Pub Date : 2024-02-01DOI: 10.47176/jafm.17.02.2141
D. Chen, L. Ming, T. Wang, M. Qiu, †. Z.Lin
The phenomenon of droplets impacting droplets is common in many fields including the chemical, nuclear, and aerospace industries. In this paper, high-speed photography technology is used to obtain the variation law and evolution properties exhibited by droplets colliding with sessile droplets of varying sizes. We further explored how the Weber number ( We ) and volume ratio ( V p / V i ) influence the behavior of droplets colliding with sessile droplets. The phenomenon of droplets impacting sessile droplets of different volumes is different from that of droplets impacting liquid films. In terms of droplet spreading, compression and the non-splashing liquid crown, the phenomena and laws reported in the present study are applicable for 1 ≤ We ≤ 165 and droplet volume ratios of 1 ≤ V p / V i ≤ 6. With a low Weber number, the droplet compresses and deforms downward without coalescence at the initial stage of collision. A high Weber number results in a no-splashing liquid crown. These findings provide important insights into the dynamics of droplet-droplet interactions.
液滴撞击液滴的现象在许多领域都很常见，包括化学、核能和航空航天工业。本文利用高速摄影技术获得了液滴与不同大小的无柄液滴碰撞时所表现出的变化规律和演化特性。我们进一步探讨了韦伯数（We）和体积比（V p / V i）如何影响液滴与无柄液滴碰撞的行为。液滴撞击不同体积的无柄液滴的现象与液滴撞击液膜的现象不同。就液滴扩散、压缩和非飞溅液冠而言，本研究报告的现象和规律适用于 1 ≤ We ≤ 165 和液滴体积比为 1 ≤ V p / V i ≤ 6 的情况。当韦伯数较低时，液滴会向下压缩变形，而不会在碰撞初期凝聚。高韦伯数会导致液冠不飞溅。这些发现为了解液滴与液滴之间的相互作用动力学提供了重要启示。
{"title":"Experimental Study on the Dynamics of a Moving Droplet Impacting a Sessile Droplet","authors":"D. Chen, L. Ming, T. Wang, M. Qiu, †. Z.Lin","doi":"10.47176/jafm.17.02.2141","DOIUrl":"https://doi.org/10.47176/jafm.17.02.2141","url":null,"abstract":"The phenomenon of droplets impacting droplets is common in many fields including the chemical, nuclear, and aerospace industries. In this paper, high-speed photography technology is used to obtain the variation law and evolution properties exhibited by droplets colliding with sessile droplets of varying sizes. We further explored how the Weber number ( We ) and volume ratio ( V p / V i ) influence the behavior of droplets colliding with sessile droplets. The phenomenon of droplets impacting sessile droplets of different volumes is different from that of droplets impacting liquid films. In terms of droplet spreading, compression and the non-splashing liquid crown, the phenomena and laws reported in the present study are applicable for 1 ≤ We ≤ 165 and droplet volume ratios of 1 ≤ V p / V i ≤ 6. With a low Weber number, the droplet compresses and deforms downward without coalescence at the initial stage of collision. A high Weber number results in a no-splashing liquid crown. These findings provide important insights into the dynamics of droplet-droplet interactions.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139684298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-01DOI: 10.47176/jafm.17.02.2071
D. Yan, C. Zhang, C. Wang, T. Zhang, F. Sun
The vibration of water injection pipeline systems in oilfields creates challenges in terms of safe long-term operation. To fully understand the vibration mechanism of plunger-powered high-pressure water injection pipelines, we conducted fluid pressure pulsation calculations and fluid structure coupling modal evaluations using finite element analysis software to study the effects of pressure, pipe length, and pipe clamp on the vibrations. The results indicate that the total displacement increases with increasing pressure, although the magnitude of the increment gradually decreases. The pipe length has a significant impact on the natural frequency. Based on the findings of the present study, we proposed that pipe clamps could be introduced to reduce the vibrations in an existing high-pressure plunger pump water injection pipeline, and the overall design was optimized. Comparative modal analysis revealed the most practical number and position of the pipe clamps to be suitable for a pressure range of 42–70 MPa.
