Pub Date : 2025-01-15DOI: 10.1016/j.ijheatfluidflow.2025.109746
Keyhan Kouzegar Ghiyasi, Siamak Hossainpour
This study investigates the effect of surface geometry on nucleate pool boiling heat transfer, focusing on smooth, rectangular finned, and trapezoidal finned surfaces. Using the Volume of Fluid (VOF) method in a two-dimensional numerical analysis, the research provides comprehensive insights into bubble dynamics, including nucleation, growth, detachment, and liquid–vapor interactions. The study shows good agreement between the numerical model results and experimental data, confirming the accuracy and reliability of the VOF method in simulating complex boiling phenomena. The results indicate that finned surfaces significantly enhance heat transfer compared to smooth surfaces, with trapezoidal fins demonstrating the best performance. Trapezoidal fins improved by 133% in the heat transfer coefficient (HTC) and 210% in heat flux compared to smooth surfaces, attributed to their optimized geometry that enhances bubble dynamics and thermal efficiency. Rectangular fins also showed sensitivity to fin height and spacing changes, with improvements of up to 95% in HTC and 150% in heat flux. This study provides practical guidelines for designing advanced heat transfer surfaces, with significant applications in thermal management systems for industries such as power generation, cooling systems, and electronics.
{"title":"Comparative analysis of heat transfer enhancement in nucleate pool boiling using different fin geometries","authors":"Keyhan Kouzegar Ghiyasi, Siamak Hossainpour","doi":"10.1016/j.ijheatfluidflow.2025.109746","DOIUrl":"10.1016/j.ijheatfluidflow.2025.109746","url":null,"abstract":"<div><div>This study investigates the effect of surface geometry on nucleate pool boiling heat transfer, focusing on smooth, rectangular finned, and trapezoidal finned surfaces. Using the Volume of Fluid (VOF) method in a two-dimensional numerical analysis, the research provides comprehensive insights into bubble dynamics, including nucleation, growth, detachment, and liquid–vapor interactions. The study shows good agreement between the numerical model results and experimental data, confirming the accuracy and reliability of the VOF method in simulating complex boiling phenomena. The results indicate that finned surfaces significantly enhance heat transfer compared to smooth surfaces, with trapezoidal fins demonstrating the best performance. Trapezoidal fins improved by 133% in the heat transfer coefficient (HTC) and 210% in heat flux compared to smooth surfaces, attributed to their optimized geometry that enhances bubble dynamics and thermal efficiency. Rectangular fins also showed sensitivity to fin height and spacing changes, with improvements of up to 95% in HTC and 150% in heat flux. This study provides practical guidelines for designing advanced heat transfer surfaces, with significant applications in thermal management systems for industries such as power generation, cooling systems, and electronics.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109746"},"PeriodicalIF":2.6,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-09DOI: 10.1016/j.ijheatfluidflow.2024.109724
Victoria Hamtiaux , Pierre Ruyer , Yann Bartosiewicz
This paper presents a numerical investigation involving Direct Numerical Simulations (DNS) of natural convection occurring within mixed domains of porous and pure fluids, featuring an internally heated solid matrix. Our study does not aim to replicate 1:1 scale of Spent Fuel Pool (SFP) scenarios during Loss of Cooling Accidents (LOCA), but rather focuses on a reduced scale mock-up of such pool while keeping essential phenomena. By doing such, this study does provide valuable insights into the intricate dynamics of fluid flow and heat transfer in such prototypical configuration. We conduct a sensitivity analysis on the parameters driving the physical modeling of the porous medium, revealing the substantial influence of the drag on key features of the heat and mass transfers such as the Large-Scale Circulation (LSC), mass flow rates, temperatures within the porous medium, and overall heat transfer process. In a domain scaled to represent a reduced-scale SFP (1:200), we explore the effects of varying rack heights relative to the bottom wall. This variation significantly affects temperature distribution within both the bottom layer and the porous medium. Notably, when the racks make contact with the bottom wall, a dual-roll LSC pattern emerges. Additionally, we examine the consequences of non-uniform heat load distribution within the racks. This distribution leads to larger maximum temperatures within the most heated region of the porous medium. However, it also results in lower area-averaged temperatures due to increased horizontal diffusion and mixing. Consequently, the Nusselt number within the pure-fluid region is reduced compared to a scenario with uniform heat load distribution.
