Cavitation is a complex phenomenon to measure, depending on site conditions in specific regions of the Earth, where there is water with various physical properties The development of ship and propulsion technology is currently intended to further explore territorial waters that are difficult to explore Climate differences affect the temperature and physical properties of water on Earth This study aimed to determine the effect of cavitation related to the physical properties of water Numerical predictions of a cavitating propeller in open water and uniform inflow are presented with computational fluid dynamics (CFD) Simulations were carried out using Ansys Numerical simulation based on Reynolds-averaged Navier–Stokes equations for the conservative form and the Rayleigh–Plesset equation for the mass transfer cavitation model was conducted with turbulent closure of the fully turbulent K-epsilon (k-e) model and shear stress transport (SST) The influence of temperature on cavitation extension was investigated between 0 and 50 ° C  The results obtained showed a trend of cavitation occurring more aggressively at higher water temperature than at lower temperature

https://www.mdpi.com/2077-1312/8/6/465/pdf

Cavitation Prediction of Ship Propeller Based on Temperature and Fluid Properties of Water

The rise in prices of traditional energy sources, the high dependence of many countries on their import, and the associated need for security of supply have led to large investments in new capacity of wind power plants. Although wind power generation is a mature technology and levelized cost of electricity low, there is still room for its improvement. A review of available literature has indicated that wind turbine development in the coming decade will be based on upscaling wind turbines and minor design improvements. These include further improvements in rotor blade aerodynamics, active control of the rotor blade rotation system, and aerodynamic brakes that will lead to increased power generation efficiency. Improvements in system maintenance and early diagnosis of transmission and power-related faults and blade surface damage will reduce wind turbine downtime and increase system reliability and availability. The manufacture of wind turbines with larger dimensions presents problems of transportation and assembly, which are being addressed by manufacturing the blades from segments. Numerical analysis is increasingly being used both in wind turbine efficiency analysis and in stress and vibration analysis. Direct drive is becoming more competitive with traditional power transmission through a gearbox. The trend in offshore wind farms is to increase the size of wind turbines and to place them farther from the coast and in deeper water, which requires new forms of floating foundations. Due to the different work requirements and more difficult conditions of the marine environment, optimization methods for the construction of offshore substructures are currently being developed. There are plans to use 66-kV cables for power transmission from offshore wind farms instead of the current 33-kV cables. Offshore wind farms can play an important role in the transition to a hydrogen economy. In this context, significant capacity is planned for the production of “green” hydrogen by electrolysis from water. First-generation wind turbines are nearing the end of their service life, so strategies are being developed to repower them, extend their life or dismantle and recycle them.

/pdf/wind-turbine-technology-trends-vb1w8rj0.pdf

Wind Turbine Technology Trends

Cavitation is a phenomenon that occurs easily during rotation of fluid machinery and can decrease the performance of a pump, thereby resulting in damage to flow passage components. To study the influence of wall roughness on the cavitation performance of a centrifugal pump, a three-dimensional model of internal flow field of a centrifugal pump was constructed and a numerical simulation of cavitation in the flow field was conducted with ANSYS CFX software based on the Reynolds normalization group k-epsilon turbulence model and Zwart cavitation model. The cavitation can be further divided into four stages: cavitation inception, cavitation development, critical cavitation, and fracture cavitation. Influencing laws of wall roughness of the blade surface on the cavitation performance of a centrifugal pump were analyzed. Research results demonstrate that in the design process of centrifugal pumps, decreasing the wall roughness appropriately during the cavitation development and critical cavitation is important to effectively improve the cavitation performance of pumps. Moreover, a number of nucleation sites on the blade surface increase with the increase in wall roughness, thereby expanding the low-pressure area of the blade. Research conclusions can provide theoretical references to improve cavitation performance and optimize the structural design of the pump.

/pdf/influence-of-wall-roughness-on-cavitation-performance-of-46gu7wnmcl.pdf

Influence of wall roughness on cavitation performance of centrifugal pump

This work analyses the growth of the usage of computers in maritime studies within five decades. Maritime studies accept to position in education and development of twenty first century. Key areas of research are environment, transport and modelling. These are criteria for analysis of maritime studies. Algorithmic search integrated with meta-analysis was developed to retrieve maritime literature from the sources of maritime digital research databases. Analysed results showed that key areas were found in maritime studies. More than half of research was modelling. The smallest number of studies was transport, and the rest of maritime research fell into environment. Conclusion draws into to the point that computer usages in maritime studies were progressing to grow in 2010s. It seems that the massive number of uses of computer will appear in 2050s. Skillset obtained from three research keys will help drive regional economics and education.

Analysis of Computing Progress in Maritime Studies

This paper evaluates the applicability of the hexahedral block structured grids for marine propeller performance predictions. Hydrodynamic characteristics for Potsdam Propeller Test Case (PPTC), namely thrust and torque coefficients, were determined using numerical simulations in two commercial solvers: Ansys Fluent and STAR-CCM+. Results were attained for hexahedral and tetrahedral hybrid grids equivalent in terms of cell count and quality, and compared to the experimental results. Furthermore, accuracy of Realizable k- ϵ and SST k- ω turbulent models when analyzing marine propeller performance was investigated. Finally, performance characteristics were assessed in cavitating flow conditions for a single advance ratio using Zwart–Gerber–Belamri and Schnerr and Sauer models. The resulting cavitation pattern was compared to cavity extents and shape noted during measurements. The results suggest that hexa and hybrid grids, in certain range of advance ratios, do provide similar results; however, for low and high ratios, structured grids in conjunction with Realizable k- ϵ model can achieve more accurate results.

