Pub Date : 2024-10-11DOI: 10.1016/j.ijmultiphaseflow.2024.105012
Akshay K. Khandelwal, Yang Zhao, Mamoru Ishii
Flow Regimes in a vertical narrow rectangular channel of cross-section are investigated up-to wispy-annular flow using a dense test matrix and double sensor conductivity probe at section mid point. The data from the probe is used to calculate void fraction, velocity of interfaces, and chord length of various flow structures. A five unit self organizing neural network is used to identify various flow regimes by using single point geometrical data of flow structures. Six separate flow regimes are found to exist. A new flow regime is identified and is called rolling-wispy flow. A discussion on boiling crisis is given regarding this flow regime. The resultant flow regime map is compared with various existing maps.
{"title":"Neural network based two-phase flow classification in a vertical narrow rectangular channel","authors":"Akshay K. Khandelwal, Yang Zhao, Mamoru Ishii","doi":"10.1016/j.ijmultiphaseflow.2024.105012","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105012","url":null,"abstract":"<div><div>Flow Regimes in a vertical narrow rectangular channel of cross-section <span><math><mrow><mn>20</mn><mo>×</mo><mn>1</mn><mspace></mspace><msup><mrow><mtext>cm</mtext></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span> are investigated up-to wispy-annular flow using a dense test matrix and double sensor conductivity probe at section mid point. The data from the probe is used to calculate void fraction, velocity of interfaces, and chord length of various flow structures. A five unit self organizing neural network is used to identify various flow regimes by using single point geometrical data of flow structures. Six separate flow regimes are found to exist. A new flow regime is identified and is called rolling-wispy flow. A discussion on boiling crisis is given regarding this flow regime. The resultant flow regime map is compared with various existing maps.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"182 ","pages":"Article 105012"},"PeriodicalIF":3.6,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-10-11DOI: 10.1016/j.ijmultiphaseflow.2024.105023
Athanasios Balachtsis, Yannis Dimakopoulos, John Tsamopoulos
We revisit the gravitational collapse of a 2D column of dry granular material surrounded by air, using a continuum mechanics approximation. By employing the Cahn-Hilliard phase-field equation as an interface capturing technique and by coupling it with the Cauchy equation, we numerically simulate this multiphase system, eliminating the need for any ad-hoc numerical adjustment to prevent the finger formation of light fluid between the material and the solid boundary due to the no-slip boundary condition. We implement the -rheology in our stabilized Finite Element method, highlighting the presence of instabilities when using this constitutive law. Our study is characterized by three main goals. First, we address the instability issue by implementing the partially regularized formulation of the -rheology proposed by Barker and Gray (2017). An important outcome is that using shock-capturing terms in the momentum equation can significantly smooth these oscillations by adding dissipation in the direction of the gradients. Second, we systematically study the fluid dynamics under realistic conditions. Our results accurately replicate the material dynamics during collapse, confirming three distinct stages: free-fall, spreading, and cessation. We identify two regions in the material during the spreading phase: a quasi-static zone with negligible velocities and deformations, and a flowing layer exhibiting high shear rates. These observations closely align with experimental data. Additionally, we examine the evolution of the yielded/unyielded regions based on the Drucker-Prager criterion, and we also explore an empirical criterion, based on a critical value of the velocity norm, that satisfactorily separates these regions. Finally, we perform an extensive parametric study covering a wide range of rheological parameters.
