INSEAN E779A Research Articles

Hydroacoustic analysis of a full-scale marine vessel: Prediction of the cavitation-induced underwater radiated noise using large eddy simulations

This numerical study provides insight into the mechanism of noise generation by a cavitating flow in the wake of a marine propeller under realistic operating conditions, which poses a significant threat to marine ecosystems. We examined a full-scale vessel with an entire hull and an isolated model-scale marine propeller (INSEAN E779A) with a maneuverable rudder under various highly turbulent inflow conditions that strongly affect the spectral characteristics of the radiated noise. Insight into the acoustic behavior was gained by employing a combination of the large eddy simulation (LES) treatment of turbulence and the Schnerr–Sauer volume of fluid cavitation model. The hydrodynamic solution was coupled with the Ffowcs Williams-Hawkings (FW-H) strategy for noise and vibration identification. We focused on the interactions between the characteristic cavitation patterns of marine propellers (sheet, tip, and hub cavities) and the dominant structures of the turbulent wake (tip, root, trailing edge, and hub vortices, as well as the distributed small-scale vorticity). The small-scale topological structures in the swirling wake of a propeller directly manifest in the radiated sound level and affect the intensity of multiple frequency ranges. Quantitative analysis of thrust, pressure fluctuations, and sound pressure levels (SPLs) demonstrates significant effects of blade loading, wake distribution, and cavitation development. The peak and average SPL distributions obtained through LES show lower dominant and higher average frequencies compared to those obtained by the FW-H method. The overall SPL obtained by LES were higher than those calculated using the FW-H acoustic analogy at all microphone locations. The overall noise was dominated by the low-frequency broadband noise, attributed to energetic helical vortices, and narrow-band peaks in the medium-high frequency range that originated from other sources, like cavitation structures.

Acoustic signature and wake structure investigation of a cavitating marine propeller operating in proximity to a rudder with an optimized leading-edge pattern

The present study implements high-fidelity numerical modeling to investigate the cavitating flow around a marine propeller operating upstream of a rudder with an optimized wavy leading-edge (WLE), based on a NACA 634-021 profile bio-inspired by a pectoral flipper of a humpback whale (Megaptera novaeangliae). The aim of the study work is to identify the acoustic signature and wake structure of the propeller-rudder system, comparing it to that with a straight leading-edge (SLE) rudder. The propeller (INSEAN E779A model) operated under diverse marine maneuvering conditions (rudder angles of attack α = 0°, 10°, and 20°) with three distinct leading-edge patterns of the rudder. Large eddy simulations (LES) in conjunction with the Sauer cavitation method and the compressive volume of fluid (VOF) model were utilized to simulate the unsteady cavitating flow using the OpenFOAM platform. Additionally, the Ffowcs Williams–Hawkings (FW-H) acoustic analogy, continuous wavelet transform (CWT), and fast Fourier transform (FFT) were employed to predict and analyze the hydroacoustic response. We propose an optimized propeller-rudder configuration for minimizing the radiated sound levels, thus mitigating the harmful effects of noise pollution on marine ecosystems, while maintaining high propulsive efficiency over a wide range of operating conditions.

Noise field properties of marine propellers in open water

Aim of the paper is to gain a physical understanding of the main noise generating mechanisms related to vorticity and turbulence downstream the disk of a marine propeller in open water. Through the application of the Ffowcs Williams and Hawkings acoustic analogy (FWH) for permeable surfaces, the analysis of the noise field generated by the INSEAN E779A propeller model at different advancing ratios allows to detect correlations between acoustic signatures in the near/mid field and wake evolution. Turbulence noise-induced effects are captured by combining the FWH formulation with a Detached Eddy Simulation (DES) of the flow past the propeller. Besides, a phase-locked post-processing of the unsteady DES data on the acoustic surface is used to yield FWH signatures governed by vorticity effects, which are then compared with the pressure fluctuations predicted by the Bernoulli equation, within a potential hydrodynamics platform solved by a Boundary Integral Element Method (BIEM). It is found that turbulence is the most annoying source of propeller noise, whereas vorticity-driven phenomena are important only in a narrow region surrounding the propeller. Moreover, numerical results highlight that acoustic pressures are correlated to the vortex pairing hydrodynamic phenomenon associated to a blade-to-shaft harmonic energy transfer, detected in literature by time-resolved visualizations and velocimetry measurements.

