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 acoustique. / In 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.

No description available.

The effect of a nozzle’s internal geometry was studied experimentally to determine the breakup of the emitted water jet when it was injected perpendicularly into a quiescent atmosphere or a subsonic air crossflow. The nozzle’s diameter, nominal surface roughness, length-to-diameter ratio and contraction angle were varied, together with the injection pressure, to find the water column’s breakup length. Photographs of the water jet at the nozzle’s exit, gave a clue as to identify the occurrence of cavitation and a hydraulic flip. On the other hand the water column’s breakup length and trajectory, in a subsonic crossflow, were measured by using a stroboscope in conjunction with a high speed CCD camera. Results agreed with previous literature that the breakup length grew with greater liquid/air momentum flux ratios for non-cavitating flows. This was true regardless of the injector nozzle. The rate of increase decreased at the inception of cavitation. On the other hand even shorter breakup lengths were observed at the inception of a hydraulic flip due to the detachment of the water jet from the internal surface of the nozzle. Increasing the nozzle’s length-to-diameter ratio eliminated the occurrence of hydraulic flip. The jet’s trajectory was correlated with the liquid/air momentum flux ratio and the nozzle’s exit diameter. The results showed that higher water jet trajectories were measured under non-cavitating conditions. Even shorter jet trajectories were measured at the inception of a hydraulic flip.

The effect of a nozzle’s internal geometry was studied experimentally to determine the breakup of the emitted water jet when it was injected perpendicularly into a quiescent atmosphere or a subsonic air crossflow. The nozzle’s diameter, nominal surface roughness, length-to-diameter ratio and contraction angle were varied, together with the injection pressure, to find the water column’s breakup length. Photographs of the water jet at the nozzle’s exit, gave a clue as to identify the occurrence of cavitation and a hydraulic flip. On the other hand the water column’s breakup length and trajectory, in a subsonic crossflow, were measured by using a stroboscope in conjunction with a high speed CCD camera. Results agreed with previous literature that the breakup length grew with greater liquid/air momentum flux ratios for non-cavitating flows. This was true regardless of the injector nozzle. The rate of increase decreased at the inception of cavitation. On the other hand even shorter breakup lengths were observed at the inception of a hydraulic flip due to the detachment of the water jet from the internal surface of the nozzle. Increasing the nozzle’s length-to-diameter ratio eliminated the occurrence of hydraulic flip. The jet’s trajectory was correlated with the liquid/air momentum flux ratio and the nozzle’s exit diameter. The results showed that higher water jet trajectories were measured under non-cavitating conditions. Even shorter jet trajectories were measured at the inception of a hydraulic flip.

The thesis traces the history of missile aerodynamic prediction methods and defines the aerodynamic requirements for the subsonic free-flight projectiles configurations under consideration. Different types of trajectory model are described with the aerodynamic input requirement being analysed. Methods of generating the required aerodynamic data for the trajectory models are discussed emphasising the aerodynamic models capabilities, weaknesses and ease of use. The method of masses aerodynamic prediction method is defined, highlighting the adaptations to the method that were carried out to generate the aerodynamic stability data required for subsequent projectile trajectory analysis. An assessment of the sensitivity and accuracy of the simulated data is carried out using experimental flight trial data on different projectile configurations. Finally, using the simulation models developed in previous chapters, a parametric analysis is carried out on different projectile configurations to optimise the trajectory performance.

No description available.

No description available.

Inductively Coupled Plasma (ICP) facilities create high enthalpy ows to recreate atmospheric entry conditions. Although no condition has been duplicated exactly in a ground test facility, it is important to characterize the condition to understand how close a facility can come to doing so. An ICP facility was constructed at the University of Vermont for aerospace material testing in 2010. The current setup can operate using air, carbon dioxide, nitrogen, and argon to test samples in a chamber. In this work we investigate di erent ways to increase measured heat ux and expand our facility to operate supersonically. To do so, a water cooled injection system was designed to overcome failure points of the prior system. An investigation of heat ux methods that provide a baseline for the facility were also examined and tested. A nozzle con guration was also developed with an overall goal of increasing the plasma ow to reach sonic and supersonic velocities, allowing it to be compared with the existing subsonic system. An iterative approach was taken to develop a nozzle design that is robust enough to handle the harsh environment, yet adaptable to the pre-existing facility components. The current design uses interchangeable sonic and supersonic nozzles which also allow for appropriate plasma gas expansion. Data are taken through retractable and goose-neck probe sample holders during testing. Heat ux can be determined by use of a Gardon gage, slug calorimeter, and water cooled calorimeter. Total and static pressure are determined from a pitot tube and pressure tap, which are then manipulated into a velocity measurement. A comparison between subsonic and supersonic operation is then made with these data. Existing literature uses correlations between jet diameter and velocity gradients to determine the e ective heat ux. This investigation found that the experimental and theoretical heat ux results scale correctly according to the correlations.