{"title":"Dry granular column collapse: Numerical simulations using the partially regularized μ(I)-model via stabilized finite elements and phase field formulation","authors":"Athanasios Balachtsis, Yannis Dimakopoulos, John Tsamopoulos","doi":"10.1016/j.ijmultiphaseflow.2024.105023","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105023","url":null,"abstract":"<div><div>We revisit the gravitational collapse of a 2D column of dry granular material surrounded by air, using a continuum mechanics approximation. By employing the Cahn-Hilliard phase-field equation as an interface capturing technique and by coupling it with the Cauchy equation, we numerically simulate this multiphase system, eliminating the need for any <em>ad-hoc</em> numerical adjustment to prevent the finger formation of light fluid between the material and the solid boundary due to the no-slip boundary condition. We implement the <span><math><mrow><mi>μ</mi><mo>(</mo><mi>I</mi><mo>)</mo></mrow></math></span>-rheology in our stabilized Finite Element method, highlighting the presence of instabilities when using this constitutive law. Our study is characterized by three main goals. First, we address the instability issue by implementing the partially regularized formulation of the <span><math><mrow><mi>μ</mi><mo>(</mo><mi>I</mi><mo>)</mo></mrow></math></span>-rheology proposed by Barker and Gray (2017). An important outcome is that using shock-capturing terms in the momentum equation can significantly smooth these oscillations by adding dissipation in the direction of the gradients. Second, we systematically study the fluid dynamics under realistic conditions. Our results accurately replicate the material dynamics during collapse, confirming three distinct stages: free-fall, spreading, and cessation. We identify two regions in the material during the spreading phase: a quasi-static zone with negligible velocities and deformations, and a flowing layer exhibiting high shear rates. These observations closely align with experimental data. Additionally, we examine the evolution of the yielded/unyielded regions based on the Drucker-Prager criterion, and we also explore an empirical criterion, based on a critical value of the velocity norm, that satisfactorily separates these regions. Finally, we perform an extensive parametric study covering a wide range of rheological parameters.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"182 ","pages":"Article 105023"},"PeriodicalIF":3.6,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-10-10DOI: 10.1016/j.ijmultiphaseflow.2024.105019
Jakub A. Cranmer , Evgenii Sharaborin , Sepideh Khodaparast , Giovanni Giustini , Mirco Magnini
<div><div>When a gas bubble is transported by a liquid flow confined within a horizontal channel of comparable size, buoyancy effects are usually assumed to be negligible if the Bond number of the flow is less than unity. However, recent experimental studies showed that buoyancy may still significantly impact the bubble dynamics even when <span><math><mrow><mi>Bo</mi><mo>≪</mo><mn>1</mn></mrow></math></span>, provided that the flow speed is sufficiently small, such that the viscous and inertial forces are weak. To derive a new criterion to assess the significance of buoyancy on the flow of small bubbles in horizontal microchannels, we have performed systematic numerical simulations using the free software Basilisk, covering a wide range of Bond, capillary and Reynolds numbers, <span><math><mrow><mi>Bo</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>004</mn><mo>−</mo><mn>0</mn><mo>.</mo><mn>4</mn></mrow></math></span>, <span><math><mrow><mi>Ca</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>−</mo><mn>0</mn><mo>.</mo><mn>5</mn></mrow></math></span> and <span><math><mrow><mi>Re</mi><mo>=</mo><mn>0</mn><mo>−</mo><mn>100</mn></mrow></math></span>, and exploring the bubble-to-channel diameter ratios <span><math><mrow><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn><mo>−</mo><mn>0</mn><mo>.</mo><mn>9</mn></mrow></math></span>. We demonstrate that the nondimensional group <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi></mrow></math></span> is effective in assessing the importance of buoyancy in flows with negligible inertial effects. When <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>1</mn></mrow></math></span>, buoyancy effects are negligible and the bubble travels along the channel axis. When <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo>></mo><mn>10</mn></mrow></math></span>, buoyancy effects dominate and the bubble travels in the vicinity of the upper wall. For intermediate values, bubbles take equilibrium positions between the channel centre and the wall, and the threshold <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo>=</mo><mn>1</mn></mrow></math></span> is effective in predicting
