Han Meng, Yuzhong Yang, Haijun Guo, Wei Hou, Xinwang Li, Fenghua An, Rui Zhang, Li Chen, Tenglong Rong, Daming Yang, Lichao Cheng, Yufen Niu
With the increasing frequency and intensity of coal and gas outburst disasters under deep mining conditions, studying the outburst mechanism of occurrence has great significance for outbursts prevention and control. The evolution law of coal and gas outbursts under different gas pressure is proposed. The outbursts law is analyzed utilizing the self-developed simulation experiment system of coal and gas outbursts, and the simulation experiment is carried out under the gas pressure of 0.45, 0.8, and 1.5 MPa. In the experiment, the gas pressure drops curves, the relative intensity change, the interval distribution of coal powder, and the evolution of outburst hole and the migration rate of coal powder are analyzed. The results indicate that (1) the gas pressure detected by the No. 4 gas pressure sensor starts to drop first; (2) the gas pressure is positively proportional to the relative outburst intensity. When the gas pressure increases from 0.45 to 0.80 MPa and then to 1.5 MPa, the farthest outburst distance of coal powder increases from 10 to 15 m and then to 21 m, and the corresponding relative outburst intensity increases from 22.94% to 35.74% and then to 45.73%, respectively. (3) The average proportion of coal particles size less than 0.28 mm and larger than 1 mm under each corresponding outburst interval is 40.75% and 22.53%, respectively. Experimental results show that the gas pressure plays an essential role in the secondary crushing and pulverization of coal samples during the outburst process. (4) The throwing velocity of the pulverized coal is increased with the gas pressure near the outburst hole. When the gas pressure is 0.8 MPa, the throwing velocity of pulverized coal reaches the maximum value of 32.40 m/s. (5) The dimensional characteristics and the location initiation of the outburst hole are obtained. The results showed that the outburst process of coal is mainly in two failure forms: pulverization and spallation. The research results provide a theoretical basis and test data support for the prevention and control of coal and gas outburst disasters.
{"title":"Experimental investigation on the gas pressure influence laws and mechanical mechanism of coal and gas outbursts","authors":"Han Meng, Yuzhong Yang, Haijun Guo, Wei Hou, Xinwang Li, Fenghua An, Rui Zhang, Li Chen, Tenglong Rong, Daming Yang, Lichao Cheng, Yufen Niu","doi":"10.1063/5.0226658","DOIUrl":"https://doi.org/10.1063/5.0226658","url":null,"abstract":"With the increasing frequency and intensity of coal and gas outburst disasters under deep mining conditions, studying the outburst mechanism of occurrence has great significance for outbursts prevention and control. The evolution law of coal and gas outbursts under different gas pressure is proposed. The outbursts law is analyzed utilizing the self-developed simulation experiment system of coal and gas outbursts, and the simulation experiment is carried out under the gas pressure of 0.45, 0.8, and 1.5 MPa. In the experiment, the gas pressure drops curves, the relative intensity change, the interval distribution of coal powder, and the evolution of outburst hole and the migration rate of coal powder are analyzed. The results indicate that (1) the gas pressure detected by the No. 4 gas pressure sensor starts to drop first; (2) the gas pressure is positively proportional to the relative outburst intensity. When the gas pressure increases from 0.45 to 0.80 MPa and then to 1.5 MPa, the farthest outburst distance of coal powder increases from 10 to 15 m and then to 21 m, and the corresponding relative outburst intensity increases from 22.94% to 35.74% and then to 45.73%, respectively. (3) The average proportion of coal particles size less than 0.28 mm and larger than 1 mm under each corresponding outburst interval is 40.75% and 22.53%, respectively. Experimental results show that the gas pressure plays an essential role in the secondary crushing and pulverization of coal samples during the outburst process. (4) The throwing velocity of the pulverized coal is increased with the gas pressure near the outburst hole. When the gas pressure is 0.8 MPa, the throwing velocity of pulverized coal reaches the maximum value of 32.40 m/s. (5) The dimensional characteristics and the location initiation of the outburst hole are obtained. The results showed that the outburst process of coal is mainly in two failure forms: pulverization and spallation. The research results provide a theoretical basis and test data support for the prevention and control of coal and gas outburst disasters.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"32 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258727","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 underground coal seam mining, changes in the working face advancement rate can easily affect the compaction state of granules in the collapse zone. This is an important factor in the induction of gas disasters and surface subsidence in mining areas. In this work, a cyclic loading and unloading mechanical test of granules under different loading rates was carried out. The changes in mechanical parameters of the granules at various stages were investigated. It is shown that the strain of each group of specimens under cyclic loading shows an increasing trend and the final strain increases with the loading rate. The input energy of the granules increases under cyclic loading, and under a low loading rate, the compaction force needs to overcome interparticle friction to destroy the relatively stable structure, which results in a need for more energy to achieve the same level of deformation. The acoustic emission ringing counts of each group of granules specimens show an overall increasing trend, with the highest proportion of ringing counts in the first loading stage. The compaction of pores and filling of particles under cyclic loading is a “uniform compaction, stable change, slow adjustment” dynamic process. When the loading is slow, the relative positions of the granule particles in each stress gradient are more adequately adjusted. The results of this study provide important theoretical support for the scientific formulation of gas control strategies and the prevention of surface subsidence in air-mining zones under different mining speeds.
