Water lubricated bearings can be used to reduce contamination due to lubricant leakage in heavy machinery such as power positioning systems of offshore platforms and ship propulsion systems. The lubrication model of a textured two-dimensional parallel friction pair and a textured water-lubricated journal bearing are developed to investigate the lubrication performance. The governing equation is solved, and the fluid cavitation is analyzed using the Zwart-Gerber-Belamri (ZGB) model. A multi-objective optimization method combining the response surface and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is used to optimize the textured journal bearings. The results indicate that a small texture width will inhibit the occurrence of liquid film cavitation. With the rise in the texture width, the cavitation effect gradually rises and stabilizes. As the texture depth deepens, the micro dynamic pressure effect is enhanced and liquid film pressure rises. Through the tests, it is found that the optimized texture parameters can be implemented to effectively diminish the friction and wear volume, also the optimized textured bearing hydrodynamic pressure effect is enhanced at the same speed.
{"title":"Investigation and Optimization of Textured Water-lubricated Journal Bearings Using Multi-objective Optimization","authors":"†. Q.Li, Y. Wang, X. Li, G. Zhang, Y. Du, W. Xu","doi":"10.47176/jafm.17.9.2581","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2581","url":null,"abstract":"Water lubricated bearings can be used to reduce contamination due to lubricant leakage in heavy machinery such as power positioning systems of offshore platforms and ship propulsion systems. The lubrication model of a textured two-dimensional parallel friction pair and a textured water-lubricated journal bearing are developed to investigate the lubrication performance. The governing equation is solved, and the fluid cavitation is analyzed using the Zwart-Gerber-Belamri (ZGB) model. A multi-objective optimization method combining the response surface and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is used to optimize the textured journal bearings. The results indicate that a small texture width will inhibit the occurrence of liquid film cavitation. With the rise in the texture width, the cavitation effect gradually rises and stabilizes. As the texture depth deepens, the micro dynamic pressure effect is enhanced and liquid film pressure rises. Through the tests, it is found that the optimized texture parameters can be implemented to effectively diminish the friction and wear volume, also the optimized textured bearing hydrodynamic pressure effect is enhanced at the same speed.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683265","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 issue of pedestrian-level wind environments around high-rise buildings is closely related to the comfort and safety of human settlements. In this paper, we study the effects of different wind direction angles and spacing ratios on the wind environment at pedestrian heights around buildings arranged in an equilateral triangle configuration. Three-dimensional steady-state numerical simulation was employed, with the standard k-ε model selected as the turbulence model. Wind speed ratios and different area ratio parameters are used to quantitatively express the degree and range of influence of wind speed by buildings. The results show that the maximum wind speed ratio at the corner of a building is greatly affected by the wind direction angle, with 45°, 135°, and 157.5° being the unfavorable wind direction angles. Conversely, the area ratio of different areas is greatly affected by the spacing ratio. As the spacing ratio increases, the mutual interference effect between buildings weakens, resulting in a better pedestrian wind environment. Owing to the unique layout of the building group, different degrees of ventilation corridors are formed among the three buildings. The wind speed amplification effect in the corridors is more significant, and the areas with poor wind environments are concentrated in these corridors.
{"title":"Integrated Impacts of Building Space Ratio and Wind Direction on Pedestrian-level Wind Environment around High-rise Buildings with Equilateral Triangle Arrangement","authors":"H. Cui, M. Ma, J. Li, L. Yang, Z. Han, Q. Liu","doi":"10.47176/jafm.17.9.2511","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2511","url":null,"abstract":"The issue of pedestrian-level wind environments around high-rise buildings is closely related to the comfort and safety of human settlements. In this paper, we study the effects of different wind direction angles and spacing ratios on the wind environment at pedestrian heights around buildings arranged in an equilateral triangle configuration. Three-dimensional steady-state numerical simulation was employed, with the standard k-ε model selected as the turbulence model. Wind speed ratios and different area ratio parameters are used to quantitatively express the degree and range of influence of wind speed by buildings. The results show that the maximum wind speed ratio at the corner of a building is greatly affected by the wind direction angle, with 45°, 135°, and 157.5° being the unfavorable wind direction angles. Conversely, the area ratio of different areas is greatly affected by the spacing ratio. As the spacing ratio increases, the mutual interference effect between buildings weakens, resulting in a better pedestrian wind environment. Owing to the unique layout of the building group, different degrees of ventilation corridors are formed among the three buildings. The wind speed amplification effect in the corridors is more significant, and the areas with poor wind environments are concentrated in these corridors.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681713","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 hydrodynamic coefficient of an underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6×103 ≤ Re ≤ 3×104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = −90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25.
