| 1. |
- Alves Lopes, Rui Miguel, 1992, et al.
(author)
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A numerical study on the influence of crossflow transition on a marine propeller in open water
- 2024
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In: Ocean Engineering. - 0029-8018. ; 310
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Journal article (peer-reviewed)abstract
- This work studies the influence of crossflow transition modelling on the performance and flow field of a controllable pitch propeller. The simulations are performed for two different crossflow terms, and baseline simulations without crossflow transition are performed as well. The results show that in the absence of a crossflow term, the flow over the propeller blades is almost fully laminar. When a crossflow term is included, a significant part of the flow becomes turbulent, thus causing a decrease in the thrust and torque coefficients. The change in the propeller performance is also due to the absence of laminar flow separation near the trailing edge, which is prevented when transition occurs upstream of that location due to crossflow. The comparison between the two crossflow terms shows that one always leads to a larger extent of turbulent flow and earlier transition than the other, although this not always translates in lower thrust and torque, depending on the considered advance coefficient. This illustrates the delicate balance in the effects taking place on the pressure and suction side of the propeller blades, and the importance of correctly including crossflow effects in simulations of model-scale propellers.
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| 2. |
- Alves Lopes, Rui Miguel, 1992, et al.
(author)
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Numerical assessment of surface roughness on a full scale propeller
- 2024
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In: Proceedings of the 8th International Symposium on Marine Propulsors.
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Conference paper (peer-reviewed)abstract
- This work addresses the performance of a full scale propeller in an open water setup for varying roughness heights, obtained with a RANS solver and the k-omega SST turbulence model. The application of roughness is done with wall functions and by resolving the boundary-layer. Two cases are considered for the same propeller geometry, one with and another without the anti-singing edge on the propeller blades. Baseline simulations without roughness are performed as well, and grid refinement studies are carried out to estimate the numerical uncertainty. The results showed that the influence of roughness is weak if wall functions are not used, whereas a significant decrease in thrust and torque is obtained if roughness is applied in conjunction with wall functions. The inclusion of the anti-singing edge leads to an increase in thrust and torque, but decrease in efficiency for low advance coefficients. The region of separated flow near the trailing edge of the propeller caused by the anti-singing edge is influenced by the roughness height, and is absent in the geometry without the anti-singing edge.
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| 3. |
- Andersson, Jennie, 1986, et al.
(author)
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CFD Simulations of the Japan Bulk Carrier Test Case
- 2015
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In: NUMERICAL TOWING TANK SYMPOSIUM. 18TH 2015. (NUTTS 2015). - 9781510815858
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Conference paper (peer-reviewed)abstract
- This computational fluid dynamics (CFD) validation study is performed as a foundation for further studies with focus on the interaction effects between propulsor and hull. To be able to study the interaction effects, an appropriate CFD methodology need to be established and validated for a bare hull, for the propulsion unit and for the combined system, a self-propelled hull. The work to validate a CFD model is initiated through the use of the JBC, Japan Bulk Carrier, open test case. The JBC test case is developed for the 2015 workshop on CFD in Ship Hydrodynamics. The tested JBC only exists in model scale with scale factor 1:40 (LPP = 7 m). Model ship speed is 1.179 m/s, corresponding to Fn = 0.142 and 14.5 kn, only calm water conditions are tested. There are two variants of the hull, with and without an energy saving device, within this study the one without is used. Test data used for validation of the CFD results are from towing tank experiments at NMRI. The aim of further studies is to study propulsor hull interaction in full scale, but since detailed test data in full scale is limited, all computations will be performed in model scale. The commercial CFD package STAR-CCM+, a finite volume method solver, is employed for all studies. STAR-CCM+ is a general purpose CFD code used for a wide variety of applications. It solves the conservation equations for momentum and mass, turbulence quantities and volume fraction of water using a segregated solver based on the SIMPLE-algorithm. A 2nd order upwind discretization scheme in space is used. It is of interest to study how a general purpose code can perform for detailed ship hydrodynamic analyses and which limitations that could be identified.
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| 4. |
- Andersson, Jennie, 1986, et al.
(author)
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Energy balance analysis of a propeller in open water
- 2018
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In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 158, s. 162-170
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Journal article (peer-reviewed)abstract
- This paper proposes a methodology based on control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results, for analyzing ship propulsion interaction effects as a complement to the well-established terminology, including thrust deduction, wake fraction and propulsive efficiency. The method, titled Energy Balance Analysis, is demonstrated on a propeller operating in open water. Through consideration of a complete energy balance, including kinetic energy flux, turbulent kinetic energy flux, internal energy flux (originating from dissipation) and pressure work, all possible hydrodynamic losses are included in the analysis, implying that it should be possible to avoid sub-optimized solutions. The results for different control volumes and grid refinements are compared. The deviation of the power obtained from the proposed energy balance analysis relative to the power based on integrated forces on the propeller is less than 1%. The method is considered promising for analyzing and understanding propulsor hull interaction for conventional, as well as novel propulsion configurations. The energy balance analysis is conducted as a post-processing step and could be used in automated optimization procedures.