{"title":"Vibrational Analysis and Optimization of a Water Injection Pipeline in a High-pressure Plunger Pump","authors":"D. Yan, C. Zhang, C. Wang, T. Zhang, F. Sun","doi":"10.47176/jafm.17.02.2071","DOIUrl":"https://doi.org/10.47176/jafm.17.02.2071","url":null,"abstract":"The vibration of water injection pipeline systems in oilfields creates challenges in terms of safe long-term operation. To fully understand the vibration mechanism of plunger-powered high-pressure water injection pipelines, we conducted fluid pressure pulsation calculations and fluid structure coupling modal evaluations using finite element analysis software to study the effects of pressure, pipe length, and pipe clamp on the vibrations. The results indicate that the total displacement increases with increasing pressure, although the magnitude of the increment gradually decreases. The pipe length has a significant impact on the natural frequency. Based on the findings of the present study, we proposed that pipe clamps could be introduced to reduce the vibrations in an existing high-pressure plunger pump water injection pipeline, and the overall design was optimized. Comparative modal analysis revealed the most practical number and position of the pipe clamps to be suitable for a pressure range of 42–70 MPa.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139685435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-01DOI: 10.47176/jafm.17.02.2073
†. H.W.Lu, Y. P. Shi, J. C. Xin, X. Z. Kong, B. L. Peng
The impact of the column number of ellipsoidal dimples on a highly-loaded compressor cascade (NACA65-K48) under design conditions was investigated by using a numerical simulation method. Ellipsoidal dimples with a thickness of 0.2 mm were located at the position of chord length ranging from 10% to 36%. The span-wise interval was 5.0 mm. The performance and flow field structures of cascades with 1 to 5 ellipsoidal dimpled columns were compared, and the results showed that the turbulent kinetic energy intensity near the wall was enhanced and the fluid separation resistance was consequently improved. The total pressure loss was reduced by all modified ellipsoidal dimples. In addition, the separation bubble of the suction side was broken or weakened, the corner separation was improved, and the influence range of the passage vortex was reduced. Moreover, the improvement effect of cascade performance parameters initially increased with the increase in the number of dimple columns and then reduced as the number of columns was further increased. The reductions in the total pressure loss of the cascade were 0.59%, 1.47%, 1.69%, 1.91%, and 1.73% for column numbers 1 to 5, respectively.
{"title":"Influence of Ellipsoidal Dimple Column Number on Performance of Highly-loaded Compressor Cascade","authors":"†. H.W.Lu, Y. P. Shi, J. C. Xin, X. Z. Kong, B. L. Peng","doi":"10.47176/jafm.17.02.2073","DOIUrl":"https://doi.org/10.47176/jafm.17.02.2073","url":null,"abstract":"The impact of the column number of ellipsoidal dimples on a highly-loaded compressor cascade (NACA65-K48) under design conditions was investigated by using a numerical simulation method. Ellipsoidal dimples with a thickness of 0.2 mm were located at the position of chord length ranging from 10% to 36%. The span-wise interval was 5.0 mm. The performance and flow field structures of cascades with 1 to 5 ellipsoidal dimpled columns were compared, and the results showed that the turbulent kinetic energy intensity near the wall was enhanced and the fluid separation resistance was consequently improved. The total pressure loss was reduced by all modified ellipsoidal dimples. In addition, the separation bubble of the suction side was broken or weakened, the corner separation was improved, and the influence range of the passage vortex was reduced. Moreover, the improvement effect of cascade performance parameters initially increased with the increase in the number of dimple columns and then reduced as the number of columns was further increased. The reductions in the total pressure loss of the cascade were 0.59%, 1.47%, 1.69%, 1.91%, and 1.73% for column numbers 1 to 5, respectively.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139687359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Bouanik, T. Azzam, N. Abbasnezhad, A. Larabi, M. Mekadem, F. Bakir
Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance.
{"title":"Active Air Injection Control to Enhance Performance of Hollow-bladed Axial Fan: A Numerical Study","authors":"A. Bouanik, T. Azzam, N. Abbasnezhad, A. Larabi, M. Mekadem, F. Bakir","doi":"10.47176/jafm.17.3.2201","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2201","url":null,"abstract":"Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139393494","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Effective deduction of air heating load and drag is a critical issue in hypersonic vehicle engineering applications. In this research, seven various geometrical models have been proposed to study and compare the effect of each configuration on the flow field, drag, and aerodynamic heating deduction under the same flow conditions. The presented configurations in this study: (a) blunt-body geometry as a reference of comparison, (b) blunt-body geometry with a spike, (c) blunt-body geometry with an counter flow jet, (d) blunt-body geometry with a spike and counter flow jet, (e) blunt-body geometry with a spike and aerodisk, (f) blunt-body geometry with a spike, aerodisk, and root counter flow jet, (g) blunt-body geometry with a spike, four aerodisks and root counter flow jet. The Reynolds-Averaged equations have been solved using the Finite Volume Method (FVM) along with the shear stress turbulence model (k-ω SST). The flow is assumed compressible, steady-state, and axisymmetric with a free stream Mach number of 6. According to the study of each configuration’s performance related to the parameters of drag, maximum pressure, and maximum heat flux factors on the blunt-body walls, (g) configuration with a drag factor of 0.2699, maximum pressure factor of 209.8, and maximum heat flux factor of 25.1, has the most deduction on the blunt-body walls among the seven configurations. The deduction percentage of drag, maximum pressure, and maximum heat flux factors of (g) configuration to (a) configuration are %72.1, %94.5, and %79.9, respectively, which significantly diminished drag and heat flux. Also, the best configuration scenarios for drag and aerodynamic heating deduction are geometrical models of g, f, d, e, c, b, and a, respectively.