On wake dynamics of a propeller operating under nonuniform behind-hull condition

The wake dynamics of the benchmark propeller INSEAN E779A operating in the nonuniform wake of a typical ship hull are investigated with large-eddy simulations. The flow features and evolution of vortex structures in the propeller wake are analyzed to evaluate the influences of the nonuniform inflow and to identify the instability mechanisms. Unlike the uniform inflow condition, the azimuthal-variant inflow velocity field results in an asymmetric and faster destabilization of the wake. Local mutual interaction among the neighboring tip vortices in the upper region of the wake, which shows a unique bridging-reconnection mechanism of vortex filaments, initiates the decomposition and destabilization of tip vortices and induces instability in the hub vortex. The power spectrum density (PSD) of kinetic energy is employed to analyze the transition characteristics of the tip vortices quantitatively. The hub vortex core circularity and trajectory envelope are calculated to quantify the long- and short-wave instabilities.

Enhancement of the Robustness on Advancing Layer Method with Trimmed Hexahedral Volume Mesh for the Generation of the Boundary Layer Grids

When performing simulations using computational fluid dynamics, the grid systems in the viscous boundary layer regions are important because the velocity and pressure change very rapidly in these regions. Especially for the turbulent flows, thin grids should be arranged densely in the direction perpendicular to the wall. In this study, the advancing layer method, which has been applied mostly to tetrahedral meshes, is applied to trimmed hexahedral meshes. To generate boundary layer meshes with non-intersecting grid lines near the wall boundaries having concave corners and narrow gaps, the directional vectors of grid lines and faces are smoothed, and the displacement vector fields calculated using the Laplace equation were utilized. Firstly, the details on the newly developed methods are introduced showing simple two-dimensional cases as examples. After applying the methods for a complex three-dimensional geometry to check its applicability and investigating the generated grid systems, the numerical simulations of propeller open water test for INSEAN E779A marine propeller were carried out by simpleFoam, one of the standard solvers of OpenFOAM. The computational results showed good agreement with the experimental results. Therefore, in conclusion, the developed advancing layer method is an appropriate method for generating boundary layer grids of a trimmed hexahedral mesh.

CFD Simulations of the Effect of Equalizing Duct Configurations on Cavitating Flow around a Propeller

This study presented the results of a computational study of cavitating flows of a marine propeller with energy saving equalizing ducts. The main purpose of the study was to estimate the cavitating flows around a propeller with a duct, and to investigate the interaction between a duct and a propeller in cavitating flows. The INSEAN E779A propeller was used as a baseline model. Validation studies were conducted for non-cavitating and cavitating flows around a hydrofoil and a propeller. A comparison with the experimental data showed good agreement in terms of sheet cavity patterns and propulsion performances of the propeller. Various duct configurations have been presented, and it was found that a duct in front of the propeller had effects on the propeller’s cavitation and propulsion performance. Higher angles of attack of the duct showed a significant effect on the propeller’s cavitation behavior, especially with a small duct. The small duct lowered the cavitation inception radius with increase in angle of attack of the duct, while the large duct had more effect on the tip cavitation. The propeller with large duct gave higher thrust, however, the higher torque loading affected the propeller efficiency. Overall, it was found that the propeller with small duct provided a higher propeller efficiency

The Effect of Mewis Duct Energy Saving Device to Propeller Performance

Installation of ESD (Energy Saving Device) can improve ship propulsion performance. Mewis Duct is one type of ESD (Energy Saving Device) multi-component device that combines nozzle and fin into the nozzle. The structure can minimize losses due to small losses at the ship's stern and rotational losses or loss of thrust in the slipstreams area. Mewis Duct can reduce power by about 3-8% and increase thrust on the propeller by about 2-5%. This study aims to improve the performance of the INSEAN e779a propeller type using Mewis Duct. The modified Mewis ducts are the number of fins four, five, six asymmetrical and four symmetrical fins using the computational fluid dynamics (CFD) approach. The CFD code is based on the RANS (Reynolds - Averaged Navier Stokes) equation with the turbulent model is k-ε. This study found that installing Mewis duct as ESD in a ship increased the propeller thrust by 3-5% and the torque by 3-4%.

