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The work presented here forms part of a project focusing on the development of cost-effective measures of classifying the noise levels from ship propellers with the use of numerical techniques available in OpenFOAM software. It is also related to the on-going research within the Faculty of Engineering and the Environment at the University of Southa...
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... interesting observation may be made when comparing the cavity extents just after the point of maximum lift for both implicit and explicit LES simulations, shown in Fig- ures 4 and 5, respectively. At this stage the attached sheet has been cut by the re-entrant jet close to the leading edge of the foil and starts being convected downstream to form a cloud. ...
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The work described here has been carried out as an MRE Knowledge exchange NERC Fellowship (NE/L014335/1) Developing and testing models of fish behaviour around tidal turbines. The
overarching aim of this project was to provide an evidence-based tool to forecast the effects of
anthropogenic noise on marine fish for Environmental Impact Assessments (...
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... Cavitation is a common physical phenomenon that occurs when the local fluid pressure drops to the saturated vapour pressure (Arndt, 2002;Long et al., 2017Long et al., , 2018. In engineering applications, cavitating flows are typically associated with complex shedding behavior (Correction Ji et al., 2014;Chen et al., 2021a;Ji et al., 2010), violent pressure fluctuations Wang et al., 2017), and high turbulence Coutier-Delgosha et al., 2003;Lidtke et al., 2014). The resulting transient pulsating force (Yu et al., 2019;Li et al., 2020a) can cause severe damage and noise pollution to hydraulic working parts, such as propellers (Sezen et al., 2021), pumps (Liu and Tan, 2020a), water turbines Tan, 2018, 2020b), and ship appendages (Ianniello et al., 2014a), among others. ...
... The time-averaged lift coefficient predicted by the PANS calculations was about 12% lower than the experimental value. Lidtke et al. (2014) investigated the same cases using three different turbulence models and observed clear differences in the predictions of the all approaches. It was mentioned that judging from the substantial difference between the RANS and LES approaches in both the lift and cavity volume variations, one may conclude that the latter should be used for this purpose whenever possible. ...
This paper presents the ongoing research on cavitation modelling so far which include validation studies to simulate the hydrodynamic characteristics of the Delft twisted hydrofoil and a controllable pitch propeller VP1304 (PPTC propeller) with zero shaft and inclined shaft cavitating flow conditions. Cavitating flow characteristics are modelled by performing Computational Fluid Dynamics (CFD) simulations using Detached Eddy Simulation (DES) method with SST (Menter) k-ω turbulence model. Multiphase viscous flow, water and air, are modelled using Eulerian multiphase approach and motion of the fluid volume throughout the computational domain is modelled with Volume of Fluid (VOF) approach capturing the interface. Cavitation is modelled by Schnerr-Sauer cavitation model with Reboud correction. The predicted three dimensional cavity structures around the twisted hydrofoil agree fairly well with the experimental observations given in open literature. Lift forces predicted using DES calculation are very close to that of the calculated ones, using a recommended quadratic function. The performance of the PPTC propeller for different conditions are conventionally represented in terms of non-dimensional coefficients, i.e., thrust coefficient, torque coefficient, and efficiency and cavity patterns on the propeller blades compared with the literature show good agreement with the experimental data.
... • parts of this work have been published as: [119], [120], [121], [122] [124], [125], [126], [133] Signed:.. ...
Anthropogenic noise from a variety of merchant ships has been reported to be a major factor adversely aecting marine organisms. Consequently, scientists and regulators have become more vocal about encouraging, and possibly enforcing, quieter ships in the future. For this to be feasible from an engineering standpoint, a range of numerical methods must be made available to allow acoustic performance of vessels to be evaluated at the design stage.
Cavitation is a major contributor to the hydroacoustic signature of a merchant vessel. The reason for this is the relatively high drop of pressure induced by the propeller, which in turn promotes the growth of vapour bubbles and cavities, oscillation and collapse of which act as strong acoustic sources. The entire process is made more dynamic by the non-uniform wake of the ship, propeller rotation, as well as the fact that vessels travel in a seaway. Because of its complexity, the problem of marine propeller noise is thus not widely studied numerically, which translates to the lack of tools readily available to designers willing to reduce the noise generated by ships.
