Air flames are nearly identical to one another for interactions with both strong and weak vortices. However, the CH4/H2/Air flames demonstrate a remarkable tendency toward surface area growth. Over comparable interaction periods, the flame surface area produced during interactions with CH4/H2/Air flames was found to be more than double that of the pure CH4/Air flames. Despite several obvious differences, all of the interactions revealed the same basic phenomena, including vortex breakdown and flame pinch-off (i.e. pocket formation). In general, the strain rate and surface curvature magnitudes were found to be lower for the CH4/H2/Air flames, and comparable between CH4/Air and CH4/CO/Air flames. Rates of flame stretching are not explicitely determined, but are, instead, addressed through observation of their individual components. Two different models are used to determine local displacement speed values. A discrepancy between practical and theoretical definitions of the displacement speed is evident based on the instantaneous results for CH4/Air and CH4/H2/Air flames interacting with weak and strong vortices.
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Ng, Chi-wing. "Interactions of vortices from two circular cylinders in bistable flow regime /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18037379.
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Michelin, Sébastien Honoré Roland. "Falling, flapping, flying, swimming,... high-Re fluid-solid interactions with vortex shedding /." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3369655.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed September 17, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 200-210).
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Gsell, Simon. "Vortex-induced vibrations of a rigid circular cylinder." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17430/1/gsell.pdf.
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When a flexible body with bluff cross-section is immersed in a flow, the unsteady fluid forces accompanying the vortex-shedding phenomenon may lead to structural vibrations. These vortexinduced vibrations (VIV) occur through a mechanism of synchronization between flow unsteadiness and body displacement, referred to as lock-in. VIV are detrimental to many industrial systems, but may also be used as mechanical energy converter in the context of flow energy harvesting. In the present work, the VIV of a rigid circular cylinder mounted on a elastic support are investigated in various configurations on the basis of direct numerical simulations. Four aspects are studied. (i) The interaction mechanisms are first examined in the early turbulent regime, where VIV have been rarely studied numerically. The Reynolds number, based on the cylinder diameter and oncoming flow velocity, is set to 3900. A combined analysis of the structural responses and fluid forcing in the case where the cylinder is free to oscillate in the in-line and cross-flow directions, i.e. the directions parallel and perpendicular to the oncoming flow, is performed over a range of the reduced velocity (inverse of the oscillator natural frequency). (ii) The system behavior when the body is free to oscillate in a single direction only is also explored, shedding some light on the possible interactions between in-line and cross-flow motions in the two-degree-of-freedom (2-dof) case; the analysis shows for instance how large-amplitude in-line oscillations may be induced by cross-flow motion. (iii) The three-dimensional wake developing downstream of the oscillating body is analyzed in the 2-dof case as well as in the fixed body case. The spanwise flow patterns, which are analyzed quantitatively in terms of wavelength and amplitude of vorticity fluctuations, are differently altered in the shear-layer and wake regions, when the body oscillates. (iv) The last physical configuration involves a cylinder immersed in a flow linearly sheared in the cross-flow direction. The impact of the symmetry breaking induced by the shear, on the flow-structure system behavior, is explored. Different interaction regimes are uncovered in the shear rate - reduced velocity domain. Some of them are associated with a profound reconfiguration of the wake and a major alteration of the fluid forces.
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伍智榮 and Chi-wing Ng. "Interactions of vortices from two circular cylinders in bistable flow regime." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B3123608X.
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Bambrey, Ross R. "Strong interactions between two co-rotating vortices in rotating and stratified flows /." St Andrews, 2007. http://hdl.handle.net/10023/341.
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Kolera-Gokula, Hemanth. "Numerical Investigation of the Mechanisms of Local Extinction Using Flame Kernel-Vortex interactions." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-07262006-192222/.
