This study examined the drag reduction properties of cylindrical flows across various asymmetric notched structures through numerical simulation and particle image velocimetry. The focus was on investigating the influence of the number of asymmetric grooves on the drag characteristics, including the mean drag, spectral characteristics, time-averaged streamlines, separation point prediction, time-averaged pressure, wake vortex strength, Reynolds stress, and turbulent kinetic energy. The results showed that the presence of asymmetric grooves significantly influenced these flow parameters. Notably, the improvement was optimal in the four-groove configuration, evidenced by the lowest mean drag coefficient (0.804), vortex shedding frequency (2.74 Hz), recirculation area length (1.208 D ), and pressure difference across the cylinder (81.76). Moreover, this configuration resulted in the weakest trailing vortex, a 45% reduction in the maximum Reynolds stress (0.011), and a 40.5% decrease in the maximum turbulent kinetic energy (0.05). Thus, the presence of asymmetric grooves had a significant positive effect on the cylindrical flow properties, though the degree of improvement decreased with further increase in the number of grooves.
{"title":"Flow Characteristics of Cylinders with Asymmetric Grooves: A Modeling and Experimental Study","authors":"F. Yan, W. Kong, H. Jiao, F. Peng, J. Zhang","doi":"10.47176/jafm.17.6.2354","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2354","url":null,"abstract":"This study examined the drag reduction properties of cylindrical flows across various asymmetric notched structures through numerical simulation and particle image velocimetry. The focus was on investigating the influence of the number of asymmetric grooves on the drag characteristics, including the mean drag, spectral characteristics, time-averaged streamlines, separation point prediction, time-averaged pressure, wake vortex strength, Reynolds stress, and turbulent kinetic energy. The results showed that the presence of asymmetric grooves significantly influenced these flow parameters. Notably, the improvement was optimal in the four-groove configuration, evidenced by the lowest mean drag coefficient (0.804), vortex shedding frequency (2.74 Hz), recirculation area length (1.208 D ), and pressure difference across the cylinder (81.76). Moreover, this configuration resulted in the weakest trailing vortex, a 45% reduction in the maximum Reynolds stress (0.011), and a 40.5% decrease in the maximum turbulent kinetic energy (0.05). Thus, the presence of asymmetric grooves had a significant positive effect on the cylindrical flow properties, though the degree of improvement decreased with further increase in the number of grooves.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141233688","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 sport of half-pipe skiing, characterized by its dynamic maneuvers and high-speed descents, often faces challenges posed by unpredictable wind conditions. To address this, an advanced wind-blocking system incorporating an air curtain capable of generating a jet flow is proposed. This pioneering design offers a dual advantage: the system can significantly reduce the windbreak size in the vertical dimension while maintaining a satisfactory wind-blocking effect. A comprehensive study is conducted to analyze the effects of the height of the windbreak and the jet emission angle from the air curtain. When the jet speed is 40 m/s, a 50° emission angle and a 2 m height of the windbreak result in an optimal wind-blocking effect. Furthermore, delving deeper to understand the underpinnings of this phenomenon, we discovered that a counterrotating vortex pair, which forms in the presence of this jet under crossflow conditions, plays a pivotal role in augmenting the wind-blocking capabilities of the system.