A set of numerical utilities are proposed which could be employed at the late design stage of a merchant ship in order to allow the designer to estimate the radiated noise and make informed decisions on how to improve the design. The methodology involves solving the turbulent flow over the propeller using Detached Eddy Simulation (DES) and modelling cavitation using a mass-transfer model. The porous Ffowcs Williams-Hawkings acoustic analogy is used to infer far-eld radiated noise caused by the blade rotation, pulsating cavitation, as well as non-linear noise sources in the propeller slip-stream. The cavitation model is also extended to incorporate Lagrangian bubbles dispersed downstream of the large cavities modelled using the baseline Schnerr-Sauer model via the volume fraction equation approach. This allows the broadband nature of cavitation noise to be captured.
The methods are applied to a NACA 66 and the Delft Twist 11 hydrofoil test cases. Although there are limited validation data allowing all of the methods to be validated simultaneously, relatively good agreement is seen at intermediate validation stages. These include comparing the non-cavitating noise of the Insean E779a propeller to reference data, conducting acoustic predictions for idealised acoustic sources, as well as comparing cavitation patterns, cavity cloud shedding frequencies, and induced pressures to experimental data for hydrofoils and propellers.
It is concluded that the presented methodology may be used to predict low-frequency noise due to cavitation in a relatively robust manner, although the method is yet to be tested and validated on more complex geometries. The hybrid Eulerian-Lagrangian model is still at an early stage and a range of areas for improvement have been identified, such as implementation of more realistic cavity break-up models as well as better coupling between the fluid and bubble solvers. Nonetheless, the method is demonstrated to be a promising tool at tackling the broadband cavitation noise components as it can capture the contribution of the mass of small, oscillating bubbles on the radiated pressure which would otherwise be unaccounted for in the baseline Eulerian framework.
... A symmetric NACA0 0 09 foil section was studied, continuing the previous studies presented by the authors [44] . The test conditions, given in Table 2 , were based on those used by Foeth for the experimental Delft Foil test case [45] . ...
Concerns about pollution of the marine environment with ship-induced noise and the scarcity of available numerical methods have recently stimulated significant amounts of research in hydroacoustic modelling. In this work, Large Eddy Simulation (LES) is used with Schnerr–Sauer mass-transfer cavitation model and a porous Ffowcs Williams–Hawkings (FW-H) acoustic analogy in order to simulate sheet cavitation on a NACA0009 hydrofoil. The aim is to investigate how well the proposed method captures the dominant noise sources associated with periodic sheet cavitation. The study further focuses on practical aspects, such as the importance of the non-linear FW-H term and convergence of the acoustic solution depending on the choice of the integration surface. This is done by correlating the radiated noise with integral and local flow quantities, such as cavity volume, lift coefficient and local vapour content. A key finding of the study is that the simulation framework is capable of correctly capturing the monopole nature of the sound generated by an oscillating cavity sheet. Results indicate that the numerical method is incapable of accurately resolving the flow during the final collapse stages of smaller cavity clouds, mainly due to mesh density limitations and the use of an incompressible flow assumption. Lack of small-scale bubble structures also causes the high-frequency range of the noise spectra to be under-predicted. Despite certain limitations the presented method offers a significant insight into the nature of cavitation-dominated noise and allows for some of the dominant sound generating mechanisms to be categorised.
... This indicates that the presented method is well suited to provide information useful throughout the propeller design cycle. Unfortunately, unsteady RANS has been recognized as not being able to predict the unsteady behaviour of the cavities particularly well (Bensow, & Liefvendahl2008) (Lidtke et al. 2014), nor is it capable of resolving the tip vortex regions accurately. Both of these phenomena may be expected to play a significant role in the noise generation mechanisms of a marine propeller (Salvatore 2009). ...
... This indicates that the presented method is well suited to provide information useful throughout the propeller design cycle. Unsteady RANS is not able to predict the unsteady behaviour of the cavities particularly well (Bensow and Liefvendahl, 2008;Lidtke et al., 2014), nor is it capable of resolving the tip vortex regions accurately. Both of these phenomena may be expected to play a significant role in the noise generation mechanisms of a complete marine propeller (Salvatore, 2009). ...
