The paper reports on the conditionally averaged turbulence kinetic energy (TKE) budget, where the conditioning is based on the invariants of the velocity gradient tensor. Three different datasets are utilized for this analysis. The particular terms of the budget are presented in the (R, Q) plane, showcasing a striking similarity (both quantitative and qualitative) among the results from each dataset. The importance of conditional averages for the overall variance of the specific terms of the TKE budget is also evaluated. Subsequently, the budgets are presented along conditional mean trajectories (CMTs), revealing the dynamics of the TKE budget associated with the evolution of local flow topology. Results obtained for different CMTs approximately collapse when suitably normalized (at least for certain parts of the trajectories). The conditional budget is clearly dominated by inertial and pressure transport terms, indicative of a “sweeping” effect.
{"title":"The topology-conditioned turbulence kinetic energy budget","authors":"Pawel Baj","doi":"10.1063/5.0224167","DOIUrl":"https://doi.org/10.1063/5.0224167","url":null,"abstract":"The paper reports on the conditionally averaged turbulence kinetic energy (TKE) budget, where the conditioning is based on the invariants of the velocity gradient tensor. Three different datasets are utilized for this analysis. The particular terms of the budget are presented in the (R, Q) plane, showcasing a striking similarity (both quantitative and qualitative) among the results from each dataset. The importance of conditional averages for the overall variance of the specific terms of the TKE budget is also evaluated. Subsequently, the budgets are presented along conditional mean trajectories (CMTs), revealing the dynamics of the TKE budget associated with the evolution of local flow topology. Results obtained for different CMTs approximately collapse when suitably normalized (at least for certain parts of the trajectories). The conditional budget is clearly dominated by inertial and pressure transport terms, indicative of a “sweeping” effect.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218381","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}
Yubao Gao, Weiyao Zhu, Wengang Bu, Ming Yue, Debin Kong
The development of low-permeability and tight oil reservoirs is challenged by insufficient natural energy and rapid production decline. Fracturing-flooding is a technique that relies on high-pressure and large-volume fluid injection to replenish reservoir energy, making it a significant method for rapidly boosting formation energy. To evaluate the energy replenishment effect of fracturing-flooding technology in low-permeability and tight reservoirs, this study proposes a semi-analytical method for quick calculation. This approach employs dimensionless simplification, Pedrosa's substitution, Laplace transformation, and Stehfest inversion methods to derive pressure solutions for both the stimulation region and the external matrix region, each with varying flow capacities. The average formation pressure (AFP) of the reservoir is determined using the area-weighted average method, and numerical verification is performed using a commercial simulator. A case study from the Binnan area, along with a sensitivity analysis, demonstrates that after 30 days of fracturing-flooding, the AFP of the reservoir increases to 46.97 MPa, the corresponding reservoir pressure coefficient rises from 1.2 to 1.68, and reservoir energy increases by 40%. The factors influencing energy replenishment are ranked as follows: reservoir thickness, injection rate, stress sensitivity coefficient, matrix permeability, stimulation region radius, and mobility ratio. This study provides theoretical guidance for optimizing fracturing-flooding development schemes in low-permeability and tight oil reservoirs and offers valuable reference for the industry.
