Dissertations / Theses: 'Subsonic'

1

Ho, S. S. H. "Subsonic intake duct flows." Thesis, University of Salford, 1990. http://usir.salford.ac.uk/2213/.

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Here both S-shaped and singly curved (here classified as S-shaped) duct diffusers for intakes in aeronautical propulsion systems are studied. The results are applicable in other situations where similar ducts occur; for example on V/STOL aircraft employing re-direction of thrust, intercomponent ducting in high bypass ratio engines, etc. An open circuit static test rig, capable of mass flow rates of 5 kg/s, and three-dimensional instrumentation were established. Flow measurements were made in S-shaped intake duct diffusers for rear mounted gas turbine engines in both aircraft and air-breathing missiles. These designs are intended for ventral type inlet installation. These ducts possess cross-sectional shape transitions, from oblate to circular, with area increase and annular ducts at the engine face. The work was aimed at both fundamental understanding of the flows and at establishing test data for the prediction methods. Tests were performed at throat Mach numbers of nominally 0.15 and 0.6 and in the unit Reynolds number range of 3x10_6/m - 2x10_7/m for three different ducts each having different upstream bends but common downstream bends. Detailed boundary layer surveys were made to establish plane of symmetry growth of the viscous region and the extent of three-dimensionality away from the plane of symmetry. Data are presented in the form of velocity profiles, streamwise and cross-flow, integral thicknesses and surface pressure fields. Engine face distortion is assessed from full outlet flow surveys. Flow visualization was recorded using surface oil flow techniques. Evidence is presented of a trend towards three-dimensional separation as the upstream bend increases in severity. For the most extreme case large regions of complex three-dimensional separated flow occur and topological analysis of the recorded surface oil flow pattern allows reconstruction of the separating flow. Clear correlations are established between flow visualization results and flow measurements yielding better understanding. Finally, results were compared with a three-dimensional compressible prediction method.

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Ho, Y. K. "Supersonic and subsonic radial jets." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378306.

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Tambe, Samir B. "Liquid Jets in Subsonic Crossflow." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100876702.

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Weil, Samuel P. "Subsonic Performance of Ejector Systems." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1428048770.

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Su, Wei-Jen Dimotakis Paul E. Dimotakis Paul E. "Aerodynamic control for a subsonic diffuser /." Diss., Pasadena, Calif. : California Institute of Technology, 2001. http://resolver.caltech.edu/CaltechETD:etd-09042007-145002.

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6

Kakkavas, Constantinos. "Computational investigation of subsonic torsional airfoil flutter." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA359731.

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Thesis (M.S. in Aeronautical Engineering) Naval Postgraduate School, December 1998.
"December 1998." Thesis advisor(s): Max F. Platzer, Kevin D. Jones. Includes bibliographical references (p. 89-90). Also available online.

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7

Murray, Nathan E. "Flow field dynamics in subsonic cavity flows /." Full text available from ProQuest UM Digital Dissertations, 2006. http://0-proquest.umi.com.umiss.lib.olemiss.edu/pqdweb?index=0&did=1299816381&SrchMode=1&sid=4&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1193667418&clientId=22256.

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8

Lawrence, Jack. "Aeroacoustic interactions of installed subsonic round jets." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/367059/.

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Additional noise sources are generated when an aircraft engine is mounted beneath a wing. The two main installation sources include: (1) reflection of the exhaust jet mixing noise from the underside of the wing, and (2) interaction between the turbulent jet plume and the trailing edge of the wing, or deployed flap. The strength, directivity and frequency content of these particular sources all serve to increase the time-averaged flyover aircraft noise level heard on the ground by residents beneath the flight path. As the bypass ratio and nacelle diameter of modern turbofan engines continues to increase, constraints on ground clearance are forcing under-wing-mounted engines to be coupled more closely to the wing and flap system, which, in turn, serves to accentuate both of these noise sources. Close-coupled nacelle-airframe designs are now a critical issue surrounding efforts to meet the future environmental targets for quieter civil aircraft. This research is principally aimed at understanding and predicting the groundpropagating noise generated by the latter of these two installed jet noise sources. In order to characterise the jet-surface interaction noise source, however, it is first necessary to isolate it. A small 1/50th model-scale acoustic experiment, therefore, is conducted in a semi-anechoic university laboratory using a single stream jet installed beneath a flat plate. Both far-field acoustic and near-field plate surface pressure data are measured to investigate the jet-surface interaction noise source. Results from this fundamental experiment are then used to help drive a larger, and more realistic, 1/10th modelscale test campaign, at QinetiQ's Noise Test Facility, where 3D wing geometry effects, Reynolds number scaling effects and static-to-flight effects are investigated. A jet-flap impingement tonal noise phenomenon is also identified and investigated at particularly closely-coupled jet-wing configurations. Finally, the first version of a fast, semi-empirical engineering tool is developed to predict the additional noise caused by jet-wing interaction noise, under static ambient flow conditions. It is hoped that this tool will serve to inform future commercial aircraft design decisions and, thus, will help to protect the acoustic environment of residents living beneath flight paths.

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9

Sheen, Shaw-Ching. "Large eddy simulation of subsonic mixing layers." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40183.

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10

Kim, Meung Jung. "Application of panel methods for subsonic aerodynamics." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/52299.