Marine propeller shaft loading analysis in moderate oblique-flow conditions

Shaft loads of marine propellers in noncavitating oblique-flow conditions are herein investigated. The application of a Boundary Element Method (BEM) hydrodynamics is verified by the analysis of two propeller models, the highly-skewed DTMB 4679 and the unskewed INSEAN E779A, for which a comparison with experimental and numerical data is addressed. Whenever available, outcomes from PROCAL, a validated panel code solver developed by MARIN, and simulations from higher-fidelity CFD (Computational Fluid Dynamics) approaches, are used for comparison purposes. For moderate oblique-inflow angles, the comparison with experiments shows a good capability of the proposed BEM formulation in capturing unsteady blade pressures. In terms of shaft loads fluctuations, satisfactory results are carried out with respect to CFD outcomes. Moreover, it is found that averaged thrust and torque, as well as the lateral and vertical moments, are comparable with PROCAL predictions and in good agreement with CFD computations, whereas lateral forces suffer from the lack of a realistic estimation of viscous effects. Good estimates are also shown for the average location of thrust eccentricity, as long as the transverse loading on the hub is negligible.

A numerical investigation of the effect of blade number on the performance of an INSEAN E779A marine propeller in a cavitating flow using computational fluid dynamics

A propeller's thrust coefficient, efficiency, and torque coefficient are important performance characteristics. They can be harmed by the presence of cavitating flow. Previous numerical studies have shown that cavitating flow can damage a marine propeller as well as reduce its performance. The work presented here investigates the effect of blade number variation on the performance of an INSEAN E779A marine propeller in a cavitating flow. The cavitating flow simulations are performed using computational fluid dynamics with four different rotational and inlet speeds using the fully turbulent standard k-ε model and the Schnerr-Sauer cavitation model. The numerical results of varying the number of blades on propeller performance characteristics are presented here. It is concluded that increasing the number of propeller blades improves propeller performance. In contrast, the cavitation area is reduced, but cavitation is more likely to occur as rotational speed increases.

Contribution of tip and hub vortex to the structural response of a marine rudder in the propeller slipstream

The structural design of the rudder, traditionally based on quasisteady loads generated during worst manoeuvres, should account for load fluctuations associated with the interaction with the wake of the propeller in order to comply with the more stringent requirements on ship vibration and noise pollution. In this context, the present work analyses the dynamic response of a marine rudder located in the wake of the INSEAN E779A propeller by the one-way fluid–structure interaction approach. The time-dependent pressure distribution on the rudder, obtained through detached eddy simulation, is used to evaluate the pressure field that is the input for a structural solver to determine the resulting deformations and stresses. The computations consider the propeller at moderate loading, and rudder deflection angles at neutral and $4^{\circ }$ . The analysis discusses the different contribution of the tip and hub vortex of the propeller on the static and vibratory response of the rudder in the two configurations.

An alternative Vorticity based Adaptive Mesh Refinement (V-AMR) technique for tip vortex cavitation modelling of propellers using CFD methods

ABSTRACT This study focuses on the investigation of cavitating flow around the benchmark INSEAN E779A model propeller with the main aim of further improving the computational efficiency of the tip vortex cavitation (TVC) modelling by using a commercial CFD solver. Also, the effects of various key computational parameters including, numerical modelling, grid size, timestep, water quality and boundary layer resolution, on the TVC formation and its extension in the propeller slipstream are investigated systematically. The numerical simulations are conducted in uniform and open water conditions using RANS, DES and LES solvers implemented in the commercial CFD code, Start CCM+. In order to achieve the aim of the study, an alternative and new Vorticity-based Adaptive Mesh Refinement (V-AMR) technique is introduced for enhanced modelling of the TVC on the blades and downstream. For the CFD modelling of cavitation, the Schneer Sauer cavitation model based on the reduced Rayleigh Plesset equation is used for the sheet, tip and hub vortex cavitation. The hydrodynamic results and cavity patterns are validated with the experimental data. The results show that the application of the V-AMR technique further improves the representation of the TVC with minimal increase in computational cost. However, the eddy viscosity at the propeller blade tips increases with applying the V-AMR technique using the RANS solver due to its inherent modelling errors for the solution of the flow inside the tip vortex. This consequently results in an insufficient extension of TVC in the propeller slipstream compared to the predictions by the DES and LES based numerical solvers. Also, the evolution of the TVC is found to be sensitive to the boundary layer resolution when the standard RANS solver is used. The study will help to widen further applications of the CFD methods involving TVC, particularly for propeller induced underwater noise prediction and analysis.