{"title":"A fast and reliable semi-analytical method for assessing energy replenishment from fracturing-flooding in low-permeability and tight oil reservoirs","authors":"Yubao Gao, Weiyao Zhu, Wengang Bu, Ming Yue, Debin Kong","doi":"10.1063/5.0225841","DOIUrl":"https://doi.org/10.1063/5.0225841","url":null,"abstract":"The development of low-permeability and tight oil reservoirs is challenged by insufficient natural energy and rapid production decline. Fracturing-flooding is a technique that relies on high-pressure and large-volume fluid injection to replenish reservoir energy, making it a significant method for rapidly boosting formation energy. To evaluate the energy replenishment effect of fracturing-flooding technology in low-permeability and tight reservoirs, this study proposes a semi-analytical method for quick calculation. This approach employs dimensionless simplification, Pedrosa's substitution, Laplace transformation, and Stehfest inversion methods to derive pressure solutions for both the stimulation region and the external matrix region, each with varying flow capacities. The average formation pressure (AFP) of the reservoir is determined using the area-weighted average method, and numerical verification is performed using a commercial simulator. A case study from the Binnan area, along with a sensitivity analysis, demonstrates that after 30 days of fracturing-flooding, the AFP of the reservoir increases to 46.97 MPa, the corresponding reservoir pressure coefficient rises from 1.2 to 1.68, and reservoir energy increases by 40%. The factors influencing energy replenishment are ranked as follows: reservoir thickness, injection rate, stress sensitivity coefficient, matrix permeability, stimulation region radius, and mobility ratio. This study provides theoretical guidance for optimizing fracturing-flooding development schemes in low-permeability and tight oil reservoirs and offers valuable reference for the industry.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218280","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}
During atmospheric reentry, the vehicle surface is exposed to highly non-equilibrium flow. The vehicle surface can experience heterogeneous recombination of reactive atoms, which contributes to its aerothermodynamic heating. This process is followed by chemical energy accommodation (CEA), where the released energy is either transferred to the surface or the internal energy modes of the recombined molecule. Heterogeneous recombination can be categorized into Eley–Rideal (ER) and Langmuir–Hinshelwood mechanisms, which differ in their methods of molecule formation and degrees of CEA. The complete CEA assumption may not consider the dependency of CEA on the mechanisms of heterogeneous recombination. This study aims to consider the mechanism-specific CEA for a more accurate prediction of surface heat flux. The authors implement mechanism-specific CEA within the direct simulation Monte Carlo framework using the finite-rate surface chemistry model, resolving elementary surface reactions and assigning a CEA coefficient, β, to each mechanism. The model is verified through comparisons with analytical solutions of surface coverage and validated against benchmark references. A parametric investigation of rarefied hypersonic flow over a two-dimensional cylinder is conducted under different freestream Mach and Knudsen numbers. Results show a reduction in total heat flux of up to 14.44% using mechanism-specific CEA compared to the complete CEA assumption. The reduction is attributed to the relative contribution of the ER mechanism, which can be a function of atomic partial pressure at the boundary layer.
在重返大气层期间，飞行器表面暴露在高度非平衡流动中。飞行器表面会发生反应原子的异质重组，从而导致其空气热力学加热。这一过程之后是化学能容纳（CEA），释放的能量会转移到表面或重组分子的内部能量模式。异质重组可分为 Eley-Rideal (ER) 和 Langmuir-Hinshelwood 机制，它们在分子形成方法和 CEA 程度上各不相同。完全 CEA 假设可能没有考虑 CEA 对异质重组机制的依赖性。本研究旨在考虑特定机制的 CEA，以更准确地预测表面热通量。作者利用有限速率表面化学模型，在直接模拟蒙特卡罗框架内实现了特定机理 CEA，解析了基本表面反应，并为每种机理分配了 CEA 系数 β。该模型通过与表面覆盖率的分析解进行比较，并根据基准参考资料进行验证。在不同自由流马赫数和努森数条件下，对二维圆柱体上的稀薄高超声速流进行了参数研究。结果表明，与完全 CEA 假设相比，使用特定机制 CEA 可使总热流量减少 14.44%。这种减少归因于 ER 机制的相对贡献，它可能是边界层原子分压的函数。
{"title":"Mechanism-specific chemical energy accommodation with finite-rate surface chemistry in non-equilibrium flow","authors":"Youngil Ko, Eunji Jun","doi":"10.1063/5.0222518","DOIUrl":"https://doi.org/10.1063/5.0222518","url":null,"abstract":"During atmospheric reentry, the vehicle surface is exposed to highly non-equilibrium flow. The vehicle surface can experience heterogeneous recombination of reactive atoms, which contributes to its aerothermodynamic heating. This process is followed by chemical energy accommodation (CEA), where the released energy is either transferred to the surface or the internal energy modes of the recombined molecule. Heterogeneous recombination can be categorized into Eley–Rideal (ER) and Langmuir–Hinshelwood mechanisms, which differ in their methods of molecule formation and degrees of CEA. The complete CEA assumption may not consider the dependency of CEA on the mechanisms of heterogeneous recombination. This study aims to consider the mechanism-specific CEA for a more accurate prediction of surface heat flux. The authors