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Several panel methods are developed to model subsonic aerodynamics. The vorticity panel method for two-dimensional problems is capable of handling general unsteady, potential, lifting flows. The lifting surface is modelled with a vortex sheet and the wakes by discrete vortices. As an imitation of the conditions at the trailing edge, stagnation conditions on both surfaces are used. The over-determined system is solved by an optimization scheme. The present predictions are in good agreement with experimental data and other computations. Moreover the present approach provides an attractive alternative to those developed earlier. Two panel methods for three-dimensional nonlifting problems are developed. One uses source distributions over curved elements and the other vorticity distributions over flat elements. For the source formulation, the effect of weakly nonlinear geometry on the numerical results is shown to accelerate the convergence of numerical values in general. In addition, the extensive comparisons between two formulations reveal that the voticity panel method is even more stable and accurate than the curved source panel method. Another vorticity panel method is developed to study the lifting l flows past three-dimensional bodies with sharp edges. The body is modelled by single vortex sheet for thin bodies and two vortex sheets for thick bodies while the wakes are modelled with a number of strings of discrete vortices. The flows are assumed to separate along the the sharp edges. The combination of continuous vorticity on the lifting surface and discrete vortices in the wakes yields excellent versatility and the capability of handling the tightly rolled wakes and predicting continuous pressure distributions on the lifting surface. The method is applied to thin and thick low-aspect-ratio delta wings and rectangular wings. The computed aerodynamic forces and wake shapes are in quantitative agreement with experimental data and other computational results.
Ph. D.

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11

Bonner, Michael Patrick. "Compressible subsonic flow on a staggered grid." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/32290.

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This work focuses on numerically modelling the dynamics of a single phase fluid at varying densities and pressures. We explore the potential of incompressible flow simulation methods in modelling compressible flow, with an eye towards computer animation applications. The methods developed capture the interesting thermodynamic effects of compressible flow, and reduce to the standard Marker and Cell incompressible flow Poisson matrix in the incompressible limit. The method works well in modelling flows in the subsonic range that normal incompressible techniques do not capture and where compressible methods are inefficient. We have also investigated adapting these techniques to granular elastic-plastic flow.
Science, Faculty of
Computer Science, Department of
Graduate

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12

Lakhamraju, Raghava R. "Liquid jets in subsonic airstream at elevated temperatures." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1116266049.

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13

Bin, Baqui Yamin. "Sound generation from coherent structures in subsonic jets." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709362.

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14

Tournier, Serge (Serge E. ). "Flow analysis and control in a subsonic inlet." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34135.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.
Includes bibliographical references (leaves 109-113).
S-duct inlets are commonly used on subsonic cruise missiles, as they offer a good compromise between compactness, low observability and aerodynamic performance. Though currently used S-ducts exhibit good performance in terms of distortion and pressure recovery at the AIP, the situation can degrade drastically when the inlet is put in off-design conditions, with the risk of compressor instabilities. Flow control is considered as a promising way to maintain inlet efficiency in off-design flight conditions. Industrial interest for flow control techniques is therefore rising, and a need for their comparative evaluation has been expressed. In response to this need, an experimental setup has been designed and fabricated, and flow control experiments have been carried out at MIT, on the selected off-design case of forebody boundary layer ingestion. The first set of experiments focused on the characterization of the inlet in a clean configuration. Then, a distortion device was added in order to simulate thick forebody boundary layer. This proved to have a strong detrimental effect on the inlet performance, as the separation bubble grew in size, the pressure recovery dropped down and the distortion level increased drastically. The selected flow control techniques were then implemented. .
(cont.) The Vortex Generators, tried in different configurations, did improve the pressure recovery and significantly decrease the distortion level. They had a strong impact on the flow structure, delaying or even suppressing separation. Injection was done with Coanda-type injectors, upstream of the separation line. Steady injection led to significant improvement of the pressure recovery, which increased with increasing injection mass flow. Separation was eliminated at least for the highest injection mass flows. The distortion level decreased with increasing injection mass flow. Overall, the results also highlighted the importance of the secondary flows as a source of distortion and pressure recovery loss
by Serge Tournier.
S.M.

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15

Roberts, Quentin David Hurt. "The trailing edge loss of subsonic turbine blades." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624758.

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16

Strganac, Thomas W. "A numerical model of unsteady, subsonic aeroelastic behavior." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74775.

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A method for predicting unsteady, subsonic aeroelastic responses has been developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The angle of attack is limited only by the occurrence of stall or vortex bursting near the wing. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flowfield are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion.
Ph. D.

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17

Yugulis, Kevin Lee. "High Subsonic Cavity Flow Control Using Plasma Actuators." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1345552086.

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18

Cavalieri, André Valdetaro Gomes. "Wavepackets as sound-source mechanisms in subsonic jets." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2253/document.