{"title":"Non-negligible buoyancy effect on bubbles travelling in horizontal microchannels of comparable size at small Bond numbers","authors":"Jakub A. Cranmer , Evgenii Sharaborin , Sepideh Khodaparast , Giovanni Giustini , Mirco Magnini","doi":"10.1016/j.ijmultiphaseflow.2024.105019","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105019","url":null,"abstract":"<div><div>When a gas bubble is transported by a liquid flow confined within a horizontal channel of comparable size, buoyancy effects are usually assumed to be negligible if the Bond number of the flow is less than unity. However, recent experimental studies showed that buoyancy may still significantly impact the bubble dynamics even when <span><math><mrow><mi>Bo</mi><mo>≪</mo><mn>1</mn></mrow></math></span>, provided that the flow speed is sufficiently small, such that the viscous and inertial forces are weak. To derive a new criterion to assess the significance of buoyancy on the flow of small bubbles in horizontal microchannels, we have performed systematic numerical simulations using the free software Basilisk, covering a wide range of Bond, capillary and Reynolds numbers, <span><math><mrow><mi>Bo</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>004</mn><mo>−</mo><mn>0</mn><mo>.</mo><mn>4</mn></mrow></math></span>, <span><math><mrow><mi>Ca</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>−</mo><mn>0</mn><mo>.</mo><mn>5</mn></mrow></math></span> and <span><math><mrow><mi>Re</mi><mo>=</mo><mn>0</mn><mo>−</mo><mn>100</mn></mrow></math></span>, and exploring the bubble-to-channel diameter ratios <span><math><mrow><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn><mo>−</mo><mn>0</mn><mo>.</mo><mn>9</mn></mrow></math></span>. We demonstrate that the nondimensional group <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi></mrow></math></span> is effective in assessing the importance of buoyancy in flows with negligible inertial effects. When <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>1</mn></mrow></math></span>, buoyancy effects are negligible and the bubble travels along the channel axis. When <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo>></mo><mn>10</mn></mrow></math></span>, buoyancy effects dominate and the bubble travels in the vicinity of the upper wall. For intermediate values, bubbles take equilibrium positions between the channel centre and the wall, and the threshold <span><math><mrow><mi>Bo</mi><mspace></mspace><msup><mrow><mrow><mo>(</mo><msub><mrow><mi>d</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>/</mo><mi>D</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>Ca</mi><mo>=</mo><mn>1</mn></mrow></math></span> is effective in predicting","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105019"},"PeriodicalIF":3.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-09DOI: 10.1016/j.ijmultiphaseflow.2024.105016
Jingyu Zhu , Yanlian Du , Meng Li , Mengdi Fu , Xuanhe Han , Fusen Peng , Rongqian Ruan , Yijun Shen
This paper conducts experiments on gas–liquid two-phase flow in airlift pumps (ALPs) using air–water as the medium, measuring liquid flow rates over a broad range of flow rates, and investigates the effects of submergence ratio and the two-phase pipe section length on the performance of ALPs. Evaluate the performance of ALPs under specified operating conditions. Experimental results show that liquid flow velocity initially increases with the increase in gas flow velocity and then stabilizes; the highest liquid flow velocity does not necessarily correspond to the highest efficiency. The performance of the ALPs increases with the two-phase pipe section length within a certain range of the two-phase pipe section length. However, once this range is exceeded, the performance of the ALPs is nearly unaffected by the two-phase pipe section length; the minimum gas flow velocity required to pump liquid increases as the submergence ratio decreases. This paper presents ALPs model that is independent of pipe diameter and flow range and validates it against experimental results. The model outcomes align well with the experimental data across all flow ranges. Additionally, the model effectively captures the sensitivity changes related to the two-phase pipe section length and the submergence ratio, and accurately predicts the minimum gas flow velocity required for liquid discharge under various operating conditions.