The need was identified to develop an analytical performance prediction code for subsonic multistage axial compressors that can be included in network analysis software. It was found that performance calculations based on an elementary one-dimensional meanline prediction method could achieve remarkable accuracy, provided that sound models are used for the losses, deviation and the onset of rotating stall. Consequently, this study focuses on gaining more expertise on the modelling of losses in such compressors through investigating the mechanisms responsible, the methods of predicting them, their implementation and possible usage. Internal losses are seen as mechanisms that increase the entropy of the working fluid through the compressor and it was found that, at a fundamental level, all internal losses are a direct result of viscous shearing that occurs wherever there are velocity gradients. Usually the methodology employed to predict the magnitudes of these mechanisms uses theoretically separable loss components, ignoring the mechanisms with negligible velocity gradients. For this study these components were presented as: Blade profile losses, endwall losses including tip leakage and secondary losses, part span shroud losses, other losses, losses due to high subsonic Mach numbers and incidence loss. A preliminary performance prediction code, with the capability of interchanging of the different loss models, is presented. Verification was done by comparing the results with those predicted by a commercial software package and the loss models were evaluated according to their ease of implementation and deviation from the predictions of the commercial package. Conclusions were made about the sensitivity of performance prediction to using the different loss models. Furthermore, the combination of loss models that include the most parameters and gave the best comparison to the commercial software predictions was selected in the code to perform parametric studies of the loss parameters on stage efficiency. This was done to illustrate the ability of the code for performing such studies to be used as an aid in understanding compressor design and performance or for basic optimization problems. It can therefore be recommended that the preliminary code can be implemented in an engineering tool or network analysis software. This may however require further verification, with a broader spectrum of test cases, for increased confidence as well as further study regarding aspects like multi-stage annulus blockage and deviation / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.

The need was identified to develop an analytical performance prediction code for subsonic multistage axial compressors that can be included in network analysis software. It was found that performance calculations based on an elementary one-dimensional meanline prediction method could achieve remarkable accuracy, provided that sound models are used for the losses, deviation and the onset of rotating stall. Consequently, this study focuses on gaining more expertise on the modelling of losses in such compressors through investigating the mechanisms responsible, the methods of predicting them, their implementation and possible usage. Internal losses are seen as mechanisms that increase the entropy of the working fluid through the compressor and it was found that, at a fundamental level, all internal losses are a direct result of viscous shearing that occurs wherever there are velocity gradients. Usually the methodology employed to predict the magnitudes of these mechanisms uses theoretically separable loss components, ignoring the mechanisms with negligible velocity gradients. For this study these components were presented as: Blade profile losses, endwall losses including tip leakage and secondary losses, part span shroud losses, other losses, losses due to high subsonic Mach numbers and incidence loss. A preliminary performance prediction code, with the capability of interchanging of the different loss models, is presented. Verification was done by comparing the results with those predicted by a commercial software package and the loss models were evaluated according to their ease of implementation and deviation from the predictions of the commercial package. Conclusions were made about the sensitivity of performance prediction to using the different loss models. Furthermore, the combination of loss models that include the most parameters and gave the best comparison to the commercial software predictions was selected in the code to perform parametric studies of the loss parameters on stage efficiency. This was done to illustrate the ability of the code for performing such studies to be used as an aid in understanding compressor design and performance or for basic optimization problems. It can therefore be recommended that the preliminary code can be implemented in an engineering tool or network analysis software. This may however require further verification, with a broader spectrum of test cases, for increased confidence as well as further study regarding aspects like multi-stage annulus blockage and deviation / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.