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On considère les paquets d'ondes hydrodynamiques comme mécanismes de génération de bruit des jets subsoniques. Cette approche résulte tout d'abord de l'analyse de données numériques - DNS d'une couche de mélange (Wei et Freund 2006) et LES d'un jet à Mach 0,9 (Daviller 2010) - permettant de déterminer les propriétés des sources en termes de compacité, d'intermittence et de structure azimutale. L'identification d'un rayonnement intermittent associé aux modifications des structures cohérentes des écoulements permet de proposer un modèle de paquet d'onde pour représenter ce phénomène dans l'analogie de Lighthill, dont l'enveloppe présente des variations temporelles d'amplitude et d'étendue spatiale. Celles-ci sont tirées de données de vitesse de simulations numériques de jets subsoniques, et un accord de l'ordre de 1,5dB entre le champ acoustique simulé et le modèle confirme sa pertinence. L'exploration du concept proposé est ensuite poursuivie expérimentalement, avec des mesures de pression acoustique et de vitesse de jets turbulents subsoniques, permettant la décomposition des champs en modes de Fourier azimutaux. On observe l'accord des directivités des modes 0, 1 et 2 du champ acoustique avec le rayonnementd'un paquet d'onde. Les modes 0 et 1 du champ de vitesse correspondent également à des paquets d'onde, modélisés comme des ondes d'instabilité linéaires à partir des équations de stabilité parabolisées. Finalement, des corrélations de l'ordre de 10% entre les modes axisymétriques de vitesse dans le jet et de pression acoustique rayonnée montrent un lien clair entre les paquets d'onde et l'émission acoustique du jet
Hydrodynamic wavepackets are studied as a sound-source mechanism in subsonic jets. We first analyse numerical simulations to discern properties of acoustic sources such as compactness, intermittency and azimuthal structure. The simulations include a DNS of a two-dimensional mixing layer (Wei and Freund 2006) and an LES of a Mach 0.9 jet (Daviller 2010). In both cases we identify intermittent radiation, which is associated with changes in coherent structures in the flows. A wave-packet model that includes temporal changes in amplitude and axial extension is proposed to represent the identified phenomena using Lighthill's analogy. These parameters are obtained from velocity data of two subsonic jet simulations, and an agreement to within 1.5dB between the model and the acoustic field of the simulations confirms its pertinence. The proposed mechanism is then investigatedexperimentally, with measurements of acoustic pressure and velocity of turbulent subsonic jets, allowing the decomposition of the fields into azimuthal Fourier modes. We find close agreement of the directivities of modes 0, 1 and 2 of the acoustic field with wave-packet radiation. Modes 0 and 1 of the velocity field correspond also to wavepackets, modelled as linear instability waves using parabolised stability equations. Finally, correlations of order of 10% between axisymmetric modes of velocity and far-field pressure show the relationship between wavepackets and sound radiated by the jet

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19

Gopala, Yogish. "Breakup characteristics of a liquid jet in subsonic crossflow." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44741.

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This thesis describes an experimental investigation of the breakup processes involved in the formation of a spray created by a liquid jet injected into a gaseous crossflow. This work is motivated by the utilization of this method to inject fuel in combustors and afterburners of airplane engines. This study aims to develop better understanding of the spray breakup processes and provide better experimental inputs to improve the fidelity of numerical models. This work adresses two key research areas: determining the time required for a liquid column to break up in the crossflow (i.e., primary breakup time) and the effect of injector geometry on spray properties. A new diagnostic technique, the liquid jet light guiding technique that utilizes ability of the liquid jet to act as a waveguide for laser light was developed to determine the location where the liquid column breaks up, in order to obtain the primary breakup time. This study found that the liquid jet Reynolds number was an important factor that governed the primary breakup time and improved the existing correlation. Optical diagnostic techniques such as Phase Doppler Particle Analyzer, Liquid Jet Light Guiding Technique, Particle Image Velocimetry and Imaging techniques were employed to measure the spray properties that include spray penetration, droplet sizes and velocities, velocity field on the surface of the liquid jet and the location of the primary breakup time. These properties were measured for two injectors: one with a sharp transition and the other with a smooth transition. It was found that the spray created by the injector with a sharp transition forms large irregular structures while one with smooth transition produces a smooth liquid jet. The spray transition creates a spray that penetrates deeper into the crossflow, breakup up earlier and produces larger droplets. Additionally, this study reports the phenomenon of the liquid jet splitting into two or more jets in sprays created by the injector with a smooth transition.

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Alvarez, Jose Oliverio. "Acoustic Resonance in a Cavity under a Subsonic Flow." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1091%5F1%5Fm.pdf&type=application/pdf.

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21

Kamps, Nathan George. "Active control of subsonic cavity flow using plasma actuators." Connect to resource, 2007. http://hdl.handle.net/1811/25082.

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Thesis (Honors)--Ohio State University, 2007.
Title from first page of PDF file. Document formatted into pages: contains x, 56 p.; also includes graphics. Includes bibliographical references (p. 47-48). Available online via Ohio State University's Knowledge Bank.

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22

Cetin, Mehmet Onur [Verfasser]. "Numerical Analysis of Subsonic Turbulent Jets / Mehmet Onur Cetin." München : Verlag Dr. Hut, 2018. http://d-nb.info/1155058054/34.

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23

Vollerthun, Hilke [Verfasser]. "Aeroacoustic Investigation of Controlled Subsonic Single Jets / Hilke Vollerthun." München : Verlag Dr. Hut, 2015. http://d-nb.info/1080754180/34.

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24

Ho, Pui Yin. "An interactive boundary layer method for subsonic aerofoil flows." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47475.

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25

Knesnik, Andrew. "Feasibility Study of an Axially-Stacked, Subsonic Propeller System." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353154024.

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26

Moret-Gabarro, Laia. "Aeroacoustic investigation and adjoint analysis of subsonic cavity flows." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT047H/document.

