| 1. |
- Alin, Niklas, 1963, et al.
(författare)
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3D Unsteady Computations for Submarine-Like Bodies
- 2005
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Ingår i: 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan. 10-13, 2005. ; , s. 353-369
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Konferensbidrag (refereegranskat)abstract
- Results from a computational study using Unsteady Reynolds Averaged Navier Stokes (URANS) models and Large Eddy Simulation (LES) of flows past submarine-like bodies are here presented. The aims are to evaluate URANS and LES for high-Re number hydrodynamic flows, to investigate the influence of the turbulence and subgrid turbulence modeling, and to discuss some features of submarine hydrodynamics. For this purpose we have chosen to examine the flow past a prolate spheroid at 10° and 20° angle of attack at a body length Re number of 4-106, and the flow past the DARPA-2 Suboff bare hull and fully appended hull configurations at a body length Re number of 12-106. For both cases experimental data is available for comparison. One finite element and one finite volume flow solver has been used - both with the capability of employing a range of turbulence models and with the capacity of using unstructured and hybrid grids. Better agreement between predictions and experimental data is obtained with LES than with the URANS models, but at a considerably higher price, due to the finer grids and finer temporal resolution in LES.
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| 2. |
- Alin, Niklas, 1963, et al.
(författare)
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Current Capabilities of DES and LES for Submarines at Straight Course
- 2010
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Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 54:3, s. 184-196
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Tidskriftsartikel (refereegranskat)abstract
- The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both “towed” and “self-propelled” conditions, whereas for the bare hull, only a “towed” condition is considered. For the AFF1 and the “towed” AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.
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| 3. |
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| 4. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Numerical Assessment of Cavitation Erosion Risk in a Commercial Water-Jet Pump
- 2022
-
Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 144:5
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the risk of cavitation erosion is assessed in a commercial water-jet pump using a recently developed numerical erosion assessment method by Arabnejad et al. [1]. This assessment is performed for two flow conditions with different cavitation erosion risk according to the experimental paint tests and the high erosion risk areas identified by the method are compared with the experimental results. This comparison shows that the applied method is capable of both identifying the regions of high erosion risk and also capturing the difference between the cavitation erosion risk in the two studied conditions. The latter capability of the numerical assessment method, which has not been reported in the literature for other published methods, is one step forward toward the application of the method in the design process of hydraulic machines. Furthermore, the numerical results are analysed to explain the reasons for different erosion risk in the two conditions. This analysis reveals that this difference is mostly related to the stronger flow non-uniformities entering the rotor in the most erosive condition. Using the numerical results, one reason behind these stronger nonuniformities is identified to be the stronger bursting of vortices shed from the shaft in the most erosive condition.
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| 5. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Numerical assessment of cavitation erosion risk using incompressible simulation of cavitating flows
- 2021
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 464-465
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a numerical method to assess the risk of cavitation erosion is proposed, which can be applied to incompressible simulation approaches. The method is based on the energy description of cavitation erosion, which considers an energy transfer between the collapsing cavities and the eroded surface. The proposed framework provides two improvements compared with other published methods. First, it is based on the kinetic energy in the surrounding liquid during the collapse instead of the potential energy of collapsing cavities, which avoids the uncertainty regarding the calculation of the collapse driving pressure in the potential energy equation. Secondly, the approach considers both micro-jets and shock-waves as the mechanisms for cavitation erosion, while previous methods have taken into account only one of these erosion mechanisms. For validation, the proposed method is applied to the cavitating axisymmetric nozzle flow of Franc et al. (2011), and the predicted risk of cavitation erosion is compared with the experimental erosion pattern. This comparison shows that the areas predicted with high erosion risk agree qualitatively well with the experimental erosion pattern. Furthermore, as the current method can be used to study the relationship between the cavity dynamics and the risk of cavitation erosion, the hydrodynamic mechanism responsible for the high risk of cavitation erosion at the inception region of the sheet cavity is investigated in detail. It is shown for the first time that the risk of cavitation erosion in this region is closely tied to the separation of the flow entering the nozzle.
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| 6. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Scale resolving simulations of the non-cavitating and cavitating flows in an axial water jet pump
- 2020
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Ingår i: 33rd Symposium on Naval Hydrodynamics.
