Tesi sul tema "Jets"
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1
Pietroniro, Asuka Gabriele. "Modelling coaxial jets relevant to turbofan jet engines". Thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200909.
Testo completoAbstract (sommario):
Simulations of subsonic turbulent coaxial hot jets were conducted on two types ofunstructured grids within the framework of STAR-CCM+. The study case is based on atypical airliner turbofan engine model with a core nozzle and a fan nozzle, having a bypassratio of five. The two meshes used are a polyhedral one, suitable for complex surfaces, and atrimmed one mainly made of hexahedral cells. The sensitivity of the study case to variousinputs is attested using second and third order upwind schemes, modelling turbulence with aSST k-omega model. The project proves to be a valid feasibility study for a steady-statesolution on which an aeroacoustic analysis could be based in future works.
2
Pietroniro, Asuka Gabrielle. "Modelling coaxial jets relevat to turbofan jet engines". Thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204020.
Testo completoAbstract (sommario):
Simulations of subsonic turbulent coaxial hot jets were conducted on two types ofunstructured grids within the framework of STAR-CCM+. The study case is based on atypical airliner turbofan engine model with a core nozzle and a fan nozzle, having a bypassratio of five. The two meshes used are a polyhedral one, suitable for complex surfaces, and atrimmed one mainly made of hexahedral cells. The sensitivity of the study case to variousinputs is attested using second and third order upwind schemes, modelling turbulence with aSST k-omega model. The project proves to be a valid feasibility study for a steady-statesolution on which an aeroacoustic analysis could be based in future works.Simuleringar av subsoniska turbulenta koaxiala varma flöden genomfördes på två typer avostrukturerade nät inom ramen för STAR-CCM+. Studiefallet är baserat på en modell av enturbofläktmotor för ett typiskt trafikflygplan, med en inre samt yttre dysa och med ett bypassförhållandeav fem. De två beräkningsnät som används är ett polyedriskt nät, lämplig förkomplexa ytor, och ett trimmat nät huvudsakligen uppbyggt av sexsidiga celler. Känslighetenav studiefallet beroende på olika indata intygas med hjälp av andra och tredje ordningens”upwind-schemes”, där turbulensen modelleras med en SST k-omega modell. Projektet visarsig vara en giltig förstudie för en steadystate-lösning på vilken en aeroakustisk analys skullekunna baseras i framtida arbeten.
3
Smith, Barton Lee. "Synthetic jets and their interaction with adjacent jets". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/18889.
Testo completo
4
Manfroi, Aldo J. "Zonal jets /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035898.
Testo completo
5
Moutoussi, Ann. "Quark and gluon jets in a three-jet environment". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297244.
Testo completo
6
Ghahremanian, Shahriar. "Near-Field Study of Multiple Interacting Jets : Confluent Jets". Doctoral thesis, Linköpings universitet, Energisystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-113259.
Testo completoAbstract (sommario):
This thesis deals with the near-field of confluent jets, which can be of interest in many engineering applications such as design of a ventilation supply device. The physical effect of interaction between multiple closely spaced jets is studied using experimental and numerical methods. The primary aim of this study is to explore a better understanding of flow and turbulence behavior of multiple interacting jets. The main goal is to gain an insight into the confluence of jets occurring in the near-field of multiple interacting jets. The array of multiple interacting jets is studied when they are placed on a flat and a curved surface. To obtain the boundary conditions at the nozzle exits of the confluent jets on a curved surface, the results of numerical prediction of a cylindrical air supply device using two turbulence models (realizable 𝑘 − 𝜖 and Reynolds stress model) are validated with hot-wire anemometry (HWA) near different nozzles discharge in the array. A single round jet is then studied to find the appropriate turbulence models for the prediction of the three-dimensional flow field and to gain an understanding of the effect of the boundary conditions predicted at the nozzle inlet. In comparison with HWA measurements, the turbulence models with low Reynolds correction (𝑘 − 𝜖 and shear stress transport [SST] 𝑘 − 𝜔) give reasonable flow predictions for the single round jet with the prescribed inlet boundary conditions, while the transition models (𝑘 − 𝑘l − 𝜔𝜔 and transition SST 𝑘 − 𝜔) are unable to predict the flow in the turbulent region. The results of numerical prediction (low Reynolds SST 𝑘 − 𝜔 model) using the prescribed inlet boundary conditions agree well with the HWA measurement in the nearfield of confluent jets on a curved surface, except in the merging region. Instantaneous velocity measurements are performed by laser Doppler anemometry (LDA) and particle image velocimetry (PIV) in two different configurations, a single row of parallel coplanar jets and an inline array of jets on a flat surface. The results of LDA and PIV are compared, which exhibit good agreement except near the nozzle exits. The streamwise velocity profile of the jets in the initial region shows a saddle back shape with attenuated turbulence in the core region and two off-centered narrow peaks. When confluent jets issue from an array of closely spaced nozzles, they may converge, merge, and combine after a certain distance downstream of the nozzle edge. The deflection plays a salient role for the multiple interacting jets (except in the single row configuration), where all the jets are converged towards the center of the array. The jet position, such as central, side and corner jets, significantly influences the development features of the jets, such as velocity decay and lateral displacement. The flow field of confluent jets exhibits asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. The velocity decays slower in the combined regio of confluent jets than a single jet. Using the response surface methodology, the correlations between characteristic points (merging and combined points) and the statistically significant terms of the three design factors (inlet velocity, spacing between the nozzles and diameter of the nozzles) are determined for the single row of coplanar parallel jets. The computational parametric study of the single row configuration shows that spacing has the greatest impact on the near-field characteristics.
7
Stan, Gheorghe. "Fundamental Characteristics of Turbulent Opposed Impinging Jets". Thesis, University of Waterloo, 2000. http://hdl.handle.net/10012/831.
Testo completoAbstract (sommario):
A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.
8
Mutter, Troy Blake. "Numerical simulations of elliptical jets : a study of jet entrainment /". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07102009-040630/.
Testo completo
9
Chakravorty, Saugata. "A Numerical Study On Absolute Instability Of Low Density Jets". Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/227.
Testo completoAbstract (sommario):
A spectacular instability has been observed in low density round jets when the density ratio of jet fluid to ambient fluid falls below a threshold of approximately 0.6. This phenomenon has been observed in non-buoyant jets of helium in air, heated air jets and heated buoyant jets. The oscillation of the flow near the nozzle is extremely regular and periodic and consists of ring vortices. Even the smaller scale structures that appear downstream exhibit similar regularity. A theory for predicting the onset of this oscillation is based on finding regions of absolute instability from linear stability analysis of parallel flow. However, experiments suggest that the theory is at least incomplete and fortuitous as the oscillation is not a linear process. The present work is to observe and understand the process of regeneration of these oscillations by conducting numerical simulations. Here, two-dimensional, plane jets were simulated because they undergo a qualitatively similar process.
A spatial and temporal picture of a heated jet has been obtained numerically. A perturbation expansion was used to obtain a system of conservation laws for compressible flows which is valid for low Mach numbers. The low Mach number approximation removes the high frequency acoustic waves from the flow field. This enables a larger time step to be taken without making the calculation unstable. To ensure that all the scales of motion are properly resolved, calculations were done at a low Reynolds number. The governing equations were discretized in space using second-order finite difference formulas on a staggered grid. Velocity fields were advanced using a second-order Adams-Bashforth explicit scheme and then corrected by solving for pressure such that continuity is satisfied at every time step. The Poisson problem for pressure requires the time derivative of the density which was approximated by a third-order backward difference formula. Gauss-Siedel iteration was used to find the pressure.