Effect of biofouling roughness on a marine propeller's performance including cavitation and underwater radiated noise (URN)

This study aims to investigate the effects of biofouling-related roughness on a propeller's hydrodynamic and underwater radiated noise (URN) performance. Selected benchmark INSEAN E779A propeller operated in uniform & open water flow under non-cavitating and cavitating conditions. The hydrodynamic flow field around the propeller was first solved using RANS (Reynolds-averaged Navier Stokes) solver. The Schnerr-Sauer cavitation model, based on reduced Rayleigh-Plesset equation, was used to model the sheet cavitation on the propeller blades and tip vortex cavitation (TVC) in the propeller's slipstream. A vorticity-based Adaptive Mesh Refinement (AMR) technique was employed for the observation of TVC. The porous form of the Ffowcs-Williams Hawkings (P-FWH) equation, which is coupled with the RANS solver, was used to predict the URN (or hydroacoustic performance) of the propeller. The propeller performance characteristics, including cavitation, were validated with the available experimental data. Following that, the roughness functions representing the different roughness configurations obtained from the literature were employed using wall function model of Computational Fluid Dynamics (CFD) solver. The results showed that roughness has detrimental impacts on the propeller's performance characteristics. That is to say that the propeller's thrust decreases while the torque increases with increasing severity of the roughness. Hence, the efficiency loss of the propeller at the most severe roughness condition can be as high as 30% and 25% at J = 0.795 and J = 0.71 & σ=1.763, respectively. Unlike its detrimental effects on the hydrodynamic performance, the roughness had some positive effects by reducing the cavitation volume, especially for the TVC and hence on the propeller underwater radiated noise (URN). The results also indicated that the URN levels might be reduced up to 10 dB between 1 kHz and 2 kHz. Besides, 2nd and 3rd BPF values decrease between 1 and 7 dB under varying roughness configurations in comparison to the smooth case. The study reported the effect of a particular biofouling roughness on the URN levels of a propeller for the first time in model-scale and using the CFD simulations.

Numerical investigation of marine propeller Underwater Radiated Noise using acoustic analogy part 1: The influence of grid resolution

This study investigates the effects of grid resolution on hydroacoustic performance of the benchmark INSEAN E779A propeller operated in uniform flow, open water and non-cavitating conditions. In the numerical calculations, an incompressible hydrodynamic solver together with the porous FW-H (Ffowcs-Williams Hawkings) equation is used to predict the propeller URN (Underwater Radiated Noise). The first aim within this study is to explore the sensitivity of the grid resolution on the prediction of propeller hydroacoustic performance. Furthermore, amongst the contribution of nonlinear noise sources on overall acoustic pressure, the role of the tip vortex is believed to be dominant under non-cavitating conditions. The inadequate extension of the tip vortex is one of the drawbacks in the RANS (Reynolds-averaged Navier-Stokes) solver for accurate prediction of propeller URN, especially at the receivers located in the propeller's slipstream. Thus, the second aim within this study is to examine the contribution of tip vortex on overall acoustic pressure. In order to visualise the numerical noise and determine the realistic extension of the vortex distributions in the propeller's slipstream, the time derivative of the pressure technique is proposed in this study. The results indicate that insufficient grid resolution in the numerical simulations causes unphysical numerical noise which is attributed to the sliding interfaces, and it leads to contamination of the overall acoustic pressures. Moreover, an increase in grid resolution reduces numerical diffusion in the RANS solver, allowing for an extended tip vortex distribution. However, an increase in tip vortex extension and intensity alongside the downstream of the propeller is not adequate itself to make a reliable prediction of propeller URN by using RANS. Consequently, a more realistic prediction of propeller URN requires the use of advanced models (i.e. LES (Large Eddy Simulation) and DES (Detached Eddy Simulation)) together with the porous FW-H equation, particularly if the receivers located in the downstream are of great interest.