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Les écoulements instationnaires au-dessus de surfaces discontinues produisent d'important bruit aérodynamique. L'objectif de ce travail de thèse est l'étude aéroacoustique d'écoulement au-dessus de cavités bidimensionnelles rectangulaires, et de trouver des stratégies de réduction du bruit. Des simulations numériques directes des équations bidimensionnelles de Navier-Stokes compressibles ont été réalisées afin d'étudier l'influence des conditions initiales sur le mode d'oscillation de l'écoulement pour des cavités profonde et peu profonde. Les résultats montrent que dans le cas de cavités profondes, l'écoulement oscille selon un régime de couche de cisaillement suivant le second mode de Rossiter, et ce quelle que soit la condition initiale choisie. En revanche, dans le cas de cavités peu profondes, le régime d'oscillation observé peut être en couche de cisaillement ou bien en mode de sillage suivant la condition initiale choisie. Une analyse de sensibilité d'écoulement dans le cas de cavités profondes a été réalisé en utilisant une méthode adjointe. Les équations adjointes ont été forcées par une perturbation localisée sinusoïdale soit de la quantité de mouvement suivant x adjointe (au voisinage de la couche de cisaillement), soit de la densité adjointe (loin de la cavité). Les résultats désignent une région de l'écoulement très sensible à l'ajout de masse, et localisée au voisinage du coin supérieur amont de la cavité. Par conséquent, un actionneur de type soufflage/aspiration placé au bord d'attaque de la cavité agira sur les fluctuations de quantité de mouvement suivant x au voisinage de la couche de cisaillement et sur les fluctuations de pression au loin
The unsteady flow over surface discontinuities produces high aerodynamic noise. The aim of this thesis is to study the aeroacoustics of two-dimensional rectangular cavities and to find strategies for noise reduction. Direct Numerical Simulation of the compressible Navier-Stokes equations is performed to investigate the influence of the initial condition on the oscillation modes in deep and shallow cavities. Results show that the deep cavity oscillates in shear layer regime at the second Rossiter mode regardless of the initial condition. On the other hand different initial conditions lead to a shear layer or wake mode in the shallow cavity case. A sensitivity analysis of the deep cavity is done by the use of adjoint methods. Local sinusoidal perturbations of x-momentum and density are applied to the adjoint equations. The results show a high sensitivity region to mass injection at the upstream corner. Therefore an actuator placed at the leading edge will modify the velocity fluctuations reaching the trailing edge and hence the pressure fluctuations in the far-field

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Zuber, Matthew E. "Investigation of magnetofluiddynamic acceleration of subsonic inductively coupled plasma." Doctoral thesis, Universite Libre de Bruxelles, 2006. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210898.

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Electromagnetic acceleration has the potential for various applications stemming from space electric propulsion systems to future air breathing hypersonic augmentation.

Electromagnetic acceleration uses electromagnetic body force produced by the interactions of currents carried in plasma which is either externally applied or self-induced magnetic fields to accelerate the whole body of gas. Historically, these plasmas sources have been arc jets, shock tube and microwaves. Never has an electromagnetic accelerator been powered by an inductively coupled plasma (ICP) source.

The von Karman Institute has experimentally investigated the acceleration of an electrically conductive fluid produce by a subsonic ICP source. This ICP source was powered with a 15 kW and 27.1 MHz radio frequency facility called the Minitorch. The electromagnetic acceleration was accomplished with the design, fabrication and testing of a linear Hall current magnetofluiddynamic accelerator (MFDA) channel. The channel was geometrically orientated into the Hall configuration to accounts for the large Hall Effect. This channel used a single pair of copper annulus electrodes powered by a 10 kW direct current power supply. The channel was water cooled and contained various diagnostics to provide greater insight to the electromagnetic acceleration process. This was the first successful magnetofluiddynamic acceleration of an ICP source and validates the proof of concept.

One-dimensional MFD modeling was formulated and used to determine the necessary performance requirements of the MFDA channel E and B field subsystems. An interaction parameter of approximately 2.25 was required for the doubling of an inlet velocity of 300 m/sec. The required subsystem need to provide a current density was 6 Amps/cm2 with a magnetic field strength of 0.50 Tesla over an acceleration length of 0.1 meters. Additional the most critical constraint was the thermal management subsystem which was designed to overcome large heat transfer fluxes to achieve a steady state condition over a test run of 10 minutes.

The dynamic pressure measured increase the inlet velocity 101% for an argon plasma flowing at 1.01 g/s at a magnetic field strength of 0.49 Tesla. his strong acceleration of the plasma was most notable near the region of the electrodes at the exit of the 0.1 m long channel. The central region of the plasma has less dynamic pressure increase corresponding to only a maximum of 15% increase in velocity at a magnetic strength of 0.49 Tesla. Experimental results showed that axial discharge voltages increased with increased magnetic fields, indicating a strong Hall Effect in the accelerator as expected.

Theoretical analysis was accomplished using the one-dimensional equation of motion and was compared to utilizing only the momentum equation. Experimental force fluxes were compared to the calculated values of the one-dimensional equation of motion and momentum equation. The reference area for the current density was selected from intensity measurement using a high speed camera with the MFDA channel on. There was significant error in the analysis concerning using the momentum Lorentz force only versus the one-dimensional equations of motion; which included joule heating. This analysis summarized the necessity to include joule heating in the formulation of the problem.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished

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Ng, Lian Lai. "Instabilities and subharmonic resonances of subsonic-heated round jets." Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185078.