{"title":"Numerical Study on the Hydrodynamic Coefficients and Flow Field Characteristics of Underwater Manipulator","authors":"S. Dai, S. Ren, X. Liu, D. Duan, H. Jin, H. Zhang","doi":"10.47176/jafm.17.9.2564","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2564","url":null,"abstract":"The hydrodynamic coefficient of an underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6×103 ≤ Re ≤ 3×104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = −90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683464","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}
F. Benzenine, C. Seladji, D. Darfilal, O. Bendermel
In this paper, an analytical approach combined with a two-dimensional computational fluid dynamics (CFD) model is pursued to simulate the fluid flow in a monopropellant thruster for satellite propulsion systems. The thruster utilizes hydrogen peroxide (H2O2) as a green propellant at a concentration of 87.5%, with a catalytic bed based on spherical silver particles. Through a parametric analysis of particle diameter, we aim to optimize the design of a monopropellant thruster capable of generating a thrust of 20N. For this purpose, a program in CFD code in the commercially available ANSYS Fluent software is used to solve the energy, momentum, mass transfer, and species transport equations governing the thruster system. The local thermal non-equilibrium (LTNE) approach is used to describe the heat transfer occurring through both the solid and fluid phases within the catalyst bed. The results demonstrate that particle size significantly affects the thermal behaviour, species mass fraction, and exit velocity. An optimum diameter of 0.65mm exhibits the optimal performance of the monopropellant thruster, ensuring efficient decomposition of H2O2 at 968K and providing the required level of thrust force with a specific impulse of about 120s.
{"title":"Effect of Spherical Silver Particles Size of the Catalyst Bed on Hydrogen Peroxide Monopropellant Thruster Performance","authors":"F. Benzenine, C. Seladji, D. Darfilal, O. Bendermel","doi":"10.47176/jafm.17.9.2349","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2349","url":null,"abstract":"In this paper, an analytical approach combined with a two-dimensional computational fluid dynamics (CFD) model is pursued to simulate the fluid flow in a monopropellant thruster for satellite propulsion systems. The thruster utilizes hydrogen peroxide (H2O2) as a green propellant at a concentration of 87.5%, with a catalytic bed based on spherical silver particles. Through a parametric analysis of particle diameter, we aim to optimize the design of a monopropellant thruster capable of generating a thrust of 20N. For this purpose, a program in CFD code in the commercially available ANSYS Fluent software is used to solve the energy, momentum, mass transfer, and species transport equations governing the thruster system. The local thermal non-equilibrium (LTNE) approach is used to describe the heat transfer occurring through both the solid and fluid phases within the catalyst bed. The results demonstrate that particle size significantly affects the thermal behaviour, species mass fraction, and exit velocity. An optimum diameter of 0.65mm exhibits the optimal performance of the monopropellant thruster, ensuring efficient decomposition of H2O2 at 968K and providing the required level of thrust force with a specific impulse of about 120s.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681606","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}
Concerning dual-carbon applications, establishing a new energy-dominated power system to achieve carbon peaking and carbon neutrality objectives is imperative. Pumped storage units excel in this context, owing to their unique advantages. During the load-shedding process of the pump turbine, the intricate flow patterns and cavitation phenomena substantially influence the flow field. This study introduces a cavitation model to perform numerical simulations of load rejection processes in pumped storage power plants, aiming to thoroughly investigate the impact of cavitation phenomena on the units. The results indicate that as the rotational speed increases, the dynamic and static interference within the no-blade region becomes notable, resulting in pressure pulsations within the guide vane region and exacerbating structural deformation and fatigue failures. Moreover, deviations from the designated operational point disrupt the symmetry of the flow field, leading to irregular changes in radial forces. Accounting for the mass disturbance and changes in wave velocity attributable to a cavitation phase transition, pressure fluctuation amplitude increases within the draft tube, consequently engendering complex flow phenomena. These findings offer indispensable guidance for the optimal design and safe operation of pump turbines within new power systems.