本文以空气-水为介质，对气举泵（ALP）中的气液两相流进行了实验，测量了较大流量范围内的液体流速，并研究了浸没比和两相管道截面长度对气举泵性能的影响。评估 ALP 在特定工作条件下的性能。实验结果表明，液体流速最初会随着气体流速的增加而增加，然后趋于稳定；最高的液体流速并不一定对应最高的效率。在两相管道截面长度的一定范围内，ALP 的性能随两相管道截面长度的增加而增加。然而，一旦超过这一范围，ALPs 的性能几乎不受两相管段长度的影响；泵送液体所需的最小气体流速随着浸没比的减小而增大。本文提出了与管道直径和流量范围无关的 ALPs 模型，并根据实验结果对其进行了验证。在所有流量范围内，模型结果都与实验数据十分吻合。此外，该模型还有效捕捉到了与两相管道截面长度和浸没比相关的灵敏度变化，并准确预测了在各种运行条件下液体排放所需的最小气体流速。
{"title":"Evaluate the performance of the vertically upward gas–liquid two-phase flow in an airlift pump system","authors":"Jingyu Zhu , Yanlian Du , Meng Li , Mengdi Fu , Xuanhe Han , Fusen Peng , Rongqian Ruan , Yijun Shen","doi":"10.1016/j.ijmultiphaseflow.2024.105016","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105016","url":null,"abstract":"<div><div>This paper conducts experiments on gas–liquid two-phase flow in airlift pumps (ALPs) using air–water as the medium, measuring liquid flow rates over a broad range of flow rates, and investigates the effects of submergence ratio and the two-phase pipe section length on the performance of ALPs. Evaluate the performance of ALPs under specified operating conditions. Experimental results show that liquid flow velocity initially increases with the increase in gas flow velocity and then stabilizes; the highest liquid flow velocity does not necessarily correspond to the highest efficiency. The performance of the ALPs increases with the two-phase pipe section length within a certain range of the two-phase pipe section length. However, once this range is exceeded, the performance of the ALPs is nearly unaffected by the two-phase pipe section length; the minimum gas flow velocity required to pump liquid increases as the submergence ratio decreases. This paper presents ALPs model that is independent of pipe diameter and flow range and validates it against experimental results. The model outcomes align well with the experimental data across all flow ranges. Additionally, the model effectively captures the sensitivity changes related to the two-phase pipe section length and the submergence ratio, and accurately predicts the minimum gas flow velocity required for liquid discharge under various operating conditions.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105016"},"PeriodicalIF":3.6,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142526837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this investigation, an alternative geometric formula is proposed to address the force between fluid nodes and fluid ghost nodes, with the aid of which the contact angles can be varied in the range of 48.3°∼131.9°. This formula is applied to the three-dimensional double-distributed thermal lattice Boltzmann method being proved to be accurate and reliable by single droplet condensation. The effects brought by varying micropillar size on the kinetic properties of condensed droplets, including nucleation, growth, coalescence and jumping, are investigated in detail. The results show that the droplet wetting state tends to be the suspended Cassie state as the width and spacing of the micropillars are decreased, and the condensed droplets can merge and jump off the micropillar surface. In the meantime, the average droplet number increases, the average diameter and the diameter of dominant droplets decrease, thus reducing the condensate coverage. When the micropillar spacing is small, increasing the micropillar height results in the condensed droplet state being changed from Wenzel to Cassie state, and the percentage of small droplets also increases. Instead, when the micropillar spacing is large, by increasing micropillar height, droplets can nucleate in the middle of micropillars, and the percentage of large droplets is improved due to increased heat transfer area. In this study, the surface self-cleaning capability is strongest with the combination of dimensionless pillar height 0.4, spacing 0.1 and width 0.1, which reduces the condensate coverage by 66 % compared to its plain competitor.
{"title":"Dropwise condensation on subcooled micropillar surfaces with 3D lattice Boltzmann method","authors":"Xiangwei Yin, Ruoxi Li, Jianchen Wei, Shengqiang Shen, Gangtao Liang","doi":"10.1016/j.ijmultiphaseflow.2024.105015","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105015","url":null,"abstract":"<div><div>In this investigation, an alternative geometric formula is proposed to address the force between fluid nodes and fluid ghost nodes, with the aid of which the contact angles can be varied in the range of 48.3°∼131.9°. This formula is applied to the three-dimensional double-distributed thermal lattice Boltzmann method being proved to be accurate and reliable by single droplet condensation. The effects brought by varying micropillar size on the kinetic properties of condensed droplets, including nucleation, growth, coalescence and jumping, are investigated in detail. The results show that the droplet wetting state tends to be the suspended Cassie state as the width and spacing of the micropillars are decreased, and the condensed droplets can merge and jump off the micropillar surface. In the meantime, the average droplet number increases, the average diameter and the diameter of dominant droplets decrease, thus reducing the condensate coverage. When the micropillar spacing is small, increasing the micropillar height results in the condensed droplet state being changed from Wenzel to Cassie state, and the percentage of small droplets also increases. Instead, when the micropillar spacing is large, by increasing micropillar height, droplets can nucleate in the middle of micropillars, and the percentage of large droplets is improved due to increased heat transfer area. In this study, the surface self-cleaning capability is strongest with the combination of dimensionless pillar height 0.4, spacing 0.1 and width 0.1, which reduces the condensate coverage by 66 % compared to its plain competitor.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"182 ","pages":"Article 105015"},"PeriodicalIF":3.6,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-10-09DOI: 10.1016/j.ijmultiphaseflow.2024.105008
Hirthick K. Nagarajan, Mario F. Trujillo
Current trends in modeling CAF of oil and water combine the interface capturing methodology of VoF with the computational savings of a RANS approach. As demonstrated mathematically, this results in an inconsistency in the overall RANS-VoF treatment and incurs a number of omissions in the solution of oil fraction advection and momentum. To quantify these inconsistencies, five CAF cases with increasing are considered and solved via DNS. Symptoms of the inconsistencies include qualitative errors in the prediction of the flow behavior in the entrance and fully-developed regions, as well as in the transition between these two regions. From a momentum perspective, the more troubling issue is the absence of unclosed terms resulting from fluctuating viscous and surface tension forces in the RANS equations. For momentum advection, terms associated with fluctuating density can be safely ignored due to the similar magnitude between oil and water density.