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When a jet is perturbed by a periodic excitation of suitable frequency, a large-scale coherent structure develops and grows in amplitude as it propagates downstream. The structure eventually rolls up into vortices at some downstream location. We approximate the "wavy flow" associated with the roll-up of a coherent structure by a parallel mean flow and a small, spatially periodic, axisymmetric wave whose phase velocity and mode shape are given by classical (primary) stability theory. The periodic wave acts as a parametric excitation in the differential equations governing the secondary instability of a subharmonic disturbance. The (resonant) conditions for which the periodic flow can strongly destabilize a subharmonic disturbance are derived. When the resonant conditions are met, the periodic wave plays a catalytic role to enhance the growth rate of the subharmonic. The stability characteristics of the subharmonic disturbance, as a function of jet Mach number, jet heating, mode number and the amplitude of the periodic wave, are studied via a secondary instability analysis using two independent but complementary methods: (i) method of multiple scales and (ii) normal mode analysis. We found that the growth rates of the subharmonic waves with azimuthal numbers β = 0 and β = 1 are enhanced strongly, but comparably, when the amplitude of the periodic wave is increased. Furthermore, compressibility at subsonic Mach numbers has a moderate stabilizing influence on the subharmonic instability modes. Heating suppresses moderately the subharmonic growth rate of an axisymmetric mode, and it reduces more significantly the corresponding growth rate for the first spinning mode (i.e., β = 1). Our calculations also indicate that while the presence of a finite-amplitude periodic wave enhances the growth rates of subharmonic instability modes, it minimally distorts the mode shapes of the subharmonic waves.

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Wolf, Claus Christian [Verfasser]. "The subsonic near-wake of bluff bodies / Claus Christian Wolf." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/105142805X/34.

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Loiodice, Sabino. "Modelling noise from rotating sources in subsonic and supersonic regimes." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3757.

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Noise is an environmental concern and due to the increasing interest in helicopters as an alternative inter-city transportation, research for more environment friendly helicopters is continuously growing. Building on this demand, this study aims at finding an efficient and accurate noise prediction tool for rotating sources. This study therefore investigates the modelling of noise from rotating sources such as helicopter rotors by addressing noise propagation in both subsonic and transonic/ supersonic regimes. The aim of this research is to explore the field of aeroacoustics prediction for rotor generated noise and to develop a noise prediction tool for sources moving in subsonic or supersonic flow regimes. The aeroacoustics predictions presented have been obtained using a hybrid approach. With such an approach the near field noise generation process is simulated by means of an aerodynamics prediction tool while the noise propagation to the near field is computed by mean of the Ffowcs Williams-Hawkings equation in time domain. For the near-field aerodynamic calculations di erent CFD tools have been exploited. More precisely, three test cases have been analysed. For the first test case of 2D aerofoil-vortex interaction, reproducing the experimental campaign of Lee et al., the near-field is computed via the commercial software Fluent. The unsteady implicit Euler solver with second order discretisation both in space and in time is exploited. This uses the ROE FDS scheme for the fluxes calculation. The same solver is used in the near-field simulations of the third test case, where the analysis of a non-lifting hovering rotor is carried out in delocalised conditions, reproducing the experiments of Purcell on the UH1H model rotor. The second test case analysed is based on the HELISHAPE experimental campaign for the ONERA model rotor in BVI conditions. Two comprehensive codes, from Agusta-Westland and Roma Tre, are used to simulate the complex aeromechanics of the rotor in low speed descent. The noise propagation phase has been performed via the new noise prediction tool developed during this study, named HelicA (for Helic-opter A-coustics). This tool is based on the Emission Surface formulation and exploits a novel root finder and Emission Surface construction algorithms. It can use control surfaces which are in subsonic or transonic/supersonic conditions. Verification and validation processes have been performed on the noise prediction tool before using this code in the aforementioned test cases. These processes are based on the comparison of the tool’s predictions with available analytical and numerical results. The verification and validation cases include sources moving at Mach numbers ranging from MT = 0 to MT > 1. The noise prediction tool is applied to the three aforementioned test cases and the results are in very good agreement with the measurements even for the strong shock delocalisation cases.

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Lu, Ming 1968. "A Lagrangian formulation of the Euler equations for subsonic flows /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103268.

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This thesis presents a Lagrangian formulation of the Euler equations for subsonic flows. A special coordinate transformation is used to define the Lagrangian coordinates, namely the stream function and the Lagrangian distance, in function of the Cartesian coordinates. This Lagrangian formulation introduces two new geometry state variables, and a Lagrangian behavior parameter defining a pseudo-Lagrangian time used during the iteration procedure to obtain the solution for subsonic flows.
The eigenstructure and characteristics analysis for the new system of equations is based on a linear Jacobian matrix-mapping procedure, which starts from the well-known eigenstructure and characteristics in the Eulerian plane and uses the coordinate transformation to find their counterparts in the Lagrangian plane. This analysis studies the basic properties of the Euler equations in the Lagrangian formulation, such as hyperbolicity, homogeneity and rotational invariance. The Riemann problem in the Lagrangian plane is also studied. Those elements are used to construct the numerical scheme for solving the Euler equations in the Lagrangian formulation.
The numerical scheme is constructed using first and second-order dimensional-splitting with hybrid flux operators, based on flux vector splitting and Godunov methods, which include a 2-D Riemann solver in the Lagrangian plane. The numerical method is validated by comparing the present solutions with the results obtained with an Eulerian formulation for several internal flows.
This numerical method based on a Lagrangian formulation has also been extended for the solution of unsteady subsonic flows by using a dual time approach. The method validation in this case has been done by comparison with the Eulerian formulation solutions for several internal subsonic flows with oscillating boundaries.