{"title":"Natural convection through and over a heating porous medium: Towards high fidelity simulations of nuclear spent fuel pools","authors":"Victoria Hamtiaux , Pierre Ruyer , Yann Bartosiewicz","doi":"10.1016/j.ijheatfluidflow.2024.109724","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109724","url":null,"abstract":"<div><div>This paper presents a numerical investigation involving Direct Numerical Simulations (DNS) of natural convection occurring within mixed domains of porous and pure fluids, featuring an internally heated solid matrix. Our study does not aim to replicate 1:1 scale of Spent Fuel Pool (SFP) scenarios during Loss of Cooling Accidents (LOCA), but rather focuses on a reduced scale mock-up of such pool while keeping essential phenomena. By doing such, this study does provide valuable insights into the intricate dynamics of fluid flow and heat transfer in such prototypical configuration. We conduct a sensitivity analysis on the parameters driving the physical modeling of the porous medium, revealing the substantial influence of the drag on key features of the heat and mass transfers such as the Large-Scale Circulation (LSC), mass flow rates, temperatures within the porous medium, and overall heat transfer process. In a domain scaled to represent a reduced-scale SFP (1:200), we explore the effects of varying rack heights relative to the bottom wall. This variation significantly affects temperature distribution within both the bottom layer and the porous medium. Notably, when the racks make contact with the bottom wall, a dual-roll LSC pattern emerges. Additionally, we examine the consequences of non-uniform heat load distribution within the racks. This distribution leads to larger maximum temperatures within the most heated region of the porous medium. However, it also results in lower area-averaged temperatures due to increased horizontal diffusion and mixing. Consequently, the Nusselt number within the pure-fluid region is reduced compared to a scenario with uniform heat load distribution.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109724"},"PeriodicalIF":2.6,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-09DOI: 10.1016/j.ijheatfluidflow.2025.109743
Runze Yan , Qinghai Zhao , Chao Zhang , Qingheng Tang , Honghui Li
Effective thermal management is crucial for the thermal safety and temperature uniformity of Lithium-ion batteries. Taking inspiration from the natural leaf-vein structure, this paper proposes a cold plate with novel internal bionic leaf-vein liquid channels. Three-dimensional cold plate models are established according to the contour of leaf-vein for multi-physical field numerical simulations. The effects of different flow rates and inlet/outlet arrangements on the heat transfer performance are investigated. The velocity, temperature, and pressure fields are calculated with the finite element method. Compared with the conventional rectangular flow channel, the results demonstrate that the maximum temperature of the cooling plate with the bionic-type structure is reduced by 10.17 K and the heat transfer efficiency is increased by 22.43 %. Finally, the properties of the test samples are compared to verify the numerical results. The proposed bionic leaf-vein cooling channels provide a positive direction for designing lithium-ion battery cooling systems to control the temperature distribution of the cell module.