/pdf/grid-type-and-turbulence-model-influence-on-propeller-3pcq5k1skv.pdf

Grid Type and Turbulence Model Influence on Propeller Characteristics Prediction

One of the big challenges, yet to be addressed, in the numerical simulation of cavitating flow on marine propellers is; the existence of laminar and turbulence transition flows over the propeller’s blades. The majority of previous studies employed turbulence models that were only appropriate for fully turbulent flows. These models mostly caused high discrepancies between numerical predictions and experimental measurements especially at low rotational speeds where, Reynolds number decreases and laminar and transient flows exist. The present paper proposes a complete and detailed procedure for the CFD simulation of cavitating flow on marine propellers using the ‘K-Kl-ω’ transition-sensitive model. Results are obtained using ‘ANSYS FLUENT 16’. The propeller under consideration is the ‘INSEAN E779A’ propeller model. The fully turbulent standard ‘k-e’ model is also adopted for comparison. Obtained results, based on both turbulence models, are validated by comparison with experimental data available in the literature. Predictions based on the ‘K-Kl-ω’ transition-sensitive model are found to be in better agreement with experiments at lower rotational speeds i.e. at low Reynolds numbers.

Numerical prediction of sheet cavitation on marine propellers using CFD simulation with transition-sensitive turbulence model

Determining and understanding the performance characteristics of marine propellers by experiments is quite a complex and costly task. Numerical predictions using computational fluid dynamics simula...

Numerical prediction of the performance of marine propellers using computational fluid dynamics simulation with transition-sensitive turbulence model:

Savonius turbine is a vertical axis wind turbine (VAWT) which is suitable to operate at low wind velocities. The experimental investigation to improve its performance is a big challenge as; it is expensive, complicating and time consuming. Numerical prediction using CFD simulation could be a valuable alternative. This paper introduces a new modification of Savonius wind rotors to improve its performance. The proposed modification consists of a curtain arrangement together with fin addition on blade. The effect of the proposed modification was predicted using a CFD simulation employing ‘ANSYS FLUENT 16′. The curtain arrangement was located in front of the rotor to avoid the opposing torque to the rotor rotation. The fins were added to exploit the space in the blade for guiding the wind flow. The performance of the rotor with different curtain arrangements and variable number of fins was predicted and assessed against that of the conventional rotor. This comparison aimed to optimize the geometrical data of the proposed curtain arrangement with the number of added fins. The maximum power coefficient of the Savonius wind rotor was found to be increased to about 42 % with the optimum curtain arrangement (lengths of the curtain blades 1000 and 1150 mm and the angles of the curtain blades 30 and 50) together with adding only one fin. The simulation results showed that the performance of Savonius wind rotors could be significantly enhanced with a proper selection of curtain arrangement and number of fins to be added on the blade. 

Numerical prediction of improvement of a Savonius rotor performance with curtaining and fin addition on blade

Counter rotating Savonius wind turbine (CRSWT) is a vertical axis wind turbine (VAWT) which is appropriate for use in low-wind conditions. Experimenting to improve its performance is a difficult task because it is costly, time demanding, and complicated. CFD simulation with numerical prediction could be a good alternative. A novel change is introduced in this paper of two counter rotating Savonius wind turbines to enhance their efficiency. The suggested change includes curtain configurations as well as the insertion of fin to the blade. A CFD simulation was used to predict the effect of the proposed adjustments employing ‘ANSYS FLUENT 16′. To avoid the opposing torque to each rotor rotation, the curtain arrangements were placed in front of both rotors. The fin was adopted to take advantage of the available area in the blade for directing wind flow. The performance of the rotor when fitted with various curtain arrangements, both with and without fin, was predicted and compared to that of the conventional CRSWT. The goal of these comparisons was to improve the geometrical data of the suggested curtain arrangements as well as to investigate the influence of fin addition on the blade. With the curtain arrangement having maximum curtain blade lengths (500 mm, 550 mm) and maximum angles (50°, 30°) and the addition of only one fin, the CRSWT's maximum power coefficient increased by nearly 48 percent. The simulation findings revealed that by selecting the right curtain arrangement and adding fins to the blade, the performance of the CRSWT could be greatly improved. 

Mohamed M. Helal

Papers

Numerical prediction of sheet cavitation on marine propellers using CFD simulation with transition-sensitive turbulence model

Numerical prediction of the performance of marine propellers using computational fluid dynamics simulation with transition-sensitive turbulence model:

Numerical prediction of improvement of a Savonius rotor performance with curtaining and fin addition on blade

Numerical investigation of improvement of counter rotating Savonius turbines performance with curtaining and fin addition on blade