Numerical Prediction of Propeller Induced Hull Pressure Pulses

Ship propeller induced pressure pulses is one of the major sources of both onboard noise and vibration as well as underwater radiated noise. The need for accurate pressure pulse prediction is increasing due to rising concerns of environmental impacts and comfort and welfare of passengers and crews. More accurate pressure pulse prediction is needed to be able to reduce the margin between high efficiency propeller design and low pressure pulse propeller design.Experimental approaches are used for pressure pulse assessments in the final verification stage where models are produced, but they are limited in early design work. Potential flow based methods have been used for early estimation of pressure pulses, but due to the complexity of the pressure pulse generation mechanisms, including interaction between hull and propeller and various types of cavitation, viscous numerical methods are being developing as a complement to potential flow method and a faster and cheaper alternative of experimental testing. This thesis deals with the numerical prediction of marine propeller induced pressure pulses adapted from typical experimental procedures, including both model scale and full scale marine propellers operating in open-water conditions and behind hull conditions with non-cavitating and cavitating flows. Simulations were conducted using open-source package OpenFOAM and commercial package Star-CCM+ with Reynolds-Averaged Navier-Stokes (RANS) method.Studied cases show that for propellers in behind conditions, the present RANS approach can provide good accuracy regarding 1 st and 2 nd order BPF (Blade Passing Frequency) hull pressure pulses early in design stage. Higher order BPF pressure pulses were also predicted reasonably well, and different mechanisms inducing higher order BPF pressure pulses, including small tip clearance, transient cavitation appearance and sheet cavitation closure and its interaction with tip vortex cavitation, are outlined in the thesis. For model scale propellers operating under nearly uniform inflows, sheet cavitation is often over-predicted and an improved cavitation mass transfer model is proposed which take laminar separation as an additional inception criteria. Studies regarding mesh resolutions and scaling effects are also included in certain cases

Numerical prediction of propeller induced hull pressure pulses and noise

An operating marine propeller is one of the major sources inducing hull pressure pulses, onboard noise and vibration as well as underwater radiated noise. There are rising concerns of environmental impacts and comfort and welfare of passengers and crews due to these negative effects. Cavitation is a significant source of these effects, but it is typically inevitable if only the hydrodynamic efficiency of the propeller is optimized. To reduce the noise and the pressure pulses caused by the cavitation, a trade-off of the hydrodynamic efficiency should be made to design and optimize a propeller that possess both high hydrodynamic performance and low noise and hull pressure pulse generation. More accurate predictions are needed to identify the best trade-off between a high efficiency propeller design and a low pressure pulse and noise one.The study focuses on the numerical prediction of hull pressure pulses and radiated underwater noise using viscous CFD including the opensource package OpenFOAM and commercial package Star-CCM+. Numerical predictions are performed regarding different experimental configurations for determining hull pressure pulses and ship noise, including propellers mounted on inclined shafts and propellers operating behind ship hulls, under different scales and scaling laws with different operating conditions and Reynolds numbers.Non-cavitating propeller induced pressure pulses are generally lower in levels and rich in blade passing frequency comparing to cavitating conditions, with blade tip clearance as a major impact factor. For cavitating conditions the rate of cavity growth/shrinkage is found to play the dominating role generating pressure fluctuations. For certain model scale configurations, numerical predictions with ordinary approaches predict massive sheet cavity on propeller blades leading to pressure pulse prediction discrepancies comparing to experimental observations and measurements. These can be significantly improved by a developed bridged model considering laminar to turbulence transition. Tip vortex cavitation bursting is a common phenomenon found on propellers operating behind the ship hull and generating significant levels of pressure pulses. The phenomenon is numerically predicted with investigations of its generation mechanisms in relation to the propeller inflow, convex shaped sheet cavitation closure line and traveling re-entrant jet underneath the sheet cavity.Propeller induced noise prediction was studied using approaches focused on the FWH (Ffowcs Williams-Hawkings) acoustic analogy with incompressible input on permeable/porous data surface (PDS). \ua0Studies show this combination between incompressible input and FWH acoustic analogy can be erroneous, though using certain PDS placements and closer receivers the error can be reduced

Numerical investigation of pressure pulse predictions for propellers mounted on an inclined shaft