{"title":"Evaluation of Various Flow Control Methods in Reducing Drag and Aerodynamic Heating on the Nose of Hypersonic Flying Objects","authors":"†. S.Abbasi, S. E. Vali","doi":"10.47176/jafm.17.3.2150","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2150","url":null,"abstract":"Effective deduction of air heating load and drag is a critical issue in hypersonic vehicle engineering applications. In this research, seven various geometrical models have been proposed to study and compare the effect of each configuration on the flow field, drag, and aerodynamic heating deduction under the same flow conditions. The presented configurations in this study: (a) blunt-body geometry as a reference of comparison, (b) blunt-body geometry with a spike, (c) blunt-body geometry with an counter flow jet, (d) blunt-body geometry with a spike and counter flow jet, (e) blunt-body geometry with a spike and aerodisk, (f) blunt-body geometry with a spike, aerodisk, and root counter flow jet, (g) blunt-body geometry with a spike, four aerodisks and root counter flow jet. The Reynolds-Averaged equations have been solved using the Finite Volume Method (FVM) along with the shear stress turbulence model (k-ω SST). The flow is assumed compressible, steady-state, and axisymmetric with a free stream Mach number of 6. According to the study of each configuration’s performance related to the parameters of drag, maximum pressure, and maximum heat flux factors on the blunt-body walls, (g) configuration with a drag factor of 0.2699, maximum pressure factor of 209.8, and maximum heat flux factor of 25.1, has the most deduction on the blunt-body walls among the seven configurations. The deduction percentage of drag, maximum pressure, and maximum heat flux factors of (g) configuration to (a) configuration are %72.1, %94.5, and %79.9, respectively, which significantly diminished drag and heat flux. Also, the best configuration scenarios for drag and aerodynamic heating deduction are geometrical models of g, f, d, e, c, b, and a, respectively.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139395727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. J. Zhao, D. Zhang, †. X.F.Lv, L. L. Song, J. W. Li, F. Chen, X. Q. Xie
Oil spill accidents in damaged submarine-buried pipelines cause tremendous economic losses and serious environmental pollution. The accurate prediction of oil spills from subsea pipelines is important for emergency response. In this study, the volume-of-fluid model, realizable k–ε turbulence model, and porous-medium model were employed to describe the process of an oil spill from a submarine pipeline to the sea surface. The effects of seawater density, seawater velocity, and pipeline buried depth on the transverse diffusion distance of crude oil and the time at which crude oil reaches the sea surface were obtained through numerical calculations. The calculation results show that, with a decrease in seawater density and an increase in seawater velocity and pipeline depth, the diffusion rate of crude oil decreases significantly, the maximum transverse diffusion distance increases and crude oil takes a long time to reach the sea surface. In particular, compared with a sea density of 1045 kg/m3, the transverse distance of a sea density of 1025 kg/m3 is increased by 0.091 m. When the seawater velocity is greater than 1.5 m/s, the diffusion of crude oil in seawater is significantly affected, the seawater velocity increases to 0.35 m/s, and the transverse diffusion distance of oil to the sea surface increases to 12.693 m. When the buried depth of the pipeline reaches 0.7 and 1.3 m compared to 0.1 m, the diffusion widths of crude oil in sea mud rise by 20% and 32.5%, respectively. The time required for crude oil to reach the sea surface and the transverse diffusion distance of crude oil migrating to the sea surface were analyzed using multiple regression, and the fitting formulas were obtained. The results provide theoretical support for accurately predicting the leakage range of submarine-buried pipelines and provide valuable guidance for submarine-buried pipeline leakage accident treatment schemes.