{"title":"Research on liquid-cooling structure for lithium-ion battery with bionic leaf-vein liquid channels","authors":"Runze Yan , Qinghai Zhao , Chao Zhang , Qingheng Tang , Honghui Li","doi":"10.1016/j.ijheatfluidflow.2025.109743","DOIUrl":"10.1016/j.ijheatfluidflow.2025.109743","url":null,"abstract":"<div><div>Effective thermal management is crucial for the thermal safety and temperature uniformity of Lithium-ion batteries. Taking inspiration from the natural leaf-vein structure, this paper proposes a cold plate with novel internal bionic leaf-vein liquid channels. Three-dimensional cold plate models are established according to the contour of leaf-vein for multi-physical field numerical simulations. The effects of different flow rates and inlet/outlet arrangements on the heat transfer performance are investigated. The velocity, temperature, and pressure fields are calculated with the finite element method. Compared with the conventional rectangular flow channel, the results demonstrate that the maximum temperature of the cooling plate with the bionic-type structure is reduced by 10.17 K and the heat transfer efficiency is increased by 22.43 %. Finally, the properties of the test samples are compared to verify the numerical results. The proposed bionic leaf-vein cooling channels provide a positive direction for designing lithium-ion battery cooling systems to control the temperature distribution of the cell module.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109743"},"PeriodicalIF":2.6,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-09DOI: 10.1016/j.ijheatfluidflow.2024.109740
Yu-Ren Chien , Chiang Fu , Ying-Hao Liao
This study investigates the impact of a DC electric field on the lift-off height and ion current of a laminar lifted non-premixed jet flame. The experimental setup includes two horizontal electrodes that creates a vertical electric field aligned with the jet flow, with a positive field directing from the burner toward the downstream electrode. Results show that a DC electric field, regardless of polarity, reduces the flame lift-off height, with sufficiently strong fields causing flame reattachment. Flames with higher fuel flow rates exhibit larger lift-off heights and require stronger electric fields for reattachment, whereas lower flow rates are more sensitive to the applied field. Negative electric fields are more effective at reducing lift-off height and generating higher ion currents than positive fields. Ion current measurements reveal a strong correlation between field strength and flame reattachment, with ion current increasing significantly as the flame transitions from lift-off to reattachment. The study proposes a scaling relation between ion current, flame lift-off height, and electric field strength, demonstrating that ionic wind driven by the electric force plays a crucial role in flame stabilization. These findings suggest that DC electric fields offer a promising approach for controlling flame behavior, with potential applications in enhancing combustion efficiency and stability.
{"title":"The ion current response of a laminar lifted non-premixed flame in a DC electric field","authors":"Yu-Ren Chien , Chiang Fu , Ying-Hao Liao","doi":"10.1016/j.ijheatfluidflow.2024.109740","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109740","url":null,"abstract":"<div><div>This study investigates the impact of a DC electric field on the lift-off height and ion current of a laminar lifted non-premixed jet flame. The experimental setup includes two horizontal electrodes that creates a vertical electric field aligned with the jet flow, with a positive field directing from the burner toward the downstream electrode. Results show that a DC electric field, regardless of polarity, reduces the flame lift-off height, with sufficiently strong fields causing flame reattachment. Flames with higher fuel flow rates exhibit larger lift-off heights and require stronger electric fields for reattachment, whereas lower flow rates are more sensitive to the applied field. Negative electric fields are more effective at reducing lift-off height and generating higher ion currents than positive fields. Ion current measurements reveal a strong correlation between field strength and flame reattachment, with ion current increasing significantly as the flame transitions from lift-off to reattachment. The study proposes a scaling relation between ion current, flame lift-off height, and electric field strength, demonstrating that ionic wind driven by the electric force plays a crucial role in flame stabilization. These findings suggest that DC electric fields offer a promising approach for controlling flame behavior, with potential applications in enhancing combustion efficiency and stability.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109740"},"PeriodicalIF":2.6,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-08DOI: 10.1016/j.ijheatfluidflow.2025.109744
Jin Wang , Jin Yao , Xuan Liang , Zhenxin Li , Fei Lu , Lidija Čuček , Dan Zheng
Intercoolers are widely employed in automotive applications, especially in turbocharged engines, to enhance engine power output by cooling the intake air, which improves combustion efficiency and reduces the risk of engine knock. This paper investigates three innovative bionic textures in channels to enhance the heat transfer characteristics of intercoolers. The thermal–hydraulic performance of the intercooler is optimized by analyzing the geometric parameters of the bionic texture structures. The investigated geometric parameters of this study are the height (hc) and radius ratio (r) of the bionic crab surface texture, the groove length (s) and groove height (hs) of the bionic shark-skin texture as well as fish scale opening angle (α) and the inclination angle (β) of the bionic fish scale texture. The application of bionic textures in channels leads to a maximum increment of 14.95% in the heat transfer performance for the intercooler. This paper compares the thermal–hydraulic performance of the three bionic channel textures. Among the three bionic textures, the bionic crab shell texture demonstrates the optimal comprehensive performance, improving the JF factor by up to 15.02%. The increment in the JF factor achieved by the bionic crab shell texture is 175.95% and 42.35% higher than the maximum increments achieved by the bionic fish scale and bionic shark-skin textures, respectively. The application of nature-inspired designs to thermal systems offers a new pathway to enhance heat transfer in intercoolers. The results provide theoretical guidance for designing high-performance intercoolers with excellent thermal–hydraulic performance. By bridging bio-inspired design with heat exchangers, this study provides innovative solutions for more efficient cooling systems in automotive and industrial applications.