Several numerical tests were conducted prior to simulations of variable density jets to check the stability and accuracy of the code. Two dimensional driven cavity flow calculations were done as a first test. Then a calculation of a forced, spatially developing, incompressible, plane mixing layer was done to check the time accuracy of the code. After obtaining satisfactory performance of the code for the different test cases, two-dimensional, variable density jets were simulated.
Since the plane jet extends ad infinitum in the streamwise direction, a sufficiently large domain was used to capture all the relevant physics in the downstream regions of the jet. An advective boundary condition was imposed at the exit plane. Rigid, slipwall conditions were employed to prescribe lateral boundary conditions.
A 2-D, incompressible plane jet was simulated first. The jet profile was approximated by two hyperbolic tangent shear layers. The most unstable mode of the inviscid shear layer for this profile, along with its first and second harmonics, was imposed on the velocity profile at the inlet plane. The amplitude of oscillation of the harmonics was chosen so as to provide sufficient energy in the perturbation to accelerate the growth of the layer. No explicit phase lag was introduced in the perturbation. The flow was allowed to develop long enough to wash out the effect of the initial condition. The results obtained for this case indicate that experimentally realized phenomena such as vortex pairing were captured in this simulation. Furthermore, to check the convective nature of instability of the incompressible jet, the forcing at the inlet plane was turned off. The disturbances were gradually convected downstream, out of the computational domain.
Next, two-dimensional heated, non-buoyant jets were studied numerically. The effects of the ratio of jet density to ambient density S, the velocity ratio R, and jet width W, on the near field behavior of an initial laminar jet and the regeneration mechanism of the self-sustaining vortices were explored. The theory based on domain of absolute/convective instability identifies these three parameters. No initial perturbation was necessary to start roll-up of the shear layer. For certain choices, e.g., S= 0.75, R = 20, W =10.5, self-sustaining oscillations appeared spontaneously, and these cycles repeated for very long simulation intervals. Waviness on the jet shear layers grow and roll-up into vortices as in constant density shear layers. But unlike the incompressible plane jet, these vortices grow much larger and mixes more with the surrounding fluid. As these vortices evolve, packets of fluid break away as trailing legs similar to side jet expulsions observed in round jets and plumes. The growing vortices disturb the upstream shear layer. Consistently with linear theory, which predicts absolute instability for these parameters, these disturbances are able to grow and roll up. If these disturbances travelled faster than the downstream vortices, it would not be possible for the cycle to repeat. With sufficient shear between the co-flowing streams (R not too small), the entire regeneration process was found to begin from roughly the same streamwise location. Furthermore, it is the symmetric, varicose mode which occurs. At a slightly larger density ratio (S = 0.8, R = 10), self-sustaining oscillations appeared, but each new cycle began slightly farther downstream. It seems likely that these values are close to the boundary in parameter space between self-sustained oscillatory and convectively unstable behaviors. Jet width also influences the selection of these two behaviors. When jet width was reduced, W = 6, even for S = 0.75,R = 20, each new cycle began to shift downstream. For larger jet width (W = 12.3), self-sustaining oscillations occur but the response is now as an asymmetric sinuous mode after a short initial varicose mode.
The detailed processes that have now been revealed in plane jets should serve as guidelines for the study of such processes in the technologically more important round jets.
10
Chakravorty, Saugata. "A Numerical Study On Absolute Instability Of Low Density Jets". Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/227.
Testo completoAbstract (sommario):
A spectacular instability has been observed in low density round jets when the density ratio of jet fluid to ambient fluid falls below a threshold of approximately 0.6. This phenomenon has been observed in non-buoyant jets of helium in air, heated air jets and heated buoyant jets. The oscillation of the flow near the nozzle is extremely regular and periodic and consists of ring vortices. Even the smaller scale structures that appear downstream exhibit similar regularity. A theory for predicting the onset of this oscillation is based on finding regions of absolute instability from linear stability analysis of parallel flow. However, experiments suggest that the theory is at least incomplete and fortuitous as the oscillation is not a linear process. The present work is to observe and understand the process of regeneration of these oscillations by conducting numerical simulations. Here, two-dimensional, plane jets were simulated because they undergo a qualitatively similar process.
A spatial and temporal picture of a heated jet has been obtained numerically. A perturbation expansion was used to obtain a system of conservation laws for compressible flows which is valid for low Mach numbers. The low Mach number approximation removes the high frequency acoustic waves from the flow field. This enables a larger time step to be taken without making the calculation unstable. To ensure that all the scales of motion are properly resolved, calculations were done at a low Reynolds number. The governing equations were discretized in space using second-order finite difference formulas on a staggered grid. Velocity fields were advanced using a second-order Adams-Bashforth explicit scheme and then corrected by solving for pressure such that continuity is satisfied at every time step. The Poisson problem for pressure requires the time derivative of the density which was approximated by a third-order backward difference formula. Gauss-Siedel iteration was used to find the pressure.
Several numerical tests were conducted prior to simulations of variable density jets to check the stability and accuracy of the code. Two dimensional driven cavity flow calculations were done as a first test. Then a calculation of a forced, spatially developing, incompressible, plane mixing layer was done to check the time accuracy of the code. After obtaining satisfactory performance of the code for the different test cases, two-dimensional, variable density jets were simulated.
Since the plane jet extends ad infinitum in the streamwise direction, a sufficiently large domain was used to capture all the relevant physics in the downstream regions of the jet. An advective boundary condition was imposed at the exit plane. Rigid, slipwall conditions were employed to prescribe lateral boundary conditions.
A 2-D, incompressible plane jet was simulated first. The jet profile was approximated by two hyperbolic tangent shear layers. The most unstable mode of the inviscid shear layer for this profile, along with its first and second harmonics, was imposed on the velocity profile at the inlet plane. The amplitude of oscillation of the harmonics was chosen so as to provide sufficient energy in the perturbation to accelerate the growth of the layer. No explicit phase lag was introduced in the perturbation. The flow was allowed to develop long enough to wash out the effect of the initial condition. The results obtained for this case indicate that experimentally realized phenomena such as vortex pairing were captured in this simulation. Furthermore, to check the convective nature of instability of the incompressible jet, the forcing at the inlet plane was turned off. The disturbances were gradually convected downstream, out of the computational domain.
Next, two-dimensional heated, non-buoyant jets were studied numerically. The effects of the ratio of jet density to ambient density S, the velocity ratio R, and jet width W, on the near field behavior of an initial laminar jet and the regeneration mechanism of the self-sustaining vortices were explored. The theory based on domain of absolute/convective instability identifies these three parameters. No initial perturbation was necessary to start roll-up of the shear layer. For certain choices, e.g., S= 0.75, R = 20, W =10.5, self-sustaining oscillations appeared spontaneously, and these cycles repeated for very long simulation intervals. Waviness on the jet shear layers grow and roll-up into vortices as in constant density shear layers. But unlike the incompressible plane jet, these vortices grow much larger and mixes more with the surrounding fluid. As these vortices evolve, packets of fluid break away as trailing legs similar to side jet expulsions observed in round jets and plumes. The growing vortices disturb the upstream shear layer. Consistently with linear theory, which predicts absolute instability for these parameters, these disturbances are able to grow and roll up. If these disturbances travelled faster than the downstream vortices, it would not be possible for the cycle to repeat. With sufficient shear between the co-flowing streams (R not too small), the entire regeneration process was found to begin from roughly the same streamwise location. Furthermore, it is the symmetric, varicose mode which occurs. At a slightly larger density ratio (S = 0.8, R = 10), self-sustaining oscillations appeared, but each new cycle began slightly farther downstream. It seems likely that these values are close to the boundary in parameter space between self-sustained oscillatory and convectively unstable behaviors. Jet width also influences the selection of these two behaviors. When jet width was reduced, W = 6, even for S = 0.75,R = 20, each new cycle began to shift downstream. For larger jet width (W = 12.3), self-sustaining oscillations occur but the response is now as an asymmetric sinuous mode after a short initial varicose mode.