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| 5. |
- Andersson, Jennie, 1986, et al.
(author)
-
Energy balance analysis of model-scale vessel with open and ducted propeller configuration
- 2018
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In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 369-379
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Journal article (peer-reviewed)abstract
- This paper focuses on performance analysis of a model scale vessel equipped with an open versus a ducted propeller in self-propulsion using a control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results. An energy balance analysis decompose the delivered power for each system into internal and turbulent kinetic energy fluxes, i.e. viscous losses, transverse kinetic energy losses, and pressure work and axial kinetic energy fluxes. Such a decomposition can facilitate understanding of system performance and pinpoint enhancement possibilities. For this specific case it is shown that the much higher required power for the ducted propeller configuration to the largest extent is due to higher viscous losses, caused by mainly propeller duct and different rudder configuration. The energy balance analysis is a post-processing tool with the only additional requirement of solving the energy equation, which can be employed with any CFD-code based on commonly available variables.
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| 6. |
- Andersson, Jennie, 1986, et al.
(author)
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On the Selection of Optimal Propeller Diameter for a 120-m Cargo Vessel
- 2021
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In: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 65:2, s. 153-166
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Journal article (peer-reviewed)abstract
- In the preliminary design of a propulsion unit, the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is, however, not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics to study a 120-m cargo vessel with an integrated rudder bulb–propeller hubcap system and a four-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3–4% smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system.
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| 7. |
- Andersson, Jennie, 1986, et al.
(author)
-
On the Selection of Optimal Propeller Diameter for a 120m Cargo Vessel
- 2018
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In: SNAME 15th Propeller and Shafting Symposium, PSS 2018.
-
Conference paper (peer-reviewed)abstract
- In the preliminary design of a propulsion unit the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is however not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics (CFD) to study a 120m cargo vessel with an integrated rudder bulb-propeller hubcap system and a 4-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3-4 % smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system
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| 8. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(author)
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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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In: 33rd Symposium on Naval Hydrodynamics.
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Conference paper (peer-reviewed)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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| 9. |
- Eslamdoost, Arash, 1982, et al.
(author)
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A body-force model for waterjet pump simulation
- 2019
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In: Applied Ocean Research. - : Elsevier BV. - 0141-1187. ; 90
-
Journal article (peer-reviewed)abstract
- The role of waterjet pump is to generate thrust by increasing the flow head. Details of the flow inside waterjet pump are important when pump performance is of the main interest. However, in waterjet self-propulsion, pump induced effects are of the main interest rather than the details of the flow inside the pump. This permits sim- plification of pump models when using numerical methods for simulating the flow. In order to find a robust and yet accurate pump model suitable for Computational Fluid Dynamics based methods, models of different so- phistication level are studied in this paper. First, a Sliding Mesh approach, which is capable of capturing the flow details, is validated against a set of cavitation tunnel measurements. Then a series of simpler models, i.e. Moving Reference Frame technique and three different body-force models, are studied and their results are compared to the ones obtained from the Sliding Mesh approach. The results indicate that one of the body-force models which takes the guide vanes as well as the impeller induced flow swirl into account has the best compromise between the robustness and accuracy among the investigated pump models.
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| 10. |
- Eslamdoost, Arash, 1982, et al.
(author)
-
A device for reducing the resistance of transom stern hulls
- 2021
-
In: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 235
-
Journal article (peer-reviewed)abstract
- A novel idea to reduce the resistance of a transom stern hull in displacement and semi-planing modes is investigated. By placing a spoon-shaped device in the recirculating zone behind the transom, the momentum of the forward-moving water will be absorbed, and a pushing force generated on the device. Numerical and experimental techniques are applied on a transom stern hull to optimize the shape and position of the device and to explore in detail the physics behind the gain. For the towed hull at a Froude number of 0.4, the maximum measured resistance reduction is 11%, while the computed maximum reduction is 17%. In self-propulsion with one propeller, the measured power reduction is 15%. The power cannot be computed with the applied propeller model, which is an axial body-force distribution in the propeller disk, but the reduction in thrust using the device is 11%. More significant gains are possible at smaller Froude numbers, while the effect is reduced at higher Froude numbers. Larger gains are achieved by splitting the thrust on two propellers. © 2021 The Authors
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