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Since the industrial revolution the ocean has become noisier. The global increasein shipping is one of the main contributors to this. In some regions, shippingcontributed to an increase in ambient noise of several decibels, especially at lowfrequencies (10 to 100 Hz). Such an increase can have a substantial negativeimpact on fish, invertebrates, marine mammals and birds interfering with key lifefunctions (e.g. foraging, mating, resting, etc.). Consequently, engineers areinvestigating ways to reduce the noise emitted by vessels when designing newships. At the same time, since the industrial revolution (starting around 1760)greenhouse gas emissions have increased the atmospheric carbon dioxidefraction x(CO2) by more than 100 mmol mol-1. The ocean uptake ofapproximately one third of the emitted CO2 decreased the average globalsurface ocean pH from 8.21 to 8.10. This decrease is modifying soundpropagation, especially sound absorption at the frequencies affected byshipping noise lower than 10 kHz, making the future ocean potentially noisier.There are also other climate change effects that may influence soundpropagation. Sea surface warming might alter the depth of the deep soundspeed channel, ice melting could locally decrease salinity and more frequentstorms and higher wind speed alter the depth of the thermocline. In particular,modification of the sound speed profile can lead to the appearance of new ductsmaking specific depths noisier. In addition, ice melting and the increase inseawater temperature will open new shipping routes at the poles increasinganthropogenic noise in these regions. This review aims to discuss parametersthat might change in the coming decades, focusing on the contribution ofshipping, climate change and economic and technical developments to thefuture underwater soundscape in the ocean. Examples are given, contrasting theopen ocean and the shallow seas. Apart from the changes in sound propagation,this review will also discuss the effects of water

Different approaches for specifying the ratio of modelled-to-total dissipation ( fε) in the PANS model, based on the k −ω SST model, are evaluated for different ratios of the modelled-to-total kinetic energy, fk. Based on theoretical reasoning it is argued that applying fε = a · fk should have little effect, and that fε = fk is not expected to improve the results. This is confirmed by applying the approaches to a turbulent channel flow at Reτ = 395 and 180, and comparing the results to the often used ‘high Reynolds number’ approach ( fε = 1.0). Reducing fε leads to a reduction in range of scales in the flow; dissipation is allowed at larger scales and therefore smaller scales are suppressed.

In this thesis, shock phenomena in cavitating flow are numerically assessed. The model relies on the homogeneous mixture assumption, equilibrium thermodynamics, and a barotropic equation of state. The method captures cavitation-induced shock-wave dynamics, its interaction with phase transition, and the feed-back with convective flow. An investigation of partial cavitation exhibiting sheet-to-cloud transition provides novel insight into the flow physics of condensation shock phenomena, an intrinsic mechanism of instability for sheet cavitation. Furthermore, cavitating flow around a model ship propeller is considered, including a quantitative assessment of flow aggressiveness., Diese Arbeit untersucht Stoß-Phänomene in kavitierenden Strömungen. Das numerische Modell stützt sich auf die Annahme einer homogenen Mischung, Gleichgewichtsthermodynamik, und eine barotrope Zustandsgleichung. Alle relevanten Zeitskalen kavitierender Strömungen werden mittels expliziter Zeitintegration aufgelöst. Die verwendete Methode erfasst kollapsinduzierte Stoßwellendynamiken, ihre Interaktion mit dem Phasenübergang, sowie die Rückkopplung mit konvektiven Skalen der Strömung. Untersuchungen einer partiellen Schichtkavitation, welche durch die wiederkehrende Ablösung großskaliger Wolkenkavitation gekennzeichnet ist, liefern neue Einblicke in die Physik von Kondensationsstößen. Als Anwendungsfall wird die kavitierende Umströmung eines Modell-Propellers untersucht, einschließlich einer quantitativen Bewertung der Strömungsaggressivität.

In this thesis, shock phenomena in cavitating flow are numerically assessed. The model relies on the homogeneous mixture assumption, equilibrium thermodynamics, and a barotropic equation of state. The method captures cavitation-induced shock-wave dynamics, its interaction with phase transition, and the feed-back with convective flow. An investigation of partial cavitation exhibiting sheet-to-cloud transition provides novel insight into the flow physics of condensation shock phenomena, an intrinsic mechanism of instability for sheet cavitation. Furthermore, cavitating flow around a model ship propeller is considered, including a quantitative assessment of flow aggressiveness., Diese Arbeit untersucht Stoß-Phänomene in kavitierenden Strömungen. Das numerische Modell stützt sich auf die Annahme einer homogenen Mischung, Gleichgewichtsthermodynamik, und eine barotrope Zustandsgleichung. Alle relevanten Zeitskalen kavitierender Strömungen werden mittels expliziter Zeitintegration aufgelöst. Die verwendete Methode erfasst kollapsinduzierte Stoßwellendynamiken, ihre Interaktion mit dem Phasenübergang, sowie die Rückkopplung mit konvektiven Skalen der Strömung. Untersuchungen einer partiellen Schichtkavitation, welche durch die wiederkehrende Ablösung großskaliger Wolkenkavitation gekennzeichnet ist, liefern neue Einblicke in die Physik von Kondensationsstößen. Als Anwendungsfall wird die kavitierende Umströmung eines Modell-Propellers untersucht, einschließlich einer quantitativen Bewertung der Strömungsaggressivität.