{"title":"Flow Characteristics Analysis of Load Rejection Transition Process in Pumped Storage Unit Based on Cavitation Model","authors":"Q. Li, L. Xin, L. Yao, S. Zhang","doi":"10.47176/jafm.17.9.2546","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2546","url":null,"abstract":"Concerning dual-carbon applications, establishing a new energy-dominated power system to achieve carbon peaking and carbon neutrality objectives is imperative. Pumped storage units excel in this context, owing to their unique advantages. During the load-shedding process of the pump turbine, the intricate flow patterns and cavitation phenomena substantially influence the flow field. This study introduces a cavitation model to perform numerical simulations of load rejection processes in pumped storage power plants, aiming to thoroughly investigate the impact of cavitation phenomena on the units. The results indicate that as the rotational speed increases, the dynamic and static interference within the no-blade region becomes notable, resulting in pressure pulsations within the guide vane region and exacerbating structural deformation and fatigue failures. Moreover, deviations from the designated operational point disrupt the symmetry of the flow field, leading to irregular changes in radial forces. Accounting for the mass disturbance and changes in wave velocity attributable to a cavitation phase transition, pressure fluctuation amplitude increases within the draft tube, consequently engendering complex flow phenomena. These findings offer indispensable guidance for the optimal design and safe operation of pump turbines within new power systems.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141682956","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}
This study utilizes numerical simulations and dimensional analysis to investigate the impact of the two-phase outlet on flow field characteristics and separation efficiency of the separator. The study revealed a boundary layer separation at the water outlet, which was subsequently addressed to reduce energy losses in the separator. Dimensional analysis considered the influences of operational, structural, and physical parameters on the separator's performance. With other structural parameters held constant, separation efficiency is directly proportional to the ratio of inlet and oil-outlet diameter. Additionally, the separation efficiency is also associated with Re and the ratio of the inlet to the water-outlet diameter. When the diameter of the water outlet is constant, the axial vortex separator achieves optimal separation when the ratio of inlet and water-outlet diameter is 0.563, with a maximum separation efficiency of 97.00%. The optimal separation efficiency is reached at Re=22,908 under various operational conditions. Separation efficiency increases with water content, peaking at an inlet water content of 0.9 across different structural parameters. Separation efficiency shows an increase followed by a decrease with the rise in inlet flow rate(vi), achieving the best performance at vi=3m/s for the different separator structures studied.
