| 1. |
- Ghahramani, Ebrahim, 1988, et al.
(författare)
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A comparative study between numerical methods in simulation of cavitating bubbles
- 2019
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 111, s. 339-359
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the performance of three different numerical approaches in cavitation modelling are compared by studying two benchmark test cases to understand the capabilities and limitations of each method. Two of the methods are the well established compressible thermodynamic equilibrium mixture model and the incompressible transport equation finite mass transfer mixture model, which are compared with a third method, a recently developed Lagrangian discrete bubble model. In the Lagrangian model, the continuum flow field is treated similar to the finite mass transfer approach, however the cavities are represented by individual bubbles. Further, for the Lagrangian model, different ways to consider how the fluid pressure influences bubble dynamics are studied, including a novel way by considering the local pressure effect in the Rayleigh–Plesset equation. The first case studied is the Rayleigh collapse of a single bubble, which helps to understand each model behaviour in capturing the cavity interface and the surrounding pressure variations. The special differences between the Lagrangian and finite mass transfer models in this case clarify some possible origin for some limitations of the latter method. The second investigated case is the collapse of a cluster of bubbles, where the collapse of each bubble is affected by the dynamics of surrounding bubbles. This case confirms the importance of considering local pressure in the improved form of the Rayleigh–Plesset equation and illustrates the influence of the liquid compressibility for cavity modelling and appropriate capturing of the collapse pressure.
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| 2. |
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| 3. |
- Ghahramani, Ebrahim, 1988, et al.
(författare)
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Realizability improvements to a hybrid mixture-bubble model for simulation of cavitating flows
- 2018
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Ingår i: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 174, s. 135-143
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Tidskriftsartikel (refereegranskat)abstract
- Cavitating multi-phase flows include an extensive range of cavity structures with different length scales, from micro bubbles to large sheet cavities that may fully cover the surface of a device. To avoid high computational expenses, incompressible transport equation models are considered a practical option for simulation of large scale cavitating flows, normally with limited representation of the small scale vapour structures. To improve the resolution of all scales of cavity structures in these models at a moderate additional computational cost, a possible approach is to develop a hybrid Eulerian mixture -Lagrangian bubble solver in which the larger cavities are considered in the Eulerian framework and the small (sub-grid) structures are tracked as Lagrangian bubbles. A critical step in developing such hybrid models is the correct transition of the cavity structures from the Eulerian mixture to a Lagrangian discrete bubble framework. In this paper, such a multi-scale model for numerical simulation of cavitating flows is described and some encountered numerical issues for Eulerian–Lagrangian transition are presented. To address these issues, a new improved formulation is developed, and simulation results are presented that show the issues are overcome in the new model.
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| 4. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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A Methodology to Indentify Erosive Collapse Events in Numerical Simulation of Cavitating Flows
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, a numerical method based on the EroCav handbook is presented for assessment of risk of erosive, useable in an incompressible simulation model. This numerical method tracks each collapsing cavity and save its kinematic features up to the final collapse. These kinematic features are then used to estimate the erosiveness based on an equation derived from a parametric study on the collapse of spherical bubbles. The proposed numerical method is applied for the cavitating flow over a 3D NACA0015 foil. Erosive collapse events are indentified and their locations are compared with experimental erosion pattern by Rijsbergen et al.[5]. The comparison shows that the proposed model is able to predict the location of erosive collapse in the middle of foil and the areas close to the side walls.
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| 5. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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A novel single-fluid cavitation model with gas content and slip velocity, applied to cavitating tip leakage vortex
- 2023
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Ingår i: International Journal of Multiphase Flow. - 0301-9322. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we develop a new model based on the single-fluid approach which consider the effects of gas content and slip velocity between the gas/vapor phase and the liquid phase in cavitation modeling. The derivation of the mathematical formulation of the model is presented in the context of Large Eddy Simulation (LES), although a similar derivation can be developed for a Reynolds-averaged Navier–Stokes (RANS) framework. To validate the model and to study the effect of including this physics, a cavitating Tip Leakage Vortex (TLV) formed around the NACA0009 foil is simulated. The results of the simulation are compared with the available experimental data and the results obtained from a conventional single-fluid approach. This comparison shows that the new model predicts cavitation regions in significantly better agreement with the experimental data, compared to the conventional single-fluid approach. This better agreement is observed for both the cavitation regions in the TLV and the cavitation regions at the leading edge. Analyzing the results, the reason for this significant improvement is shown to be the accumulation of non-dissolved gas due to the consideration of the slip velocity, and the effect of this accumulation in the cavitation formation. Furthermore, the effects of gas content and the size of nuclei in the incoming flow to the TLV are investigated, and these effects are discussed in detail.