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Konferensbidrag (refereegranskat)abstract
- In this paper, the non-cavitating and cavitating flows in the AxWJ-2 axial water jet pump of Johns Hopkins University are simulated using a Large Eddy Simulation(LES) approach. The non-cavitating simulations are performed on grids with different mesh resolutions and the effect of mesh resolution on predicting the performance and capturing the structure of Tip Leakage Vortex (TLV) is investigated. Based on this investigation, it can be concluded that the main feature of the non-cavitating TLV can be well captured compared with the experiment provided that a refinement region with at least 40 cells in the tip gap is used. The cavitating simulation using the same grid refinement also shows that the cavitating structures described in the experiment are predicted by the simulation. Furthermore, the structure of non-cavitating and cavitating TLVs are compared and the effects of cavitation on the structure of TLV are analyzed using the simulation results.
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| 7. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Analysis of tip vortex inception prediction methods
- 2018
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 187-203
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Tidskriftsartikel (refereegranskat)abstract
- The current study investigates different cavitation inception prediction methods to characterize tip vortex flows around an elliptical foil, and a high skewed low-noise propeller. Adapted inception models cover different levels of complexity including wetted flow, Eulerian cavitation simulations, and Rayleigh-Plesset bubble dynamics models. The tip vortex flows are simulated by Implicit Large Eddy Simulation on appropriate grid resolutions for tip vortex propagation, at least 32 cells per vortex diameter according to previous studies guidelines. The results indicate that the cavitation inception predictions by the minimum pressure criterion of the wetted flow analysis are similar to weak water inception measurements. In the wetted flow analysis, the proposed energy criterion is noted to provide reasonably accurate inception predictions, similar to the predictions by Eulerian cavitation simulations with much lower computational costs. Comparison between high speed videos and numerical results of the propeller shows the capability of the numerical methodology in predicting tip vortex structures in different conditions. The interaction between vortices and their impact on the pressure field and the cavitation inception are also highlighted. The strong dependency of the inception on the initial nuclei sizes are demonstrated, and it is shown that for weaker tip vortices this dependency becomes more significant.
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| 8. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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COMPARATIVE ANALYSIS OF TIP VORTEX FLOW USING RANS AND LES
- 2017
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Ingår i: VII International Conference on Computational Methods in Marine Engineering.
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Konferensbidrag (refereegranskat)abstract
- The current study focuses on the numerical analysis of tip vortex flows, with the emphasis on the investigation of turbulence modelling effects on tip vortex prediction. The analysis includes comparison of RANS and LES methods at two different mesh resolutions. Implicit LES, ILES, modelling is employed here to mimic the turbulent viscosity. In RANS, the two equation k-ω SST model is adopted. In order to also address possible benefits of using streamline curvature variations in RANS, two curvature correction methods proposed for k-ω SST are tested, and compared. ILES results show very good agreement with the experimental observations. The predicted vortex in ILES is also stronger than RANS predictions. ILES has predicted accelerated vortex core axial velocity very well, while tested RANS models under predict the axial velocity. Adoption of curvature correction has not improved the tip vortex prediction, even though it has reduced the turbulent viscosity at the vortex core.
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| 9. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Evaluation of Curvature Correction Methods for Tip Vortex Prediction in SST kOmega Turbulence Model Framework
- 2019
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Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier BV. - 0142-727X. ; 75, s. 135-152
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents and studies effects of curvature correction (CC) methods to improve two equation RANS simulations of tip vortex flows, exemplified using the SST kOmega turbulence model. Performance of the CC models is first evaluated in the classical Rankine vortex flow field, and then extended into the study of tip vortex flows over an elliptical foil. The results have been compared with experimental measurements in terms of the vortex strength and velocity field, and the importance of the turbulence closure in tip vortex simulations is highlighted. Contribution of the CC models in different terms of the turbulent kinetic energy and specific dissipation transport equations are described, and it is discussed why a CC model may have mesh resolution dependent results. By considering the distribution of the CC function, it is shown that although some of the models can predict the location of the tip vortex core accurately, they still do not significantly improve the vortex prediction as the impact on the turbulent viscosity is wrong or not enough. It is further noted that as some of these models have been calibrated on specific vortex flows, they may not be completely applicable for other cases without recalibration. It is shown that some CC models provide accurate tip vortex predictions, primarily the ones based on the sensitization of the turbulent viscosity. Further, it is noteworthy that the successful models are active not only around the vortex, but also change the boundary layer characteristics on the foil, and the boundary layer separation lines, which consequently can provide the required momentum for the vortex core accelerated axial velocity.