{"title":"Numerical Investigation of an Innovative Windbreak Design with Jet Flow Generated by an Air Curtain for Half-pipe Skiing","authors":"K. Liu, F. Liu, Q. Liu","doi":"10.47176/jafm.17.6.2400","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2400","url":null,"abstract":"The sport of half-pipe skiing, characterized by its dynamic maneuvers and high-speed descents, often faces challenges posed by unpredictable wind conditions. To address this, an advanced wind-blocking system incorporating an air curtain capable of generating a jet flow is proposed. This pioneering design offers a dual advantage: the system can significantly reduce the windbreak size in the vertical dimension while maintaining a satisfactory wind-blocking effect. A comprehensive study is conducted to analyze the effects of the height of the windbreak and the jet emission angle from the air curtain. When the jet speed is 40 m/s, a 50° emission angle and a 2 m height of the windbreak result in an optimal wind-blocking effect. Furthermore, delving deeper to understand the underpinnings of this phenomenon, we discovered that a counterrotating vortex pair, which forms in the presence of this jet under crossflow conditions, plays a pivotal role in augmenting the wind-blocking capabilities of the system.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141233702","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}
D. Wang, C. Song, C. Qiu, Y. Xu, W. Wang, P. I. Mihailovich
Radial pre-swirl systems are widely applied in the aviation industry to supply cooling air to high-pressure turbine blades in aircraft engines. The efficiency of the film cooling can significantly decline when the air pressure is insufficient. This study explored the synergistic optimization of pre-swirl nozzles and receiver holes to improve the pressure ratio of a radial pre-swirl system. To attain this objective, we established a surrogate model using an artificial neural network and adopted the particle swarm optimization algorithm to pinpoint the optimized geometric parameters within the defined design scope. The results revealed that the optimal performance was achieved when the pre-swirl-nozzle tangential angle reached 40.4368°, the receiver-hole axial angle reached 2.0286°, and the tangential angle reached 30°. Additionally, multiple computational simulations were performed under diverse operational conditions to validate the efficacy of this optimization. The results revealed a significant enhancement in the pressure-boosting efficiency of the radial pre-swirl system, with negligible impact on temperature increment. The optimized model exhibited a 16.93% higher pressure ratio and 1.6% higher temperature ratio than the baseline model. This improvement can be attributed to enhancements in the flow field and reductions in local losses.
{"title":"Cooperative Optimization of Pre-swirl Nozzles and Receiver Holes in a Radial Pre-swirl System Using an ANN-PSO Approach","authors":"D. Wang, C. Song, C. Qiu, Y. Xu, W. Wang, P. I. Mihailovich","doi":"10.47176/jafm.17.6.2441","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2441","url":null,"abstract":"Radial pre-swirl systems are widely applied in the aviation industry to supply cooling air to high-pressure turbine blades in aircraft engines. The efficiency of the film cooling can significantly decline when the air pressure is insufficient. This study explored the synergistic optimization of pre-swirl nozzles and receiver holes to improve the pressure ratio of a radial pre-swirl system. To attain this objective, we established a surrogate model using an artificial neural network and adopted the particle swarm optimization algorithm to pinpoint the optimized geometric parameters within the defined design scope. The results revealed that the optimal performance was achieved when the pre-swirl-nozzle tangential angle reached 40.4368°, the receiver-hole axial angle reached 2.0286°, and the tangential angle reached 30°. Additionally, multiple computational simulations were performed under diverse operational conditions to validate the efficacy of this optimization. The results revealed a significant enhancement in the pressure-boosting efficiency of the radial pre-swirl system, with negligible impact on temperature increment. The optimized model exhibited a 16.93% higher pressure ratio and 1.6% higher temperature ratio than the baseline model. This improvement can be attributed to enhancements in the flow field and reductions in local losses.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141232322","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 investigates the cooling features of sweeping jets with phase changes, providing insights into how parameters affect heat transfer. The study aims to improve heat transfer by investigating the cooling effects of a sweeping jet impinging on a concave wall. The Eulerian-Lagrangian particle tracking method was used to examine the impact of Reynolds number, droplet diameter, mist capacity, and impingement distance on heat transfer properties during the sweeping jet impingement cooling. Increasing the Reynolds number from 20,000 to 35,200 results in a 7.1% and 3.3% decrease in average temperature at the axial centerline of the impingement wall, attributed to the cooling effect from droplet phase change. Decreasing droplet diameter from 20 µm to 10 µm reduces temperature amplitude by 11K. At 5% and 7.5% mist ratios, the cooling performance is similar to that of dry air. However, a mist injection of 10% significantly amplifies the cooling effect by 18.8%, providing a more efficient cooling experience. This investigation provides essential perspectives on impingement cooling, offering insights into the impact of various parameters on heat transfer enhancement.