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| 6. |
- Arabnejad Khanouki, Mohammad Hossein, 1988
(författare)
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Assessment of cavitation erosion risk based on single-fluid simulation of cavitating flows
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cavitation erosion is material loss due to the repetitive collapse of cavities near the surface. This phenomenon is one of the limiting factors in the design of high-performance marine propulsors as it restricts their reliability and increases their operational cost. To avoid such consequences, erosion assessment using experimental methods are traditionally performed in the design process of marine propulsors. These methods are, however, expensive and can be applied only in model-scale at a late stage of the design. Alternative to these are numerical assessment methods which can be applied both in model-scale and full-scale at any stage of the design. Development and application of such numerical methods are the main objectives of this thesis. Two numerical erosion assessment methods are included in this thesis and both are based on single-fluid simulation of cavitating flows. The first method which is developed in this thesis, can assess the risk of cavitation erosion based on incompressible simulations of cavitating flows. This method which considers an energy transfer between collapsing cavities and eroded surface, offers two advantages over other published methods. First, the method takes into account both shock-waves and micro-jets as the mechanisms for cavitation erosion, while previous published methods have considered only one of these erosion mechanisms. Secondly, the method estimates the risk of cavitation erosion based on the collapse induced kinetic energy in the surrounding liquid 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. The second numerical assessment method is based on compressible simulation of cavitating flows which has been developed by Schnerr et al. [1] and Mihatsch et al. [2]. This method captures the collapse-induced shock-waves and uses the strength and the frequency of these shock-waves to identify the erosion-sensitive areas. These numerical assessment methods are implemented in the OpenFOAM framework and the implementation has been validated against analytical solutions and an experimental study. Using the above mentioned numerical assessment methods, three types of cavitating flows are investigated. These are 3D leading edge cavitation over a wing, a cavitating flow in an axisymmetric nozzle, and cavitating flows in water-jet pumps. For the leading edge cavitation, the numerical methods are combined with experimental techniques in order to investigate the relation between the shedding mechanisms of transient cavities and aggressive collapse events. This investigation shows that the leading-edge cavitation leads to the shedding of small and large-scale cavitating structures, both of which are associated with high risk of cavitation erosion. The small-scale cavitating structures are, however, shown to possess a higher risk of cavitation erosion, as they result in a large number of aggressive collapse events which are close to the surface. The second studied case is the cavitating flow in an axisymmetric nozzle which is simulated with the objective of validating the numerical erosion assessment methods included in this thesis. The risk of cavitation erosion predicted by these methods is compared with the experimental erosion investigation by Franc et al. [3] and this comparison shows both methods are capable of identifying areas with high erosion risk. Furthermore, using the numerical results, the hydrodynamic mechanism responsible for the high risk of cavitation erosion at the inception region of the sheet cavity is investigated in detail. This investigation indicates that the high erosion risk in this region is closely tied to the separation of the flow entering the nozzle. The third type of studied flow is the cavitating flow in water-jet pumps. These cavitating flows are numerically investigated with two specific objectives, 1) to identify the mesh resolution requirement for high quality simulation of water-jet pumps, 2) to perform numerical erosion assessment on water jet pumps. For the first objective, the AxWJ-2 pump from Johns Hopkins University is simulated using different mesh resolutions and the results are compared with available experimental data in the literature. For the second objective, the cavitating flows in a commercial water-jet pump are investigated. The investigation includes applying the developed incompressible erosion assessment method to two flow conditions with different risk of cavitation erosion. The results of these numerical erosion assessments are compared with the experimental paint tests performed at Kongs- berg Hydrodynamic Research Centre (KHRC). This comparison shows that the developed numerical erosion assessment method is not only able to distinguish between the conditions with different levels of cavitation erosion risk but also capable of identifying the regions of high erosion risk in the most erosive flow condition. Furthermore, the hydrodynamic mechanisms leading to different risk of cavitation erosion in the two studied conditions are investigated using numerical simulation results. It is shown that this difference is due to a different distribution of axial velocity in the flow entering the pump in the two studied conditions.
