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- 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. |
- Alves Lopes, Rui Miguel, 1992, et al.
(author)
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Resistance Decomposition of a Self-propelled Ship in Full Scale
- 2023
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Conference paper (other academic/artistic)abstract
- The simulation of ships at full scale includes several physically challenging aspects for Computational Fluid Dynamics such as wall roughness [1], free-surface effects, and interaction effects (e.g. between the hull and propeller) when considering self-propulsion scenarios where the propeller is included. On the other hand, the high Reynolds number (around 10^9) observed in these flows results in a high computational cost for CFD, due to the thin boundary-layer that develops along the hull, requiring an extremely large cell count if wall functions are not used. A third obstacle lies in the lack of measured data to compare the results against [2], which makes validation of the results impossible. In this paper, the flow around the JoRes 1 vessel is considered, for which measured data at full-scale is available through the efforts of the JoRes project [3]. Several sets of simulations with the Reynolds-Averaged Navier-Stokes equations are performed for this geometry, with a focus on the friction and pressure components of the resistance: a self-propulsion setup, fully resolving the propeller, a double-body setup with the propeller, to shed some light on the resistance due to the waves and a double-body setup without the propeller, which will be used in order to investigate the propeller-hull interaction. Different approaches for the surface roughness are considered as well, and grid refinement studies are performed in order to quantify the numerical error. The distinct simulation setups will assist in understanding the relative importance of each aspect, and provide a clearer picture in the comparison of the results obtained in the complete self-propulsion simulations with the sea trial data. REFERENCES [1] J. Anderson, D. R. Oliveira, I. Yeginbayeva, M. Leer-Andersen and R. Bensow, “Review and comparison of methods to model ship hull roughness”, Applied Ocean Research, Vol. 99, (2020). [2] H. Jasak, V. Vukcevic, I. Gatin and I. Lolovic, “CFD validation and grid sensitivity studies of full scale ship self propulsion”. International Journal of Naval Architecture and Ocean Engineering, Vol. 11, pp 33-43, (2019). [3] D. Ponkratov and G. D. Struijk, “JoRes JIP – a unique Joint Industry Project to close the knowledge gap on Ship Hydrodynamics”, Full Scale Ship Performance Conference, the Royal Institution of Naval Architect, London, UK, (October 2018).
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| 4. |
- Khraisat, Qais, 1995, et al.
(author)
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Assessing Scale Effects on a Propeller in Uniform Inflow Condition
- 2023
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In: NuTTS 2023 - 25th Numerical Towing Tank Symposium Proceedings.
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Conference paper (peer-reviewed)abstract
- Open water testing for model scales is a universally accepted method to evaluate the thrust, torque, and efficiency of a propeller. Even so, due to the Reynolds number dissimilarity in tests, the development of the boundary layer and the natural transition to turbulence is not the same. This creates discrepancies in the force ratios known as scale effects. To overcome this issue, the standardized ITTC 78 method was developed as an extrapolation procedure to estimate the full scale propeller delivered power and performance. With the development of Computational Fluid Dynamics numerical tools, the scaling issue could be avoided by modeling the geometry in its real sea conditions. This paper aims at studying the scaling effects of a marine propeller in uniform open water condition. The geometry can be described as a moderately skewed 4-bladed controllable pitch propeller mounted on a simplified hub, and the geometrical scaling ratio for the model λ = 27.143. A comparison of the propeller performance across a range of advance ratios J at varying scales will be presented. Results of the numerical simulations will be compared with model scale experimental measurements carried out at Kongsberg’s research facility. The overall aim of this study is to gain a perception of how the scaling effects will influence the performance of this specific propeller.
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