Now showing1 - 2 of 2
- 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