{"title":"Numerical Simulation Study of the Effect of Outlet on the Axial Vortex Separator","authors":"H. Lou, †. X.Zhang, X. Liu, Y. Wang, R. Liao","doi":"10.47176/jafm.17.9.2461","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2461","url":null,"abstract":"This study utilizes numerical simulations and dimensional analysis to investigate the impact of the two-phase outlet on flow field characteristics and separation efficiency of the separator. The study revealed a boundary layer separation at the water outlet, which was subsequently addressed to reduce energy losses in the separator. Dimensional analysis considered the influences of operational, structural, and physical parameters on the separator's performance. With other structural parameters held constant, separation efficiency is directly proportional to the ratio of inlet and oil-outlet diameter. Additionally, the separation efficiency is also associated with Re and the ratio of the inlet to the water-outlet diameter. When the diameter of the water outlet is constant, the axial vortex separator achieves optimal separation when the ratio of inlet and water-outlet diameter is 0.563, with a maximum separation efficiency of 97.00%. The optimal separation efficiency is reached at Re=22,908 under various operational conditions. Separation efficiency increases with water content, peaking at an inlet water content of 0.9 across different structural parameters. Separation efficiency shows an increase followed by a decrease with the rise in inlet flow rate(vi), achieving the best performance at vi=3m/s for the different separator structures studied.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681024","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}
In order to investigate the influence of plasma actuation on cavitation in the flow field around a hydrofoil, the RNG k-ε turbulence model with density correction, the Schnerr–Sauer cavitation model, and the plasma phenomenological model were used to analyze the influence of forward and reverse plasma actuation on the cavitation characteristics of the NACA66(MOD) hydrofoil at an angle of attack of 8. The cavitation number of the incoming flow was 0.99. The results showed that under the positive excitation condition, the cavitation volume on the suction side of the hydrofoil was reduced by about 30%, and the time-averaged lift–drag ratio was reduced by about 5%, which had little influence on the re-entrant jet, vortex and shear flow. Therefore, the cavitation suppression effect on the hydrofoil flow field was weak. Under the condition of reverse actuation, the volume of cavitation on the suction side of the hydrofoil was reduced by about 87%, and the time-averaged lift–drag ratio was increased by about 21%, which effectively worsened the development conditions of cavitation. By greatly reducing the intensity of the re-entrant jet and eliminating the vortex and shear flow in the flow field, cavitation in the hydrofoil flow field was obviously suppressed. This shows that reasonable plasma actuation is an effective means to control hydrofoil cavitation.
{"title":"Numerical Study on the Influence of Plasma Actuation on the Cavitation Characteristics of Hydrofoil","authors":"R. Guo, L. Wang, R. Li, X. Zhang","doi":"10.47176/jafm.17.9.2553","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2553","url":null,"abstract":"In order to investigate the influence of plasma actuation on cavitation in the flow field around a hydrofoil, the RNG k-ε turbulence model with density correction, the Schnerr–Sauer cavitation model, and the plasma phenomenological model were used to analyze the influence of forward and reverse plasma actuation on the cavitation characteristics of the NACA66(MOD) hydrofoil at an angle of attack of 8. The cavitation number of the incoming flow was 0.99. The results showed that under the positive excitation condition, the cavitation volume on the suction side of the hydrofoil was reduced by about 30%, and the time-averaged lift–drag ratio was reduced by about 5%, which had little influence on the re-entrant jet, vortex and shear flow. Therefore, the cavitation suppression effect on the hydrofoil flow field was weak. Under the condition of reverse actuation, the volume of cavitation on the suction side of the hydrofoil was reduced by about 87%, and the time-averaged lift–drag ratio was increased by about 21%, which effectively worsened the development conditions of cavitation. By greatly reducing the intensity of the re-entrant jet and eliminating the vortex and shear flow in the flow field, cavitation in the hydrofoil flow field was obviously suppressed. This shows that reasonable plasma actuation is an effective means to control hydrofoil cavitation.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681120","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. A. Hussain, M. A. Al-Obaidi, A. S. Mohammed, Y. M. John, F. L. Rashid
Understanding the ecological conditions of vegetation growth in water sources is vital to appraise the influence of vegetation on river engineering. Based on the experimental information that is accessible, the consequences of vegetation on flow resistance is described as an alteration in the drag coefficient and the planned area. The current study analytically estimates the vertical distribution of stream-wise velocity in open-channel flow while considering rigid and flexible vegetation. The flow is vertically separated into top free water layer and bottom vegetation layer using the projected deflection height of both vegetation. Related momentum calculations for each layer are then derived. Based on the gathered experimental data, a 3D numerical model with various simulation situations is used to model, calibrate, and evaluate the artificial cylinders. A considerable deflection analysis is utilised to calculate the velocity-dependent stem height. This has proven to be more precise compared to formerly deflection investigation. The estimated outcomes show that precise predictions may be made for the vertical contours of vertical Reynolds shear stress based on mean horizontal velocity. The numerical simulations demonstrate that plant flexibility reduces the vertical Reynolds shear stress and prompted flow resistance force of the vegetation.