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The response of premixed flames to unsteady stretch is studied via kernel-vortex interactions. In this configuration a spark ignited kernel interacts with a vortex pair of variable strength. Both detailed and simple chemistry approaches are explored. In the detailed chemistry effort a dilute Hydrogen-air mixture is used. The vortex causes significant distortion of the kernel topography. Two distinct regimes; ?Breakthrough? and ?Extinction? are observed. A continuous increase in flame area and volumetric reaction rate values are observed throughout interactions in the breakthrough regime. However, corresponding consumption speed values are lower than 1-D laminar flame speed values. Detailed chemistry analysis of downstream interaction at the leading edge is carried out. During intermediate stages of the interaction, the mixture in between the interacting flames shows rich burning conditions. As the interaction proceeds the pool of products expands against the counter velocity gradient imposed by the vortex. The decrease in the temperature causes a steady decrease in the rates of reaction of the chain branching reactions causing. The behavior of various reaction layers is dictated to a large extent by their arrangement across the region of interaction. A simple two-step global reaction mechanism is formulated for lean methane combustion. These simple chemistry computations are carried out in an axis-symmetric configuration in a spherical frame of reference. Four distinct regimes of interaction: 1) the no-effect regime, 2) the wrinkling regime 3) the break-through regime, and the 4) global extinction regime are observed. Interactions in the no-effect regime show only minor deviations from unperturbed kernel values. Vortices in the wrinkling regime impose substantial stretch on the kernel causing major deviations from unperturbed kernel values. A sharp drop in the flame surface area and the integrated reaction rate is observed during breakthrough. The primary mechanism governing global extinction is downstream flame-flame interaction. A turbulent combustion diagram was derived for kernel-vortex interactions. Predominance of the breakthrough regime was observed. The turbulent combustion diagram represents an important contribution of this work.
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Morgan, Claire Elizabeth. "Unsteady vortex interactions related to a Formula One car front wing and wheel." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608608.
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Patel, Rupa Ashyinkumar. "Theory and computation on nonlinear vortex/wave interactions in internal and external flows." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/8597.
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Sellin, Karl. "Phase transitions and vortex structures in multicomponent superconductors." Licentiate thesis, KTH, Statistisk fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177141.
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Theoretical aspects of multicomponent superconductivity and systemswith competing interactions are studied using Monte Carlo techniques.Motivated by recent experimental and theoretical results of complex struc-ture formation of vortices in multicomponent systems, possible vortex struc-ture formations due to vortex interactions that are not purely attractive orrepulsive are considered. Vortex structures such as clusters, superclusters,hierarchical structure formation, stripes, gossamer patters, glassy phases, aswell as checkerboard lattices and loops are demonstrated to be possible.The order of the superconducting phase transition is considered for multi-component lattice London superconductors. The phase transition is demon-strated to be either rst-order or continuous depending on the strength of asymmetry-breaking Josephson intercomponent interaction. It is argued thatthe rst-order phase transition is caused by a vortex phase separation due toa uctuation-induced attractive interaction between vortex lines.QC 20151117
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Yemenici, Oznur. "Investigation Of Rotor Wake Interactions In Helicopters Using 3d Unsteady Free Vortex Wake Methodology." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611374/index.pdf.
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This thesis focuses on developing and examining the capabilities of a new in-house
aerodynamic analysis tool, AeroSIM+, and investigating rotor-rotor aerodynamic
interactions for two helicopters, one behind the other in forward flight. AeroSIM+ is a 3-D
unsteady vortex panel method potential flow solver based on a free vortex wake
methodology. Validation of the results with the experimental data is performed using the
Caradonna-Tung hovering rotor test case. AeroSIM+ code is improved for forward flight
conditions so that, the blades are allowed to move according to the rotor dynamics. In the
simulations, blade airload prediction is seen to be sensitive to changes in vortex core size.
Blade Vortex Interaction (BVI) locations differ depending on the relative position of the rear
rotor with respect to the front rotor as well as on the forward flight speed. It was observed
that the performance characteristics of the rear rotor alter depending on the relative positions
of the rotors within the asymmetric wake flow field. The results of this thesis study such as
the computed forces and moments on each rotor and the frequency characteristics of these
loads can be also used in helicopter dynamics simulators.
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Moulin, Frédéric Y. "Interactions onde-vortex en milieu stratifié tournant et transport à travers une barrière dynamique." Université Joseph Fourier (Grenoble), 2002. http://www.theses.fr/2002GRE10156.
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Ghadimi, nassiri Mikaël. "Mise en forme topologique large-bande de la lumière." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0187/document.