{"title":"Numerical Simulation of Crude Oil Leakage from Damaged Submarine-Buried Pipeline","authors":"H. J. Zhao, D. Zhang, †. X.F.Lv, L. L. Song, J. W. Li, F. Chen, X. Q. Xie","doi":"10.47176/jafm.17.1.2061","DOIUrl":"https://doi.org/10.47176/jafm.17.1.2061","url":null,"abstract":"Oil spill accidents in damaged submarine-buried pipelines cause tremendous economic losses and serious environmental pollution. The accurate prediction of oil spills from subsea pipelines is important for emergency response. In this study, the volume-of-fluid model, realizable k–ε turbulence model, and porous-medium model were employed to describe the process of an oil spill from a submarine pipeline to the sea surface. The effects of seawater density, seawater velocity, and pipeline buried depth on the transverse diffusion distance of crude oil and the time at which crude oil reaches the sea surface were obtained through numerical calculations. The calculation results show that, with a decrease in seawater density and an increase in seawater velocity and pipeline depth, the diffusion rate of crude oil decreases significantly, the maximum transverse diffusion distance increases and crude oil takes a long time to reach the sea surface. In particular, compared with a sea density of 1045 kg/m3, the transverse distance of a sea density of 1025 kg/m3 is increased by 0.091 m. When the seawater velocity is greater than 1.5 m/s, the diffusion of crude oil in seawater is significantly affected, the seawater velocity increases to 0.35 m/s, and the transverse diffusion distance of oil to the sea surface increases to 12.693 m. When the buried depth of the pipeline reaches 0.7 and 1.3 m compared to 0.1 m, the diffusion widths of crude oil in sea mud rise by 20% and 32.5%, respectively. The time required for crude oil to reach the sea surface and the transverse diffusion distance of crude oil migrating to the sea surface were analyzed using multiple regression, and the fitting formulas were obtained. The results provide theoretical support for accurately predicting the leakage range of submarine-buried pipelines and provide valuable guidance for submarine-buried pipeline leakage accident treatment schemes.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139128327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cycloidal propellers constitute a specialized category of underwater propulsion devices, widely employed in vehicles requiring exceptional maneuverability. The parameters of the blade-driving mechanism directly impact the propeller performance. Hence, the effect of variations in the geometric parameters of the blade-driving mechanism on the hydrodynamic performance of cycloidal propellers must be investigated. In this study, a specific set of four-bar and mixed four-bar/five-bar mechanisms are taken as examples, and the effect of linkage-length variations on the hydrodynamic performance of cycloidal propellers was analyzed using numerical simulation methods. First, we established a physical model of the cycloidal propeller, and then derived the relationship between blade-rotation and revolution angles. Subsequently, by solving the Navier–Stokes equations and employing computational fluid dynamics simulations based on viscosity, an analysis is conducted to reveal the trends in the impact of different linkage-length combinations on the hydrodynamic performance of the cycloidal propeller. Finally, the outcomes of the numerical simulations are interpreted using the wing element theory. In similar blade-driving mechanisms, the effects of varying linkage lengths on propeller hydrodynamic performance are determined through alterations in the blade rotation angle range and equilibrium position. An increase in the range of the blade-rotation angle significantly enhances the hydrodynamic performance of the cycloidal propeller. This research employs a more realistic auto-propulsion mode for numerical simulations, establishing a mapping relationship between the blade-driving mechanism and hydrodynamic performance of the cycloidal propeller, while analyzing the underlying influencing mechanisms. Furthermore, crucial numerical simulations and theoretical foundations are employed for designing the four-bar and mixed four-bar/five-bar mechanism cycloidal propellers. The findings of this study could also be used in similar cycloidal propellers with multilinkage mechanism.