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| 7. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Experimental and Numerical Investigation of the Cavitating Flows over a Modified NACA0009 Foil
- 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
- In this study, the cavitating flow over a modified NACA0009 foil has been investigated using experimental and numerical methods. In the experimental investigation, high-speed visualization is used to study the behavior of the cavitating flow at ? = 1.2, ? = 5, ? = 20?/?. In order to identify the location of erosive collapse, a preliminary soft paint test is performed. In the numerical part of this study, the flow condition subjected to the soft paint study is simulated with Large Eddy Simulation using a mixture assumption coupled with the Schnerr-Sauer mass transfer model. In order to validate the simulation, the numerical results are compared with experimental high-speed visualization of the flow at the same condition. These comparisons show that the numerical simulation is capable of reproducing the main features of the cavitating flow. The validated numerical results and the high-speed visualization are then used to explain the hydrodynamic mechanism of erosive events that have been identified in the experimental investigation.
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| 8. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Hydrodynamic mechanisms of aggressive collapse events in leading edge cavitation
- 2020
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Ingår i: Journal of Hydrodynamics. - : Springer Science and Business Media LLC. - 1001-6058 .- 1878-0342. ; 32:1, s. 6-19
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Tidskriftsartikel (refereegranskat)abstract
- Transient cavities generated from unsteady leading-edge cavitation may undergo aggressive collapses which are responsible for cavitation erosion. In this paper, we studied the hydrodynamic mechanisms of these events in the leading edge cavitation formed over a modified NACA0009 hydrofoil using experimental and numerical methods. In the experimental investigation, high-speed visualization (HSV) and paint test are employed to study the behavior of the cavitating flow at σ = 1.25, β = 5°, U∞ = 20 m/s. In the numerical part, the same cavitating flow is simulated using an inviscid density-based compressible solver with a barotropic cavitation model. The numerical results are first compared with the experimental HSV to show that the simulation is able to reproduce the main features of the cavitating flow. Then, as the compressible solver is capable of capturing the shock wave upon the collapse of cavities, the location of collapse events with high erosion potential are determined. The location of these collapse events are compared with the paint test results with a qualitatively good agreement. It is clearly observed, in both the experiments and the numerical simulation, that there exists four distinct regions along the hydrofoil with higher risks of erosion: (1) A very narrow strip at the leading edge, (2) an area of accumulated collapses at around 60 percent of the sheet cavity maximum length, (3) an area around the closure line of the sheet cavity with the highest erosion damage, and (4) a wide area close to the trailing edge with dispersed collapse events. A combined analysis of the experimental and numerical results reveals that the small-scale structures generated by secondary shedding are more aggressive than the large-scale cloud cavities (primary shedding). It is also observed that the high risk of cavitation erosion in regions 2 and 3 is mainly due to the collapses of the small cavity structures that are formed around the sheet cavity closure line or the rolling cloud cavity.
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| 9. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Investigation of Flow-Induced Instabilities in a Francis Turbine Operating in Non-Cavitating and Cavitating Part-Load Conditions
- 2023
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Ingår i: Fluids. - : MDPI AG. - 2311-5521. ; 8:2
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Tidskriftsartikel (refereegranskat)abstract
- The integration of intermittent renewable energy resources to the grid system requires that hydro turbines regularly operate at part-load conditions. Reliable operation of hydro turbines at these conditions is typically limited by the formation of a Rotating Vortex Rope (RVR) in the draft tube. In this paper, we investigate the formation of this vortex using the scale-resolving methods SST-SAS, wall-modeled LES (WMLES), and zonal WMLES. The numerical results are first validated against the available experimental data, and then analyzed to explain the effect of using different scale-resolving methods in detail. It is revealed that although all methods can capture the main features of the RVRs, the WMLES method provides the best quantitative agreement between the simulation results and experiment. Furthermore, cavitating simulations are performed using WMLES method to study the effect of cavitation on the flow in the turbine. These effects of cavitation are shown to be highly dependent on the amount of vapor in the RVR. If the amount of vapor is small, cavitation induces broadband high-frequency fluctuations in the pressure and forces exerted on the turbine. As the amount of cavitation increases, these fluctuations tend to have a distinct dominant frequency which is different from the frequency of the RVR.
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| 10. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Large-eddy Simulation of Cavitating Tip Leakage Vortex
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tip Leakage Vortices (TLV) are very common in axial turbomachines. This type of vortex forms as the result of an interaction between the leakage flow, a flow from the pressure side of a blade to its suction side, and the upstream flow. In hydraulic machines, the high rotation in TLVs can cause a significant pressure drop at the core of the vortex leading to formation of cavitating structures. Previous experimental studies have shown that the formation of these cavitating structures is responsible for many adverse effects such as cavitation breakdown and a high level of noise and vibration [1, 2, 3]. To avoid such adverse effects, a better understanding of the flow dynamics in TLVs is needed. Numerical simulations can be a useful tool for this purpose as they provide a complete access to the flow field, especially near the cavitating regions where it is difficult to get optical access in the experiments. In this study, we numerically investigate non-cavitating and cavitating TLVs around a NACA0009 foil using a large-eddy simulation approach. The results of the non-cavitating simulation are validated against the experimental data provided in Dreyer et al. [4]. This comparison, shown in Fig. 1, indicates that the simulation can capture the main features of the flow field. Furthermore, a cavitating condition is simulated and the effect of cavitation on the structure of the TLV is discussed in detail.