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Aujourd'hui les outils permettant de moduler la phase d'une onde lumineuse sont nombreux etpour certains disponibles commercialement, seulement ces éléments ne fonctionnentgénéralement que pour une seule longueur d'onde de travail simultanément. Nous développonsplusieurs approches expérimentales pour la mise en forme de la phase de faisceaux à largebande spectrales. Après un état de l'art sur les principales techniques, nous focalisons notreétude sur la mise en forme de vortex optiques large-bande par l'intermédiaire d'élémentspermettant de moduler la phase géométrique, dont nous abordons quatre approches. Lapremière est basée sur la réflexion de Fresnel anisotrope sur les dioptres mettant en jeu aumoins un matériau biréfringent uniaxe, un choix optimal de leurs indices de réfraction et de leursdispersions permet de réfléchir un faisceau dont la phase dépend de l'orientation de l'axe optiquedes milieux. Dans la seconde, également réflective, nous exploitons le phénomène de réflexionde Bragg circulaire qui se produit au sein des cristaux liquides cholestériques, dont la particularitéest de réfléchir efficacement toute une bande spectrale avec acquisition d'une phase de naturegéométrique. Nous appliquons cette propriété en particulier pour la conception d'élémentsinhomogènes pour la mise en forme, à une bonne approximation, de modes de Laguerre-Gauss.Les deux dernières approches sont basées sur la mise en forme de vortex optiques par desmilieux biréfringents inhomogènes en transmission, en particulier les défauts se formantspontanément dans les films de cristaux liquides nématiques à anisotropie diélectrique négative.L'une consiste à mettre deux éléments en série permettant de traiter successivement différentescomposantes spectrales. L'autre consiste à paralléliser ce procédé en séparant le faisceau initialen différents canaux spectraux, adressés sur des défauts topologiques localisés en réseau etindividuellement contrôlables électriquement. Cette dernière solution peut être vue comme unmodulateur spatial de lumière dont les pixels sont inhomogènes et nous a amené à proposer desapplications potentielles en imagerie optique super-résolue et pour la mise en forme spatiotemporelled'impulsions ultracourtesToday, several beam shaping tools are available, some of them commercially, but most of themare designed for only one working wavelength. This thesis aims to develop several experimentalapproaches for broadband topological beam shaping of light. After the presentation of the state ofthe art, our work focuses on vortex shaping of polychromatic beam exploiting the spin-orbitinteraction of light. Concretely, we report the development of four techniques to modulate the socalledgeometric phase of polychromatic light fields. First, we describe anisotropic reflection frominterfaces that involves at least one uniaxial crystal. We identify a refractive index matchingcriterion enabling highly pure broadband phase control. Then we discuss the use of circularBragg reflection phenomenon inherent to the optics of cholesteric liquid crystals. This propertyallows the selective reflection of circularly polarized light over a bandgap while the reflected fieldacquires a geometric phase. These properties are exploited to design, fabricate and characterizestructured mirrors reflecting Laguerre-Gauss optical modes to a good approximation. The last twosolutions consist of vortex beam shaping using inhomogeneous anisotropic planar opticalelements, namely, topological defects that spontaneously appear in homeotropic nematic liquidcrystal films characterized by negative dielectric anisotropy. The first option is based on using twodefects in series while the other is based of parallel processing using an array of independentlycontrolled topological defects, each of them being dedicated to process distinct spectralchannels. The latter approach can be viewed as a spatial light modulator whose pixels areinhomogeneous and potential applications are proposed in the field of super-resolution opticalimaging and spatio-temporal beam shaping of ultrashort pulses
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Basu, Saikat. "Dynamics of vortices in complex wakes: modeling, analysis, and experiments." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/51749.
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The thesis develops singly-periodic mathematical models for complex laminar wakes which are formed behind vortex-shedding bluff bodies. These wake structures exhibit a variety of patterns as the bodies oscillate or are in close proximity of one another. The most well-known formation comprises two counter-rotating vortices in each shedding cycle and is popularly known as the vk vortex street. Of the more complex configurations, as a specific example, this thesis investigates one of the most commonly occurring wake arrangements, which consists of two pairs of vortices in each shedding period. The paired vortices are, in general, counter-rotating and belong to a more general definition of the 2P mode, which involves periodic release of four vortices into the flow. The 2P arrangement can, primarily, be sub-classed into two types: one with a symmetric orientation of the two vortex pairs about the streamwise direction in a periodic domain and the other in which the two vortex pairs per period are placed in a staggered geometry about the wake centerline. The thesis explores the governing dynamics of such wakes and characterizes the corresponding relative vortex motion.
In general, for both the symmetric as well as the staggered four vortex periodic arrangements, the thesis develops two-dimensional potential flow models (consisting of an integrable Hamiltonian system of point vortices) that consider spatially periodic arrays of four vortices with their strengths being +/-1 and +/-2. Vortex formations observed in the experiments inspire the assumed spatial symmetry. The models demonstrate a number of dynamic modes that are classified using a bifurcation analysis of the phase space topology, consisting of level curves of the Hamiltonian. Despite the vortex strengths in each pair being unequal in magnitude, some initial conditions lead to relative equilibrium when the vortex configuration moves with invariant size and shape.