implement mechanism-specific CEA within the direct simulation Monte Carlo framework using the finite-rate surface chemistry model, resolving elementary surface reactions and assigning a CEA coefficient, β, to each mechanism. The model is verified through comparisons with analytical solutions of surface coverage and validated against benchmark references. A parametric investigation of rarefied hypersonic flow over a two-dimensional cylinder is conducted under different freestream Mach and Knudsen numbers. Results show a reduction in total heat flux of up to 14.44% using mechanism-specific CEA compared to the complete CEA assumption. The reduction is attributed to the relative contribution of the ER mechanism, which can be a function of atomic partial pressure at the boundary layer.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218336","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}
Sara Tomasi Masoni, Alessandro Mariotti, Chiara Galletti, Roberto Mauri, Maria Vittoria Salvetti, Elisabetta Brunazzi
Experiments and simulations are used jointly to gain a comprehensive insight into the pinching mechanism that generates alginate droplets in an X-microdevice operating in a hydrodynamic flow-focusing configuration. The X-microdevice is fed with an aqueous alginate solution into one inlet channel, while sunflower oil and Span80 are fed into the other two inlet channels. The use of the adaptive mesh refinement and volume of fluid method allows accurate tracking of the interface in numerical simulations. The sensitivities of numerical predictions to the contact angle and the surface tension are estimated through dedicated sets of simulations. Subsequently, numerical simulations and experiments are compared for different flow rates with a satisfactory agreement. We observe that the pinch-off mechanism may lead to the formation of several satellite drops in addition to the main droplet. A pinching performance indicator is suggested based on the amount of alginate that is encapsulated in the main droplet. The effect of operating conditions on the pinching efficiency, frequency, and droplet diameter is discussed to provide valuable information to optimize the droplets production. The pinching efficiency is closely related to the length and diameter of the liquid thread. At low flow rates, a short liquid thread is observed. This leads to the formation of few satellites and, thus, to high pinching efficiency but low droplet production. Increasing the dispersed-phase flow rate slightly reduces the efficiency but significantly increases the production.
实验和模拟相结合，全面了解了在流体动力流聚焦配置下运行的 X 微装置中产生藻酸盐液滴的捏合机制。在 X 微装置的一个入口通道中注入海藻酸水溶液，而在另外两个入口通道中注入葵花籽油和斯盘80。使用自适应网格细化和流体体积法可以在数值模拟中准确跟踪界面。通过专门的模拟集估算了数值预测对接触角和表面张力的敏感性。随后，对不同流速下的数值模拟和实验进行了比较，结果令人满意。我们观察到，除主液滴外，捏合机制还可能导致形成多个卫星液滴。根据主液滴中包裹的海藻酸数量，我们提出了一种捏合性能指标。讨论了操作条件对捏合效率、频率和液滴直径的影响，为优化液滴生产提供了有价值的信息。捏合效率与液体螺纹的长度和直径密切相关。在低流速下，观察到的液体螺纹较短。这导致形成的卫星数量少，因此捏合效率高，但液滴产量低。提高分散相流速会略微降低效率，但会显著提高产量。
{"title":"Formation of sodium-alginate droplets in an X-microdevice: Characterization of the pinching efficiency","authors":"Sara Tomasi Masoni, Alessandro Mariotti, Chiara Galletti, Roberto Mauri, Maria Vittoria Salvetti, Elisabetta Brunazzi","doi":"10.1063/5.0223938","DOIUrl":"https://doi.org/10.1063/5.0223938","url":null,"abstract":"Experiments and simulations are used jointly to gain a comprehensive insight into the pinching mechanism that generates alginate droplets in an X-microdevice operating in a hydrodynamic flow-focusing configuration. The X-microdevice is fed with an aqueous alginate solution into one inlet channel, while sunflower oil and Span80 are fed into the other two inlet channels. The use of the adaptive mesh refinement and volume of fluid method allows accurate tracking of the interface in numerical simulations. The sensitivities of numerical predictions to the contact angle and the surface tension are estimated through dedicated sets of simulations. Subsequently, numerical simulations and experiments are compared for different flow rates with a satisfactory agreement. We observe that the pinch-off mechanism may lead to the formation of several satellite drops in addition to the main droplet. A pinching performance indicator is suggested based on the amount of alginate that is encapsulated in the main droplet. The effect of operating conditions on the pinching efficiency, frequency, and droplet diameter is discussed to provide valuable information to optimize the droplets production. The pinching efficiency is closely related to the length and diameter of the liquid thread. At low flow rates, a short liquid thread is observed. This leads to the formation of few satellites and, thus, to high pinching efficiency but low droplet production. Increasing the dispersed-phase flow rate slightly reduces the efficiency but significantly increases the production.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218338","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}