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32

Yuan, Xin. "Model-based feedback control of subsonic cavity flows - control design." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1158032317.

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33

Kiran, Amit. "Jet noise : aeroacoustic distribution of a subsonic co-axial jet." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/3914/.

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The noise generated by aircraft can be easily heard by those living under the flight path of passenger or cargo carriers. It is considered an environmental pollutant and is treated as such by the International Civil Aviation Organization (ICAO) who monitor and review noise levels. The ICAO imposes substantial fines on those carriers who do not adhere to the decibel limitations. With the new limit or `stage' enforced in 2006, aircraft manufacturers (including jet engine manufacturers) are seeking ways to reduce the noise created by an aircraft. A 1/150th scale model, based on the exit geometry typically found on commercial jet engines, was designed and manufactured at Warwick. The laboratory jet flow conditions operated at 0.7 Mach. The work presented in this thesis looks at the noise generated in a subsonic, co- owing jet, with particular focus given to the distribution sound sources from 5 kHz to 80 kHz (0.375 St to 6.0 St). An acoustic mirror mounted on a motorized 3-way traverse measured radiated sound in the co-flowing jet to produce 2D sound source maps. This is done using combinations of smooth cowl and chevrons for the core and bypass nozzles. For frequencies less than 30 kHz, a reduction of noise was observed using the bypass chevron nozzle compared with the bypass smooth cowl nozzle. Laser Doppler Anemometry (LDA) was used to reveal the 2D flow dynamics of the jet, supporting the acoustic distribution results with velocity profiles of the flow. The change in the flow dynamics with different nozzle combinations is discussed and different regions of the flow were identified.

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Duong, Hao Q. (Hao Quang) Carleton University Dissertation Engineering Mechanical. "Two point correlations of temperature in a hot subsonic jet." Ottawa, 1990.

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35

Sykes, James Henry Carleton University Dissertation Engineering Mechanical and Aerospace. "A higher order panel method for linearized unsteady subsonic aerodynamics." Ottawa, 1994.

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36

Roland, Hannah. "Instability and receptivity of subsonic flow in the boundary layer." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/64819.

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In this thesis, the main focus is on the interaction of an incoming Tollmien–Schlichting wave with an isolated, stationary wall roughness in subsonic flow. In Part I, this problem is analysed by means of the Triple Deck theory. The linearised sublayer equations are solved under the assumption that the horizontal extent of the roughness is of O(L Re^(−3/8)) and that its height h is small, and an expression for the pressure perturbation is found. The transmission coefficient T_I , defined as the amplitude of the T–S wave downstream of the roughness divided by its initial amplitude, is then calculated, where |T_I | > 1 means that the wave is amplified and |T_I | < 1 represents an attenuation of the T–S wave. The transmission coefficient is dependent on the frequency ω, the height h of the roughness and on the Fourier transform of the roughness shape evaluated at zero value of the wavenumber. The same setup is investigated in Part II through numerical calculations: a DNS solver provides the base flows for 25 different gaps of varying width and height, which are then run through a PSE analysis to examine the stability of the flow. From the results of both methods it can be concluded that a surface indentation amplifies an incoming T–S wave, and that the amplification increases with the width and depth of the roughness. An additional geometry is studied in Part I by again employing the Triple Deck theory to investigate the effect small elastic vibrations of a semi-infinite plate attached to a stationary plate have on the boundary layer, and the receptivity coefficient is calculated for varying ω.

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37

Bitomsky, Uwe. "Pressure distribution on wing-body-flap configurations at subsonic speed." Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357812.

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38

Al, Haddabi Naser Hamood. "Subsonic open cavity flows and their control using steady jets." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/9096/.

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Cavity flow induces strong flow oscillations, which increase noise, drag, vibration, and structural fatigue. This type of flow impacts a wide range of low speed applications, such as aircraft wheel wells, ground transportations, and pipelines. The objective of the current study is to examine the reverse flow interaction inside the cavity, which has a significant impact on the cavity flow oscillations. The study also investigates the impact of steady jets with different-configurations on the time-average field and the oscillations of the cavity separated shear layer. The purpose of the steady jets is suppressing the oscillations of the cavity separated shear layer. The experiments were performed for an open cavity with L/D = 4 at Reθ between 1.28×103 to 4.37×103. The steady jets were applied with different: momentum fluxes (J = 0.11 kg/m.s2,0.44 kg/m.s2 and 0.96 kg/m.s2), slot configurations (sharp edge and coanda), and blowing locations (blowing from the cavity leading and trailing edges). The data were acquired using qualitative (surface oil flow visualisation) and quantitative (hot-wire anemometry, laser Doppler anemometry, particle image velocimetry, and pressure measurements) flow diagnostics techniques. The study found that a low-frequency instability dominates the velocity spectra of the cavity separated shear layer. This instability decreases with increasing Reθ and is related to the reverse flow interaction. This interaction takes place when the reverse flow influences the sensitive separation point of the cavity separated shear layer. As a result, a large amplitude flapping wave is generated and propagates downstream of the cavity separated shear. It was also revealed that increasing J for the leading and trailing edges blowing enhances the reverse flow interaction and increases the broadband level of the unsteady wall pressure spectra. Thus, these types of jet blowing are not suitable for controlling the oscillations of the cavity separated shear layer.

