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Item type:Publication, Access status: with files , Modelling the acoustic radiation of propeller tip vortex cavitation in potential flow simulations(Elsevier, 2024-11-01); ; ; ; Propeller cavitation and its effect on underwater radiated noise (URN) are topics of increasing interest within the marine hydrodynamics community. Numerical prediction of the URN characteristics of a given propeller design is vital in achieving the design of low-noise propellers. In this context, the current paper investigates different acoustic models for the numerical evaluation of propeller tip vortex cavitation-induced-noise, using potential flow simulations. Two acoustic modelling approaches are discussed, considering an elongated cylindrical representation of helical tip vortex cavities. Model 2D is a two-dimensional geometrical representation of the tip vortex cavity, wherein equivalent acoustic sources are defined along the cavity surface. Model 1D is an axisymmetric one-dimensional model with equivalent point sources that are distributed along the cavity axis. The applicability and limitations of the two acoustic models are assessed through a verification study of an analytical case for harmonic oscillations of a circular cylinder. The influence and sensitivity of important parameters are discussed, along with their relevance and application when extended to typical tip vortex cavity structures emanating from ship propellers. Finally, the practicality of the acoustic models for propeller tip vortex cavities is investigated through a validation study for the ‘Princess Royal’ propeller. The hydrodynamic flow solution is obtained from a potential flow solver, which includes flow models for sheet cavitation and tip vortex cavitation. Tip vortex cavity acoustics is obtained using the time-varying tip vortex cavity geometry from the potential flow solution. Acoustic contributions due to the blade rotation and sheet cavity fluctuations are separately computed. The simulation results are then compared with experimental measurements.Publicationtype: Journal Article56 174 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Numerical study on the evolution of vortex structures at the propeller tip and their influence on cavitation inception(Norwegian University of Science and Technology, Department of Marine Technology, 2024-04-04); ; ; ; In this paper, we study the behaviour of propeller leading edge vortices, local tip vortices and trailing vortices for different operation conditions and tip geometries. It turns out that the pressure drop in the trailing vortex being relevant for cavitation inception strongly depends on the nature of the local tip vortex and of the leading edge vortex. Further, we demonstrate that applying tip rake to a given propeller design is an effective instrument to steer the vorticity distribution in the tip region allowing to increase cavitation inception speed while maintaining the propeller’s efficiency. Open water simulations were carried out using a RANS method and the k-ω SST turbulence closure model with curvature correction. The computational mesh was appropriately refined along the leading edge, the propeller tip and along the axis of the trailing vortex. An intuitive method for evaluating vortex quantities such as circulation, viscous core radius, the level of vorticity and pressure drop at different stations along the vortex axis is presented and applied. Finally, our findings are underpinned by experimental results from a cavitation inception test.Publicationtype: Conference Paper74 100 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Propeller cavitation noise in hybrid viscous flow/FWH simulations using robust impermeable surface formulations(Norwegian University of Science and Technology, Department of Marine Technology, 2024-04-04); ; ; ; The recent years have seen increasing interest in the numerical evaluation of the underwater noise from cavitating propellers. When Ffowcs-Williams-Hawkings (FWH) based acoustic analogy methods are extended to cavity surfaces, the adequacy of different formulations is still debatable. The acoustic sources may be defined on either impermeable (or non-porous or solid) data surfaces which coincide with physical body surfaces; or on a permeable data surface that encompasses the entire noise generating flow region. In a permeable-FWH approach, the acoustic solution is dependent on the porous enclosure selected; and there is no unanimous agreement about its extent. In a viscous finite volume solver with impermeable-FWH approach, the acoustic effects of cavity fluctuations are not completely captured, due to the absence of any physical cavity surface within the simulations. In this paper, a novel hybrid approach is investigated, wherein the accuracy of the cavitation flow dynamics from a viscous CFD solver is combined with the simplicity of an acoustic source definition using impermeable surfaces. The flow simulations are performed in Star-CCM+ using incompressible two-phase Detached Eddy Simulations (DES) and the Schnerr-Sauer cavitation model. The instantaneous cavity surface geometry is extracted from the simulation results and used to define equivalent acoustic sources. The acoustic predictions from the model are verified by comparing with hydrodynamic pressure pulses from DES. Finally, the results are compared with experimental measurements, in order to evaluate the performance of each method.Publicationtype: Conference Paper40 73 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Numerical analysis of propeller-induced higher-order pressure fluctuations on the ship hull(2018-02); This thesis documents and explains the development and validation of a hybrid simulation method for investigating higher-order hull pressure fluctuations induced by cavitating propellers. Two forms of propeller cavitation are considered in this work: coherent structures of sheet cavitation on the propeller blades and tip vortex cavitation. The interaction between sheet cavitation and developed tip vortex cavitation can be responsible for notable higher-order pressure fluctuations. The essential element of this novel simulation method is panMARE, the in-house panel code used to calculate the propeller flow including effects of sheet cavitation. Furthermore, relevant parts of the hull surface above the propeller are incorporated in the panel model in order to evaluate fluctuations of pressure in the aft ship region. The propeller operates in the effective wake field of the ship which results from the viscous interaction between hull and propeller flow. It is calculated by a RANSE solver in combination with panMARE. A body force coupling approach is used to couple both methods. Herein, the viscous hull flow is determined by the RANSE solver and the impact of the propeller is approximated by a corresponding distribution of body forces applied to the viscous flow which in return is calculated by means of panMARE. In order to model tip vortex cavitation, the vortex cavity is divided into a large number of cylindrical segments, where each of them are treated separately. This breaks down the formerly three-dimensional