The detailed processes that have now been revealed in plane jets should serve as guidelines for the study of such processes in the technologically more important round jets.
11
Kogan, Lucy Anne. "The jet energy scale uncertainty derived from gamma-jet events for small and large radius jets and the calibration and performance of variable R jets with the ATLAS detector". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:b70b8c23-ffce-4d7a-b3d0-2cc5c9fd1d69.
Testo completoAbstract (sommario):
In this thesis the jet energy scale uncertainty of small and large radius jets at the ATLAS detector is evaluated in-situ using gamma-jet events. The well calibrated photon in the gamma-jet events is used to probe the energy scale of the jets. The studies of the jet energy scale of small radius jets are performed using 4.7 fb-1 of data collected at sqrt{s} = 7 TeV in 2011. The gamma-jet methods which were developed are then adapted and applied to large radius jets, using 20.3 fb^-1 of data collected at sqrt{s} = 8 TeV in 2012. The new jet energy scale uncertainties are found to be ~1 % for |eta| < 0.8, rising to 2-3 % for |eta| > 0.8. These uncertainties are significantly lower than the 3-6 % precision which has previously been achieved at ATLAS using track jets as a reference object. Due to the increase in precision, uncertainties due to pile-up and the topology of the jet also had to be evaluated. The total energy scale uncertainties for large radius jets are reduced by ~1-2 % (0.5-1 %) for |eta| < 0.8 (> 0.8). This reduction will be beneficial to analyses using large radius jets and it is specifically shown to benefit the t-tbar resonance search in the semi-leptonic channel. The t-tbar search looks for events with two top quarks in the final state, where one decays leptonically and the other hadronically. The hadronically decaying top quark is reconstructed using a large radius jet, and the jet energy scale uncertainty is a dominant source of uncertainty in the analysis. In addition to the studies of the jet energy scale of large radius jets, the first derivation of a calibration, and jet energy scale uncertainties derived with gamma-jet events, are shown for Variable R jets. The Variable R jet algorithm is a new type of jet algorithm with a radius that is inversely proportional to the size of the jet, making it useful for the study of high momentum top quarks. It is shown that similar methods can be used to calibrate and assess the uncertainties of Variable R jets as are used for standard, fixed radius jets at the ATLAS detector, although some adaptations will be necessary. The studies provide a basis for the calibration of Variable R jets in the future.
12
Lin, Kuanchung J. "Modeling viscoelastic jets /". The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970651388.
Testo completo
13
Wannassi, Manel. "Etude des transferts thermiques par batteries de jets pour la trempe du verre". Thesis, Valenciennes, 2013. http://www.theses.fr/2013VALE0022/document.
Testo completoAbstract (sommario):
La trempe à l’air est largement utilisée dans les procédés de production de verre de sécurité. L’obtention d’une distribution de contraintes adéquate requiert un refroidissement intense et homogène à la fois, et ces deux propriétés sont difficiles à obtenir sur la courte durée de la trempe. Les batteries de jets utilisées dans la plupart des systèmes de trempe produisent un refroidissement adéquat mais souffrent d’inhomogénéité, à l’origine de défauts de trempe et de casse durant le processus.L’objectif de cette thèse est d’explorer des nouvelles configurations qui améliorent l’homogénéité du refroidissement en préservant son intensité. L’approche choisie consiste à implanter des jets rotatifs dans les réseaux de manière à accentuer le mélange des jets avant impact. Les études ont été menées principalement par simulation numérique, corroborées par des visualisations par enduit gras sur un banc d’essai dédié, conçu et réalisé dans le cadre de cette thèse.La première phase a été consacrée à la conception des générateurs de jets rotatifs et à l’étude de leur dynamique en mode isolé. Le développement d’une structure tourbillonnaire se formant à l’entrée de chaque lobe du dispositif de mise en rotation a été mis en évidence. L’interaction des jets rotatifs dans le réseau de refroidissement constitue la deuxième phase. Il apparait que la structure cellulaire du schéma d’impact n’est que marginalement perturbée par les jets rotatifs et que la présence de ces derniers n’influe que peu sur la dynamique de l’écoulement. Enfin, la modélisation détaillée des transferts de chaleur sur la plaque d’impact montre que les jets rotatifs ne contribuent que faiblement au refroidissement, mais que l’interférence avec le réseau de jets simples augmente légèrement le transfert de chaleur local au niveau de leur impact. Sans avoir obtenu les résultats escomptés, cette thèse a toutefois montré la complexité du système et le couplage fort entre les phases d’alimentation et d’évacuation de l’air de refroidissementAir quenching is widely applied in security glass manufacturing processes. Proper residual stresses distribution requires strong and homogeneous cooling and both are difficult to achieve over the very short time of the tempering process. Jet arrays used in most processes provide with sufficient cooling but suffer from inherent inhomogeneity, leading to quality loss of the glass product and, in extreme cases, to unacceptable breaking numbers during production.The objective of the present study is to investigate ways to improve cooling homogeneity while maintaining efficiency. For this purpose, swirling jets are located inside the jet arrays to enhance jet mixing prior to impingement. Numerical simulation is performed, corroborated by oil flow visualization and a dedicated test bench has been designed and set up within the frame of this thesis.The first part was concerned with the design of swirlers and their dynamic behaviour in standalone mode. It has been shown that a vortex is forming at the inlet of each swirl compartment. Inserting the swirlers within jet arrays constitutes the seconf phase. It turns out that the cellular structure of the impingement pattern is only marginally affected by the swirlers, which have a weak influence on the flow dynamics. Last, the detailed heat transfer modeling on the impingement surface shows that the swirlers themselves do barely contribute to the overall cooling, while the coupling with the simple jet array slightly improves the local heat transfer close to the impingement area. Although the expected outcome was not achieved, this thesis showed the flow complexity as well as the strong coupling between the feeding and the exhaust phases experienced by the cooling air
14
Fletcher, Gregory. "A Measurement of W+jets Z+jets with the ATLAS Detector". Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8047.
Testo completoAbstract (sommario):
A study is presented on the production of vector boson (W and Z0) events in association with recoiling hadronic activity in the form of hadronic jets, using proton-proton collisions at the LHC. The dataset was taken by the ATLAS detector during the 2011 data-taking run, at a centre of mass energy p s = 7 TeV, and corresponds to an integrated luminosity of 4.6 fb 1. A measurement of the cross-section ratio of W+jets Z+jets events is de ned, reducing the large systematic uncertainties inherent in the experimental measurement of such events. Inclusive and di erential cross-sections are presented for W+jets Z+jets , as a function of a range of kinematic variables, and are compared to state-of- the-art theoretical predictions.
15
Gao, Nan Ewing Daniel. "Offset attaching planar jets with and without a co-flowing jet". *McMaster only, 2006.