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Malla, Bhupatindra. "Study of High-speed Subsonic Jets using Proper Orthogonal Decomposition." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352397174.

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LAKHAMRAJU, RAGHAVA RAJU. "LIQUID JET BREAKUP STUDIES IN SUBSONIC AIRSTREAM AT ELEVATED TEMPERATURES." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1116266049.

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41

Fransson, Torsten Henry. "Numerical investigation of unsteady subsonic compressible flows through an oscillating cascade /." Lausanne : EPFL, 1986. http://library.epfl.ch/theses/?nr=613.

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Chang, J. M. "A flexible, subsonic high altitude long endurance UVA conceptual design methodology." Thesis, Cranfield University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245445.

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43

Skordos, Panayotis Augoustos. "Modeling flue pipes--subsonic flow, lattice Boltzmann, and parallel distributed computers." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36534.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.
Includes bibliographical references (p. 251-256).
by Panayotis A. Skordos.
Ph.D.

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Thangamani, V. "The effects of scaling and high subsonic cavity flow and control." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/8646.

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The effects of scaling a cavity with respect to a fixed incoming boundary layer thickness on its flow dynamics and control was studied experimentally. Three cavity models with constant length-to-depth ratio of 5 and length-to-width ratio of 2 and with corresponding linear dimensions in the ratio 0.5 : 1 : 2 were tested at freestream Mach number 0.71. Additionally, the 0.5 and 1 scale models were tested at freestream Mach number of 0.85. The experiments involved timeaveraged pressure measurements, unsteady pressure measurements, and PIV measurements. Time-averaged pressure measurements made at the floor were used to study the ’flow-type’ of the cavities. Unsteady pressure measurements were used to study the acoustic characteristics of the cavity. The cavity length-to-boundary layer thickness ratios tested were 10, 20 and 40. The Cp distribution on the clean cavities indicated a change in the cavity flowtype with change in the cavity scale. Varying the L/δ from 10 to 40 changed the cavity flow-type from open to transitional. Analysis of the frequency spectra of the cavity revealed an increase in tonal amplitudes and OASPL with increasing L/δ . The PIV measurements indicated that this could be caused by an increase in energy exchange between the freestream and the cavity. The velocity magnitudes inside the cavities were found to increase with increase in L/δ . A comparative study of different passive control methods on the largest cavity showed that leading-edge spoilers were superior in cavity tone suppression. Of these, the effectiveness of a sawtooth spoiler on the three cavities of different scales was tested. The results showed that while the spoiler was effective in eliminating tones and suppression of noise for the smaller cavities, it was unable to eliminate the tones completely for the largest cavity. To find the correct method for scaling the spoilers with the cavity dimensions, different spoiler heights were tested on the three cavities. The results showed that the cavity noise suppression for a given cavity attains saturation level at a particular spoiler height, called the critical spoiler height. An increase in spoiler height beyond the critical spoiler height was found to have no effect on the noise suppression. It is also found that this critical spoiler height can be scaled with the length of the cavity (for given L/D, M and spoiler profile) irrespective of the boundary layer thickness.

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45

Mancini, Simone. "Boundary integral methods for sound propagation with subsonic potential mean flows." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/413760/.

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This work deals with including non-uniform mean flow effects into boundary integral solutions to acoustic wave propagation. A time harmonic boundary integral solution is proposed for low Mach number potential flows with small non-uniform mean flow velocities and a free-field Green’s function is recovered to solve the corresponding kernel. The boundary integral formulation can be used as a means of solving both wave extrapolation and boundary element problems. For boundary element solutions to external sound propagation, the non-uniqueness issue is worked around by extending the conventional combined Helmholtz integral equation formulation and the Burton–Miller approach to non-uniform mean flows. Nonetheless, the proposed integral formulation is shown to be consistent with a combination of the physical models associated with the Taylor and Lorentz transforms. The combined Taylor–Lorentz transformation allows mean flow effects on acoustic wave propagation to be resolved by using a standard boundary integral formulation for the Helmholtz problem with quiescent media in a transformed space. Numerical experiments are performed to benchmark the proposed integral formulations against finite element solutions based on the linearised potential equation. Numerical examples are also used to validate a weakly-coupled approach exploiting the proposed integral formulations in order to predict forward fan noise installation effects. Nonetheless, the integral formulations in a transformed space are used to simulate mean flow effects based on standard boundary element solvers for quiescent media. The results suggest that, for low Mach numbers, boundary element solutions to wave propagation with non-uniform mean flows represent a good approximation of finite element solutions based on the linearised potential equation. It is shown that the boundary element solutions including non-uniform mean flow effects improve on the corresponding approximations assuming a uniform flow in the whole computational domain. This is observed when sound propagation is predicted in the near field and in a region where the non-uniformity in the mean flow velocity is significant.

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46

Rosa, Victor. "RANS-based prediction of noise from isothermal and hot subsonic jets." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/417861/.