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| 10. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Implicit Large Eddy Simulation of Tip Vortex on an Elliptical Foil
- 2017
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Ingår i: Fifth International Symposium on Marine Propulsion.
-
Konferensbidrag (refereegranskat)abstract
- In this study, Implicit Large Eddy Simulation (ILES) in OpenFOAM has been employed to study tip vortex flow on an elliptical foil. This type of foils has similar tip vortex behaviour as a propeller, making it a suitable benchmark for both numerical and experimental investigations of tip vortex flows in cavitating and non-cavitating conditions. The study includes investigation of the impact of streamwise and inplane mesh resolutions in tip vortex roll- up and its transportation. Vortex properties such as trajectory, axial and inplane velocity distributions, and also vortex core pressure distributions are computed for each mesh resolution and compared with available experimental data. Comparisons show that at least 16 cells per vortex diameter in inplane section is required to predict the tip vortex in the near field region. Results of varying foil angle of attack show the capability of the current numerical approach in ranking tip vortex properties. Employed numerical approach is fully capable of capturing the accelerated axial velocity at the vortex core for different operating conditions, and shows very good agreement with the experimental observations.
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| 11. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Investigations of Tip Vortex Mitigation By Using Roughness
- 2020
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1089-7666 .- 1070-6631. ; 32:6
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Tidskriftsartikel (refereegranskat)abstract
- The application of artificial roughness to mitigate tip vortex cavitation inception is analyzed through numerical and experimental investigations carried out on an elliptical foil. Different roughness configurations and sizes are tested and effects on cavitation inception, drag, and lift, are studied. Implicit Large Eddy Simulation (ILES) is employed to conduct the simulation on a proper grid resolution having the tip vortex spatial resolution as fine as 0.062 mm. Two different approaches including using a rough wall function and resolving the flow around roughness elements are evaluated. New experiments, performed in the cavitation tunnel at Kongsberg Hydrodynamic Research Centre, for the rough foil are presented. The vortical structures and vorticity magnitude distributions are employed to demonstrate how different roughness patterns and configurations contribute to the vortex roll-up and consequently on the tip vortex strength. It is found that the application of roughness on the leading edge, tip region and trailing edge of the suction side are acceptable to mitigate the tip vortex and also to limit the performance degradation. This is regarded to be in close relation with the way that the tip vortex forms in the studied operating condition. The analysis of boundary layer characteristics shows a separation line caused by roughness is the reason for a more even distribution of vorticity over the tip compared to the smooth foil condition leading to a reduction in vortex strength. For the optimum roughness pattern, both the numerical results and experimental measurements show a decrease in the tip vortex cavitation inception as large as 33 % compared to the smooth foil condition with a drag force increase observed to be less than 2 %.
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| 12. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Large Eddy Simulations of cavitating tip vortex flows
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 195
-
Tidskriftsartikel (refereegranskat)abstract
- In the current study, tip vortex flows are numerically studied by employing Large Eddy Simulation. Wet flow, cavitation inception, and cavitating tip vortex simulations are carried out on an elliptical foil. The mesh resolution requirements for tip vortex prediction are evaluated by employing different mesh resolutions. Two different LES models, Implicit LES and Localized Dynamic Kinematic Model, are utilized to model the sub-grid scale viscosity, and its impacts on the tip vortex prediction. For the wet flow, vortex properties are computed for each resolution and compared with experimental data. Comparisons show that at least 16 cells per vortex radius is required to predict the tip vortex in the near field region. Employed numerical approach is fully capable of capturing the accelerated axial velocity at the vortex core, and shows good agreement with the experimental observations. The analysis of bubble dynamics shows that tip vortex inception strongly depends on the initial bubble radius, especially where the radius is smaller than 50 μm. The predicted azimuthal velocity, the diameter of the cavitating tip vortex, and the velocity flow fields are compared with experimental measurements. The comparisons show that the current numerical approach can provide accurate prediction of tip vortex flows also in cavitating conditions.