{"title":"Numerical Investigation of the Impingement Cooling Characteristics of Sweeping Jets with Phase Change","authors":"W. He, A. Adam, P. Su, H. An, D. Han, C. Wang","doi":"10.47176/jafm.17.6.2258","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2258","url":null,"abstract":"This study investigates the cooling features of sweeping jets with phase changes, providing insights into how parameters affect heat transfer. The study aims to improve heat transfer by investigating the cooling effects of a sweeping jet impinging on a concave wall. The Eulerian-Lagrangian particle tracking method was used to examine the impact of Reynolds number, droplet diameter, mist capacity, and impingement distance on heat transfer properties during the sweeping jet impingement cooling. Increasing the Reynolds number from 20,000 to 35,200 results in a 7.1% and 3.3% decrease in average temperature at the axial centerline of the impingement wall, attributed to the cooling effect from droplet phase change. Decreasing droplet diameter from 20 µm to 10 µm reduces temperature amplitude by 11K. At 5% and 7.5% mist ratios, the cooling performance is similar to that of dry air. However, a mist injection of 10% significantly amplifies the cooling effect by 18.8%, providing a more efficient cooling experience. This investigation provides essential perspectives on impingement cooling, offering insights into the impact of various parameters on heat transfer enhancement.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141232967","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}
J. Chu, L. L. Xiao, C. S. Lin, S. Liu, K. X. Zhang, P. Wei
Bifurcated vessels represent a typical vascular unit of the cardiovascular system. In this study, the blood flow in symmetric and asymmetric bifurcated vessels are simulated based on computational fluid dynamics method. The blood is modeled as non-Newtonian fluid, and the pulsatile flow velocity is applied on the inlet. The effects of the fluid model, bifurcation angle and symmetry of the geometry of the vessel are investigated. The results show that the wall shear stress (WSS) on the outer wall of daughter branches for the non-Newtonian fluid flow is greater than that for Newtonian fluid flow, and the discrepancy between the flow of two fluid models is obvious at relatively low flow rates. With the bifurcation angle increases, the peak axial velocity of the cross-section of daughter branch decreases, so the WSS increases. For the non-Newtonian fluid flow in the asymmetric bifurcated vessels, more flow passes through the daughter vessel with a lower angle, and the WSS along the outer wall of which is lower. Furthermore, the region with a low time-averaged wall stress (TAWSS) and high oscillating shear index(OSI) distributed on the outer wall of bifurcation vessels are larger for the flow in the vessel with smaller bifurcation angle
{"title":"Simulation of Non-Newtonian Blood Flow in Diverging Bifurcated Vessels","authors":"J. Chu, L. L. Xiao, C. S. Lin, S. Liu, K. X. Zhang, P. Wei","doi":"10.47176/jafm.17.6.2329","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2329","url":null,"abstract":"Bifurcated vessels represent a typical vascular unit of the cardiovascular system. In this study, the blood flow in symmetric and asymmetric bifurcated vessels are simulated based on computational fluid dynamics method. The blood is modeled as non-Newtonian fluid, and the pulsatile flow velocity is applied on the inlet. The effects of the fluid model, bifurcation angle and symmetry of the geometry of the vessel are investigated. The results show that the wall shear stress (WSS) on the outer wall of daughter branches for the non-Newtonian fluid flow is greater than that for Newtonian fluid flow, and the discrepancy between the flow of two fluid models is obvious at relatively low flow rates. With the bifurcation angle increases, the peak axial velocity of the cross-section of daughter branch decreases, so the WSS increases. For the non-Newtonian fluid flow in the asymmetric bifurcated vessels, more flow passes through the daughter vessel with a lower angle, and the WSS along the outer wall of which is lower. Furthermore, the region with a low time-averaged wall stress (TAWSS) and high oscillating shear index(OSI) distributed on the outer wall of bifurcation vessels are larger for the flow in the vessel with smaller bifurcation angle","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141229893","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 self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that