Two-stage gas-gun ballistic experiments are performed to investigate the feasibility of stratified mixtures with variable global equivalence ratios Φglobal for the formation of sphere-induced oblique detonation wave (ODW) and quantify their critical behaviors, which include local quenching and transitional structure to ODW, by testing conventional detonation criteria for uniform mixtures. 2 Φglobal H2 + O2 + 3Ar mixtures are tested with different concentration gradients for each fuel-lean/fuel-rich global composition. Opposite responses are observed depending on the global equivalence ratio: the lean mixture of Φglobal = 0.7, which forms ODW in the uniform mixture, fails partly in the strongest stratification, whereas the richest mixture of Φglobal = 2.0 turns to ODW in the strongly stratified conditions. As elucidated in the authors' previous work, Chapman–Jouguet (C–J) theory, including the curvature effects, reproduces the wave angles of the stable ODWs, as well as provides a good prediction on the local quenching of ODW occurring in the area with less reactive composition. Comparison of different wave regimes observed in the explored conditions reveals that wave curvature governs the critical behaviors of ODW far away from the projectile, whereas the initiation structure around the projectile is also influenced by the non-dimensional diameter. Surface energy theory is proven to quantify well the initiation structure on the projectile using a local equivalence ratio. These results indicate a new possibility of controlling the methodology of ignition and stabilization of detonation in aerospace engines, in which perfect mixing is difficult and non-stoichiometric and non-uniform mixtures are expected.
{"title":"Experiments on critical behavior of oblique detonation wave in stratified mixtures","authors":"K. Iwata, N. Hanyu, S. Maeda, T. Obara","doi":"10.1063/5.0225498","DOIUrl":"https://doi.org/10.1063/5.0225498","url":null,"abstract":"Two-stage gas-gun ballistic experiments are performed to investigate the feasibility of stratified mixtures with variable global equivalence ratios Φglobal for the formation of sphere-induced oblique detonation wave (ODW) and quantify their critical behaviors, which include local quenching and transitional structure to ODW, by testing conventional detonation criteria for uniform mixtures. 2 Φglobal H2 + O2 + 3Ar mixtures are tested with different concentration gradients for each fuel-lean/fuel-rich global composition. Opposite responses are observed depending on the global equivalence ratio: the lean mixture of Φglobal = 0.7, which forms ODW in the uniform mixture, fails partly in the strongest stratification, whereas the richest mixture of Φglobal = 2.0 turns to ODW in the strongly stratified conditions. As elucidated in the authors' previous work, Chapman–Jouguet (C–J) theory, including the curvature effects, reproduces the wave angles of the stable ODWs, as well as provides a good prediction on the local quenching of ODW occurring in the area with less reactive composition. Comparison of different wave regimes observed in the explored conditions reveals that wave curvature governs the critical behaviors of ODW far away from the projectile, whereas the initiation structure around the projectile is also influenced by the non-dimensional diameter. Surface energy theory is proven to quantify well the initiation structure on the projectile using a local equivalence ratio. These results indicate a new possibility of controlling the methodology of ignition and stabilization of detonation in aerospace engines, in which perfect mixing is difficult and non-stoichiometric and non-uniform mixtures are expected.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218281","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}
Ahmad Masoudi, Hossein Ali Pakravan, Hamed Bazrafshan Drissi
Recent studies have demonstrated the superior efficacy of bilateral internal thoracic artery (BITA) grafts compared to other graft methods in treating coronary artery disease. Competitive flow (CF) is a primary factor contributing to graft failure in the long term. For the first time, the CF of the BITA-Y graft has undergone rigorous numerical analysis. Through the application of transit time flow measurement (TTFM) and hemodynamic parameters, this study provides a new perspective on graft performance. Simulation results indicate that average flow, TTFM, and hemodynamic parameters fall within the critical range for stenosis severities below 90%. Specifically, at 80% stenosis, the mean graft flow (MGF) and pulsatility index (PI) of the left internal thoracic artery (LITA) were 0.071 cc/s and 27, respectively, while those of the right internal thoracic artery (RITA) were 0.211 cc/s and 11. With increasing stenosis severity, TTFM parameters remained within the clinical permissible limit (MGF > 0.34 cc/s and PI < 5). At 95% stenosis severity, the MGF and PI for LITA were 0.526 cc/s and 1.2, respectively, while those for RITA were 0.790 cc/s and 0.9. The results indicate the presence of competitive flow within the BITA-Y graft for stenosis severities below 90% area reduction, suggesting a potential risk of graft failure in the long term. Additionally, the results indicated that when there are significant differences in stenosis severity between the two native arteries, the BITA-Y graft is not optimal due to CF, characterized by low MGF and high reverse flow.