{"title":"Quantifying a common inconsistency in RANS-VoF modeling of water and oil core annular flow","authors":"Hirthick K. Nagarajan, Mario F. Trujillo","doi":"10.1016/j.ijmultiphaseflow.2024.105008","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105008","url":null,"abstract":"<div><div>Current trends in modeling CAF of oil and water combine the interface capturing methodology of VoF with the computational savings of a RANS approach. As demonstrated mathematically, this results in an inconsistency in the overall RANS-VoF treatment and incurs a number of omissions in the solution of oil fraction advection and momentum. To quantify these inconsistencies, five CAF cases with increasing <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>w</mi></mrow></msub></mrow></math></span> are considered and solved via DNS. Symptoms of the inconsistencies include qualitative errors in the prediction of the flow behavior in the entrance and fully-developed regions, as well as in the transition between these two regions. From a momentum perspective, the more troubling issue is the absence of unclosed terms resulting from fluctuating viscous and surface tension forces in the RANS equations. For momentum advection, terms associated with fluctuating density can be safely ignored due to the similar magnitude between oil and water density.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105008"},"PeriodicalIF":3.6,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142444866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-10-09DOI: 10.1016/j.ijmultiphaseflow.2024.105022
Ibrahim Kipngeno Rotich , László E. Kollár
Wind turbine blades are prone to icing and their performance is affected significantly by the roughness caused by icing and erosion. Numerical models are constructed to simulate the effects of sand grain roughness on the mass of accreted ice and aerodynamic performance. The sand grain roughness height is considered by applying the NASA and Shin et al. models, and the cloud characteristics studied are the liquid water content (LWC), median volume diameter (MVD) and air temperature covering freezing drizzle and in-cloud icing conditions resulting in glaze ice and rime ice, respectively. The numerical model applied the multi-shot approach, and the effects of the number of shots on the ice accretion and aerodynamic performance was examined to determine the optimum number of shots which can be used in the simulation in order to minimize the computational time without affecting the accuracy. The relationship between the sand grain roughness height and aerodynamic performance is studied, revealing that the shallowest roughness heights cause less performance degradation. The mass of ice increases with increasing LWC from 0.05g/m3 to 0.3g/m3 and MVD from 20 µm to 100 µm, which results in a reduction in the lift-to-drag ratio (CL/CD).