{"title":"Effect of loading rate on characteristics of cyclic structural adjustment of sandstone granules","authors":"Tengfei Ma, Quanle Zou, Fanjie Kong, Qican Ran, Dengke Qin, Yulin Hu, Feixiang Lv, Haolong Zheng","doi":"10.1063/5.0218578","DOIUrl":"https://doi.org/10.1063/5.0218578","url":null,"abstract":"During underground coal seam mining, changes in the working face advancement rate can easily affect the compaction state of granules in the collapse zone. This is an important factor in the induction of gas disasters and surface subsidence in mining areas. In this work, a cyclic loading and unloading mechanical test of granules under different loading rates was carried out. The changes in mechanical parameters of the granules at various stages were investigated. It is shown that the strain of each group of specimens under cyclic loading shows an increasing trend and the final strain increases with the loading rate. The input energy of the granules increases under cyclic loading, and under a low loading rate, the compaction force needs to overcome interparticle friction to destroy the relatively stable structure, which results in a need for more energy to achieve the same level of deformation. The acoustic emission ringing counts of each group of granules specimens show an overall increasing trend, with the highest proportion of ringing counts in the first loading stage. The compaction of pores and filling of particles under cyclic loading is a “uniform compaction, stable change, slow adjustment” dynamic process. When the loading is slow, the relative positions of the granule particles in each stress gradient are more adequately adjusted. The results of this study provide important theoretical support for the scientific formulation of gas control strategies and the prevention of surface subsidence in air-mining zones under different mining speeds.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"101 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258687","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}
To enhance the aerodynamic performance of compressors in advanced aeroengines, a compound flow control method combining positively bowed blades and bionic-wavy leading edges is proposed for improving the aerodynamic performance of compressor cascades with controlled diffusion airfoils. This study verified the effectiveness of the compound control method through low-speed wind tunnel experiments using five-hole probe measurements and surface oil-flow visualization techniques. Additionally, the flow field structure was analyzed, and vortex models were established to thoroughly discuss the mechanism of the compound flow control method. The results show that within the incidence angle range of 0°–4° studied in this paper, the composite control method achieved significantly effective control, with a maximum reduction in overall total pressure loss of 25.8% compared to straight blade cascades. Three vortex models were established. The positive bowed blade cascade induced a complex vortex structure in the concentrated shedding vortex region, increasing losses in the concentrated shedding vortex (CSV) region but reducing profile losses. The coupled method further reduced profile losses and optimized the flow field in the CSV region. This study not only validates the feasibility of the compound method but also provides guidance for applying flow control methods to bowed blade cascades.