{"title":"Competitive flow of bilateral internal thoracic artery Y-graft: Insights from hemodynamics and transit time flow measurement parameters","authors":"Ahmad Masoudi, Hossein Ali Pakravan, Hamed Bazrafshan Drissi","doi":"10.1063/5.0222166","DOIUrl":"https://doi.org/10.1063/5.0222166","url":null,"abstract":"Recent studies have demonstrated the superior efficacy of bilateral internal thoracic artery (BITA) grafts compared to other graft methods in treating coronary artery disease. Competitive flow (CF) is a primary factor contributing to graft failure in the long term. For the first time, the CF of the BITA-Y graft has undergone rigorous numerical analysis. Through the application of transit time flow measurement (TTFM) and hemodynamic parameters, this study provides a new perspective on graft performance. Simulation results indicate that average flow, TTFM, and hemodynamic parameters fall within the critical range for stenosis severities below 90%. Specifically, at 80% stenosis, the mean graft flow (MGF) and pulsatility index (PI) of the left internal thoracic artery (LITA) were 0.071 cc/s and 27, respectively, while those of the right internal thoracic artery (RITA) were 0.211 cc/s and 11. With increasing stenosis severity, TTFM parameters remained within the clinical permissible limit (MGF &gt; 0.34 cc/s and PI &lt; 5). At 95% stenosis severity, the MGF and PI for LITA were 0.526 cc/s and 1.2, respectively, while those for RITA were 0.790 cc/s and 0.9. The results indicate the presence of competitive flow within the BITA-Y graft for stenosis severities below 90% area reduction, suggesting a potential risk of graft failure in the long term. Additionally, the results indicated that when there are significant differences in stenosis severity between the two native arteries, the BITA-Y graft is not optimal due to CF, characterized by low MGF and high reverse flow.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218317","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}
The interaction between droplets and a liquid pool is a widely observed fluid phenomenon with significant relevance to various industrial applications. This study numerically investigates the impact of both a single droplet and two successive droplets on a liquid pool with a fixed thickness. Particular emphasis was focused on the evolution of cavity depth and width during the deformation process. For single droplet impacts, the cavity depth exhibits linear growth with time in the early stage, consistent with predictions based on energy balance. This growth is independent of the Weber number (We) within the explored range of 96<We<345. Similarly, the cavity width shows weak dependence on the Weber number during early development, deviating and reaching a maximum width at later times. The maximum cavity width follows a power-law relationship with the Weber number, with a 0.5 exponent. In the case of successive droplet impacts with small initial separation, cavity depth also evolves linearly with time in the early stage but over an extended period. This prolonged growth is attributed to droplet merging, resulting in an effectively larger merged droplet. However, for successive droplets with large separation, the two linear growth stages exhibit intermittent interruptions due to the second impact occurring at a later time. The variation in cavity width due to different initial spacings between two successive droplets still exhibits similarity until a larger spacing causes a change in the rate of cavity width development.