Cerca il testo completo
16
Fendt, Christian. "Formation of astrophysical jets". Thesis, [S.l. : s.n.], 2002. http://pub.ub.uni-potsdam.de/2003/0014/door.htm.
Testo completo
17
Zahniser, Russell 1982. "Instabilities of rotating jets". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32752.
Testo completoAbstract (sommario):
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (p. 33-34).
When a jet of water is in free fall, it rapidly breaks up into drops, since a cylinder of water is unstable. This and other problems involving the form of a volume of water bound by surface tension have yielded a wealth of theoretical and experimental results, and given insight into such phenomena as the shape of the Earth. Particularly interesting behaviors tend to emerge when the fluid in question is rotating; a drop may, for example, form a toroidal or ellipsoidal shape or even stretch out into some multi-lobed, non-axisymmetric form. In this paper, we investigate the properties of a rotating jet of water, and determine what regime of the parameter space are dominated by the various forms of instability. This is both predicted theoretically and demonstrated to be accurate experimentally. If we watch a jet of water as the rotation rate is gradually increased from zero, the drop size will start shrinking gradually, and then suddenly, rather than a single row of drops, we will see the jet breaking up into two-lobed, bar shaped forms, like the rung of a ladder. The point at which this transition occurs is characterized in terms of the rotational Bond number, B₀ = ... . The critical B₀ may be as low as 6, if there is a strong bias imparted by vibration of the table at an appropriate frequency, but for a perfectly quiescent rotating jet the second mode does not become dominant until a higher B₀. As the rotation rate is increased above this, the instability grows gradually more dramatic, and eventually the two lobes of each drop are breaking apart and flying outward. Then a transition to a third mode will occur, with three lobes in each drop; this is possible from a B₀ of 12, and dominant above a B₀ slightly higher than that. In general, mode m may occur whenever
(cont.) B₀ > m(m + 1).
by Russell Zahniser.
S.B.
18
Wadhwa, Navish. "Non-coalescence of Jets". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42636.
Testo completoAbstract (sommario):
Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. While there has been much work on coalescing jets of fluid and non-coalescence in other systems like drop-drop, drop on a bath, jet on a bath, non-coalescence of fluid jets has been little studied. A simple experimental setup was developed to stably demonstrate and study the non-coalescence of jets upon collision. This thesis presents the results of an experimental investigation of oblique collision between two fluid jets. The transition from bouncing to coalescence of jets is examined for various jet sizes and angles. Results indicate that the transition from bouncing to coalescence can be rationalized in terms of critical value of the dimensionless parameter Normal Weber Number, which represents the ratio between inertial and surface tension forces. A parametric study of the characteristic of bouncing jets, conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. These scaling laws help us in elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertiaMaster of Science
19
Ben-Yeoshua, Moshe 1957. "Coaxial jets with swirl". Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/291734.
Testo completoAbstract (sommario):
The near field of coaxial air jets, with swirl in the outer one, was investigated experimentally. Axial and azimuthal velocities were mapped using hot-wire anemometry, and static pressure measurements were obtained using a pitot tube. The flow was visualized using a double-pass schlieren system. The flow is sensitive to both the amount of swirl, characterized by the swirl number S, and the mass flow ratio between the outer and inner jets, mr. A necessary condition for recirculation to occur was that S > 0.58 and mr > 8.5. The magnitude of a pressure deficit in the centerline strongly depends on mr, while the existence of swirl appears to have a triggering effect on setting up this pressure gradient. Spectral analysis shows distinct characteristics dependent on the occurrence of recirculation. Because these features were observed upstream of the recirculation region, the vortex breakdown in this experiment may be related to flow instabilities.
20
Norenius, Linus. "Geoeffectiveness of Magnetosheath Jets". Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-164846.
Testo completoAbstract (sommario):
In this report we present spacecraft and ground-based observations of magnetosheath jets impacting the magnetosphere, both as a case study and a statistical study. In the case study, jets were detected in the magnetosheath by the Magnetospheric MultiScale mission, MMS. By utilizing a data-based magnetosphericmodel (Tsyganenko T96 [29]), we estimated which jets were likely to impact the magnetopause and where they would do so. We examined ground based magnetometers, GMAGs, at the expected foot-point to the affected magnetic fieldline and compared this with the spacecraft observations. Theoretical transfertimes for a jet to be detectable by GMAGs have been estimated and compared with the observed time delay, from detection to GMAG response, and they were in good agreement for all cases. The times found for this geoeffective responsewere found to be around 1-2 min, and the response in the GMAGs was in the form of a pulse with an amplitude of around 50 nT. We suggest that jets of along enough time duration can be geoeffective in a way that they are detectable at ground level by GMAGs. It was also found that GMAGs fluctuate more during periods containing many detected jets. We performed our statistical study with the intention of comparing fluctuations in GMAG observations during Interplanetary Magnetic Field, IMF, configurations which is suggested to be favorable for jet creation. The IMF observationswas provided by the THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. This was done by selecting periods of steady IMF with different orientations, and examining the GMAGs observed variations. GMAGs were selected based on a region where most of our foot-points were found in our previous case study. We performed this study over a three year interval, and found that GMAGs observe about 2 nT higher variation, according to their standard deviations, during radial IMF compared to northward IMF. During northward IMF we expect less effects from magnetopause phenomena, thus making it suitable to compare with radial IMF. Our statistical investigation support our findings that magnetosheath jets can be geoeffective in a waythat GMAGs can detect them.
21
Goparaju, Kalyan. "Flow and Acoustic Characteristics of Complex Supersonic Jets". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1510933315034965.
Testo completo
22
Algwari, Q. Th. "Plasma jet formation and interactions between atmospheric pressure dielectric barrier discharge jets". Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545999.
Testo completo
23
Koeksal, Ayda. "Determination of differences between quark and gluon jets in 3-jet events". Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388708.
Testo completo
24
Ma, Frank Teng. "Detailed characterization of jets in heavy ion collisions using jet fragmentation functions". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83823.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 159-163).
In this thesis the jet fragmentation function of inclusive jets with transverse momentum PT > 100 GeV/c in PbPb collisions is measured for reconstructed charged particles with PT > 1 GeV/c within the jet cone. A data sample of PbPb collisions collected in 2011 at a center-of-mass energy of [square root of]sNN = 2.76 TeV corresponding to an integrated luminosity of 150 [mu]b-1 is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on pp data collected at the same collision energy. A centrality-dependent modification of the fragmentation function is revealed. For the most central collisions a significant enhancement is observed in the PbPb/pp fragmentation function ratio for the charged particles with PT less than 3 GeV/c.
by Frank Teng Ma.
Ph.D.
25
Sauvan, Jean-Baptiste. "Z+jets au LHC : calibration des jets et mesure de sections efficaces avec le détecteur ATLAS". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00747024.
Testo completoAbstract (sommario):
La recherche du boson de Higgs ainsi que celle de nouvelle physique auprès du LHC requiert une excellente compréhension des processus du Modèle Standard du fait de leurs signatures expérimentales similaires. La capacité de mesurer le plus précisément possible l'énergie des objets reconstruits dans les détecteurs est par ailleurs primordiale à la fois pour effectuer des mesures de précision et pour accroître la sensibilité des analyses à des signaux de physique au-delà du Modèle Standard. Les travaux présentés dans cette thèse s'attachent à ces deux points par l'étude d'événements contenant un ou plusieurs jets associés à un boson Z avec le détecteur ATLAS. D'une part, ces événements sont utilisés pour améliorer la calibration en énergie des jets de faible impulsion transverse, d'une importance capitale pour les analyses utilisant le dénombrement de jets ou leur veto. D'autre part la section efficace différentielle de production de ces événements est mesurée en fonction de nombreuses observables et comparée à diverses prédictions théoriques. Ces mesures pourront être utilisées pour améliorer les prédictions qui servent de modèles de bruit de fond dans des analyses sur le boson de Higgs et de recherche de physique au-delà du Modèle Standard.