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| 13. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Numerical and experimental analysis of cavitation inception behaviour for high-skewed low-noise propellers
- 2018
-
Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187. ; 79, s. 197-214
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Tidskriftsartikel (refereegranskat)abstract
- Numerical and experimental investigations of two highly skewed low-noise propellers with a slight alteration in the tip geometry are conducted in both wetted and cavitating flows. The performance of the propellers is measured in open water and inclined setups at different operating conditions and high speed video recordings are used to determine tip vortex cavitation inception behaviour. The numerical simulations are conducted by employing the Implicit Large Eddy Simulation on appropriate grid resolutions for tip vortex propagation, at least 32 cells per vortex diameter according to our previous studies. In order to investigate cavitation inception characteristics of the propellers, different inception prediction methods are employed and evaluated at different advance ratios. It is shown that in addition to the well-captured difference in e.g. the amount of cavitation, the simulations are capable of correctly predicting the small but crucial differences in flow features and cavitation inception characteristics of the two propeller designs. Numerical predictions of the cavitation inception charts are also compared successfully with the measured data where three different types of cavitation patterns are investigated in details. Supported by the experimental videos, the interaction between the tip vortex and trailing vortices and their impact on the pressure field and the cavitation inception are analyzed. It is shown that the numerical simulation can provide further details about the vortical flow structures, and their contributions to cavitation, and is a powerful tool in advanced propeller design stages.
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| 14. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Propeller tip vortex cavitation mitigation using roughness
- 2019
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Ingår i: 8th International Conference on Computational Methods in Marine Engineering, MARINE 2019. - 9788494919435 ; , s. 383-392
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Konferensbidrag (refereegranskat)abstract
- This paper presents an investigation of roughness application on marine propellers in order to alter their tip vortex properties, and consequently mitigate tip vortex cavitation. SST kOmega model along with a curvature correction is employed to simulate the flow on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter. The roughness is modelled by using a rough wall function to increase the turbulent properties in roughed areas. In one case, roughness geometry is included as a part of the blade geometry, and the flow around them are resolved. To minimize the negative effects of the roughness on the propeller performance, the roughness area is optimized by simultaneous consideration of the tip vortex mitigation and performance degradation. For the considered operating condition, it is found that having roughness on the tip region of suction side can reduce the cavitation inception by 18 % while keeping the performance degradation in a reasonable range, less than 2%.
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| 15. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Propeller tip vortex mitigation by roughness application
- 2021
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Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187. ; 106
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the application of surface roughness on model and full scale marine propellers in order to mitigate tip vortex cavitation is evaluated. To model the turbulence, SST k−ω model along with a curvature correction is employed to simulate the flow on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter according to our previous guidelines. The effect of roughness is modelled by modified wall functions. The analysis focuses on two types of vortices appearing on marine propellers: tip vortices developing in lower advance ratio numbers and leading edge tip vortices developing in higher advance ratio numbers. It is shown that as the origin and formation of these two types of vortices differ, different roughness patterns are needed to mitigate them with respect to performance degradation of propeller performance. Our findings clarify that the combination of having roughness on the blade tip and a limited area on the leading edge is the optimum roughness pattern where a reasonable balance between tip vortex cavitation mitigation and performance degradation can be achieved. This pattern in model scale condition leads to an average TVC mitigation of 37% with an average performance degradation of 1.8% while in full scale condition an average TVC mitigation of 22% and performance degradation of 1.4% are obtained.