{"title":"Study of the Self-starting Performance of a Vertical-axis Wind Turbine","authors":"Z. Xu, X. Dong, K. Li, Q. Zhou, Y. Zhao","doi":"10.47176/jafm.17.6.2295","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2295","url":null,"abstract":"The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. \"The minimum 1st derivative of angular acceleration in the lift acceleration state\" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141229804","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 diffusion porous media combustion is one possible way to eliminate the drawbacks of the existing combustion systems. Inverse diffusion flame (IDF) has features of both premixed and non-premixed flames. To integrate the advantages of porous media combustion with IDF, inverse diffusion porous (IDP) medium burner is tested for change in flame morphology and emissions at different equivalence ratio ( ɸ ). The porous media located at the exit of IDF burner has potential to deliver minimum flame length with low emissions. Flame appearance, flame height, flame zones etc. and emissions are experimentally investigated. Methane is used as fuel. Visible flame height is captured digitally and evaluated using ImageJ software. Central plane flame temperature is measured experimentally. CO and NO X emissions are recorded with Testo-340 flue gas analyser. The use of porous media at flame base is beneficiary in terms of achieving better air-fuel mixing and radial diffusion of air-fuel mixture. This reduces flame height with porous medium at all range of ɸ . Increase in ɸ reduces CO and enhances NO X emissions. Porous media reduces CO by 75 % and NO X by 60 %. Inverse diffusion porous medium burner emits lowest emissions in rich conditions.
扩散多孔介质燃烧是消除现有燃烧系统弊端的一种可行方法。反向扩散火焰（IDF）同时具有预混火焰和非预混火焰的特点。为了将多孔介质燃烧的优点与 IDF 相结合，反向扩散多孔介质（IDP）燃烧器在不同等效比（ɸ）下进行了火焰形态和排放变化测试。位于 IDF 燃烧器出口处的多孔介质具有提供最小火焰长度和低排放的潜力。实验研究了火焰外观、火焰高度、火焰区等和排放情况。燃料为甲烷。使用 ImageJ 软件对可见火焰高度进行数字捕捉和评估。实验测量了中心平面火焰温度。使用 Testo-340 烟气分析仪记录 CO 和 NO X 的排放量。在火焰底部使用多孔介质有利于实现更好的空气-燃料混合和空气-燃料混合物的径向扩散。这就降低了多孔介质在所有 ɸ 范围内的火焰高度。增加 ɸ 可减少 CO 排放，增加 NO X 排放。多孔介质可减少 75% 的 CO 和 60% 的 NO X。反向扩散多孔介质燃烧器在富油条件下的排放量最低。
{"title":"Effect of Equivalence Ratio on Flame Morphology, Thermal and Emissions Characteristics of Inverse Diffusion Porous Burner","authors":"A. Dekhatawala, P. V. Bhale, †. R.Shah","doi":"10.47176/jafm.17.6.2419","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2419","url":null,"abstract":"The diffusion porous media combustion is one possible way to eliminate the drawbacks of the existing combustion systems. Inverse diffusion flame (IDF) has features of both premixed and non-premixed flames. To integrate the advantages of porous media combustion with IDF, inverse diffusion porous (IDP) medium burner is tested for change in flame morphology and emissions at different equivalence ratio ( ɸ ). The porous media located at the exit of IDF burner has potential to deliver minimum flame length with low emissions. Flame appearance, flame height, flame zones etc. and emissions are experimentally investigated. Methane is used as fuel. Visible flame height is captured digitally and evaluated using ImageJ software. Central plane flame temperature is measured experimentally. CO and NO X emissions are recorded with Testo-340 flue gas analyser. The use of porous media at flame base is beneficiary in terms of achieving better air-fuel mixing and radial diffusion of air-fuel mixture. This reduces flame height with porous medium at all range of ɸ . Increase in ɸ reduces CO and enhances NO X emissions. Porous media reduces CO by 75 % and NO X by 60 %. Inverse diffusion porous medium burner emits lowest emissions in rich conditions.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141234139","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}
Unmanned Combat Aerial Vehicles (UCAVs) are designed to be lightweight and compact, which can impact their overall lift and aerodynamic capabilities. This study focuses on enhancing the Coefficient of Lift (C L ) by optimising the Back Sweep Angle in the Lambda wing-UCAV. The model's baseline geometry remains unchanged during the experimental and numerical analysis, while different back sweep angles ranging from δ=0 0 to δ=50 0 are investigated at varied free-stream velocities and angles of attack. This helps to understand the generation of induced lift in the intricate shapes of the Lambda Wing. The results indicate a 5% to 10% increase in the lift for every 10 0 increments of the Back Sweep Angle, and the vortices' strength increases and reaches a maximum at δ=40 0 . At greater angles (δ >40 0 ), the lift drops gradually with the Reynolds number. The stagnation point shifts from 25% to 35% along the chord towards the pressure surface as the angles of attack increase from α=5 0 to α=10 0 . The angle of attack α>10 0 .