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| 11. |
- Arabnejad Khanouki, Mohammad Hossein, 1988
(författare)
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Numerical and Experimental Investigation of Hydrodynamic Mechanisms in Erosive Sheet Cavitation
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cavitation erosion is one of the limiting factors in the design of hydraulic machinery as it is associated with the reduction in the operating life-time of a hydraulic machine and a significant increase in maintenance cost. In order to be able to design a hydraulic machine with a low risk of cavitation erosion, understanding the hydrodynamic mechanisms controlling the cavitation erosion is of great importance. A precondition of these hydrodynamic mechanisms is the creation of a transient cavity that collapses violently as it travels into the high-pressure regions; this creation is often called the shedding of cavity structures. Therefore, understanding the shedding process of the cavity structures plays an important role in providing the knowledge related to hydrodynamic mechanisms of cavitation erosion. In this thesis, the dynamics of cavitating flows over a NACA0009 foil are investigated using numerical and experimental methods. The shedding behavior of cavity structures is analyzed based on the results from the numerical simulations and high-speed videos. For erosion assessment, the location of erosive collapses in the cavitating flow is determined using a paint test method. These locations and the detectable collapse events in the high-speed videos are used to find the relation between the erosion patterns and cavitation dynamics. In order to numerically assess the areas with high risk of cavitation erosion, the cavitating flow is simulated using a compressible solver, capable of capturing the shock-waves upon the collapse of cavities. The areas with high risk of cavitation erosion, identified with the compressible solver, is compared with the results from paint test. The results from the compressible solver are used to investigate the hydrodynamic mechanisms of erosive collapses.
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| 12. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Numerical and experimental investigation of shedding mechanisms from leading-edge cavitation
- 2019
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 119, s. 123-143
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Tidskriftsartikel (refereegranskat)abstract
- Leading-edge cavitation is responsible of the generation of transient cavities, usually made of clouds of bubbles. These transient cavities travel downstream to high-pressure regions and collapse violently, leading to noise and vibration as well as erosion. In the present paper, the focus is on the mechanisms generating transient cavities to better understand the starting point of the erosion process. The case studied is the cavitating flow over a NACA0009 hydrofoil which is investigated using experiments and numerical simulation. In the experimental part, which is conducted in EPFL high-speed cavitation tunnel, the shedding behavior is studied using high-speed visualization (HSV). In the numerical part, the cavitating flow is simulated using an incompressible solver coupled with isothermal homogeneous two-phase mixture cavitation model and Implicit Large Eddy Simulation (ILES) turbulence modelling. Owing to high speed visualization and numerical simulations, we identified two shedding mechanisms of transient cavities: (i) A primary shedding, characterized by a periodic generation of large cloud cavities and (ii) a secondary shedding of small-scale horse-shoe vortices, which are revealed for the first time. These small-scale structures, which are believed to play a major role in the erosion process, result from a complex interaction between the sheet cavity, the cloud cavity and re-entrant jets of different types. Furthermore, the detailed comparison between HSV and simulation confirms that the current numerical approach is capable of capturing the two types of shedding mechanisms very well.
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| 13. |
- 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
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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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| 14. |
- 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
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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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| 15. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Scale-resolving simulations of the flow in the Francis-99 turbine at part-load condition
- 2022
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Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 1079:1
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the formation of the Rotating Vortex Rope (RVR) using scale-resolving methods, SAS and Wall-Modeled LES (WMLES). We compare the results from these simulation methods with the experimental data of the Francis-99 workshop. This comparison shows that the general features of the RVR can be captured with both methods. However, using WMLES methods would lead to a better quantitative agreement between the velocity profiles in the draft tube in the simulation and the experiment. The reasons for this better agreement are discussed in detail. A comparison of the pressure fluctuations in the draft tube captured in the simulations and the experiment is also presented. This comparison shows that all simulations under-predict the Root Mean Square (RMS) of these pressure fluctuations, although the RMS values predicted by the WMLES simulation are closer to the experimental values.