{"title":"Numerical investigation on thermal–hydraulic performance of an intercooler with bionic channel textures","authors":"Jin Wang , Jin Yao , Xuan Liang , Zhenxin Li , Fei Lu , Lidija Čuček , Dan Zheng","doi":"10.1016/j.ijheatfluidflow.2025.109744","DOIUrl":"10.1016/j.ijheatfluidflow.2025.109744","url":null,"abstract":"<div><div>Intercoolers are widely employed in automotive applications, especially in turbocharged engines, to enhance engine power output by cooling the intake air, which improves combustion efficiency and reduces the risk of engine knock. This paper investigates three innovative bionic textures in channels to enhance the heat transfer characteristics of intercoolers. The thermal–hydraulic performance of the intercooler is optimized by analyzing the geometric parameters of the bionic texture structures. The investigated geometric parameters of this study are the height (<em>h<sub>c</sub></em>) and radius ratio (<em>r</em>) of the bionic crab surface texture, the groove length (<em>s</em>) and groove height (<em>h</em><sub>s</sub>) of the bionic shark-skin texture as well as fish scale opening angle (<em>α</em>) and the inclination angle (<em>β</em>) of the bionic fish scale texture. The application of bionic textures in channels leads to a maximum increment of 14.95% in the heat transfer performance for the intercooler. This paper compares the thermal–hydraulic performance of the three bionic channel textures. Among the three bionic textures, the bionic crab shell texture demonstrates the optimal comprehensive performance, improving the <em>JF</em> factor by up to 15.02%. The increment in the <em>JF</em> factor achieved by the bionic crab shell texture is 175.95% and 42.35% higher than the maximum increments achieved by the bionic fish scale and bionic shark-skin textures, respectively. The application of nature-inspired designs to thermal systems offers a new pathway to enhance heat transfer in intercoolers. The results provide theoretical guidance for designing high-performance intercoolers with excellent thermal–hydraulic performance. By bridging bio-inspired design with heat exchangers, this study provides innovative solutions for more efficient cooling systems in automotive and industrial applications.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109744"},"PeriodicalIF":2.6,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-08DOI: 10.1016/j.ijheatfluidflow.2024.109696
Shumpei Hara , Koji Fukudome , Kyoji Inaoka
Understanding scalar transport phenomena is crucial for effective turbulent mixing in various applications. However, this process is complex and challenging to grasp. Coherent structures offer insight into the mechanisms governing scalar dynamics in turbulent flows and can serve as a valuable tool for developing turbulence models. This study presents theoretical and numerical investigations of the transport equation for the vorticity–temperature correlation, known as “scalicity.” The transport equation for scalicity was derived through order estimation. Direct numerical simulations of turbulent-plane Couette flows with passive scalar transport were conducted. A notable spanwise-averaged scalicity fluctuation component was identified in the viscous and buffer layers. This component was analyzed by examining the high correlation between spanwise vorticity and temperature fluctuations, evaluating quadrant contributions, and decomposing the terms. Visualization of the instantaneous field with spanwise scalicity fluctuations highlighted the cyclical relationship between velocity streaks and longitudinal vortices and the unstable wall vorticity layer in turbulent heat transfer. Budget analysis of the transport equation provided insights into the velocity and temperature streaks associated with turbulent eddy structures.