{"title":"Effects of sand grain roughness height on the performance of wind turbine blade section under extreme weather conditions","authors":"Ibrahim Kipngeno Rotich , László E. Kollár","doi":"10.1016/j.ijmultiphaseflow.2024.105022","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105022","url":null,"abstract":"<div><div>Wind turbine blades are prone to icing and their performance is affected significantly by the roughness caused by icing and erosion. Numerical models are constructed to simulate the effects of sand grain roughness on the mass of accreted ice and aerodynamic performance. The sand grain roughness height is considered by applying the NASA and Shin et al. models, and the cloud characteristics studied are the liquid water content (LWC), median volume diameter (MVD) and air temperature covering freezing drizzle and in-cloud icing conditions resulting in glaze ice and rime ice, respectively. The numerical model applied the multi-shot approach, and the effects of the number of shots on the ice accretion and aerodynamic performance was examined to determine the optimum number of shots which can be used in the simulation in order to minimize the computational time without affecting the accuracy. The relationship between the sand grain roughness height and aerodynamic performance is studied, revealing that the shallowest roughness heights cause less performance degradation<sub>.</sub> The mass of ice increases with increasing LWC from 0.05g/m<sup>3</sup> to 0.3g/m<sup>3</sup> and MVD from 20 µm to 100 µm, which results in a reduction in the lift-to-drag ratio (C<sub>L</sub>/C<sub>D</sub>).</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105022"},"PeriodicalIF":3.6,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-05DOI: 10.1016/j.ijmultiphaseflow.2024.105005
Sandro Ianniello
The simulation of incompressible multiphase flows through the so-called fractional step method needs to solve a variable coefficient Poisson equation for discontinuous functions. Recently, it has been shown how the solution of this equation may be found out through a novel coding of the Ghost Fluid Method (named GFMxP), by avoiding any fit to evaluate the interface position and providing, anyhow, a perfect sharp modeling of the same interface. Furthermore, the accuracy order of the numerical solutions exactly corresponds to the order of the adopted finite difference scheme. The effectiveness and reliability of the new procedure were successfully checked by a lot of tests. However, the a-priori knowledge of the unknown function allowed to elude a fundamental aspect of the numerical approach: the appropriate encoding of the boundary conditions. This topic has often been debated in the past, especially from a theoretical viewpoint, and still represents a rather thorny point in the whole simulation process. The paper shows how to handle the problem in practice and in the context of the GFMxP approach, i.e. by accounting for the presence of the discontinuity and the possible use of high-order solving schemes on a staggered grid.
{"title":"On the boundary conditions for GFMxP high-order schemes on staggered grids in the simulation of incompressible multiphase flows","authors":"Sandro Ianniello","doi":"10.1016/j.ijmultiphaseflow.2024.105005","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105005","url":null,"abstract":"<div><div>The simulation of incompressible multiphase flows through the so-called fractional step method needs to solve a variable coefficient Poisson equation for discontinuous functions. Recently, it has been shown how the solution of this equation may be found out through a novel coding of the Ghost Fluid Method (named GFMxP), by avoiding any fit to evaluate the interface position and providing, anyhow, a perfect sharp modeling of the same interface. Furthermore, the accuracy order of the numerical solutions exactly corresponds to the order of the adopted finite difference scheme. The effectiveness and reliability of the new procedure were successfully checked by a lot of tests. However, the <em>a-priori</em> knowledge of the unknown function allowed to elude a fundamental aspect of the numerical approach: the appropriate encoding of the boundary conditions. This topic has often been debated in the past, especially from a theoretical viewpoint, and still represents a rather thorny point in the whole simulation process. The paper shows how to handle the problem in practice and in the context of the GFMxP approach, i.e. by accounting for the presence of the discontinuity and the possible use of high-order solving schemes on a staggered grid.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105005"},"PeriodicalIF":3.6,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-10-03DOI: 10.1016/j.ijmultiphaseflow.2024.105011
Ahmed Ja , Saad Benjelloun , Jean Michel Ghidaglia , Faical Ait Lahbib
The transportation of phosphate slurry through large-scale pipelines presents significant challenges due to the complex behavior of multiphase flows, particularly with varying solid content, density, and dynamic viscosity. Efficient and accurate prediction of flow behavior is critical for optimizing the operation of such pipelines. This work aims to develop a dynamic computational model to simulate phosphate slurry flow in pipelines. The case study focuses on the OCP Group’s main slurry pipeline, which links the mining sites at Khouribga to the industrial plants at Jorf Lasfar, Morocco. This pipeline system spans a total length of 187.124 km, consisting of 5237 pipes with an inner diameter ranging from 0.8546 m to 0.8578 m, and features several elevation changes along its ground level. Using a section-averaged, dynamic approach and the Finite Volume scheme, the model computes essential flow parameters, including density, dynamic viscosity, and pressure, for the incompressible and non-Newtonian slurry and process water flows. The model’s accuracy is validated against on-site measured data, showing an average deviation of for outlet density, and below 10% for pressure along the pipeline, underscoring the model’s reliability. Additionally, a sensitivity analysis was conducted to illustrate the impact of key parameters on the predicted head losses and pressures along the pipeline. This analysis shows that the slurry viscosity is the most critical parameter, significantly influencing these predictions. This model provides high accuracy and reasonable CPU time for real-time simulation and monitoring, while also offering significant potential for optimizing pipeline operations and ensuring the reliability of phosphate transport.