{"title":"Impact of single and two successive droplets on a liquid pool","authors":"Bo-Fu Wang, Yang Li, Kai Leong Chong, Quan Zhou","doi":"10.1063/5.0225934","DOIUrl":"https://doi.org/10.1063/5.0225934","url":null,"abstract":"The interaction between droplets and a liquid pool is a widely observed fluid phenomenon with significant relevance to various industrial applications. This study numerically investigates the impact of both a single droplet and two successive droplets on a liquid pool with a fixed thickness. Particular emphasis was focused on the evolution of cavity depth and width during the deformation process. For single droplet impacts, the cavity depth exhibits linear growth with time in the early stage, consistent with predictions based on energy balance. This growth is independent of the Weber number (We) within the explored range of 96&lt;We&lt;345. Similarly, the cavity width shows weak dependence on the Weber number during early development, deviating and reaching a maximum width at later times. The maximum cavity width follows a power-law relationship with the Weber number, with a 0.5 exponent. In the case of successive droplet impacts with small initial separation, cavity depth also evolves linearly with time in the early stage but over an extended period. This prolonged growth is attributed to droplet merging, resulting in an effectively larger merged droplet. However, for successive droplets with large separation, the two linear growth stages exhibit intermittent interruptions due to the second impact occurring at a later time. The variation in cavity width due to different initial spacings between two successive droplets still exhibits similarity until a larger spacing causes a change in the rate of cavity width development.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227234","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}
Hongkang Liu, Kehui Peng, Youjun Zhang, Di Sun, Yatian Zhao
Geometric deviations arising from manufacturing and assembly processes can significantly impact the aerodynamic stability of scramjet inlets. This study aims to quantify the uncertainty and sensitivity of the inlet aerodynamics caused by geometric deviations. Specifically, three representative operating modes are considered: start, half-start, and unstart. Five geometric parameters are extracted as random uncertain variables, including the first and second ramp angle (α1, α2), the horizontal and vertical distance between the lip point and the throat point (dh, dv), and the inner angle of the cowl lip (α3). To achieve the quantification objective, the non-intrusive polynomial chaos method is employed for uncertainty quantification. Sobol indices are utilized to assess the impact of each geometric parameter on the uncertainty of quantities of interest. Results indicate that geometric deviations for only ±1% can have a significant impact on the aerodynamic performance of the inlet. Specifically, the pressure uncertainty in the shock region is more than four times that of the non-shock region, exceeding 40%. With respect to the performance parameters, the mass capture ratio demonstrates a high sensitivity to geometric deviations, with the uncertainty for 6.76%. Sensitivity analysis indicates that the three primary factors affecting the aerodynamic stability within the isolator are dv, α2, and dh. Therefore, deviations in their manufacturing and assembly should be strictly controlled.
{"title":"Quantification of geometric uncertainty on hypersonic aerodynamics in scramjet inlets","authors":"Hongkang Liu, Kehui Peng, Youjun Zhang, Di Sun, Yatian Zhao","doi":"10.1063/5.0227619","DOIUrl":"https://doi.org/10.1063/5.0227619","url":null,"abstract":"Geometric deviations arising from manufacturing and assembly processes can significantly impact the aerodynamic stability of scramjet inlets. This study aims to quantify the uncertainty and sensitivity of the inlet aerodynamics caused by geometric deviations. Specifically, three representative operating modes are considered: start, half-start, and unstart. Five geometric parameters are extracted as random uncertain variables, including the first and second ramp angle (α1, α2), the horizontal and vertical distance between the lip point and the throat point (dh, dv), and the inner angle of the cowl lip (α3). To achieve the quantification objective, the non-intrusive polynomial chaos method is employed for uncertainty quantification. Sobol indices are utilized to assess the impact of each geometric parameter on the uncertainty of quantities of interest. Results indicate that geometric deviations for only ±1% can have a significant impact on the aerodynamic performance of the inlet. Specifically, the pressure uncertainty in the shock region is more than four times that of the non-shock region, exceeding 40%. With respect to the performance parameters, the mass capture ratio demonstrates a high sensitivity to geometric deviations, with the uncertainty for 6.76%. Sensitivity analysis indicates that the three primary factors affecting the aerodynamic stability within the isolator are dv, α2, and dh. Therefore, deviations in their manufacturing and assembly should be strictly controlled.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218295","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}
Xueyu Wang, Zehua Wen, Li Zou, Xinyu Ma, Zongbing Yu, Tao Zhao
Polarity change is an important mechanism for internal waves shoaling. In this study, a numerical model for simulating the real-scale internal wave passing over slope-shelf topography is established based on the Fourier pseudo-spectral method and weakly nonlinear theory. By numerical simulation, the effects of shelf height, initial wave amplitude, and inclination angle on the waveform characteristics and energy properties of the internal wave during its shoaling are investigated. In the polarity change process, the initial internal wave converts into a depression wave and a generated elevation wave behind it. The distance between the peak of the elevation wave and the trough of the depression wave is a key feature to describe the polarity change. In terms of energy properties, the energy ratio of depression and generated elevation waves compared with the initial wave as well as their relative magnitude is mainly determined by the shelf height. In addition, the initial wave amplitude also affects the generation of the elevation wave and the attenuation of the depression wave to a certain extent. The increase in the inclination angle hinders the formation of the elevation wave but has little effect on the depression wave energy.