26
Rajakuperan, E. "Experimental And Computational Investigations Of Underexpanded Jets From Elliptical Sonic Nozzles". Thesis, Indian Institute of Science, 1994. https://etd.iisc.ac.in/handle/2005/158.
Testo completoAbstract (sommario):
Three dimensional nozzles and jet flows have attracted the attention of many researchers due to their potential application to many practical devices. Rectangular nozzles are considered for short/vertical take off and landing aircrafts for achieving powered lift. Axisymmetric nozzles with lobes, tabs or slots and elliptical nozzles are considered for noise reduction in aircrafts and mixing augmentation in airbreathing rockets. Interaction of supersonic jets with solid
surface, as in the case of retro and ullage rockets in launch vehicles and interaction of multiple jets as in the case of launch vehicles with multiple booster rockets/multiple nozzle engines are of practical importance. Design of rockets and aircrafts employing these nozzles needs the understanding of the structure and behaviour of the complex three dimensional supersonic jets issuing from these nozzles. The problem is so complex that different investigators have addressed only some specific aspects of the problem and there is much more to be done to fully understand these flows. For example, in the case of rectangular nozzle with semi circular ends (known as elliptical nozzle), the investigations have been limited to a single nozzle of aspect ratio 3,0 and pressure ratio (ratio of the total pressure to ambient pressure) 3.0. Further, the measurements were made in the far field subsonic region beyond a distance of 20 times the equivalent nozzle radius (RJ.
For the present study, the elliptical sonic nozzle of the type mentioned above was chosen, as it offered simplicity for manufacturing and carrying out computations, but has all the complex features associated with the three dimensional jets. A systematic study to understand the mean flow structure and the effect of important governing parameters like
ratio and pressure ratio on the flow development process of the jet issuing from Navier-Stokes equations.
The experimental study revealed many interesting flow features. It was found that the Underexpanded jet issuing from elliptical sonic nozzle spreads rapidly in the minor axis plane while it maintains almost constant width or contracts in the major axis plane. However, the gross spreading of this jet is much higher compared to the axisymmetric jet. The higher spreading rates experienced in the minor axis plane compared to the major axis plane of this 'et, results in the jet width in the minor axis plane to become higher than that in the major axis plane. The longitudinal location, where this occurs is called the axis switching location. This kind of axis switching phenomenon is known to exist for subsonic elliptical jets. However, for the present supersonic jets, the axis switching locations are much closer to the nozzle exit compared to the subsonic cases reported. It was further found that this location strongly depends on the pressure and aspect ratios. A critical pressure ratio was found to exist for each nozzle at which the axis switching location is the farthest. Above the critical pressure ratio, the axis switching location was observed to move upstream with the increase in the pressure ratio and is controlled by the
complex interactions of shock and expansion waves near the nozzle exit. Below the critical pressure ratio, the axis switching location moves upstream with the decrease in pressure ratio and is controlled by some kind of instability in the minor axis plane.
The shock structure present in the underexpanded jet from an elliptical nozzle was also observed to depend on both pressure and aspect ratios. For some aspect ratios and pressure ratios, the shock pattern observed in both the major and minor axis planes are similar to that of an axisymmetric jet, where the incident barrel shock and the Mach reflection (from the edges of the Mach disk) are present. But for all other cases, this shock
continues to be seen only in the major axis plane. Whereas, in the minor axis plane, the incident shock is absent in the shock pattern.
Detailed measurement in the jet cross sectional planes, for the case of aspect ratio 2.0 nozzle, shows that the cross sectional shape changes along the length and it becomes almost a circle at the axis switching location. Further downstream, the jet spreads rapidly in the minor axis plane whereas no significant change in the width of the jet in the major axis plane is observed. Far downstream, the jet boundary appears like a distorted ellipse with its major and minor dimensions lying respectively in the minor and major axis planes of the nozzle. The elongated shape of the jet cross sections at locations downstream of the axis switching point gives the impression that the entire flow in the major axis plane is turned towards the minor axis plane. This effect appears to be predominant at high pressure ratios.
The computed near field shock structure in the planes of symmetry, pitot pressure distributions, cross sectional shape of the jet and the spreading pattern agree very well with the experimental results. In addition to this, the present computational method gives the detailed near field flow structure including the azimuthal extent of the incident shock, cross flow details and distributions of flow variables. It is shown that the present inviscid methodology can also predict the axis switching point accurately if it occurs before the formation of the Mach disk and it demonstrates that the jet growth phenomenon in the near field, atleast, is mainly controlled by the inviscid flow process. The computed results have shown that changes in the jet cross sectional shape in the near field is caused mainly by the interaction of compression and expansion waves with each other and with the constant pressure boundary. The inviscid method seems to be able to capture the complicated secondary cross flow structure (indicating presence of longitudinal vortices) of the elliptical jet.
The complex mean flow structure in the near field region of the jet issuing from elliptical nozzles and the effect of nozzle aspect ratio and pressure ratio on the structure are brought out clearly in the present study. The mechanism governing the spreading and the axis switching characteristics are also brought out. Thus the present experimental and computational investigations give a comprehensive understanding of the mean flow structure of the underexpanded jets issuing from elliptical nozzles. Further studies are required to understand the other aspects of the elliptical jets as well as other three-dimensional jets. Some of these studies are identified for future work.
27
Rajakuperan, E. "Experimental And Computational Investigations Of Underexpanded Jets From Elliptical Sonic Nozzles". Thesis, Indian Institute of Science, 1994. http://hdl.handle.net/2005/158.
Testo completoAbstract (sommario):
Three dimensional nozzles and jet flows have attracted the attention of many researchers due to their potential application to many practical devices. Rectangular nozzles are considered for short/vertical take off and landing aircrafts for achieving powered lift. Axisymmetric nozzles with lobes, tabs or slots and elliptical nozzles are considered for noise reduction in aircrafts and mixing augmentation in airbreathing rockets. Interaction of supersonic jets with solid
surface, as in the case of retro and ullage rockets in launch vehicles and interaction of multiple jets as in the case of launch vehicles with multiple booster rockets/multiple nozzle engines are of practical importance. Design of rockets and aircrafts employing these nozzles needs the understanding of the structure and behaviour of the complex three dimensional supersonic jets issuing from these nozzles. The problem is so complex that different investigators have addressed only some specific aspects of the problem and there is much more to be done to fully understand these flows. For example, in the case of rectangular nozzle with semi circular ends (known as elliptical nozzle), the investigations have been limited to a single nozzle of aspect ratio 3,0 and pressure ratio (ratio of the total pressure to ambient pressure) 3.0. Further, the measurements were made in the far field subsonic region beyond a distance of 20 times the equivalent nozzle radius (RJ.
For the present study, the elliptical sonic nozzle of the type mentioned above was chosen, as it offered simplicity for manufacturing and carrying out computations, but has all the complex features associated with the three dimensional jets. A systematic study to understand the mean flow structure and the effect of important governing parameters like
ratio and pressure ratio on the flow development process of the jet issuing from Navier-Stokes equations.