{"title":"Experimental study on flow field and performance of bionic-wavy leading edge in an axial compressor with positive bowed blades","authors":"Longye Zheng, Cong Zeng, Shaowen Chen","doi":"10.1063/5.0230122","DOIUrl":"https://doi.org/10.1063/5.0230122","url":null,"abstract":"To enhance the aerodynamic performance of compressors in advanced aeroengines, a compound flow control method combining positively bowed blades and bionic-wavy leading edges is proposed for improving the aerodynamic performance of compressor cascades with controlled diffusion airfoils. This study verified the effectiveness of the compound control method through low-speed wind tunnel experiments using five-hole probe measurements and surface oil-flow visualization techniques. Additionally, the flow field structure was analyzed, and vortex models were established to thoroughly discuss the mechanism of the compound flow control method. The results show that within the incidence angle range of 0°–4° studied in this paper, the composite control method achieved significantly effective control, with a maximum reduction in overall total pressure loss of 25.8% compared to straight blade cascades. Three vortex models were established. The positive bowed blade cascade induced a complex vortex structure in the concentrated shedding vortex region, increasing losses in the concentrated shedding vortex (CSV) region but reducing profile losses. The coupled method further reduced profile losses and optimized the flow field in the CSV region. This study not only validates the feasibility of the compound method but also provides guidance for applying flow control methods to bowed blade cascades.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"81 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258773","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}
This article investigates thermal convection in Kelvin–Voigt fluids saturating a Brinkman–Darcy-type porous medium. We examine the linear (stationary and oscillatory), nonlinear, and unconditional nonlinear stability of this fluid under the generalized Maxwell–Cattaneo law with couple stress effects. Using the normal mode technique, we calculate the critical Rayleigh number for the linear stability under stress-free boundary conditions for both stationary and oscillatory convection. Additionally, we employ the energy method to determine the critical Rayleigh number for nonlinear and unconditional nonlinear stabilities under the same boundary conditions. All critical values were determined numerically, and various graphs were plotted to illustrate the results. Our findings reveal that a higher couple stress parameter leads to increased critical Rayleigh numbers for stationary, oscillatory, and nonlinear stability, indicating greater fluid stability and reduced susceptibility to convection. Additionally, the Kelvin–Voigt parameter significantly affects oscillatory convection, though it remains crucial within the nonlinear stability framework. These findings provide a detailed understanding of the stability behavior in this complex fluid system.
{"title":"Convective heat transfer in Brinkman–Darcy–Kelvin–Voigt fluid with couple stress and generalized Maxwell–Cattaneo law","authors":"Saravanan P, Amit Mahajan","doi":"10.1063/5.0230052","DOIUrl":"https://doi.org/10.1063/5.0230052","url":null,"abstract":"This article investigates thermal convection in Kelvin–Voigt fluids saturating a Brinkman–Darcy-type porous medium. We examine the linear (stationary and oscillatory), nonlinear, and unconditional nonlinear stability of this fluid under the generalized Maxwell–Cattaneo law with couple stress effects. Using the normal mode technique, we calculate the critical Rayleigh number for the linear stability under stress-free boundary conditions for both stationary and oscillatory convection. Additionally, we employ the energy method to determine the critical Rayleigh number for nonlinear and unconditional nonlinear stabilities under the same boundary conditions. All critical values were determined numerically, and various graphs were plotted to illustrate the results. Our findings reveal that a higher couple stress parameter leads to increased critical Rayleigh numbers for stationary, oscillatory, and nonlinear stability, indicating greater fluid stability and reduced susceptibility to convection. Additionally, the Kelvin–Voigt parameter significantly affects oscillatory convection, though it remains crucial within the nonlinear stability framework. These findings provide a detailed understanding of the stability behavior in this complex fluid system.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"5 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258906","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}
Mining disturbances can rupture the closed pores, releasing the gas and potentially triggering gas accidents. The pre-drainage of gas via boreholes is the primary measure for preventing coal and gas outbursts. Nevertheless, the influence of closed pores on gas migration remains unclear, leading to suboptimal borehole spacing and radius. Therefore, a gas–solid coupled model incorporating closed pores was developed to investigate the influence of closed pores on gas migration during gas drainage (GD). Subsequently, response surface methodology was employed to investigate the input parameters and their interactions on residual gas content (RGC) and pre-drainage time (PDT). Finally, an optimization methodology for borehole spacing/radius was presented. The results show that both RGC and PDT exhibit a positive correlation with the ratio of closed porosity to total porosity (λ) and the ratio of closed pore diffusion coefficient to that of the open pore (Do/Dc). Initially, the total gas production is primarily extracted from fractures and open pores, followed by closed pores in the later stages. Single-factor analysis demonstrates that λ, permeability, and Do/Dc have a more significant impact on RGC and PDT compared to borehole spacing and borehole radius. Borehole spacing interacts more strongly with λ, permeability and Do/Dc than borehole radius. An optimization method for borehole spacing and borehole radius, constrained by PDT, RGC, and the number of boreholes, is proposed using response surface optimization maps. This method provides guidance for borehole construction to optimize GD efficiency and minimize RGC.