The scaled comparisons of the model results with experiments conducted in a flowing soap film with an airfoil, which was imparted with forced oscillations, are satisfactory and validate the reduced order modeling framework. The experiments have been performed by a collaborator group at the Department of Physics and Fluid Dynamics at the Technical University of Denmark (DTU), led by Dr. Anders Andersen. Similar experiments have also been run at Virginia Tech as part of this dissertation and the preliminary results are included in this treatise.
The thesis also employs the same dynamical systems techniques, which have been applied to study the 2P regime dynamics, to develop a mathematical model for the P+S mode vortex wakes, with three vortices present in each shedding cycle. The model results have also been compared favorably with an experiment and the predictions regarding the vortex circulation data match well with the previous results from literature.
Finally, the thesis introduces a novel concept of clean and renewable energy extraction from vortex-induced vibrations of bluff bodies. The slow-moving currents in the off-shore marine environments and riverine flows are beyond the operational capabilities of the more established hydrokinetic energy converters and the discussed technology promises to be a significant tool to generate useful power from these copiously available but previously untapped sources.Ph. D.
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Loyez, Marc Jason. "Free Lagrange simulations of flame/vortex interactions, including detailed finite rate chemical kinetics and heat release." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241965.
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Rajamani, Gokul Krishnan, and s3076297@student rmit edu au. "CFD analysis of air flow interactions in vehicle platoons." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061114.122130.
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The increasing use of Intelligent Transport System (ITS) can enable very close vehicle spacings which generally results in a net drag reduction for the resulting convoys. The majority of vehicle development has, to date, been for vehicles in isolation, thus the study of interaction effects is becoming increasingly important. The main objective of this research is to investigate the use of Computational Fluid Dynamics (CFD) for understanding convoy aerodynamics and to further the understanding of airflow interaction between vehicles via CFD. In this study, time-averaged characteristics of a simplified, generic passenger vehicle, called the Ahmed car model, after Ahmed et.al (1984) is investigated computationally using the available commercial CFD code, Fluent version 6.1.22. Three different platoon combinations were analysed for the current study which includes a two, three and six model platoons for various rear end configurations of the Ahmed model geometry. Experiments were conducted in RMIT University Industrial Wind Tunnel for analysing the effects of drafting on drag coefficients using two different scales of Ahmed car models. This is an extension to the previous study performed on two 100% scales of Ahmed models (Vino and Watkins, 2004) and the results for both the current and previous experiments were compared using CFD. The CFD proved to be a useful technique since its results compared reasonably well for both the current and the previous experiments on drafting, using Ahmed models of identical (30°) rear slant configurations. However, near critical rear slant angles (~30°) for isolated vehicles some discrepancies were noted. The reasonable validation of experimental results enabled the study to be extended further computationally using CFD, to analyse the effects of inter-vehicle spacing on a platoon of 3 and 6 models for various rear end configurations (between 0° and 40°), in an attempt to provide useful information on vehicle-wake interaction for the Future Generation Intelligent Transport System (FGITS). Critical gaps were identified via CFD for the case of a two, three and six model platoons and the simulations clearly exposed the reasons for these critical gaps. At extremely close proximity, the models experienced more pressure recovery at their rear vertical base, which reduced the drag coefficient. Surprisingly, at some of the close vehicle spacings, the drag coefficients reached values that were higher than that of a vehicle in isolation. This was found due to the high momentum flow impingement to the fore body of the model and was similar to results found in physical experiments. Thus the current CFD analysis revealed that rear slant angle of the model and the inter-vehicle spacing greatly influences the wake structures and ultimately the vehicles aerodynamic drag coefficients in platoons. Even though the current CFD model (Realizable k-B turbulence model) predicted the basic flow structures such as the C-pillar vortices from the rear slant and 2D horse shoe vortices in the model's vertical rear base, the separation bubble on the rear slant that supplies energy to the strong C-pillar vortices was not replicated accurately, which is evidenced from the flow structure analysis. Hence it is recommended for further work, that the study should be extended using the Reynold's stress models or the Large Eddy Simulation (LES) turbulence models for flow structure observation and analysing vortex interactions between the models.
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Bambrey, Ross R. "Strong interaction between two co-rotating vortices in rotating and stratified flows." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/341.