There is increased interest in the ability to predict the noise associated with commercial ship propellers. Key components of the computational analysis process are considered for two test cases and the future direction in resolving the associated challenges is presented. Firstly, the Potsdam Propeller Test Case is used to compute tonal blade passage noise using the Ffowcs Williams-Hawkings acoustic analogy. Cavitation extents predicted using the Sauer and Schnerr mass transfer model agree well with the experiment but show little unsteadiness due to URANS being used. A complementary study of initial results from the study of cavitation noise modelling attempt is presented for a NACA0009 section, used as a simplified representation of a propeller blade. Large Eddy Simulation and FW-H acoustic analogy are used in order to estimate the cavitation-induced noise. Results indicate that the discussed approach provides the means for identifying low-frequency noise generation mechanisms in the flow, but does not allow for the fine-scale bubble dynamics or shockwave formation to be resolved. It is concluded that the discussed approach is a viable option to predict large parts of the marine propeller noise spectra but still further work is needed in order to account for the broadband components.
... This indicates that the presented method is well suited to provide information useful throughout the propeller design cycle. Unfortunately, unsteady RANS has been recognized as not being able to predict the unsteady behaviour of the cavities particularly well (Bensow, & Liefvendahl2008) (Lidtke et al. 2014), nor is it capable of resolving the tip vortex regions accurately. Both of these phenomena may be expected to play a significant role in the noise generation mechanisms of a marine propeller (Salvatore 2009). ...
Two computational studies are presented in this paper. First, the Potsdam Propeller Test Case which is used to demonstrate the capabilities of mass transfer cavitation models, more precisely the model by Sauer and Schnerr, in tackling the problem of marine propeller cavitation. It is shown that the extents of the predicted cavitation regions agree well with the experiment but suffer from the fact that the tip vortices and the associated low pressure regions are under resolved when URANS is utilised. Next, preliminary results from the study of cavitation noise modelling attempt are presented for a NACA 0009 section, used as a simplified representation of a propeller blade. Large Eddy Simulation and Ffowcs Williams-Hawkings porous acoustic analogy are used in order to estimate the cavitation-induced noise. Results indicate that the discussed approach provides the means for identifying low-frequency noise generation mechanisms in the flow, yielding sound pressure levels of the order of 40 dB re 20 microPa, but does not allow for finescale bubble dynamics to be resolved. One may conclude that the discussed approach is a viable option to predict large parts of marine propeller noise spectra but further work is needed in order to account for the high frequency components.
In this study, cavitating flow modeling around the Delft hydrofoil by using Computational Fluid Dynamics (CFD) is presented. In this context, 2 different cavitating flow conditions around the 3-D Delft hydrofoil are simulated. Drag and lift forces, cavitation volume on the hydrofoil and cavitation pattern are processed via CFD analysis. The results obtained from the CFD analysis are validated by the cavitation tunnel test results besides the results of various numerical analysis studies obtained from the literature.
In order to model the cavitation accurately with CFD; all properties of cavitating flows such as turbulence, unsteady pressure and velocity fluctuations, two-phase flow, mass transfer from liquid phase to vapor phase, three-dimensionality, viscosity, dynamics of cavitation bubbles and interactions between bubbles should also be included in the solution. In this study, cavitating flow is simulated by using various models for the aforementioned properties by means of rapidly developing computational technology. Three-dimensional, unsteady cavitating flow around the hydrofoil is solved by the Detached Eddy Simulation (DES) technique with the SST Menter k-⍵ turbulence model. Two phase flow is modelled by the Volume of Fluid (VOF) method. Cavitation is modeled by the Schnerr-Sauer cavitation model, which solves the simplified Rayleigh-Plesset bubble equation. In the analysis, simulations are carried out initially using normal meshes. Thus the regions, where high pressure, velocity fluctuations and cavitation occur are determined. Then the mesh is refined in those regions. Eventually, the regions where high pressure and velocity fluctuations and cavitation occur, have better mesh resolution. Also, the mesh density in the all computational domain is increased and the mesh is enhanced to match the DES model. In this way, the computational errors related to the mesh has been minimized. In addition, the analyses are repeated with three systematically refined meshes and three different time steps. Numerical uncertainties of the analysis under simulated flow conditions are calculated by using lift force results obtained from these analysis and it is demonstrated that the study is independent of grid and time.