{"title":"Role of coherent structures in the transport equation for the vorticity–temperature correlation","authors":"Shumpei Hara , Koji Fukudome , Kyoji Inaoka","doi":"10.1016/j.ijheatfluidflow.2024.109696","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109696","url":null,"abstract":"<div><div>Understanding scalar transport phenomena is crucial for effective turbulent mixing in various applications. However, this process is complex and challenging to grasp. Coherent structures offer insight into the mechanisms governing scalar dynamics in turbulent flows and can serve as a valuable tool for developing turbulence models. This study presents theoretical and numerical investigations of the transport equation for the vorticity–temperature correlation, known as “scalicity.” The transport equation for scalicity was derived through order estimation. Direct numerical simulations of turbulent-plane Couette flows with passive scalar transport were conducted. A notable spanwise-averaged scalicity fluctuation component was identified in the viscous and buffer layers. This component was analyzed by examining the high correlation between spanwise vorticity and temperature fluctuations, evaluating quadrant contributions, and decomposing the terms. Visualization of the instantaneous field with spanwise scalicity fluctuations highlighted the cyclical relationship between velocity streaks and longitudinal vortices and the unstable wall vorticity layer in turbulent heat transfer. Budget analysis of the transport equation provided insights into the velocity and temperature streaks associated with turbulent eddy structures.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109696"},"PeriodicalIF":2.6,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-06DOI: 10.1016/j.ijheatfluidflow.2024.109741
Ziwei Xia , Minxiang Su , Shuai Li , Jiaxin Shi , Wei Yu
Employing a combined approach of offline experiments and numerical simulations, this study investigates the temperature distribution of steel rods under various air temperatures during forced air-cooling to elucidate the cooling mechanisms of steel rods. At a wind speed of 22 m/s, an increase in air temperature significantly reduces the convective heat transfer coefficient. Continuous airflow creates regions of low Reynolds numbers at the top of the rod and high Reynolds numbers along its sides, significantly enhancing the side convective heat transfer coefficient over the top. Empirical formulas for heat transfer coefficients at different rod positions were derived from experimental and simulation results and validated experimentally with a calculation error of less than 4 %.
{"title":"The influence of air temperature on heat transfer coefficient under forced air-cooling conditions","authors":"Ziwei Xia , Minxiang Su , Shuai Li , Jiaxin Shi , Wei Yu","doi":"10.1016/j.ijheatfluidflow.2024.109741","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109741","url":null,"abstract":"<div><div>Employing a combined approach of offline experiments and numerical simulations, this study investigates the temperature distribution of steel rods under various air temperatures during forced air-cooling to elucidate the cooling mechanisms of steel rods. At a wind speed of 22 m/s, an increase in air temperature significantly reduces the convective heat transfer coefficient. Continuous airflow creates regions of low Reynolds numbers at the top of the rod and high Reynolds numbers along its sides, significantly enhancing the side convective heat transfer coefficient over the top. Empirical formulas for heat transfer coefficients at different rod positions were derived from experimental and simulation results and validated experimentally with a calculation error of less than 4 %.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109741"},"PeriodicalIF":2.6,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-04DOI: 10.1016/j.ijheatfluidflow.2024.109742
Weiwei Cui , Yuqiang Liu , Long Zhang , Xinyuan Chen , Cuiping Wang
The clearance flow is closely linked to the tip flow characteristics and instability mechanisms of axial compressor rotor. Therefore, both experimental and numerical studies were conducted to investigate the influences of variations in clearance size on tip flow behaviors and instability mechanisms within a subsonic compressor rotor. The results show that the subsonic rotor has two distinct low-velocity zones due to tip leakage flow and suction surface separation at near-stall condition. As clearance size increases, suction surface separation decreases while tip leakage flow increases continuously. Within the small clearance size range (SCS range), the energy of leakage flow remains significantly lower than that of the surrounding mainstream at near-stall condition, leading it to be expelled from the tip channel by the mainstream. Thus, the substantial separation near suction surface induced by a pronounced positive angle of attack at leading edge, becomes the primary factor for tip flow instability in rotor at near-stall condition. Conversely, as clearance size further increased into large clearance size range (LCS range), suction surface separation nearly vanished near blade tip at near-stall condition, and the strong tip leakage vortex then dominates major disturbance in tip region. The low-velocity fluids generated by leakage vortex during unsteady fragmentation and dissipation obstructs the incoming mainstream in tip channel, contributing significantly to rotor stall. Consequently, it’s this progressively increasing leakage flow that leads to the stall margin of rotor showing an increasing and then decreasing trend in the clearance size monotonically increasing process, and fundamentally changes the stall inducing mechanism of the subsonic compressor rotor.