problem into a two-dimensional one, which is much easier to handle. For each segment, the momentum equations in cylindrical coordinates, leading to a Rayleigh-Plesset-like equation for the dynamical behaviour of the cavitating core, are solved. Interaction with sheet cavitation is taken into account by correlating the initial cavitation radius with the cavity thickness at the trailing edge of the blade in the tip region. This and other tip vortex parameters are extracted from detailed RANS simulations of the blade tip flow made in advance for a number of representative loading conditions. For validation purposes, three vessels are investigated. The numerical results are compared to those obtained from experiments and - if available - from full-scale measurements. Furthermore, two types of scale effects due to the Reynolds number are investigated by the method: the wake scale effect on sheet cavitation and the influence of the viscous core radius on moderate and tip vortex cavitation in the stage of formation in an idealised manner.Publicationtype: Doctoral Thesis1686 2433 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of Reynolds Number Scale Effects on Propeller Tip Vortex Cavitation and Propeller-Induced Hull Pressure FluctuationsA two-dimensional viscous vortex model with a cylindrical cavity at its center is applied to investigate Reynolds number scale effects on propeller tip vortex cavitation. First, the behaviour of small isolated cavities inside the viscous core are studied. In order to study Reynolds number scale effects, the viscous core radius of the vortex is varied. Thereafter, the investigation is extended to the cavitating tip vortex of a propeller as a whole. A generic scenario is set up which is representative for real propeller flows. It can be shown that apart from the viscous core radius, the blade load and the presence of sheet cavitation influence hull pressure fluctuations due to tip vortex cavitation in a significant manner.Publicationtype: Conference Paper84 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A Hybrid Numerical Method for Investigating Underwater Sound Propagation of Cavitating Propellers(VTT Technical Research Centre of Finland Ltd, 2017-06); ; ; The present article deals with the prediction of the underwater noise induced by ship propellers under consideration of sheet cavitation on the propeller blades. The calculation method is a hybrid approach combining a boundary element calculation method with the Ffowcs-Williams Hawkings equation. The method is applied to different simulation cases with increasing complexity. The final case considers the noise propagation in full-scale for a cavitating propeller in combination with a part of a ship stern. This simulation result is compared to a full-scale measurement.Publicationtype: Conference Paper81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Entwicklung von panMARE als Paneelverfahren für interdisziplinäre maritime AnwendungenComputational methods based on the potential flow theory are common powerful tools for calculating the hydrodynamic behavior of lifting and non-lifting bodies. Potential flow methods can provide a valuable support for applications, where the pressure forces are dominant. Beside their short computing time, the accuracy of the results is mostly adequate for design purposes. Potential computational methods can also be used to simulate complex operation scenarios such as installation of offshore wind turbine involving different ship units. The development of computational methods for potential flow is usually carried out as problem-specific codes, i.e., certain methods are suitable only for a certain class of problems such as propeller flow or wave making resistance applications. In order to avoid this limitation, the development of a panel method panMARE was initiated several years ago at the Institute for Fluid Dynamics and Ship Theory, Hamburg University of Technology. A key point in the development of panMARE is the interdisciplinary applicability of the method for steady and unsteady flow problems under consideration of different physical models such as cavitation or influence of a free water surface. The motion of the investigated bodies can be either specified or calculated by solving the equation of motions. In addition panMARE has interfaces to various RANS solvers, thus it can be used in RANS-BEM simulations, as well as an interface to solvers that address structural and mechanical problems. Therefore, the method can be used to carry out coupled fluid-structure simulations. After explaining the theoretical background of the numerical method its capability will be demonstrated. In addition to typical shipbuilding problems such as calculation of propeller cavitation, pressure fluctuations or maneuver simulation in waves, different applications in the field of offshore wind energy will be presented.Publicationtype: Conference Paper133 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient Numerical Investigation of Propeller Cavitation Phenomena causing Higher-Order Hull Pressure FluctuationsPublicationtype: Conference Paper77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical Simulation of Propeller-Rudder Interaction for Non-Cavitating and Cavitating Flows Using Different ApproachesThe present article deals with the numerical investigation of propeller-rudder interaction. The involved simulation method is based on coupling a RANS solver and a potential-theory based panel method, where the panel method primarily handles the propeller flow and the RANS solver is used for the simulation of the complex rudder flow. Compared to full RANS simulations, this separation allows numerical investigations in a time-saving manner. In a numerical study, a rudder-propeller combination is evaluated by means of the developed simulation method for different propeller advance coefficients and rudder angles. Rudder cavitation is also adressed. The results are compared to results obtained by a full RANS simulation.Publicationtype: Conference Paper96 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Testing a semi-automated tool for the optimisation of full-scale marine propellers working behind a ship(Internat. Center for Numerical Methods in Engineering, 2013); ; ; A procedure for the optimization of full-scale marine propellers working be-hind a ship ispresented. This procedure consists of two stages: the actual optimization and a detailed investigation of a few selected propeller geometry variants. In the first step, an evolutionary algorithm in combination with the in-house panel code panMARE is used to solve the multi-objective propeller optimization problem. An efficient method for the evaluation of the individuals and a parameterization strategy for propeller shapes are presented. Proceeding from the results of the optimisation, a set of selected propeller variants is investigated in detail in the second stage of the procedure. The applied algo-rithm is based on coupling panMARE with a viscous flow solver. An enhancement of this method allows investigating several propeller variants sequentially without stopping the solvers.Publicationtype: Conference Paper77