The experimental study revealed many interesting flow features. It was found that the Underexpanded jet issuing from elliptical sonic nozzle spreads rapidly in the minor axis plane while it maintains almost constant width or contracts in the major axis plane. However, the gross spreading of this jet is much higher compared to the axisymmetric jet. The higher spreading rates experienced in the minor axis plane compared to the major axis plane of this 'et, results in the jet width in the minor axis plane to become higher than that in the major axis plane. The longitudinal location, where this occurs is called the axis switching location. This kind of axis switching phenomenon is known to exist for subsonic elliptical jets. However, for the present supersonic jets, the axis switching locations are much closer to the nozzle exit compared to the subsonic cases reported. It was further found that this location strongly depends on the pressure and aspect ratios. A critical pressure ratio was found to exist for each nozzle at which the axis switching location is the farthest. Above the critical pressure ratio, the axis switching location was observed to move upstream with the increase in the pressure ratio and is controlled by the
complex interactions of shock and expansion waves near the nozzle exit. Below the critical pressure ratio, the axis switching location moves upstream with the decrease in pressure ratio and is controlled by some kind of instability in the minor axis plane.
The shock structure present in the underexpanded jet from an elliptical nozzle was also observed to depend on both pressure and aspect ratios. For some aspect ratios and pressure ratios, the shock pattern observed in both the major and minor axis planes are similar to that of an axisymmetric jet, where the incident barrel shock and the Mach reflection (from the edges of the Mach disk) are present. But for all other cases, this shock
continues to be seen only in the major axis plane. Whereas, in the minor axis plane, the incident shock is absent in the shock pattern.
Detailed measurement in the jet cross sectional planes, for the case of aspect ratio 2.0 nozzle, shows that the cross sectional shape changes along the length and it becomes almost a circle at the axis switching location. Further downstream, the jet spreads rapidly in the minor axis plane whereas no significant change in the width of the jet in the major axis plane is observed. Far downstream, the jet boundary appears like a distorted ellipse with its major and minor dimensions lying respectively in the minor and major axis planes of the nozzle. The elongated shape of the jet cross sections at locations downstream of the axis switching point gives the impression that the entire flow in the major axis plane is turned towards the minor axis plane. This effect appears to be predominant at high pressure ratios.
The computed near field shock structure in the planes of symmetry, pitot pressure distributions, cross sectional shape of the jet and the spreading pattern agree very well with the experimental results. In addition to this, the present computational method gives the detailed near field flow structure including the azimuthal extent of the incident shock, cross flow details and distributions of flow variables. It is shown that the present inviscid methodology can also predict the axis switching point accurately if it occurs before the formation of the Mach disk and it demonstrates that the jet growth phenomenon in the near field, atleast, is mainly controlled by the inviscid flow process. The computed results have shown that changes in the jet cross sectional shape in the near field is caused mainly by the interaction of compression and expansion waves with each other and with the constant pressure boundary. The inviscid method seems to be able to capture the complicated secondary cross flow structure (indicating presence of longitudinal vortices) of the elliptical jet.
The complex mean flow structure in the near field region of the jet issuing from elliptical nozzles and the effect of nozzle aspect ratio and pressure ratio on the structure are brought out clearly in the present study. The mechanism governing the spreading and the axis switching characteristics are also brought out. Thus the present experimental and computational investigations give a comprehensive understanding of the mean flow structure of the underexpanded jets issuing from elliptical nozzles. Further studies are required to understand the other aspects of the elliptical jets as well as other three-dimensional jets. Some of these studies are identified for future work.
28
Dubois, Julien. "Etude expérimentale de jets libres, compressibles ou en présence d'un obstacle". Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22010/document.
Testo completoAbstract (sommario):
L’objectif de ces travaux est d’étudier expérimentalement la dispersion d’hydrogène pour évaluer l’impact des fuites chroniques ou accidentelles qui peuvent intervenir en milieu libre ou encombré, à faible ou à forte pression, sur un véhicule fonctionnant avec une pile à combustible. Les fuites étudiées sont assimilées à des jets verticaux, turbulents, axisymétriques, à densité variable, et issus d’orifices cylindriques de 1 à 3 mm de diamètre. Un banc expérimental a été conçu pour étudier ces fuites : l’hydrogène a été remplacé par de l’hélium pour des raisons de sécurité. Il résiste à une pression de 200 bars et permet de positionner un obstacle dans le jet. La technique BOS (Background Oriented Schlieren) a été adaptée aux jets millimétriques et à la présence d’un obstacle. Un soin particulier à été apporté à la mise en place de cette technique. Les résultats obtenus sont en accord avec ceux de la littérature quand il en existe. De nouvelles lois de similitude sont proposées, plus représentatives de la physique des jets : libres subsoniques, libres sousdétendus, et subsoniques en présence d’un obstacle (sphère). À partir de l’analyse de la structure compressible des jets sous-détendus, de nouvelles lois sont aussi proposées pour estimer la position et le diamètre du disque de Mach puis la longueur du cône potentiel. Enfin, deux lois d’estimation du volume et de la masse inflammables de jets libres d’hydrogène sont proposées : elles sont fonction du débit massique de la fuiteThe aim of this work is to experimentally investigate the hydrogen dispersion to evaluate the impact of chronic or accidental leaks that may occur in a free or in a congested environment, from a low or a high pressure tank, on a fuel cell vehicle. The leaks are assimilated to vertical turbulent and axisymmetric jets with variable density. They are issued from cylindrical orifices from 1 to 3 mm diameter. An experimental set-up was designed to investigate the leaks : hydrogen has been replaced by helium for safety reasons. It supports a 200 bar pressure and allows to position an obstacle in the jet flow. The BOS (Background Oriented Schlieren) technique has been adapted to millimeter jets and to the presence of an obstacle. Particular attention has been given to the development of this technique. The results show good agrement with the available litterature data.New similarity laws are proposed, more representative of the flows of : subsonic free jets, under-expanded free jets, and subsonic impinging (a sphere) jets. From the structure analysis of compressible under-expanded free jets, new relations are proposed to estimate the Mach disk position and diameter as well as the potential core length. Finally, two new laws are found from the analysis of flammable volume and flammable mass : they are based on the leak mass flow rate
29
Forti, Nicola. "Study of jets produced at LHC and measurements of their substructures". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24278/.
Testo completoAbstract (sommario):
I jets sono prodotti dalla pioggia di adronizzazione di partoni prodotti negli hard scattering ad alta energia e sono osservabili fondamentali per comprendere i processi fisici nei collisori ad alta energia. Negli ultimi anni lo studio della loro struttura interna è diventato un tema scottante. Considerando il grande centro di energia di massa a LHC, molte particelle che decadono possono produrre partoni quasi collineari. La comprensione della struttura interna dei jets ci permette di comprendere le interazioni e le dinamiche che portano alla produzione, in particolare, di large-R jets. In questa tesi verrà innanzitutto fornita una descrizione di cosa sono i jet e di come vengono ricostruiti con diversi algoritmi,
come per esempio con l'algoritmo anti-kt, che è uno dei più utilizzati. Verranno poi descritte le variabili di sottostruttura dei jets che ci consentono di discriminare i vari tipi di processo che stiamo considerando, ad esempio per distinguere gli eventi a tre vertici dai processi a due od uno. Lo studio prosegue con l'analisi di un campione simulato di eventi generati con Monte Carlo in cui, attraverso una serie di selezioni sulle variabili τ32 e D2, è stata dimostrata la validità di queste due variabili che possono permettere di distinguere i decadimenti bosonici da quelli del quark top.