{"title":"Variations of stall mechanism induced by the changes of tip clearance size in a subsonic compressor rotor","authors":"Weiwei Cui , Yuqiang Liu , Long Zhang , Xinyuan Chen , Cuiping Wang","doi":"10.1016/j.ijheatfluidflow.2024.109742","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109742","url":null,"abstract":"<div><div>The clearance flow is closely linked to the tip flow characteristics and instability mechanisms of axial compressor rotor. Therefore, both experimental and numerical studies were conducted to investigate the influences of variations in clearance size on tip flow behaviors and instability mechanisms within a subsonic compressor rotor. The results show that the subsonic rotor has two distinct low-velocity zones due to tip leakage flow and suction surface separation at near-stall condition. As clearance size increases, suction surface separation decreases while tip leakage flow increases continuously. Within the small clearance size range (SCS range), the energy of leakage flow remains significantly lower than that of the surrounding mainstream at near-stall condition, leading it to be expelled from the tip channel by the mainstream. Thus, the substantial separation near suction surface induced by a pronounced positive angle of attack at leading edge, becomes the primary factor for tip flow instability in rotor at near-stall condition. Conversely, as clearance size further increased into large clearance size range (LCS range), suction surface separation nearly vanished near blade tip at near-stall condition, and the strong tip leakage vortex then dominates major disturbance in tip region. The low-velocity fluids generated by leakage vortex during unsteady fragmentation and dissipation obstructs the incoming mainstream in tip channel, contributing significantly to rotor stall. Consequently, it’s this progressively increasing leakage flow that leads to the stall margin of rotor showing an increasing and then decreasing trend in the clearance size monotonically increasing process, and fundamentally changes the stall inducing mechanism of the subsonic compressor rotor.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109742"},"PeriodicalIF":2.6,"publicationDate":"2025-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-01-04DOI: 10.1016/j.ijheatfluidflow.2024.109728
Van Thuan Hoang, Azadeh Jafari, Benjamin Cazzolato, Maziar Arjomandi
Burst events in the near-wall region of turbulent boundary layers are the main contributors to skin friction drag in wall flows. This paper shows how synthetic jets modify the near-wall burst events in turbulent boundary layers, leading to local drag reduction. Different characteristics of synthetic jets including various non-dimensional jet frequencies, ranging from 0.025 to 0.063, at two non-dimensional jet amplitudes of 0.1 and 0.2 were examined by conducting hot-wire measurements at a Reynolds number of 1050. Statistical analysis utilizing a variable-interval time-averaging (VITA) technique illustrated a reduction of up to 15% in burst intensity and a decrease of approximately 10% in burst durations within the near-wall region, , indicating that synthetic jets lifted turbulent kinetic energy and weakened burst events in this region. Consequently, there was a reduction of up to approximately 14% in turbulence intensity near the wall, contributing to diminished shear stresses and local skin-friction drag. Furthermore, the synthetic jets generated a displacement of the inner peak of turbulent energy away from the wall, indicating that the synthetic jets shifted turbulent kinetic energy away from the wall. As the jet frequency or amplitude increased, the modification of the boundary layer became more pronounced.