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| 16. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Roughness Effects on the Tip Vortex Strength and Cavitation Inception
- 2019
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Ingår i: Proceedings of the ... International Symposium on Marine Propulsors. - 2414-6129. - 9788876170478 ; 1, s. 267-273
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Konferensbidrag (refereegranskat)abstract
- The possibility and effectiveness of roughness application to mitigate tip vortex flows are evaluated by numerical simulations of an elliptical foil. The analysis includes investigation of the roughness size and area covered by the roughness, as well as the impact on the cavitation inception. Implicit Large Eddy Simulation (ILES) in OpenFOAM has been employed along with a wall-function incorporating the roughness effects to conduct the simulation on a proper grid resolution having the tip vortex spatial resolution as fine as 0.062 mm. The impact of the roughness size on the tip vortex is noted, and it is observed that for the studied condition, the roughness size of 250 micor m is sufficient. The negative effects of roughness on the forces are also observed where application of roughness leads to lower lift and higher drag forces. To minimize the negative effects of the roughness on the performance, the roughness area optimization is conducted and it is found that the application of roughness on the leading edge and trailing edge of the suction side are acceptable to mitigate the tip vortex and also to limit the performance degradation. This is regarded to be in close relation with the way that the tip vortex forms in the studied operating condition. The study shows while the inception occurs at the cavitation number equal to 6.35 in the smooth condition, application of the roughness on the optimum area will delay the inception to the cavitation number equal to 4.1 while only increasing the drag coefficient 1.7 %. This is found to be in a good agreement with the experimental measurements.
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| 17. |
- Bensow, Rickard, 1972, et al.
(författare)
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Controlled Surface Roughness Application in Tip Vortex Mitigation and Inception Delay
- 2021
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Ingår i: 11th International Symposium on Cavitation (CAV2021).
-
Konferensbidrag (refereegranskat)abstract
- The current study summarizes findings of the RoughProp project aiming to develop and utilize controlled surface roughness to mitigate tip vortex cavitation (TVC). The analysis is conducted through numerical and experimental investigations of tip vortex flows over an elliptical foil and a high-skewed propeller by focusing on how the roughness should be applied to have an optimum balance between TVC mitigation and hydrodynamic performance degradation. To model the tip vortex, LES is employed on a proper grid resolution having at least 32 grid points across the tip vortex diameter. The CFD analysis is supported by new sets of experiments conducted in the cavitation tunnel at Kongsberg Hydrodynamic Research Centre. The outcome of CFD results and experimental observations clarify the capability of roughness application in TVC mitigation with a reasonable performance degradation. For the propeller, it is found that the combination of having roughness on the blade tip and a limited area on the leading edge is the optimum roughness pattern that can provide a reasonable balance between tip vortex cavitation mitigation and performance degradation over a wide range of operating conditions. This pattern leads to an average TVC mitigation of 21% with an average performance degradation of 1.5%.
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| 18. |
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| 19. |
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| 20. |
- Bensow, Rickard, 1972, et al.
(författare)
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Large Eddy Simulations for Marine Flows
- 2007
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Ingår i: STG-Lectureday "CFD in Ship Design", Hamburg, Germany.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 21. |
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| 22. |
- Ge, Muye, 1991, et al.
(författare)
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Improved prediction of sheet cavitation inception using bridged transition sensitive turbulence model and cavitation model
- 2021
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Ge, Muye, 1991, et al.
(författare)
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Investigation on Numerical Prediction of Propeller Induced Hull Pressure Pulses
- 2018
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Ingår i: Proceedings of the 10th International Symposium on Cavitation (CAV2018). - : ASME Press. - 9780791861851
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 24. |
- Ge, Muye, 1991, et al.
(författare)
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Investigation on RANS prediction of propeller induced pressure pulses and sheet-tip cavitation interactions in behind hull condition
- 2020
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- 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. © 2020 Elsevier Ltd
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| 25. |
- Ge, Muye, 1991, et al.
(författare)
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Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Ge, Muye, 1991, et al.
(författare)
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Numerical investigation of pressure pulse predictions for propellers mounted on an inclined shaft
- 2019
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Ingår i: Proceedings of the Sixth International Symposium on Marine Propulsors. - 2414-6129. - 9788876170478 ; 1, s. 284-292
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Konferensbidrag (refereegranskat)abstract
- 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 cavitation mass transfer model, massive cavitation was predicted which lead to inaccurate pressure pulse predictions. The transition sensitive turbulence model γ − Re θ model is used to study the cases, and simulation results reveal the 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.
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| 27. |
- Ge, Muye, 1991, et al.
(författare)
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Numerical investigation of propeller induced hull pressure pulses using RANS and IDDES
- 2021
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Ingår i: Proceedings of IX International Conference on Computational Methods in Marine Engineering.