The last decades there is a strong interest in predicting cavitation dynamics as it is a prerequisite in order to predict cavitation erosion. Industrial applications require accurate results in an acceptable time span and as a result there is a focus on large scale dynamics. In this paper the RANS equations are used to investigate the shedding frequency of sheet cavities in two-dimensional simulations. First a verification study is made for the NACA 0015 in 6 degrees angle of incidence. A grid sensitivity study is conducted in wetted flow and in steady (non-shedding) cavitating condition (σ=1.6). Then an investigation is conducted in order to capture the shedding frequency. The results show that only when a correction for turbulent viscosity at the cavity-water interface is used it was possible to capture the shedding frequency as found in other numerical studies. Furthermore, a validation study is conducted on a NACA66-312 α=0.8 for two different angles of attack. The obtained results are compared and validated with the experimental data from Leroux et al. They indicate that the 2D shedding frequency predicted by the numerical simulations is in good agreement with the frequency obtained in the experiment.

The present paper analyses a series of Computational Fluid Dynamic simulations of the cavitating flow around a two-dimensional NACA0015 foil. The foil is placed at 6◦ angle of attack and the cavitation number is 1.1. Two mesh designs, namely a block-structured topology and an unstructured topology, are compared; additionally, grid refinements and time step refinements are carried out. Solution Verification is addressed with calculation of the discretization error and the numerical uncertainty. The numerical uncertainty for the average lift coefficient is found to be large, up to 15%. The reason is the difficulty of achieving a grid independent solution: with very fine meshes, the flow shifts from an attached, oscillating sheet cavity pattern to a regime dominated by shedding of cavity clouds. On the other hand, neither the time resolution nor the choice of grid topology influence largely the flow pattern; instead, they only lead to differences in the maximum and minimum cavity size.

This thesis reports on the development and application of a low Mach number consistent approach for the simulation of cavitating flows including wave dynamics. A new flux function is presented and an efficient thermodynamic equilibrium cavitation model is discussed. The approach is applied to simulate cavitating flows in 6-hole injectors, around hydrofoils as well as around a sphere and a prismatic body. High pressure loads due to collapsing vapor patterns are analyzed and the foot prints of these loads at the surfaces of the devices are presented., Im Fokus dieser Arbeit steht die Entwicklung und Anwendung eines auch für kleine Machzahlen konsistenten Verfahrens zur Simulation kavitierender Strömungen unter Einbeziehung wellendynamischer Effekte. Eine neu entwickelte Flussfunktion und ein effizientes thermodynamisches Gleichgewichtsmodell werden diskutiert. Als Einsatzbeispiele werden Simulationen kavitierender Strömungen in einem 6-Loch Injektor, um verschiedene Schaufelmodelle sowie um eine Kugel und einen prismatischen Körper diskutiert. Druckspitzen als Folge kollabierender Dampfgebiete sowie die an den Wänden der Testkörper wirksamen Lasten werden analysiert.

This thesis reports on the development and application of a low Mach number consistent approach for the simulation of cavitating flows including wave dynamics. A new flux function is presented and an efficient thermodynamic equilibrium cavitation model is discussed. The approach is applied to simulate cavitating flows in 6-hole injectors, around hydrofoils as well as around a sphere and a prismatic body. High pressure loads due to collapsing vapor patterns are analyzed and the foot prints of these loads at the surfaces of the devices are presented., Im Fokus dieser Arbeit steht die Entwicklung und Anwendung eines auch für kleine Machzahlen konsistenten Verfahrens zur Simulation kavitierender Strömungen unter Einbeziehung wellendynamischer Effekte. Eine neu entwickelte Flussfunktion und ein effizientes thermodynamisches Gleichgewichtsmodell werden diskutiert. Als Einsatzbeispiele werden Simulationen kavitierender Strömungen in einem 6-Loch Injektor, um verschiedene Schaufelmodelle sowie um eine Kugel und einen prismatischen Körper diskutiert. Druckspitzen als Folge kollabierender Dampfgebiete sowie die an den Wänden der Testkörper wirksamen Lasten werden analysiert.