{"title":"Dynamic fluid flow model for phosphate slurry pipeline: OCP main pipeline as case study","authors":"Ahmed Ja , Saad Benjelloun , Jean Michel Ghidaglia , Faical Ait Lahbib","doi":"10.1016/j.ijmultiphaseflow.2024.105011","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105011","url":null,"abstract":"<div><div>The transportation of phosphate slurry through large-scale pipelines presents significant challenges due to the complex behavior of multiphase flows, particularly with varying solid content, density, and dynamic viscosity. Efficient and accurate prediction of flow behavior is critical for optimizing the operation of such pipelines. This work aims to develop a dynamic computational model to simulate phosphate slurry flow in pipelines. The case study focuses on the OCP Group’s main slurry pipeline, which links the mining sites at Khouribga to the industrial plants at Jorf Lasfar, Morocco. This pipeline system spans a total length of 187.124 km, consisting of 5237 pipes with an inner diameter ranging from 0.8546 m to 0.8578 m, and features several elevation changes along its ground level. Using a section-averaged, dynamic approach and the Finite Volume scheme, the model computes essential flow parameters, including density, dynamic viscosity, and pressure, for the incompressible and non-Newtonian slurry and process water flows. The model’s accuracy is validated against on-site measured data, showing an average deviation of <span><math><mrow><mo>±</mo><mn>0</mn><mo>.</mo><mn>32</mn><mtext>%</mtext></mrow></math></span> for outlet density, and below 10% for pressure along the pipeline, underscoring the model’s reliability. Additionally, a sensitivity analysis was conducted to illustrate the impact of key parameters on the predicted head losses and pressures along the pipeline. This analysis shows that the slurry viscosity is the most critical parameter, significantly influencing these predictions. This model provides high accuracy and reasonable CPU time for real-time simulation and monitoring, while also offering significant potential for optimizing pipeline operations and ensuring the reliability of phosphate transport.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105011"},"PeriodicalIF":3.6,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-28DOI: 10.1016/j.ijmultiphaseflow.2024.105007
Diego Perissutti , Cristian Marchioli , Alfredo Soldati
We investigate the morphodynamics of an ice layer over a turbulent stream of warm water using numerical simulations. At low water speeds, characteristic streamwise undulations appear, which can be explained by the Reynolds analogy between heat and momentum transfer. As the water speed increases, these undulations combine with spanwise ripples of a much greater length scale. These ripples are generated by a melting mechanism controlled by the instability originating from the ice–water interactions, and, through a melting/freezing process, they evolve downstream with a migration velocity much slower than the turbulence characteristic velocity.
{"title":"Morphodynamics of melting ice over turbulent warm water streams","authors":"Diego Perissutti , Cristian Marchioli , Alfredo Soldati","doi":"10.1016/j.ijmultiphaseflow.2024.105007","DOIUrl":"10.1016/j.ijmultiphaseflow.2024.105007","url":null,"abstract":"<div><div>We investigate the morphodynamics of an ice layer over a turbulent stream of warm water using numerical simulations. At low water speeds, characteristic streamwise undulations appear, which can be explained by the Reynolds analogy between heat and momentum transfer. As the water speed increases, these undulations combine with spanwise ripples of a much greater length scale. These ripples are generated by a melting mechanism controlled by the instability originating from the ice–water interactions, and, through a melting/freezing process, they evolve downstream with a migration velocity much slower than the turbulence characteristic velocity.</div></div>","PeriodicalId":339,"journal":{"name":"International Journal of Multiphase Flow","volume":"181 ","pages":"Article 105007"},"PeriodicalIF":3.6,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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