{"title":"Modification of burst events in the near-wall region of turbulent boundary layers by synthetic jets","authors":"Van Thuan Hoang, Azadeh Jafari, Benjamin Cazzolato, Maziar Arjomandi","doi":"10.1016/j.ijheatfluidflow.2024.109728","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109728","url":null,"abstract":"<div><div>Burst events in the near-wall region of turbulent boundary layers are the main contributors to skin friction drag in wall flows. This paper shows how synthetic jets modify the near-wall burst events in turbulent boundary layers, leading to local drag reduction. Different characteristics of synthetic jets including various non-dimensional jet frequencies, ranging from 0.025 to 0.063, at two non-dimensional jet amplitudes of 0.1 and 0.2 were examined by conducting hot-wire measurements at a Reynolds number of <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>≈</mo></mrow></math></span> 1050. Statistical analysis utilizing a variable-interval time-averaging (VITA) technique illustrated a reduction of up to 15% in burst intensity and a decrease of approximately 10% in burst durations within the near-wall region, <span><math><mrow><msup><mrow><mi>y</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>≤</mo><mn>12</mn></mrow></math></span>, indicating that synthetic jets lifted turbulent kinetic energy and weakened burst events in this region. Consequently, there was a reduction of up to approximately 14% in turbulence intensity near the wall, contributing to diminished shear stresses and local skin-friction drag. Furthermore, the synthetic jets generated a displacement of the inner peak of turbulent energy away from the wall, indicating that the synthetic jets shifted turbulent kinetic energy away from the wall. As the jet frequency or amplitude increased, the modification of the boundary layer became more pronounced.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109728"},"PeriodicalIF":2.6,"publicationDate":"2025-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The elliptical heat exchanger tube at the low-temperature heating surface of a 600 MW unit is taken as an example, and under the action of plane standing wave field, the whole domain solution is carried out inside and outside the boundary layer of the elliptical tube by numerical simulation method. Considering the influence of the parameters such as the aspect ratio (AR), the pulsating Strouhal number St0 and pulsating Reynolds number Re0 on the characteristics of the acoustic streaming outside the tube, the intrinsic mechanism of the enhanced heat transfer and the removal of fouling is elucidated by in-depth discussion of the acoustic streaming structure, the strength, the scale and so on. Research results indicate that as the AR increases from 0.2 to 1, the external acoustic streaming structure around the tube transitions from four internal vortices to eight vortices (four internal and four external) under different St0 and Re0, with the internal and external vortices rotating in opposite directions. Due to the influence of internal and external vortices, the velocity in the direction of the central angle α exhibits peak-to-trough fluctuations, showcasing rich velocity distribution characteristics at different distances s from the elliptical tube. The larger the AR, the better the heat transfer effect closer to the wall surface. The inner and outer vortex sizes show a similar variation pattern; the smaller the inner vortex size, the better the ash removal effect. The relative Nusselt number NU and relative shear rate SH quantify the effects of heat transfer and ash removal, respectively, and low-frequency high-intensity acoustic streaming is favourable for both. When given Re0 or St0, the SH reaches a maximum at AR = 0.4. This is due to drastic changes in the acoustic streaming characteristics for this tube shape, which is reflected in the first-order sound pressure, radial acoustic streaming velocity, and the size of internal and external vortices.
{"title":"Study on heat transfer characteristics of elliptical heat exchange tubes under acoustic streaming","authors":"Yu Zhou, Genshan Jiang, Yu Jiang, Jianhao Sun, Hao Li, Zishu Zhou","doi":"10.1016/j.ijheatfluidflow.2024.109738","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109738","url":null,"abstract":"<div><div>The elliptical heat exchanger tube at the low-temperature heating surface of a 600 MW unit is taken as an example, and under the action of plane standing wave field, the whole domain solution is carried out inside and outside the boundary layer of the elliptical tube by numerical simulation method. Considering the influence of the parameters such as the aspect ratio (AR), the pulsating Strouhal number St<sub>0</sub> and pulsating Reynolds number Re<sub>0</sub> on the characteristics of the acoustic streaming outside the tube, the intrinsic mechanism of the enhanced heat transfer and the removal of fouling is elucidated by in-depth discussion of the acoustic streaming structure, the strength, the scale and so on. Research results indicate that as the AR increases from 0.2 to 1, the external acoustic streaming structure around the tube transitions from four internal vortices to eight vortices (four internal and four external) under different St<sub>0</sub> and Re<sub>0</sub>, with the internal and external vortices rotating in opposite directions. Due to the influence of internal and external vortices, the velocity in the direction of the central angle <em>α</em> exhibits peak-to-trough fluctuations, showcasing rich velocity distribution characteristics at different distances <em>s</em> from the elliptical tube. The larger the AR, the better the heat transfer effect closer to the wall surface. The inner and outer vortex sizes show a similar variation pattern; the smaller the inner vortex size, the better the ash removal effect. The relative Nusselt number NU and relative shear rate SH quantify the effects of heat transfer and ash removal, respectively, and low-frequency high-intensity acoustic streaming is favourable for both. When given Re<sub>0</sub> or St<sub>0</sub>, the SH reaches a maximum at AR = 0.4. This is due to drastic changes in the acoustic streaming characteristics for this tube shape, which is reflected in the first-order sound pressure, radial acoustic streaming velocity, and the size of internal and external vortices.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109738"},"PeriodicalIF":2.6,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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