In the presented study, two high-skew model scale marine propellers were tested in the cavitation tunnel and the induced pressure pulses were measured during the test. Propeller shaft was inclined about 10 degrees to create blade load variations. The cavitation pattern were recorded using high speed videos. The open-source package openFOAM and commercial package Star-ccm+ are used as simulation tools to predict pressure pulses numerically. By using the fully turbulent SST k − ω model, the predicted wetted flow pressure pulse levels agreed well compared to experimental measurements, but together with Schnerr-Sauer\ua0cavitation mass transfer model, massive cavitation was predicted which lead to inaccurate pressure pulse predictions.\ua0The transition sensitive turbulence model γ − Re θ model\ua0is used to study the cases, and simulation results reveal\ua0the existence of laminar-transition zone and vortex structures on the propeller blades. Attempts are made to linking correlation-based separation region from the transition model and the cavitation model, and good predictions of cavitation pattern are achieved but the predicted pressure pulses levels are merely improved

Improved prediction of sheet cavitation inception using bridged transition sensitive turbulence model and cavitation model

Sheet cavitation inception can be influenced by laminar boundary layer flow separation under Reynolds numbers regimes with transitional flow. The lack of accurate prediction of laminar separation may lead to massive over-prediction of sheet cavitation under certain circumstances, including model scale hydrofoils and marine propellers operating at relatively low Reynolds number. For non-cavitating flows, the local correlation based transition model, γ − Reθ transition model, has been found to provide predictions of laminar separation and resulting boundary layer transition. In the present study, the predicted laminar separation using γ − Reθ transition model is bridged with a cavitation mass transfer model to improve sheet cavitation predictions on hydrofoils and model scale marine propellers. The bridged model is developed and applied to study laminar separation and sheet cavitation predictions on the NACA16012 hydrofoil under different Reynolds numbers and angles of attack. As a reference case, the open case of the PPTC VP1304 model scale marine propeller tested on an inclined shaft is studied. Lastly as an application case, the predictions of cavitation on a commercial marine propeller from Kongsberg is presented for model scale conditions. Simulations using the bridged model and the standard unbridged approach with k − ω SST turbulence model are performed using the open-source package OpenFOAM, both using the Schnerr–Sauer cavitation mass transfer model, and the respective results are compared with available experimental results. The predictions using the bridged model agree well compared to experimental measurements and show significant improvements compared to the unbridged approach

Comparison of Free Surface Capturing Approaches in OpenFOAM for Ship Resistance Prediction

The prediction of calm water ship resistance by computational fluid dynamics (CFD) has matured considerably in recent years. For displacement ships, accurate prediction of the free-surface is normallyreasonably robust, provided the mesh resolution is sufficient. For more complex situations, such as for high speed vessels where spray becomes important or when in situations where the transom is only partially dry on medium speed ships, the numerical schemes to be used are still in development; even more so perhaps if ship motions and ocean waves are considered. Thus, in the open source package OpenFOAM, there are a wide range of options to choose from when setting up the free-surface simulation, all with different impact on performance. Thus, in the present study, free-surface prediction by different interface capturing are presented for the KCS (KRISO Container Ship) hull resistance simulation. Focus is on some of the options available in OpenFOAM, but also the commercial package Star-CCM+ has been investigated. All simulations have been performed by considering incompressible RANS and the k − ωS S T turbulence model

Investigation on Numerical Prediction of Propeller Induced Hull Pressure Pulses

Simulation of a cavitating propeller in behind conditions and analysis of induced hull pressure fluctuations are presented. All the simulations were performed using RANS method in the commercial package Star-CCM+. Cavitation patterns show good agreement with experimental measurements, especially the blade tip refined meshes which captured the dynamic behaviour of tip vortex cavitation. The predicted pressure pulse amplitudes agree reasonably well with experimental measurements up to 3rd to 4th order of blade passing frequency

Numerical investigation of tip vortex bursting and induced hull pressure pulses on a container vessel

A rotating marine propeller generates pressure pulses on the hull above it. The dynamics of cavitation, especially the tip vortex cavitation (TVC) bursting and TVC destruction by sheet cavity collapse have been found to induce high levels of pressure pulses on the ship hull body. The present study is focused on the numerical prediction of propeller induced pressure pulses on the hull with analysis on the interactions between ship wake, sheet cavitation and TVC. The predicted 1st – 2nd order Blade Passing Frequency (BPF) agree well with experimental measurements and higher order BPF pressure pulses are reasonably predicted as well. The study shows that the re-entrant jet, which can be related to the propeller inflow and convex shaped sheet cavity closure line, plays an important role regarding sheet cavitation collapse as well as violent TVC dynamics, and induce significant levels of hull pressure pulses

Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input

Ship noise predictions using FWH acoustic analogy with incompressible flow solution inputs are investigated for a model scale container vessel with a cavitating propeller. Numerical predictions of cavitation and hull pressure pulse predictions are validated first, comparing simulations performed for the tunnel test section and experimental measurements inside a large-size cavitation tunnel. The predictions agree well including the sheet cavitation development, tip vortex cavitation (TVC) bursting, convex shaped sheet cavitation closure line and the traveling re-entrant jet underneath the sheet cavity triggers the TVC bursting behavior. Noise predictions are performed within a large open simulation domain instead of the cavitation tunnel test section. With incompressible solutions, noise levels are predicted based on two different placements of Permeable/Porous Data Surfaces (PDS) where one encloses the cavitating propeller, rudder and downstream wake (PDS−L1) and one encloses the whole ship as a rectangular box (PDS−L2). The FWH noise predictions with impermeable surfaces (S−FWH) are also studied. Differences between predictions using PDS−L1, PDS−L2, and S−FWH are discussed. To compare calculated noise source level (Ls) at different noise receivers at varying distances, normalization assuming spherical spreading acoustic wave is used. In certain combinations of receiver point and method of acoustic computation, the predicted Ls agreed well comparing to experimental measurements, including the prediction with PDS−L2 and receiver close to the PDS and direct probed incompressible hydrodynamic pressure at similar receiver locations. However, with increasing distance to the receiver, the predicted Ls increases for higher frequencies and levels out at unrealistically high levels. To study this phenomenon, a free-field monopole representing the cavity structure dynamics is tested with different combination of PDS and receiver placements, using both incompressible and compressible input. This analysis gives a clear indication that the origin of this erroneous effect is the combination of the FWH acoustic analogy with an incompressible solver

Numerical investigation of propeller induced hull pressure pulses using RANS and IDDES

This paper investigates the numerical predictions of pressure pulses induced by a cavitating marine propeller operating in behind-hull condition in model scale. Simulations are performed using the commercial package Star-CCM+ using RANS and IDDES approaches. The predicted sheet cavitation agreed well compared to experimental recordings and the 1st- and 2ndorder blade passing frequency (BPF) pressure pulses also agreed well compared to measurements via pressure transducers mounted on the model scale ship hull. Tip vortex cavitation (TVC)bursting was observed in the experiments and predicted as well in the numerical simulations. A traveling re-entrant jet from blade leading edge to blade tip was predicted underneath the sheet cavity structure, and triggered the partly collapse of sheet cavitation and strong TVCdynamics. The hull pressure uctuations are found to be correlated with the rate of cavitation volume growth/shrinkage and the TVC dynamics are found generating high levels of higherorder BPF pressure pulses, according to the deduced TVC volume time series. Significant cavitation variations were recorded between blade passings and propeller revolutions in the experiments, while in the numerical predictions no noticeable cavitation difference was predicted, and the predicted 3rd- to 5th-order BPF pressure pulse tonal values are generally higher than experimental measurements. The cavitation variations in the experiments are suspected to be related with sheet cavitation inception rather than blade loading difference induced by wake dynamics

Investigation on RANS prediction of propeller induced pressure pulses and sheet-tip cavitation interactions in behind hull condition

This paper investigates the numerical prediction of cavitation and hull pressure pulses induced by a marine propeller operating in behind-hull conditions of a container vessel in model scale. Simulations are performed using commercial package Star-CCM+ and opensource package OpenFOAM using RANS approach and predictions are compared with experimental measurements. A mesh dependency study with respect to wake prediction is also presented. Operating conditions scaled to two different Reynolds numbers with the same propulsion characteristics and cavitation number are considered to study scaling effect. Simulations using tip refined mesh are performed and compared with using base mesh to study the tip vortex generation, tip vortex cavitation, its interaction with sheet cavity and induced pressure pulses. The influence of time step length is also investigated. Star-CCM+ and OpenFOAM predict consistent results. The predicted cavitation patterns agree well compared to experimental measurements as well as pressure pulse levels up to 3~4 times blade passing frequency (BPF) especially for the predictions with tip refined mesh. The sheet cavitation is the major contribution to 1st and 2nd order BPF pressure pulses and its closure has significant contributions to higher-order pressure pulses. Deduced pressure pulses by tip vortex cavitation (TVC) are significant ranging from 3rd order to 10th order of BPFs. The TVC induced pressure pulses are related to its violent bursting behavior which is influenced by the closure of the sheet cavity.\ua0\ua9 2020 Elsevier Lt