{"title":"Numerical study on the polarity change process during internal wave shoaling","authors":"Xueyu Wang, Zehua Wen, Li Zou, Xinyu Ma, Zongbing Yu, Tao Zhao","doi":"10.1063/5.0223970","DOIUrl":"https://doi.org/10.1063/5.0223970","url":null,"abstract":"Polarity change is an important mechanism for internal waves shoaling. In this study, a numerical model for simulating the real-scale internal wave passing over slope-shelf topography is established based on the Fourier pseudo-spectral method and weakly nonlinear theory. By numerical simulation, the effects of shelf height, initial wave amplitude, and inclination angle on the waveform characteristics and energy properties of the internal wave during its shoaling are investigated. In the polarity change process, the initial internal wave converts into a depression wave and a generated elevation wave behind it. The distance between the peak of the elevation wave and the trough of the depression wave is a key feature to describe the polarity change. In terms of energy properties, the energy ratio of depression and generated elevation waves compared with the initial wave as well as their relative magnitude is mainly determined by the shelf height. In addition, the initial wave amplitude also affects the generation of the elevation wave and the attenuation of the depression wave to a certain extent. The increase in the inclination angle hinders the formation of the elevation wave but has little effect on the depression wave energy.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218297","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}
Amalendu Rana, Motahar Reza, Gopal Chandra Shit, Klaus Stefan Drese
Rough surfaces in microchannels effectively enhance liquid mixing, thermal performance, and chemical reactions in electrically actuated microfluidic devices. Rotation of the microchannel with surface roughness intensifies this enhancement. We investigate the combined effects of electromagnetohydrodynamics and surface roughness on transient rotating flow in microchannels. We present a mathematical model considering the variable zeta potential, heat transfer characteristics, and entropy generation within the microchannel. We obtain analytical solutions using the separation of variables method and Fourier series expansion. The surface roughness of the microchannel, when combined with rotation, impacts the temperature enhancement. Higher rotation rates result in the formation of multiple vortices. The secondary flow pushes the primary velocity toward the boundary layer, which affects the flow pattern. Surface roughness and electroosmotic flow significantly affect secondary flow, resulting in complex flow patterns and reversals. The interaction between centrifugal and viscous forces results in maximum velocities at the boundary layers. Higher roughness and electromagnetic effects enhance temperature by intensifying fluid-solid friction and joule heating. Surface roughness causes an increase in wall shear stress and friction factor, resulting in a higher Poiseuille number. Moreover, surface roughness increases entropy production by enhancing fluid mixing and internal friction despite improved heat transfer. Higher rotation also elevates entropy generation due to additional vortices induced by secondary flow.
{"title":"Electromagnetohydrodynamic flow and thermal performance in a rotating rough surface microchannel","authors":"Amalendu Rana, Motahar Reza, Gopal Chandra Shit, Klaus Stefan Drese","doi":"10.1063/5.0224263","DOIUrl":"https://doi.org/10.1063/5.0224263","url":null,"abstract":"Rough surfaces in microchannels effectively enhance liquid mixing, thermal performance, and chemical reactions in electrically actuated microfluidic devices. Rotation of the microchannel with surface roughness intensifies this enhancement. We investigate the combined effects of electromagnetohydrodynamics and surface roughness on transient rotating flow in microchannels. We present a mathematical model considering the variable zeta potential, heat transfer characteristics, and entropy generation within the microchannel. We obtain analytical solutions using the separation of variables method and Fourier series expansion. The surface roughness of the microchannel, when combined with rotation, impacts the temperature enhancement. Higher rotation rates result in the formation of multiple vortices. The secondary flow pushes the primary velocity toward the boundary layer, which affects the flow pattern. Surface roughness and electroosmotic flow significantly affect secondary flow, resulting in complex flow patterns and reversals. The interaction between centrifugal and viscous forces results in maximum velocities at the boundary layers. Higher roughness and electromagnetic effects enhance temperature by intensifying fluid-solid friction and joule heating. Surface roughness causes an increase in wall shear stress and friction factor, resulting in a higher Poiseuille number. Moreover, surface roughness increases entropy production by enhancing fluid mixing and internal friction despite improved heat transfer. Higher rotation also elevates entropy generation due to additional vortices induced by secondary flow.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142218328","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}
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