{"title":"Hydrodynamic Performance of Cycloidal Propellers with Four-Bar and Mixed Four-bar/Five-bar Mechanisms: A Numerical Study","authors":"H. Yan, Z. Zhou, M. Lei, Z. Li, †. D.Xia","doi":"10.47176/jafm.17.3.2114","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2114","url":null,"abstract":"Cycloidal propellers constitute a specialized category of underwater propulsion devices, widely employed in vehicles requiring exceptional maneuverability. The parameters of the blade-driving mechanism directly impact the propeller performance. Hence, the effect of variations in the geometric parameters of the blade-driving mechanism on the hydrodynamic performance of cycloidal propellers must be investigated. In this study, a specific set of four-bar and mixed four-bar/five-bar mechanisms are taken as examples, and the effect of linkage-length variations on the hydrodynamic performance of cycloidal propellers was analyzed using numerical simulation methods. First, we established a physical model of the cycloidal propeller, and then derived the relationship between blade-rotation and revolution angles. Subsequently, by solving the Navier–Stokes equations and employing computational fluid dynamics simulations based on viscosity, an analysis is conducted to reveal the trends in the impact of different linkage-length combinations on the hydrodynamic performance of the cycloidal propeller. Finally, the outcomes of the numerical simulations are interpreted using the wing element theory. In similar blade-driving mechanisms, the effects of varying linkage lengths on propeller hydrodynamic performance are determined through alterations in the blade rotation angle range and equilibrium position. An increase in the range of the blade-rotation angle significantly enhances the hydrodynamic performance of the cycloidal propeller. This research employs a more realistic auto-propulsion mode for numerical simulations, establishing a mapping relationship between the blade-driving mechanism and hydrodynamic performance of the cycloidal propeller, while analyzing the underlying influencing mechanisms. Furthermore, crucial numerical simulations and theoretical foundations are employed for designing the four-bar and mixed four-bar/five-bar mechanism cycloidal propellers. The findings of this study could also be used in similar cycloidal propellers with multilinkage mechanism.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139454779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The present work reports a CFD study of the magneto-convection of a ferrofluid (Fe3O4/water) circulating in a mini-channel under the influence of different vortex generators (fins and permanent magnets). The lower surface of the mini-channel is maintained at a constant temperature, while the upper surface is thermally insulated. The influence of fins, magnetic field intensity, and Reynolds number on the thermal and dynamic characteristics of the flow was numerically investigated using the finite volume method. The obtained results show that the coexistence of these two types of vortex generators considerably affects the flow structure; Entropy generation and heat transfer rate. Finally, the analysis of the different results shows that the concurrent presence of both the magnetic field and the fins results in a notably more efficient system. Using magnetic sources and fins simultaneously in a system with an intense magnetic field and a low Reynolds number can lead to a large gain in heat transfer.
{"title":"Impact of Magnetic Fields and Fins on Entropy Generation, Thermal, and Hydrodynamic Performance in the Ferrofluids Flow within a Mini Channel","authors":"L. Boutas, M. Marzougui, J. Zinoubi, S. Gannouni","doi":"10.47176/jafm.17.3.2134","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2134","url":null,"abstract":"The present work reports a CFD study of the magneto-convection of a ferrofluid (Fe3O4/water) circulating in a mini-channel under the influence of different vortex generators (fins and permanent magnets). The lower surface of the mini-channel is maintained at a constant temperature, while the upper surface is thermally insulated. The influence of fins, magnetic field intensity, and Reynolds number on the thermal and dynamic characteristics of the flow was numerically investigated using the finite volume method. The obtained results show that the coexistence of these two types of vortex generators considerably affects the flow structure; Entropy generation and heat transfer rate. Finally, the analysis of the different results shows that the concurrent presence of both the magnetic field and the fins results in a notably more efficient system. Using magnetic sources and fins simultaneously in a system with an intense magnetic field and a low Reynolds number can lead to a large gain in heat transfer.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139457827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Wu, F. Jin, Y. Luo, Y. Ge, Q. Wei, C. Zeng, X. Liu, W. Zhang, D. Miao, H. Bai
For the purpose of automatic generation control (AGC), a portion of the propeller hydro-turbine units in China is adjusted to operate within a restricted range of 75%-85% load using computer-controlled AGC strategies. In engineering applications, it has been observed that when a propeller hydro-turbine unit operates under off-design conditions, a large-scale vortex rope would occur in the draft tube, leading to significant pressure fluctuations. Injecting air into the draft tube to reduce the amplitude of pressure fluctuations is a common practice, but its effectiveness has not been proven on propeller hydro-turbine units. In this study, a CFD model of a propeller hydro-turbine was established, and 15 cases with different guide vane openings (GVO, between 31° and 45°) under unsteady conditions were calculated and studied. Two air admission measures were introduced to suppress the vortex rope oscillation in the draft tube and to mitigate pressure fluctuations. The reason for the additional energy loss due to air admission was then explained by the entropy production theory, and its value was quantified. This study points out that when injecting air, it is necessary to first consider whether the air will obstruct the flow in the draft tube. Finally, based on simulation and experimental data under various load conditions, pressure fluctuation analysis (based on fast Fourier transform, FFT) was conducted to assess the effectiveness of air admission measures. This study can provide an additional option for balancing unit efficiency and stability when scheduling units using an AGC strategy.