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| 16. |
- 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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| 17. |
- Arabnejad Khanouki, Mohammad Hossein, 1988, et al.
(författare)
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Zero-emission propulsion system featuring, Flettner rotors, batteries and fuel cells, for a merchant ship
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- To meet the International Maritime Organization’s (IMO) goal of decarbonising the shipping sector by 2050, zero-emission ship propulsion systems should be developed to replace conventional fossil fuel-based ones. In this study, we propose a zero-emission hybrid hydrogen-wind-powered propulsion system to be retrofitted to a benchmark merchant ship with a conventional propulsion system. The ship and its propulsion systems are modelled using an in-house platform. We analyse power and energy requirements for the ship over a realistic route and one-year schedule, factoring in actual sea and weather conditions. Initially, we examine the battery-powered propulsion system, which proves impractical even with a reduction in the ship’s speed and the addition of a charging station. This retrofitted battery-powered propulsion system will occupy a significant portion of the existing ship’s deadweight due to its substantial weight, consequently reducing the ship’s cargo capacity. To address this, we evaluate integrating a hydrogen-powered fuel cell system with power equal to the non-propulsive constant load in the ship. We demonstrate that under these conditions, and with four Flettner rotors and the charging station positioned mid-port on the ship’s route, the size of the zero-emission propulsion system can be approximately 20% of the deadweight, rendering such a system feasible.
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| 18. |
- Fahlbeck, Jonathan, 1992, et al.
(författare)
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Cavitation Simulations of a Low Head Contra-rotating Pump-turbine
- 2023
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Ingår i: OpenFOAM Workshop (OFW18) Book of abstracts. ; , s. 348-349
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To meet the demands of a larger share of the electrical energy produced by intermittent renewable energy sources, an increasing amount of plannable energy sources is needed. One solution to handle this is to increase the amount of energy storage in the electrical grids. The most widespread energy storage technology today is by far pumped hydro storage (PHS). In an attempt to enable PHS at low-head sites, the ALPHEUS (augmenting grid stability through low head pumped hydro energy utilization and storage) EU Horizon 2020 research project was formed. In ALPHEUS, new axial flow, low-head, contra-rotating pump-turbine (CRPT) designs are investigated. A CRPT has two individual runners rotating in opposite directions. CRPTs developed within the ALPHEUS project have already been thoroughly analysed at stationary and transient operating conditions by the authors. However, the effects on the CPRT's performance due to potential cavitation on the runner blade surfaces have previously not been investigated. For that reason, the current study focuses on running cavitation simulations on a model scale CRPT using the OpenFOAM computational fluid dynamics (CFD) software. In the CFD simulations, cavitation is modelled as a two-phase liquid-vapour mixture using the interPhaseChangeDyMFoam solver. The two runner domains have a prescribed solid body rotation. Condensation and evaporation processes are handled with the Schnerr-Sauer model. Turbulence is managed with the k-omega shear stress transport-scale adaptive simulation (kOmegaSSTSAS) model. Flow-driving pressure differences over the computational domain are achieved with the headLossPressure boundary condition to emulate a larger experimental test facility of which the CRPT is part. Figure 1 shows a snapshot in time of an iso-surface (light blue) of cavitating cloud with alpha_liquid=0.9 in turbine mode. At this operating point, a small amount of cavitating flow is found by the suction side of the leading edges of the left runner, which is facing a lower reservoir. In Figure 2, the same type of iso-surface is shown, however now in pump mode. It is seen that the pump mode operating condition is much worse than the turbine mode. The cavitating cloud covers most of the suction side of the left runner, additionally, the tip-clearance region is also exposed to cavitation. Furthermore, traces of cavitation are found on the leading edges of the right runner as well as on the left small-support struts. It is thus important to, at least, analyse the pump mode to determine if and how much cavitation affects the CRPS's operating performance.
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| 19. |
- Özgünoglu, Mehmet, 1989, et al.
(författare)
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Numerical Assessment of Cavitation Erosion for a Nozzle Flow Configuration
- 2021
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Ingår i: 11th International Symposium on Cavitation (CAV2021).
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Konferensbidrag (refereegranskat)abstract
- The main purpose of this study is to numerically investigate and predict the cavitation erosion mechanisms in a nozzle flow configuration. To do this, an injector type geometry is numerically investigated with the open-source CFD package OpenFOAM. A compressible Euler approached is applied for two operating conditions, where results are compared with other studies from the literature. Spectral statistics and maximum surface pressure results are compared with experiments. Results show that the proposed modelling approach is capable to explain main cavitation structures that promotes erosion.
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