{"title":"Aerodynamic Performance of Lambda Wing-UCAV at Different Back-sweep Angles","authors":"†. S.SyamNarayanan, Y. Gangurde, P. Rajalakshmi","doi":"10.47176/jafm.17.6.2403","DOIUrl":"https://doi.org/10.47176/jafm.17.6.2403","url":null,"abstract":"Unmanned Combat Aerial Vehicles (UCAVs) are designed to be lightweight and compact, which can impact their overall lift and aerodynamic capabilities. This study focuses on enhancing the Coefficient of Lift (C L ) by optimising the Back Sweep Angle in the Lambda wing-UCAV. The model's baseline geometry remains unchanged during the experimental and numerical analysis, while different back sweep angles ranging from δ=0 0 to δ=50 0 are investigated at varied free-stream velocities and angles of attack. This helps to understand the generation of induced lift in the intricate shapes of the Lambda Wing. The results indicate a 5% to 10% increase in the lift for every 10 0 increments of the Back Sweep Angle, and the vortices' strength increases and reaches a maximum at δ=40 0 . At greater angles (δ >40 0 ), the lift drops gradually with the Reynolds number. The stagnation point shifts from 25% to 35% along the chord towards the pressure surface as the angles of attack increase from α=5 0 to α=10 0 . The angle of attack α>10 0 .","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141232688","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 : 2024-05-01DOI: 10.47176/jafm.17.05.2330
J. Chen, †. H.Jia, L. Zhang, Z. Wang, R. Xie
In this study, we aim to examine the influence of water entry velocity of a single and two tandem projectile(s) on the supercavitation flow and projectile loading under wave conditions using numerical simulation. The volume of fluid model, renormalization group (RNG) κ-ε turbulence model, and Schnerr–Sauer cavitation model are adopted to simulate the multiphase, turbulent, and cavitation flow, respectively. The projectile movement is considered using overlapping grids and a six-degree-of-freedom model. The results show that as the projectile velocity increases, both the dimensionless maximum radius and length of the cavity, as well as the yaw angle, also increase with the rising water entry velocity. For the two tandem projectiles, the cavity pattern on the second projectile varies as the projectile velocity changes. With a lower projectile velocity, the second projectile cannot directly access the front cavity, and there may be situations wherein the part of the second projectile is not enveloped by cavity. As the projectile velocity increases, the second one can directly enter the cavity of the first projectile without forming a separate cavity around itself. In all of the examined cases, the peak pressure on the first projectile is approximately an order of magnitude higher than that on the second one. Furthermore, with increasing projectile velocity, the pressure peak ratio between the first and second projectiles increases.