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Konferensbidrag (refereegranskat)abstract
- 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 TVC dynamics. 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.
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| 28. |
- Ge, Muye, 1991, et al.
(författare)
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Numerical investigation of tip vortex bursting and induced hull pressure pulses on a container vessel
- 2021
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Ingår i: Proceedings of the 11th International Symposium on Cavitation (CAV2021).
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 29. |
- Ghahramani, Ebrahim, 1988, et al.
(författare)
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Numerical Simulation of Tip Vortex Cavitation Inception
- 2021
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Ingår i: Proceedings of the 11th International Symposium on Cavitation (CAV2021).
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Konferensbidrag (refereegranskat)abstract
- Tip vortex cavitating flow is known as challenging to study. The objective of this paper is to investigate the effective parameters in numerical modelling of tip vortex cavitation (TVC) inception through the comparison of three different models. The models are (1) a commonly used homogenous mixture model, in which inception is based on pressure drop criterion; (2) a Lagrangian bubble model, in which cavitation is initiated from free nuclei in the liquid; and (3) a hybrid Eulerian-Lagrangian model, in which the cavities are initiated based on the pressure drop criterion, but the growth of initially small cavities are modelled using the more accurate Lagrangian equations. The simulations are conducted on the tip vortex flow around an elliptical foil. The results show that the commonly applied pressure drop assumption is not a sufficient criterion for cavitation inception. Also, it is seen that the water quality and nuclei transport towards the vortex core influence the cavity pattern at inception.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Svennberg, Urban, 1967, et al.
(författare)
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Experimental analysis of tip vortex cavitation mitigation by controlled surface roughness
- 2020
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Ingår i: Journal of Hydrodynamics. - : Springer Science and Business Media LLC. - 1001-6058 .- 1878-0342. ; 20:73
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Tidskriftsartikel (refereegranskat)abstract
- This study presents the results of experiments where roughness applications are evaluated in delaying the tip vortex cavitation inception of an elliptical foil. High-speed video recordings and laser doppler velocimetry (LDV) measurements are employed to provide further details on the cavitation behavior and tip vortex flow properties in different roughness pattern configurations. The angular momentum measurements of the vortex core region at one chord length downstream of the tip indicate that roughness leads to a lower angular momentum compared with the smooth foil condition while the vortex core radius remains similar in the smooth and roughened conditions. The observations show that the cavitation number for tip vortex cavitation inception is reduced by 33% in the optimized roughness pattern compared with the smooth foil condition where the drag force increase is observed to be around 2%. During the tests, no obvious differences in the cavitation inception properties of uniform and non-uniform roughness distributions are observed. However, the drag force is found to be higher with a non-uniform roughness distribution.
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| 35. |
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| 36. |
- svennberg, urban, et al.
(författare)
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New Insights into Roughness Applications in Tip Vortex Cavitation Inception Mitigation
- 2020
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Ingår i: Symposium on Naval Hydrodynamics.
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Konferensbidrag (refereegranskat)abstract
- Tip vortex cavitation (TVC) is usually the first type of cavitation that appears on a propeller. Therefore, it is considered as the main cavitation characteristics to avoid in the design procedure of low-noise propellers, where their operating profiles demand very low radiated noise emissions. The current study includes both numerical and experimental analyses of blade surface roughness application in order to mitigate TVC inception. The investigation consists of applying roughness application on a classical benchmark, an elliptical foil, and on a propeller selected from a Kongs-berg research series of highly skewed propellers having a low effective tip load. The numerical simulations are performed on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter by using Implicit Large Eddy Simulation (ILES) for unsteady simulations, and RANS using the SST k − ω model with a curvature correction for steady simulations. Two approaches are considered to include roughness in the numerical simulations: using a rough wall function and resolving the flow around the roughness elements. To minimize the negative effects of the roughness on the propeller performance, the roughness area is optimized by simultaneous consideration of the tip vortex mitigation and performance degradation. Experimental measurements of the elliptical foil are conducted to support the CFD study at different operating conditions and with different roughness patterns while LDV and high-speed video recordings are used to collect the data. The tested conditions include both cavitating and inception of TV flows on the smooth and roughened foil to provide further insights on the usage of roughness. For the elliptical foil, it is found that the application of roughness can reduce the cavitation number for cavitation inception, σ i , by 35 % while keeping the performance degradation less than 1% compared to the smooth foil condition. The average reduction of the TVC inception number achieved by using roughness on the propeller is around 21% with a performance degradation of around 1.5% compared to the smooth propeller condition.