30
Biolchini, Romain. "Etudes des effets de température sur le bruit de jet subsonique par simulation des grandes échelles". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC064.
Testo completoAbstract (sommario):
Ces travaux de recherche sont consacrés à l’étude des effets de température sur le développement aérodynamique et l’acoustique rayonnée d’un jet subsonique par simulation des grandes échelles. Ces simulations sont réalisées avec un solveur 3D résolvant les équations de Navier-Stokes compressibles par une approche Volumes Finis. De plus, des schémas de discrétisation spatiale et d’intégration temporelle peu dissipatifs et peu dispersifs sont utilisés pour permettre l’étude des phénomènes acoustiques. La propagation acoustique est réalisée grâce à l’analogie acoustique de Ffowcs-Williams et Hawkings.Dans un premier temps, une configuration de jet simple est étudiée. Deux points de fonctionnement sont simulés. Dans les deux simulations, la vitesse d’éjection est fixée avec un nombre de Mach acoustique M=0.9 et seule la température du jet est modifiée. Pour les deux simulations les nombres de Reynolds sont supérieurs à 105. Pour valider la méthodologie de calcul, l’aérodynamique et l’acoustique ont été comparées avec succès à des données expérimentales. Une étude plus approfondie sur les effets induits par la température sur la distribution azimutale et l’émergence de nouvelles sources acoustiques est également menée. Dans un second temps, une tuyère représentative de l’arrière corps de moteur d’avion civil est considérée. La méthodologie de calcul appliquée sur cette géométrie est identique à celle utilisée sur les jets simples flux. Deux simulations sont réalisées en gardant les vitesses d’éjection constantes et en ne modifiant uniquement la température d’éjection du flux primaire (multipliée par un facteur 2). Les différences observées entre les deux simulations sont moins importantes que pour le cas simple flux. Cependant, le rayonnement acoustique amont est influencé significativement par la différence de température. Dans le cas froid, des ondes acoustiques remontant l’écoulement sont observées au centre du jet et rentrent en interaction avec le corps central. Ce phénomène n’est pas observé pour le cas le plus chaud, expliquant ainsi les différences sur le rayonnement acoustiqueIn this PhD thesis, the effects of temperature on aerodynamic development and acoustic radiation of subsonic jets are studied. This is done thanks to 3D compressible Large Eddy Simulations with low dissipative and dispersive numerical schemes that propagate the acoustic waves properly. The far-field noise is then determined with the acoustics analogy proposed by Ffowcs-Williams and Hawkings.First, single round jets are studied. Two operating points are computed: an isothermal jet and a hot jet with an exhaust temperature twice the one of the ambient air (Tj = 2T0). The comparison of both cases is based on a similar exhaust velocity. In both cases, Reynolds number based on the nozzle diameter is above 105. To validate numerical methodology, aerodynamic and acoustic results are successfully compared against experiments. Further analyses are conducted to highlight the new acoustic sources that result from the temperature increase and the effects on the azimuthal mode distribution.Secondly, a more complex geometry representative of a real turbofan engine is considered, including two streams and the plug. The same methodology as the one used for the single jet nozzle is applied. Again, two simulations are computed where the exhaust velocities of both streams are kept constant and only the exhaust primary stream temperature is modified (multiplied by two). Differences on aerodynamic development are less important than the ones observed on single stream jets. However, the upstream acoustic radiation is significantly influenced by the modification of the exhaust temperature. In the colder case, upstream acoustic trapped waves are evidenced in the core jet and interact with the plug. This phenomenon is not reproduced when the primary stream is heated and explains the observed differences on the acoustic radiation
31
Cutler, Philip Robert Edward. "On the structure and mixing of a jet in crossflow : Ph.D. thesis". Title page, abstract and table of contents only, 2002. http://web4.library.adelaide.edu.au/theses/09PH/09phc9895.pdf.
Testo completo
32
Caron, Sascha. "Jets in photoproduction at HERA". [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=96548209X.
Testo completo
33
Lai, Chung-kei Chris. "Mixing of inclined dense jets". Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B4423661X.
Testo completo
34
Stuland, Eirik Martin. "Computation of impinging gas jets". Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9716.
Testo completoAbstract (sommario):
Abstract This dissertation has been produced during the spring semester of 2008 to serve to the requirements for the degree of Master of Technology at the Norwegian University of Science and Technology (NTNU). The thesis has been written at the department of Energy and Process Engineering, with supervision of Professor Helge I. Andersson from the Fluid Dynamics department. The thesis has the title Computation of Impinging Gas Jets, and aims to investigate the Impinging Jet Flow (IJF) problem presented in section[2] by means of Computational Fluid Dynamics (CFD). For the work of this thesis the commercially available program package of FLUENT 6.3, and Gambit 2.4 was used for all the simulation and geometry generation tasks. The specific IJF case treated in the thesis work, is the Single Round Nozzle (SRN ) IJF geometry explained in section[2.2] , and displayed in Figure 2.2 . The numerical simulations were carried out by means of 2D and 3D Reynolds Averaged Navier Stokes ( RANS) simulations , and Large Eddy Simulation (LES) with related theory described in the theory section[3]. The work with the simulations of this thesis can roughly be divided into two main components. Firstly there is the part comprising all tasks and operations involved in creating and running the simulations, about which relevant information is provided in section[4]. Secondly, there is the work involving all the tasks related to gathering, interpreting, and analyzing the yielded simulation results. These tasks and their results are mainly treated in sections[5 to 9]. Both numerical and experimental reference IJF cases were used in this thesis work. The reference cases were at first used to guide the beginning of the simulation effort (Figure 6.1). In the later stages of the thesis, the reference results were used to analyze and interpret the results of the thesis simulations. Overall the results from the RANS simulations of this thesis, are found to give good agreement with the reference simulations and experiments, within the limits of what can be expected from the RNG k-ε model which was used. The LES simulations on the other hand, proves to be far more demanding both computation wise, and in relation to issues concerning simulation preparations and setup. In addition the LES simulation is found to be outperformed by the RANS simulations in some regions of the IJF geometry. When analyzed, it is found that this is probably caused by an unfortunate combination of regions with low local mesh quality, and a quite mesh sensitive feature in the Sub Grid Scale model. Nevertheless the LES simulation is found to provide results of good agreement with experimental data in some of the most difficult regions to simulate on the IJF geometry. In this region the LES simulation is also found to outperform the RANS simulations.
35
Lekholm, Ville. "Schlieren imaging of microrocket jets". Thesis, Uppsala University, Ångström Space Technology Centre, ÅSTC, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-127219.