Numerical investigation of marine propeller underwater radiated noise using acoustic analogy Part 2: The influence of eddy viscosity turbulence models

The present study focuses on the impact of eddy viscosity turbulence models on the benchmark INSEAN E779A marine propeller hydroacoustic performance under non-cavitating and open water conditions. In the numerical calculations, Realisable k-epsilon (k-ε), k-ω Shear Stress Transport (k-ω SST) and Spalart-Allmaras turbulence models, which are widely used in hydrodynamic fields, are selected. Hydroacoustic performance of the model propeller is predicted with the porous FW-H formulation coupled with Reynolds-averaged Navier Stokes (RANS) solver. This study aims to show the effects of different turbulence models on marine propeller hydroacoustic performance at high and low blade loading conditions both in the near and far-fields. The numerical results show that the underwater radiated noise (URN) levels, which are predicted by using different eddy viscosity turbulence models together with the porous FW-H formulation, are found to be similar at low blade loading conditions. The reason behind this similarity is due to the analogous wake structure and hydrodynamic field. However, when the propeller loading is high, the propeller's wake loses its stability; hence, the coherent vortex structures break-up and evolve into the far-field of the propeller's slipstream. The instability process of the propeller's wake is predicted in a different manner by eddy viscosity turbulence models, and these differences cause dissimilar prediction of the URN in the far-field. Consequently, the underwater pressure field is considerably affected by the instability of the vortex structures (as a non-linear noise source) for far-field noise estimations. As a result, vortex instability in the propeller's slipstream might be the main noise source of the URN for far-field noise estimations under non-cavitating and high blade loading conditions.

Numerical Study on the Unsteady Characteristics of the Propeller Cavitation in Uniform and Nonuniform Wake Flows

Propeller cavitation is a problematic issue because of its negative effects, such as performances losses, noise, vibration and erosion. Numerical methodology is an effective and efficient technical tool for the study of propeller cavitation, however, it is hard to capture tip-vortex cavitation in the previous work by using common turbulence models based on turbulent-viscosity hypothesis. In this work, the Reynolds-Averaged Naiver-Stokes (RANS) approach, adopting the Reynolds stress turbulence model (RSM), is taken to study the unsteady characteristics of the cavitation on the four-bladed INSEAN E779A model propeller. The numerical simulation was carried out using the commercial CFD software ANSYS Fluent 14.0. One kind of uniform wake flow and two kinds of nonuniform wake flows are considered here. The results in the uniform flow show a good agreement with previous experimental results on both the sheet cavitation and the tip vortex cavitation and prove the ability of the RSM on capturing the tip vortex cavitation. Two kinds of nonuniform wake flows are designed based on the previous experimental researches and the unsteady characteristics of the propeller cavitation are analyzed by comparing the results in the uniform and two nonuniform wake flows together.

On the instability mechanisms of ship propeller wakes

This paper evaluates the propeller wake characteristics of the benchmark ship propeller INSEAN E779A using large eddy simulations and identifies instability mechanisms that lead to wake breakdown. The effects of propeller blade loading on wake stability are considered by conducting simulations at different advance coefficients (J = 0.85, J = 0.65 and J = 0.45). The hydrodynamic results capture the propeller wake vortical structures and flow features from the onset and evolution of the instability to the far wake. The simulation results are verified and validated against experimental measurements from the literature. A new instability mechanism concerning mutual interaction among adjacent helical vortex sheets in the transition region is identified. Further, the formation of short wave instabilities in the vortex filaments is found to be initiated by the same mutual interactions among sheets. Lastly, it is shown that interaction of sheets with the preceding tip vortex induces the onset of tip vortical filaments breakup, mutual-interaction and long wave instability.