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| 37. |
- Svennberg, Urban, 1967
(författare)
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On Turbulence Modelling for Bilge Vortices: A Test of Eight Models for Three Cases
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is a test, in three steps, of turbulence models for the calculation of the flow field around ships. Eight models ranging from k-e and k-w models to a Reynolds-stress model (RSM) are tested. All three of the steps contain vortices: the first is the case of a vortex in a free- stream, the second is a vortex pair embedded in a turbulent boundary layer, and the third is the flow field, with vortices, around a ship hull. The first case is divided into three parts which are all vortices in a free-stream but have different axial velocities in the vortex core; this tests the capability of the models to predict the shear stress driven decay of a vortex. The second case tests the capacities to predict the decay of a vortex in a turbulent environment and to predict a boundary layer with cross-flow. The third case adds to the problem the formation of a vortex over a curved surface, a boundary layer over curved surfaces and pressure gradients. The RSM model gave the most accurate results in a majority of the cases. The simpler turbulence models turned out to be the best for one of the parts in the first case. One combination of the k-e and k-w models (SST) predicted the most accurate resistance in the third case; it also predicted the second most accurate flow field at the propeller plane. One of the algebraic stress models (CLS) had approximately the same values as the RSM in the first case. It gave results in closer agreement with the RSM model than the other models in the second case; it was also among the three best models in the third case when the overall flow field was of concern. The SST model is an alternative to the RSM model (which may be too expensive), for wall-bounded flows with adverse pressure gradients. The CLS model is an alternative for other flows containing vortices.
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| 38. |
- Vikström, Marko, et al.
(författare)
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The Effect of Porous Data Surface Shape and Size on Ship Noise Prediction using the FWH Acoustic Analogy with Incompressible Solver for a Cavitating Propeller
- 2022
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Ingår i: Proceedings of the seventh International Symposium on Marine Propulsors - smp'22. - 2414-6129. - 9788269112030 ; , s. 166-173
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Konferensbidrag (refereegranskat)abstract
- Using Ffowcs-Williams and Hawkings (FWH) acoustic analogy with an incompressible solver has become a rather common approach for ship noise prediction. Here the method is studied for a model scale container vessel. The numerical study includes both the ship hull and a rotating propeller, using the sliding mesh approach. The simulations are performed for a condition with cavitation around the tip of the propeller blades to study the propeller induced noise including the contribution from cavitation. To complement this study, e.g., to exclude any wall reflections and rotating sources, an additional pure monopole source case study was performed with both incompressible and compressible methodology. Since cavitation is a volume source acoustic term there is a need to use a Porous Data Surface (PDS) in combination with the FWH acoustic analogy. The choice of PDS shape and size using FWH is studied both for the model scale container vessel as well as for the pure monopole source case. The results show that when using different PDS shapes, a directionality effect is evident when using the incompressible solver. The Sound Pressure Level (SPL) is dependent on the receiver angular location in relation to the PDS. The directionality effect is largest for a PDS shape where there is a large variation in distance from the source to the PDS faces, e.g. box. Furthermore, there is also a receiver distance discrepancy for the incompressible solver with FWH. The SPL curves for different receiver distance do not coincide for higher frequencies. Using a compressible solver and FWH, the shape effect and receiver distance discrepancy is not present.
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| 39. |
- Zhang, Baili, et al.
(författare)
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CFD modeling of propeller tip vortex over large distances
- 2013
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. - 9781880653999 ; , s. 947-952
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Konferensbidrag (refereegranskat)abstract
- In this paper, a numerical study has been conducted to investigate the evolution of a ship propeller tip vortex over large distance using Reynolds-averaged Navier Stokes (RANS) CFD method. In order to reduce numerical dissipation in tracking the tip vortex, a unique hybrid mesh structure was designed and a vorticity confinement method is also introduced to further enhance the high resolution of the tip vortex.
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