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In this study we investigate the interactions between two co-rotating vortices. These vortices are subject to rapid rotation and stable stratification such as are found in planetary atmospheres and oceans. By conducting a large number of simulations of vortex interactions, we intend to provide an overview of the interactions that could occur in geophysical turbulence. We consider a wide parameter space covering the vortices height-to-width aspect-ratios, their volume ratios and the vertical offset between them. The vortices are initially separated in the horizontal so that they reside at an estimated margin of stability. The vortices are then allowed to evolve for a period of approximately 20 vortex revolutions. We find that the most commonly observed interaction under the quasi-geostrophic (QG) regime is partial-merger, where only part of the smaller vortex is incorporated into the larger, stronger vortex. On the other hand, a large number of filamentary and small scale structures are generated during the interaction. We find that, despite the proliferation of small-scale structures, the self-induced vortex energy exhibits a mean `inverse-cascade' to larger scale structures. Interestingly we observe a range of intermediate-scale structures that are preferentially sheared out during the interactions, leaving two vortex populations, one of large-scale vortices and one of small-scale vortices. We take a subset of the parameter space used for the QG study and perform simulations using a non-hydrostatic model. This system, free of the layer-wise two-dimensional constraints and geostrophic balance of the QG model, allows for the generation of inertia-gravity waves and ageostrophic advection. The study of the interactions between two co-rotating, non-hydrostatic vortices is performed over four different Rossby numbers, two positive and two negative, allowing for the comparison of cyclonic and anti-cyclonic interactions. It is found that a greater amount of wave-like activity is generated during the interactions in anticyclonic situations. We also see distinct qualitative differences between the interactions for cyclonic and anti-cyclonic regimes.
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Violette, Rémi. "Modèle linéaire des vibrations induites par vortex de structures élancées." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005094.
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Les structures dites « offshores » vibrent sous l'effet des courants marins. Ces vibrations, induites par le détachement périodique de tourbillons dans le sillage de la structure (d'où le nom vibrations induites par vortex), endommagent par fatigue les câbles et les éléments de tuyauteries qui relient à la plateforme d'exploitation les têtes de puits de pétrole situés au niveau du sol marin. Une compréhension du comportement dynamique de ces structures sous l'effet du détachement tourbillonnaire est donc essentielle à l'étape de design. A l'intérieur de cette thèse, nous démontrons qu'en utilisant le concept d'oscillateur fluide et stabilité linéaire, on peut comprendre et reproduire de façon qualitative les caractéristiques principales des VIV sur les structures élancées en écoulements uniformes et non uniformes. Les arguments justifiant l'utilisation de la méthode de modélisation choisie sont présentés au deuxième chapitre. Les troisième et quatrième chapitres sont respectivement dédiés aux écoulements uniformes et non uniformes. Dans les deux cas, la théorie est développée à partir d'une analyse de stabilité linéaire des systèmes d'ondes structure-sillage. La méthodologie proposée constitue un outil de design efficace, puisqu'il permet la connaissance de la dynamique de configurations complexes et que son coût en terme de temps de calcul est très faible.
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Geyman, Matthew Kenneth. "Wing/Wall Aerodynamic Interactions in Free Flying, Maneuvering MAVs." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1335113432.
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Belakroum, Rassim. "Contribution à la modélisation des interactions fluides-structures." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS009/document.