{"title":"Suppressing the Vortex Rope Oscillation and Pressure Fluctuations by the Air Admission in Propeller Hydro-Turbine Draft Tube","authors":"H. Wu, F. Jin, Y. Luo, Y. Ge, Q. Wei, C. Zeng, X. Liu, W. Zhang, D. Miao, H. Bai","doi":"10.47176/jafm.17.1.1994","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1994","url":null,"abstract":"For the purpose of automatic generation control (AGC), a portion of the propeller hydro-turbine units in China is adjusted to operate within a restricted range of 75%-85% load using computer-controlled AGC strategies. In engineering applications, it has been observed that when a propeller hydro-turbine unit operates under off-design conditions, a large-scale vortex rope would occur in the draft tube, leading to significant pressure fluctuations. Injecting air into the draft tube to reduce the amplitude of pressure fluctuations is a common practice, but its effectiveness has not been proven on propeller hydro-turbine units. In this study, a CFD model of a propeller hydro-turbine was established, and 15 cases with different guide vane openings (GVO, between 31° and 45°) under unsteady conditions were calculated and studied. Two air admission measures were introduced to suppress the vortex rope oscillation in the draft tube and to mitigate pressure fluctuations. The reason for the additional energy loss due to air admission was then explained by the entropy production theory, and its value was quantified. This study points out that when injecting air, it is necessary to first consider whether the air will obstruct the flow in the draft tube. Finally, based on simulation and experimental data under various load conditions, pressure fluctuation analysis (based on fast Fourier transform, FFT) was conducted to assess the effectiveness of air admission measures. This study can provide an additional option for balancing unit efficiency and stability when scheduling units using an AGC strategy.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139126338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Oil–air flow within an oil bath lubrication tapered roller bearing is essential for the lubrication and cooling of the bearing. In this paper, we develop a simulation model to investigate the flow field of tapered roller bearings with oil bath lubrication. The multiple reference frame (MRF) approach is used to describe the physical motion of the bearing, and the volume of fluid (VOF) two–phase flow model is used to track the oil–air interface in the flow field. The effects of mesh scale, geometric gap, and oil reservoir size on calculation time and convergence accuracy are examined in detail, and the effects of inner ring rotational speed and lubricant viscosity on frictional torque are systematically studied. The results of the numerical simulation indicate that as the gap distance between the raceway and the rolling elements decreases, the frictional torque is mainly generated by churning losses at the inner raceway and the rolling elements. The frictional torque increases with increasing inner ring speed and lubricating oil viscosity, with the rolling element contributing the largest portion at approximately 50% of the total. We demonstrate the effectiveness of a method to reduce frictional torque by optimizing the internal structure of the bearing to control oil flow. By optimizing the cage structure and reducing the roller half-cone angle, frictional torque can be reduced by 29.1% and 26.2%, respectively.
{"title":"Numerical Investigation of Oil–Air Flow Inside Tapered Roller Bearings with Oil Bath Lubrication","authors":"Z. Wang, F. Wang, H. Duan, W. Wang, R. Guo, Q. Yu","doi":"10.47176/jafm.17.1.1944","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1944","url":null,"abstract":"Oil–air flow within an oil bath lubrication tapered roller bearing is essential for the lubrication and cooling of the bearing. In this paper, we develop a simulation model to investigate the flow field of tapered roller bearings with oil bath lubrication. The multiple reference frame (MRF) approach is used to describe the physical motion of the bearing, and the volume of fluid (VOF) two–phase flow model is used to track the oil–air interface in the flow field. The effects of mesh scale, geometric gap, and oil reservoir size on calculation time and convergence accuracy are examined in detail, and the effects of inner ring rotational speed and lubricant viscosity on frictional torque are systematically studied. The results of the numerical simulation indicate that as the gap distance between the raceway and the rolling elements decreases, the frictional torque is mainly generated by churning losses at the inner raceway and the rolling elements. The frictional torque increases with increasing inner ring speed and lubricating oil viscosity, with the rolling element contributing the largest portion at approximately 50% of the total. We demonstrate the effectiveness of a method to reduce frictional torque by optimizing the internal structure of the bearing to control oil flow. By optimizing the cage structure and reducing the roller half-cone angle, frictional torque can be reduced by 29.1% and 26.2%, respectively.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139126305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：