Numerical simulation of propeller wake vortex–rudder interaction in oblique flows

ABSTRACT The Large Eddy Simulation (LES) method was used to study the interaction between propeller wake and a rudder. The INSEAN E779A propeller and the NACA0020 rudder were used, and the method was employed to analyse the vortices. The evolution of the propeller-wake in oblique flows and the effect of oblique flows on the propeller wake vortex were studied. The pulsating pressures on the rudder surface for different oblique-flow angles were compared. The results show that the hydrodynamic coefficients of the propeller and the rudder increased under oblique flows. The vortex of the propeller shifted as the angle changed, but it did not completely coincide with the oblique-flow angle. Under the effects of the propeller-wake, the rudder surface generated a pulsating pressure. The frequency of this pulsating pressure relates to the blade frequency of the propeller, and the amplitude of the pulsating pressure increased with the oblique-flow angle.

The Numerical Analysis of Marine-Ship Propeller

In this paper, numerical simulationwas done to decide the hydrodynamic qualities in a cavitatingviscous stream of the standard INSEAN E779A in single and couple propeller arrangement utilizing cavitation show executed in FLUENT Software. Next, figure

Numerical prediction of sheet cavitation on marine propellers using CFD simulation with transition-sensitive turbulence model

One of the big challenges, yet to be addressed, in the numerical simulation of cavitating flow on marine propellers is; the existence of laminar and turbulence transition flows over the propeller’s blades. The majority of previous studies employed turbulence models that were only appropriate for fully turbulent flows. These models mostly caused high discrepancies between numerical predictions and experimental measurements especially at low rotational speeds where, Reynolds number decreases and laminar and transient flows exist. The present paper proposes a complete and detailed procedure for the CFD simulation of cavitating flow on marine propellers using the ‘K-Kl-ω’ transition-sensitive model. Results are obtained using ‘ANSYS FLUENT 16’. The propeller under consideration is the ‘INSEAN E779A’ propeller model. The fully turbulent standard ‘k-ε’ model is also adopted for comparison. Obtained results, based on both turbulence models, are validated by comparison with experimental data available in the literature. Predictions based on the ‘K-Kl-ω’ transition-sensitive model are found to be in better agreement with experiments at lower rotational speeds i.e. at low Reynolds numbers.

An improved Mesh Adaption and Refinement approach to Cavitation Simulation (MARCS) of propellers

This paper presents the improvements of cavitation modelling for marine propellers particularly developing tip vortex cavitation. The main purpose of the study is to devise a new approach for modelling tip vortex cavitation using Computational Fluid Dynamics (CFD) methods with commercial software, STAR-CCM+. The INSEAN E779A model propeller was used for this study as a benchmark propeller. Utilizing this propeller, firstly, validation studies were conducted in non-cavitating conditions together with grid and time step uncertainty studies. Then, the cavitation was simulated on the propeller using a numerical cavitation model, which is known as the Schnerr–Sauer model, based on the Rayleigh-Plesset equation. While a Reynolds Averaged Navier Stokes (RANS) model was used for open water simulations, Detached Eddy Simulations (DES) and Large Eddy Simulations (LES) models were preferred for cavitation simulations to capture the cavitation and evaluate its effect on propeller performance accurately. Although the comparison with the benchmark experimental data showed good agreement for the thrust and torque coefficients as well as sheet cavitation pattern, tip vortex cavitation could not be adequately simulated using the existing method. After an evaluation of the interaction between cavitation modelling and generated meshes, two techniques, which involved volumetric control and adaptive mesh refinement, were used in combination on the region where the tip vortex cavitation is likely to occur. The first technique, which is called a ‘volumetric control method’, was developed using spiral geometry around the propeller tip region to generate a finer mesh for capturing tip vortex cavitation. Although this method gave better tip vortex cavitation extension than the method without any mesh refinement or with tube refinement, it still required to be improved to extend the tip vortices further into the propeller slipstream. The second method, which is called ‘adaptive mesh refinement’, was introduced using the pressure distribution data from the results of the ‘volumetric control method’. This improved approach, which is called “Mesh Adaption and Refinement for Cavitation Simulation (MARCS)”, has been successfully applied to simulate the tip vortices trailing from the blades of the INSEAN E779A propeller as demonstrated in the paper. The results of the simulations showed an excellent agreement with the experiments in the open literature by tracking the tip vortex cavitation along this propeller's slipstream.