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Current civil aircraft are significantly quieter than the civil aircraft of the 20th century. But the overall impact of aircraft noise has not been reduced by the same token because the number of aircraft operations has been steadily increasing. So to compensate for the increase in aircraft operations and reduce the overall impact of aircraft noise, we must design quieter aircraft. The noise generated by the jet leaving the engine exhaust is the dominant source when the aircraft is taking off, so its reduction will lead to significant reduction of the total aircraft noise. The current engine design employs decades of research on jet noise, so noise technology has reached a mature state. Thus to further reduce jet noise we must assess the impact of once secondary elements or employ disruptive designs. These assessments would have such a large design space that it is not possible to rely on experimental campaigns and scaling laws, hence the need to develop numerical methods to predict jet noise. This thesis studies methods to predict jet noise that use an acoustic analogy and information from a steady RANS solution of the flow to compute turbulence two-point statistics. RANS-based methods rely on empirical modelling but may provide the optimum balance between computational cost and generality needed by the industry to design the next generation of jet engines. The goal of the thesis is to reduce the empiricism of RANS-based prediction whilst keeping the low computational cost. The contributions of the thesis are summarised in three aspects: (1) introduce a model for the additional sound source in hot jets, (2) formulate the empirical model of turbulence statistics in frequency domain, and (3) compute the effect of turbulence anisotropy on jet noise directivity. The contributions of the thesis update an existing prediction method (C. R. S. Il´ario et al. Prediction of jet mixing noise with Lighthill’s acoustic analogy and geometrical acoustics. J. Acoust. Soc. Am., 141 (2), 2017.) which can be applied by industry, and provide background for further research in academia.

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47

Polen, David M. "Integrated aerodynamic-structural design of a subsonic, forward- swept transport wing." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/46059.

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The introduction of composite materials and the ability to tailor these materials to improve aerodynamic and structural performance is having a distinct effect upon aircraft design. In order to optimize the efficiency of the design procedure, a design process which is more integrated than the traditional approach is required. Currently the utilization of such design procedures produces enormous computational costs. An ongoing effort to reduce these costs is the development of efficient methods for cross-disciplinary sensitivities and approximate optimization techniques.

The present research concentrates on investigating the integrated design optimization of a subsonic, forward-swept transport wing. A modular sensitivity approach for calculating the cross-sensitivity derivatives is employed. These derivatives are then used to guide the optimization process. The optimization process employed is an approximate technique due to the complexity of the analysis procedures. These optimization results are presented and the impact of the modular technique is discussed.

Master of Science

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48

Vincent, Tyler Graham. "Total Temperature Probe Performance for Subsonic Flows using Mixed Fidelity Modeling." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/88867.

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An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been previously investigated, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer. A parametric study was conducted considering three non-dimensional probe geometric ratios (vent location to shield length (0.029-0.806), sensor diameter to shield inner diameter (0.252-0.672), and shield outer diameter to strut/mount thickness (0.245-0.759)) and three operating conditions (total temperature (70, 850, 2500°F) and pressure (1, 1, 10 atm), respectively) at a moderate Mach number of 0.4. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for evaluating radiation and transient influences on sensor performance. These new flow and heat transfer correlations together with the new Reduced Order Modeling technique developed here greatly enhance the capabilities of designers to evaluate performance of current and future probe designs, with higher accuracy and with significant reductions in computational resources.
Doctor of Philosophy
An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been thoroughly described and quantified in the past, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer (CHT) capabilities. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling (ROM) technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for readily predicting the impact of radiation environment and transient errors on sensor performance.

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Boehm, Brian Patrick. "Performance optimization of a subsonic Diffuser-Collector subsystem using interchangeable geometries." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/49589.

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A subsonic wind tunnel facility was designed and built to test and optimize various diffuser-collector box geometries at the one-twelfth scale. The facility was designed to run continuously at an inlet Mach number of 0.42 and an inlet hydraulic diameter Reynolds number of 340,000. Different combinations of diffusers, hubs, and exhaust collector boxes were designed and evaluated for overall optimum performance. Both 3-hole and 5-hole probes were traversed into the flow to generate multiple diffuser inlet and collector exit performance profile plots. Surface oil flow visualization was performed to gain an understanding of the complex 3D flow structures inside the diffuser-collector subsystem. The cutback radial hardware was found to increase the subsystem pressure recovery by over 10% from baseline resulting in an approximate 1% increase in gas turbine power output.
Master of Science

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50

Elzebda, Jamal M. "Two-degree-of-freedom subsonic wing rock and nonlinear aerodynamic interference." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/50011.

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In many situations the motion of the fluid and the motion of the body must be determined simultaneously and interactively. One example is the phenomenon of subsonic wing rock. A method has been developed that accurately simulates the pitching and rolling motions and accompanying unsteady flowfield for a slender delta wing. The method uses a predictor-corrector technique in conjunction with the general unsteady vortex-lattice method to compute simultaneously the motion of the wing and the flowfield, fully accounting for the dynamic/aerodynamic interaction. For a single degree of freedom in roll, the method predicts the angle of attack at which the symmetric configuration of the leading-edge vortex system becomes unstable, the amplitude, and the period of the resulting self-sustained limit cycle, in close agreement with two wind-tunnel experiments. With the development of modern aerodynamic configurations employing close-coupled canards, such as the X-29, comes the need to simulate unsteady aerodynamic interference. A versatile method based on the general unsteady vortex-lattice technique has been developed. The method yields the time histories of the pressure distribution on the lifting surfaces, the distribution of vorticity in the wakes, and the position of the wakes simultaneously. As an illustration of the method, the unsteady flowfield for a configuration closely resembling the X-29 is presented. The results show the strong influence of the canards on the main wing, including the time lag between the motions of the canards and the subsequent changes in the vorticity and hence the pressure distributions and loads on the main wing.
Ph. D.
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Dissertations / Theses on the topic 'Subsonic'

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