{"title":"Distribution of the Velocity Profile via Analytical and Three-Dimensional Numerical Vegetation Modeling","authors":"A. A. Hussain, M. A. Al-Obaidi, A. S. Mohammed, Y. M. John, F. L. Rashid","doi":"10.47176/jafm.17.9.2487","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2487","url":null,"abstract":"Understanding the ecological conditions of vegetation growth in water sources is vital to appraise the influence of vegetation on river engineering. Based on the experimental information that is accessible, the consequences of vegetation on flow resistance is described as an alteration in the drag coefficient and the planned area. The current study analytically estimates the vertical distribution of stream-wise velocity in open-channel flow while considering rigid and flexible vegetation. The flow is vertically separated into top free water layer and bottom vegetation layer using the projected deflection height of both vegetation. Related momentum calculations for each layer are then derived. Based on the gathered experimental data, a 3D numerical model with various simulation situations is used to model, calibrate, and evaluate the artificial cylinders. A considerable deflection analysis is utilised to calculate the velocity-dependent stem height. This has proven to be more precise compared to formerly deflection investigation. The estimated outcomes show that precise predictions may be made for the vertical contours of vertical Reynolds shear stress based on mean horizontal velocity. The numerical simulations demonstrate that plant flexibility reduces the vertical Reynolds shear stress and prompted flow resistance force of the vegetation.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141682212","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 working fluids at supercritical pressures will experience abnormal heat transfer compared with those in a sub-critical state. In particular, the heat transfer deterioration (HTD) can make the wall temperature increase sharply in the tube, posing a challenge for the design of heat exchangers in the supercritical organic Rankine cycle (SORC). It is generally acknowledged that the effects of buoyancy and flow acceleration lead to abnormal heat transfer. However, a clear understanding of the interactions between the turbulent flow and heat transfer characteristics still needs to be further improved by obtaining the internal flow mechanism. The current study analyses the contours of the turbulent flow information under the different boundary conditions by means of validated CFD numerical simulation based on the previous experimental data and reveals the main causes of HTD and the impact mechanism of boundary conditions. The results reveal that two deteriorated extreme points are generated in a vertical upward tube with uniform heat flux for hexamethyldisiloxane at supercritical pressures. The buoyancy and flow acceleration effects caused by the drastic variation in fluid density near the pseudo-critical temperature can deform the velocity profile, thus reducing the local shear stress and turbulence intensity, and leading to the HTD. Moreover, HTD gets worse with the increase in heat flux and moderate with the rise in supercritical pressure. This study should support the data and theory for the refined design of heaters applied to the SORC in the future.