Testo completoAbstract (sommario):
In this report, microrockets from the company NanoSpace were studied using schlieren imaging techniques. The rocket chips are manufactured using MEMS technology, which requires compromises regarding the shape of the nozzle. The rocket chips are 22x22x0.85 mm, manufactured from laminated silicon. The nozzles are approximately 20 µm wide at the throat, and 350 µm wide at the exit. A semi in-line schlieren apparatus was designed, set up, and aligned. A small vacuum chamber was constructed, and a series of tests was conducted in order to qualitatively evaluate the consequences of these compromises, and other performance issues. It was found that the existing 1 kW quartz-tungsten-halogen lamp was sufficient as a light source, standard photographic equipment served well as an imaging device, and a 400 mm, f/7.9 achromatic doublet as schlieren lens, resolved enough detail in the exhaust gas to perform the studies. At maximum magnification, the viewing area was 7 by 4.5 mm, captured at 14 Mpixel, or about 1.5 µm/pixel. Several different rocket chips were studied, with helium, nitrogen and xenon as propellant gases. Feed pressure ranged from 0.5 bar to 3.5 bar, and the rockets were studied at atmospheric pressure and in vacuum, and with and without heaters activated. Through these studies, verification and visualization of the basic functionality of the rockets were possible. At atmospheric pressure, slipping of the exhaust was observed, due to the severe overexpansion of the nozzle. In vacuum, the nozzle was underexpanded, and the flow was seen to be supersonic. There was a measurable change in the exhaust with the heaters activated. It was also shown that the method can be used to detect leaks, which makes it a valuable aid in quality control of the components.
36
Mazurek, Kerry Anne. "Scour of clay by jets". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60324.pdf.
Testo completo
37
Zou, Yue. "Air jets in ventilation applications". Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3146.
Testo completo
38
Brinkert, Jacob. "Particle jets in fluidised beds". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319390.
Testo completo
39
Kurosoy, Ersel. "Opposed jets, flames and extinction". Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402177.
Testo completo
40
Outten, Stephen. "Easterly Tip Jets Around Greenland". Thesis, University of East Anglia, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514267.
Testo completo
41
Hardcastle, M. J. "The jets in radio galaxies". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603680.
Testo completoAbstract (sommario):
I present high-resolution, high-sensitivity images of four FRI radio galaxies and seventeen FRII radio galaxies, made with the aim of detecting and imaging jets and counterjets. For the FRIs, I show images of the detailed total intensity and polarisation structure in the jets and counterjets and in the sources as a whole. I argue that models in which the jets are initially relativistic but decelerate are a good fit to the overall behaviour of the objects, but that some recent models of the polarisation structure are ruled out by the observations. The radio-optical spectrum of the jet in one object is discussed in some detail. For the seventeen FRIIs (part of a complete sample of 21 objects) I detect new jets or possible jets in a number of objects; there are jets or probable jets in 76% of the sample as a whole. The properties of the hot spots of the objects and their implications for models of radio sources are discussed. I use my observations, together with data from previous work, to define an unbiased sample of 50 radio galaxies, and measure quantities of interest from the maps available to me. Trends in this sample are discussed and compared with those seen in samples of other classes of object. Using Monte Carlo simulation, I show that the prominences and sidednesses of jets in the sample are consistent with relativistic beaming models, and constrain the velocities required and the efficiency of a typical beam.
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Lai, Chung-kei Chris, e 黎頌基. "Mixing of inclined dense jets". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B4423661X.
Testo completo
43
Baker, Laura. "Sting jets in extratropical cyclones". Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.541952.
Testo completo
44
Ho, Y. K. "Supersonic and subsonic radial jets". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378306.
Testo completo
45
Cox, Christopher Ian. "Numerical simulations of astrophysical jets". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335736.
Testo completo
46
Kuo, Chih-yu. "The acoustics of impinging jets". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624916.
Testo completo
47
Bence, Stephen John. "Stellar jets and molecular outflows". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627089.
Testo completo
48
Liamini, Mokhtar. "Étude des jets supersoniques impactants". Mémoire, Université de Sherbrooke, 2005. http://savoirs.usherbrooke.ca/handle/11143/1289.
Testo completoAbstract (sommario):
Un large éventail d'applications industrielles fait appel aux jets supersoniques impactants. Notamment leur utilisation pour la manutention sans contact des objets de faible masse. Il s'avère donc nécessaire de pouvoir prédire les profils de pression et de température que crée un jet supersonique sous-détendu sur l'objet impacté ainsi que de démonter les phénomènes qui gouvernent l'écoulement. Dans une étude ultérieure menée par J.-M. Papillon et commanditée conjointement par l'Université de Sherbrooke et IBM, un banc d'essai de jets supersoniques sous-détendus impactants a été réalisé. Ce banc d'essai permet d'abord de faire jaillir un jet supersonique sous-détendu sur un disque plan constituant la surface inférieure d'un diffuseur radial, puis d'en mesurer les pressions et les températures surfaciques. Notre étude s'inscrit ainsi dans la continuité de celle qui est décrite plus haut. Elle consiste à reprendre en main le banc d'essai pour reproduire, valider et approfondir l'étude expérimentale. Afin d'atteindre une meilleure appréciation quantitative des champs de pression et de température, une modélisation numérique est également effectuée dans chaque cas investigué. Le modèle mathématique utilisé tient compte de la compressibilité du fluide et des effets de la turbulence et repose sur les équations de conservation de la masse, de la quantité de mouvement et de l'énergie. Des améliorations sont apportées également au montage dans le but de mesurer les pressions et températures sur la surface de la buse. La confrontation des résultats obtenus par les essais expérimentaux à la modélisation numérique permet ainsi une compréhension approfondie des phénomènes en jeu.
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Craske, John. "Unsteady turbulent jets and plumes". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/44208.
Testo completoAbstract (sommario):
This thesis investigates the physics of statistically unsteady axisymmetric turbulent jets and plumes using theory and direct numerical simulation. The focus is on understanding and modelling the physics that govern the behaviour of radially integrated quantities, such as the integral scalar flux, momentum flux and buoyancy flux. To this end, a framework is developed that generalises previous approaches, making no assumption about the longitudinal velocity profile, turbulence transport or pressure. The framework is used to develop well-posed integral models that exhibit a good agreement with simulation data. In the case of passive scalar transport, shear-flow dispersion is observed to be dominant in comparison with longitudinal turbulent mixing. A dispersion closure for free-shear flows based on the classical work of Taylor (Proc. R. Soc. Lond. A, vol. 219 1954b, pp. 186-203) is therefore developed. In the analysis of jets whose source momentum flux undergoes an instantaneous step change, it is demonstrated that a momentum-energy framework, of the kind used by Priestley & Ball (Q. J. R. Meteorol. Soc., vol. 81 1955, pp. 144-157), is the natural choice for unsteady free-shear flows. The framework is used to demonstrate why existing top-hat models of unsteady jets and plumes are ill-posed and that jets and plumes with Gaussian velocity profiles remain approximately straight-sided and are insensitive to source perturbations. Contrary to the view that the unsteady jet and plume equations are parabolic, it is shown that the generalised system of equations is hyperbolic. In unsteady plumes, the relative orientation of three independent families of characteristic curves determines whether propagating waves are lazy, forced or pure. To relate findings that are based on the momentum-energy framework to the classical mass-momentum framework, an unsteady entrainment coefficient is defined that generalises the decomposition proposed by Kaminski et al. (2005, J. Fluid Mech., vol. 526, pp. 361-376).
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Sol, Hélène. "Jets et sources radio extragalactiques". Paris 7, 1987. http://www.theses.fr/1987PA077163.
Testo completoAbstract (sommario):
Travaux sur les proprietes radiatives et dynamiques des jets associes a des galaxies ou a des quasars. L'etude du jet optique de la galaxie active pks 0521-36 est abordee en detail. On decrit ensuite le passage d'un jet vlbi de quelques pc a un jet observe a grande echelle sur plusieurs dizaines de kpc. On traite, sur ce sujet, des mecanismes physiques qui entrent en jeu pour interpreter ce phenomene. En derniere partie on pose le probleme de la determination de la constante de hubble en termes de mirages gravitationnels et celui des jets d'echelle stellaire