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Les buts principaux recherchés de la présente thèse visent au développement et à l’expertise d’une méthodologie de simulation numérique des problèmes d’interactions fluides-structures. Afin de cerner progressivement le problème étudié, nous nous sommes intéressés en premier lieu à la simulation numérique des écoulements autour d’obstacles solides, plus particulièrement au phénomène d’éclatements tourbillonnaires dans la zone de sillage d’obstacles de différentes formes. Nous avons utilisé la méthode des éléments finis en adoptant la technique de stabilisation GLS (Galerkin Least-Square). Pour le traitement de la turbulence, nous avons opté pour la méthode LES (Large-Eddy Simulation) en utilisant le filtre de Smagorinsky. En deuxième phase, nous nous sommes intéressés aux écoulements en milieux déformables. Nous avons entrepris la formulation ALE (Arbitrairement Lagrangienne Eulérienne) en considérant un maillage déformable. Pour la mise à jour de la grille du maillage dynamique, nous avons utilisé une approche pseudo-élastique. Afin d’expertiser la méthodologie mise en oeuvre, nous avons choisi d’aborder le problème des ballottements à la surface libre de réservoirs partiellement remplis de liquide. En dernière partie, nous nous sommes intéressés au comportement vibratoire d’un corps solide sous l’effet d’un écoulement de fluide. Par l’utilisation d’un algorithme de couplage totalement implicite basé sur la méthode de Gauss-Seidel par Bloc, nous avons abordé le phénomène des instabilités aéroélastiques des ponts à haubans. Pour la validation du modèle numérique traitant les interactions fluides-structures par les données expérimentales, nous nous sommes intéressés au comportement vibratoire d’une maquette sectionnelle d’un tablier de pont réel sous l’effet d’un vent soufflant uniformeThe main goals sought by this thesis target the development and expertise of a methodology for numerical simulation of fluid-structure interactions problems. In order to identify the studied problem progressively, we are interested primarily in numerical simulation of flows around bluff bodies, especially the phenomenon of vortex shedding in the wake zone of a bluff body of different shapes. We used the finite element method by adopting the stabilized GLS (Galerkin Least-Square) technique. For the treatment of turbulence, we opted the LES (Large-Eddy Simulation) method using the Smagorinsky filter. In the second phase, we were interested in flows in deformable media. We undertook the ALE (Arbitrary Lagrangian Eulerian) formulation by considering a deformable mesh. To update the grid of the dynamic mesh, we used a pseudo-elastic approach. To appraise the implemented methodology, we decided to approach the problem of sloshing at the free surface of a tank partially filled with liquid. In the final part, we were interested in vibration behavior of a solid body under the effect of fluid flow. By using a fully implicit coupling algorithm based on a relaxed Bloc Gauss-Seidel method, we studied the phenomenon of aeroelastic instability of cable-stayed bridges. To validate the numerical model treating fluid-structure interactions by experimental data, we investigated the vibration behavior of a real deck sectional model under the effect of a uniform wind
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Watterson, John Kenneth. "A new, pressure-based, unstructured mesh, Navier-Stokes solver and application to 3D compressible vortex/boundary layer interactions." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337910.
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Mycek, Paul. "Etude numérique et expérimentale du comportement d'hydroliennes." Thesis, Le Havre, 2013. http://www.theses.fr/2013LEHA0010/document.
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$aCe manuscrit traite de la caractérisation numérique et expérimentale du comportement d’hydroliennes. D’un point de vue expérimental, des essais ont été réalisés au bassin à houle et courant de l’IFREMER de Boulogne-Sur-Mer, sur des maquettes d’hydroliennes tri-pales à axe horizontal. Des configurations comprenant une seule hydrolienne, d’une part, et deux hydroliennes alignées avec l’écoulement, d’autre part, ont été considérées pour une large gamme de TSR et, le cas échéant, de distances interhydroliennes. Le comportement des hydroliennes est analysé à la fois en termes de performances (coefficients de puissance et de traînée) et de développement du sillage. Les effets du taux de turbulence ambiante sont également examinés. Par ailleurs, des simulations numériques, obtenues à l’aide d’un code tridimensionnel instationnaire, fondé sur la méthode Vortex particulaire et développé au LOMC (UMR 6294, CNRS –Université du Havre) en partenariat avec l’IFREMER, sont présentées. Le code de calcul permet également d’étudier les performances et le sillage d’une hydrolienne. Ce dernier a été complètement réécrit dans le cadre de cette thèse et le support théorique et technique des différents aspects du code est fourni dans ce manuscrit, où la méthode Vortex telle qu’elle est utilisée dans le code est exposée en détailThis manuscript deals with the numerical and experimental characterisation of the behaviour of marine current turbines. In the experimental part, trials were run at IFREMER’s wave and current flume tank in Boulogne-Sur-Mer, on prototypes of three-bladed horizontal axis turbines. Configurations with one single turbine on the one hand, and two turbines aligned with the incoming flow on the other hand, were considered for a large range of TSRs and, when relevant, of inter-device distances. The behaviour of the turbines is analysed in terms of performances (power and thrust coefficients) and development of the wake. The effects of the ambient turbulence intensity rate are also considered. Besides, numerical computations, obtained from a tridimensional unsteady software, based on the Vortex particle method and developed at the LOMC (UMR 6294, CNRS – University of Le Havre) in partnership with IFREMER, are presented. The numerical tool also enables to study the performances and the wake of a turbine. It was rewritten during this PhD and its technical and theoretical support is available in the manuscript, where the Vortex method, as it is used in the software, is described in details