{"title":"Numerical Analysis of Mechanism on Heat Transfer Deterioration of Hexamethyldisiloxane in a Vertical Upward Tube at Supercritical Pressures","authors":"J. Fu, H. Y. Liu, Y. Wang","doi":"10.47176/jafm.17.9.2600","DOIUrl":"https://doi.org/10.47176/jafm.17.9.2600","url":null,"abstract":"The working fluids at supercritical pressures will experience abnormal heat transfer compared with those in a sub-critical state. In particular, the heat transfer deterioration (HTD) can make the wall temperature increase sharply in the tube, posing a challenge for the design of heat exchangers in the supercritical organic Rankine cycle (SORC). It is generally acknowledged that the effects of buoyancy and flow acceleration lead to abnormal heat transfer. However, a clear understanding of the interactions between the turbulent flow and heat transfer characteristics still needs to be further improved by obtaining the internal flow mechanism. The current study analyses the contours of the turbulent flow information under the different boundary conditions by means of validated CFD numerical simulation based on the previous experimental data and reveals the main causes of HTD and the impact mechanism of boundary conditions. The results reveal that two deteriorated extreme points are generated in a vertical upward tube with uniform heat flux for hexamethyldisiloxane at supercritical pressures. The buoyancy and flow acceleration effects caused by the drastic variation in fluid density near the pseudo-critical temperature can deform the velocity profile, thus reducing the local shear stress and turbulence intensity, and leading to the HTD. Moreover, HTD gets worse with the increase in heat flux and moderate with the rise in supercritical pressure. This study should support the data and theory for the refined design of heaters applied to the SORC in the future.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141680721","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}
Noise is one of the key indicators to evaluate axial flow fans, and in many cases, it is also the only indicator for determining their suitability for use. In this study, a new method to reduce axial fan’s noise was proposed for changing the section chord length to transform the blades of two axial fans with the same design parameters but distinct chord lengths to wavy blades. The aerodynamic calculations and noise reduction mechanism of the wavy configuration of the two fans were studied by combining CFD of large eddy simulation with the Lighthill acoustic analogy method. The results showed that the main mechanism contributing to noise reduction through wavy configuration was the promotion of transformation of the blade surface's layered vortex structure into an uncorrelated comb vortex structure. For fan blades with smaller chord lengths, the comb structure with low spanwise correlation was still maintained after the trailing edge, while for fan blades with larger chord lengths, the comb structure of the shedding vortex rapidly dissipated downstream of the trailing edge. Under the rated design conditions, the implementation of wavy leading edge blades resulted in noise reductions of 1.9 dB and 1.5 dB for the two fans, respectively, while wavy trailing edge blades yielded reductions of 2.6 dB and 2.1 dB, respectively. Furthermore, the adoption of wavy configuration induced a phenomenon of pressure increase and efficiency decrease in both axial fans at medium and low flow rates, with minimal impact at high flow rates. These outcomes underscored the superior noise reduction efficacy of the wavy trailing edge blades, offering a promising way for the noise reduction design of axial flow fans.
{"title":"Enhancing Axial Fan Noise Reduction through Innovative Wavy Blade Configurations","authors":"W. C. Qi, K. Cheng, P. C. Li, †. J.Y.Li","doi":"10.47176/jafm.17.7.2442","DOIUrl":"https://doi.org/10.47176/jafm.17.7.2442","url":null,"abstract":"Noise is one of the key indicators to evaluate axial flow fans, and in many cases, it is also the only indicator for determining their suitability for use. In this study, a new method to reduce axial fan’s noise was proposed for changing the section chord length to transform the blades of two axial fans with the same design parameters but distinct chord lengths to wavy blades. The aerodynamic calculations and noise reduction mechanism of the wavy configuration of the two fans were studied by combining CFD of large eddy simulation with the Lighthill acoustic analogy method. The results showed that the main mechanism contributing to noise reduction through wavy configuration was the promotion of transformation of the blade surface's layered vortex structure into an uncorrelated comb vortex structure. For fan blades with smaller chord lengths, the comb structure with low spanwise correlation was still maintained after the trailing edge, while for fan blades with larger chord lengths, the comb structure of the shedding vortex rapidly dissipated downstream of the trailing edge. Under the rated design conditions, the implementation of wavy leading edge blades resulted in noise reductions of 1.9 dB and 1.5 dB for the two fans, respectively, while wavy trailing edge blades yielded reductions of 2.6 dB and 2.1 dB, respectively. Furthermore, the adoption of wavy configuration induced a phenomenon of pressure increase and efficiency decrease in both axial fans at medium and low flow rates, with minimal impact at high flow rates. These outcomes underscored the superior noise reduction efficacy of the wavy trailing edge blades, offering a promising way for the noise reduction design of axial flow fans.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141693561","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}
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