{"title":"Examining the Influence of the Water Entry Velocity of Projectiles on Supercavity Flow and Ballistic Characteristics under Wave Conditions","authors":"J. Chen, †. H.Jia, L. Zhang, Z. Wang, R. Xie","doi":"10.47176/jafm.17.05.2330","DOIUrl":"https://doi.org/10.47176/jafm.17.05.2330","url":null,"abstract":"In this study, we aim to examine the influence of water entry velocity of a single and two tandem projectile(s) on the supercavitation flow and projectile loading under wave conditions using numerical simulation. The volume of fluid model, renormalization group (RNG) κ-ε turbulence model, and Schnerr–Sauer cavitation model are adopted to simulate the multiphase, turbulent, and cavitation flow, respectively. The projectile movement is considered using overlapping grids and a six-degree-of-freedom model. The results show that as the projectile velocity increases, both the dimensionless maximum radius and length of the cavity, as well as the yaw angle, also increase with the rising water entry velocity. For the two tandem projectiles, the cavity pattern on the second projectile varies as the projectile velocity changes. With a lower projectile velocity, the second projectile cannot directly access the front cavity, and there may be situations wherein the part of the second projectile is not enveloped by cavity. As the projectile velocity increases, the second one can directly enter the cavity of the first projectile without forming a separate cavity around itself. In all of the examined cases, the peak pressure on the first projectile is approximately an order of magnitude higher than that on the second one. Furthermore, with increasing projectile velocity, the pressure peak ratio between the first and second projectiles increases.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141029596","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 : 2024-05-01DOI: 10.47176/jafm.17.05.2240
Y. Xu, †. C.Ruan, Z. Zhang
Superhydrophobic surfaces have garnered attention for their ability to decrease fluid resistance, which can significantly reduce energy consumption. This study aims to accurately capture critical flow phenomena in a microchannel and explore the internal drag-reduction mechanism of the flow field. To achieve this, the three-dimensional (3D) superhydrophobic surface flow field with conical microstructure is numerically simulated using the gas–liquid two-phase flow theory and Volume of Fluid (VOF) model, combined with a Semi-implicit method for the pressure-linked equation (SIMPLE) algorithm. The surface drag-reduction effect of the conical microstructure is investigated and compared it to that of the V-longitudinal groove and V-transverse groove surfaces. Additionally, the changes in the drag-reduction effect during the wear of the conical microstructure were explored. The numerical results reveal that the drag-reduction effect improves with a larger period spacing of the conical microstructure, the drag reduction rate can reach 25.23%. As the height of the conical microstructure increases, the aspect ratio (ratio of width to height) decreases, and the dimensionless pressure drop ratio and the drag-reduction ratio increase. When the aspect ratio approaches 1, the drag reduction rate can reach over 28%. indicating a more effective drag-reduction. The microstructure is most effective in reducing drag at the beginning of the wear period but becomes less effective as the wear level increases, when the high wear reaches 10, the drag reduction rate decreases to 3%. Compared to the V-shaped longitudinal groove and V-shaped transverse grooves, the conical microstructure is the most effective in reducing drag.
超疏水表面能够减少流体阻力，从而显著降低能耗，因此备受关注。本研究旨在准确捕捉微通道中的临界流动现象，并探索流场的内部阻力降低机制。为此，采用气液两相流理论和流体体积（VOF）模型，结合压力方程半隐式方法（SIMPLE）算法，对具有锥形微结构的三维（3D）超疏水表面流场进行了数值模拟。研究了锥形微结构的表面减阻效果，并与 V 形纵向凹槽和 V 形横向凹槽表面的减阻效果进行了比较。此外，还探讨了锥形微结构磨损过程中阻力降低效果的变化。数值结果表明，锥形微结构的周期间距越大，阻力降低效果越好，阻力降低率可达 25.23%。随着锥形微结构高度的增加，长宽比（宽度与高度之比）减小，无量纲压降比和阻力降低率增加。当长宽比接近 1 时，阻力减小率可达 28% 以上，表明阻力减小效果更好。在磨损初期，微观结构对减少阻力最为有效，但随着磨损程度的增加，微观结构对减少阻力的作用逐渐减弱，当磨损程度达到 10 时，阻力减少率降至 3%。与 V 形纵向沟槽和 V 形横向沟槽相比，锥形微结构在减少阻力方面最为有效。
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