Turbocharging is used as a means to downsize petrol engines, thereby, producing more power for a lower engine size, when compared with a naturally aspirated engine. Due to the presence of a throttle valve in the intake system in petrol engines, flow is restricted at the outlet pipe of the compressor during low load engine operation. For example, during transient tip out tip in maneuvers. Hence, there is a chance of the turbocharger operating in near surge or surge conditions and, thus, generating surge noise. This Thesis describes an experimental and simulation method to predict and measure the turbocharger surge noise. Initially, experimental transient tip-in and tip-out maneuver was performed on a non turbocharged car with a petrol engine. The measured noise level in the intake manifold, at a low frequency of up to 1200 Hz, was analysed and was shown not to represent surge noise. Next, a one dimensional simulation method was applied to simulate the noise of the engine and this demonstrated an increase in the acoustic pressure level in the intake manifold during the tip in and tip out maneuver. However, a surge noise pattern was not observed in the analysis of acoustic pressure signals in the intake system using Short Time Fourier Transform (STFT). The simulation procedure was also used to inform the design of an experimental rig to recreate the surge noise under laboratory conditions. An experimental turbocharger noise rig, designed and built for this purpose, is explained in the Thesis. Important component parts likely to be involved in the surge noise generation such as the intake system, compressor, throttle body, compressor recirculation valve and measurement and control systems were integrated into the test rig. Background noise contributions from the electric motor, AC mains, supercharger pulley, throttle body, inverter fan, throttle body gearing and structural vibration of the supporting structure were identified from the analysed frequency components of the signals from surface microphone measurements taken at the intake system. This helped to clearly identify the surge noise frequency components (3250 Hz) in the STFT analysis. The fundamental mechanism of noise generation was identified using an analysis of the experimental results and a frequency calculation for vortex shedding and the radial acoustic resonances. One of the main conclusions of the Thesis is that the compressor recirculation valve (CRV) open or close position, the CRV delay time and the throttle position are major contributing factors to the cause of the surge noise. Another major conclusion is that the radial acoustic resonance may be a mechanism of surge noise generation. Finally, a passive solution to reduce the surge noise is proposed. A pipe with cross ribs is designed as a passive solution using the radial acoustic resonance calculation and the corresponding nodal patterns. This solution demonstrated a measured intake system noise reduction of up to 10dB under compressor surge conditions.

Cette recherche se focalise sur les problèmes d’instabilités de combustion hautes fréquences dans les moteurs fusées. Ces instabilités sont connues pour avoir des effets néfastes et peuvent, dans certains cas, causer la destruction du système propulsif. Pour éviter l’apparition de ces instabilités, il est important de connaître les mécanismes qui entretiennent ces phénomènes dynamiques et de comprendre le couplage complexe entre l’injection, la combustion et la résonnance acoustique du système. Ce travail comprend trois parties.La première partie traite de la simulation numérique de jets non-réactifs et réactifs soumis à différentes conditions de modulation afin de comprendre les interactions entre les jets, les flammes et leur environnement. Les calculs numériques de jets ronds non-réactifs ainsi que des flammes plus complexes formées par des injecteurs coaxiaux dans des conditions transcritiques ont été effectuées avec des simulations aux grandes échelles (SGE), adaptées aux conditions gaz réels à l’aide du solveur AVBP-RG. Les jets ronds ont été soumis à des fluctuations de vitesse transverse. Il a été trouvé que pour toutes les amplitudes et fréquences de modulation, le jet est déformé et oscille dans la direction transverse. Ce comportement peut être représenté par un modèle. Les flammes coaxiales ont été soumises à une modulation de débit et de pression. La modulation induit des variations du dégagement de chaleur global. Un modèle mathématique reliant les paramètres modulés au dégagement de chaleur est proposé.La seconde partie contient les travaux expérimentaux. Dans ce cadre, un nouveau banc expérimental a été développé pour l’étude de cavités couplées pressurisées (NPCC). Le couplage entre le plénum (ou dôme) et la chambre a été étudié. Un modèle reliant les fluctuations de pression et de vitesse en sortie des injecteurs a été développé et comparés aux données d’essais. Le banc NPCC a aussi été utilisé pour acquérir plus de connaissances sur le niveau d’amortissement. Les coefficients d’amortissement ont été déterminés.La dernière partie de ce document traite du développement d’un modèle ordre réduit qui représente des mécanismes qui entretiennent et amortissent les instabilités de combustion hautes fréquences. Cette description dynamique a été incorporée dans un code de stabilité haute fréquence (STAHF). Ce code a été utilisé pour étudier un moteur à ergols liquides d’une puissance de 87 MW (le banc BKD du DLR en Allemagne) qui présente des instabilités hautes fréquences. Après le recalage de certains paramètres de contrôle, STAHF a été capable de retrouver des résultats obtenus d’essais au DLR. / This research concerns some of the issues raised by high frequency combustion instabilities in rocket engines. These instabilities are known to have detrimental effects leading, in some cases, to the destruction of the propulsion system. To avoid the appearance of such instabilities it is important to gain an understanding of the processes driving such dynamical phenomena. One has to consider the complex coupling between injection, combustion and the acoustic resonances of the system. The present work contributes to this objective by developing three items.The first deals with numerical simulations of non-reactive and reactive jets submitted to different modulation conditions to understand the interaction between jets, flames and their environment. Numerical simulations of non-reactive round jets as well as more complex flames formed by coaxial injectors operating under transcritical conditions were carried out using large eddy simulation (LES) adapted to real gas situations by making use of the AVBP-RG flow solver. Round jets were submitted to transverse velocity fluctuations. It has been found that for all amplitudes and frequencies of modulation, the modulated jet is deformed and oscillates. This behavior can be represented by a model. The coaxial flames were submitted to mass flow rate and pressure modulation. For these cases it has been found that the modulation induces variations of the global heat release rate. A mathematical relationship between the modulated parameters and the heat release rate has been proposed.The second item includes experimental investigations. For this purpose a New Pressurized Coupled Cavities (NPCC) laboratory test rig has been developed. The possible coupling between the plenum and the thrust chamber was studied. A model, linking pressure and velocity fluctuations between the plenum and the thrust chamber, has been developed. The laboratory test rig was also used to gather some knowledge on the levels of damping and the damping coefficients could be determined.The last item of this document deals with the development of a reduced order dynamical model which includes some of the driving and damping mechanisms of high frequency combustion instabilities. This dynamical description was implemented in a high frequency stability code (STAHF). This code was used to examine a 87 MW liquid rocket engine (BKD operated at DLR, Germany) exhibiting high frequency oscillations. After the adjustment of some control parameters, STAHF was able to retrieve some the features observed in experiments carried out at DLR.