{"title":"Impact of closed pores on gas transport and its implication for optimizing drainage borehole design","authors":"Hexiang Xu, Ting Liu, Cheng Zhai, Jizhao Xu, Yangfeng Zheng, Xinyu Zhu, Yu Wang, Ting Huang","doi":"10.1063/5.0230148","DOIUrl":"https://doi.org/10.1063/5.0230148","url":null,"abstract":"Mining disturbances can rupture the closed pores, releasing the gas and potentially triggering gas accidents. The pre-drainage of gas via boreholes is the primary measure for preventing coal and gas outbursts. Nevertheless, the influence of closed pores on gas migration remains unclear, leading to suboptimal borehole spacing and radius. Therefore, a gas–solid coupled model incorporating closed pores was developed to investigate the influence of closed pores on gas migration during gas drainage (GD). Subsequently, response surface methodology was employed to investigate the input parameters and their interactions on residual gas content (RGC) and pre-drainage time (PDT). Finally, an optimization methodology for borehole spacing/radius was presented. The results show that both RGC and PDT exhibit a positive correlation with the ratio of closed porosity to total porosity (λ) and the ratio of closed pore diffusion coefficient to that of the open pore (Do/Dc). Initially, the total gas production is primarily extracted from fractures and open pores, followed by closed pores in the later stages. Single-factor analysis demonstrates that λ, permeability, and Do/Dc have a more significant impact on RGC and PDT compared to borehole spacing and borehole radius. Borehole spacing interacts more strongly with λ, permeability and Do/Dc than borehole radius. An optimization method for borehole spacing and borehole radius, constrained by PDT, RGC, and the number of boreholes, is proposed using response surface optimization maps. This method provides guidance for borehole construction to optimize GD efficiency and minimize RGC.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"31 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258782","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}
Extensional flow is vital in droplet dynamics, influencing their formation, size, stability, and functionality across diverse applications from industrial processes to biomedical technology. Ferrofluid droplets are pivotal in many such applications, where magnetic fields enable non-contact manipulation without undesirable heating effects. However, controlling ferrofluid droplet dynamics in magnetically influenced extensional flows is challenging due to the complex interplay of induced magnetization, intrinsic magnetic properties, and flow kinematics. Here, we present a first-principle-based theory delving into the morphology of a ferrofluid droplet under the combined influence of an external magnetic field and extensional flow. Unlike previous studies, we employ an asymptotic analysis that delves on the shape alterations by considering local magnetization as dependent on magnetic field intensity. Additionally, we develop a numerical model based on phase-field hydrodynamics to establish the practical applicability of the asymptotic solution and to explore large droplet-deformation regimes. The study demonstrates that increasing the magnetic field intensity, the saturation magnetization of the ferrofluid, and the initial magnetic susceptibility each independently improve droplet deformation. Additionally, we found that in a uniform magnetic field, the extensional viscosity of a ferrofluid emulsion is influenced by the strain rate, leading to strain-thickening behavior in the dilute emulsion. Our findings offer new insights into field-assisted manipulation of ferrofluid droplets, emphasizing their potential in applications ranging from process engineering to biomedical technology.
{"title":"Magnetic field-mediated ferrofluid droplet deformation in extensional flow","authors":"Debdeep Bhattacharjee, Arnab Atta, Suman Chakraborty","doi":"10.1063/5.0227028","DOIUrl":"https://doi.org/10.1063/5.0227028","url":null,"abstract":"Extensional flow is vital in droplet dynamics, influencing their formation, size, stability, and functionality across diverse applications from industrial processes to biomedical technology. Ferrofluid droplets are pivotal in many such applications, where magnetic fields enable non-contact manipulation without undesirable heating effects. However, controlling ferrofluid droplet dynamics in magnetically influenced extensional flows is challenging due to the complex interplay of induced magnetization, intrinsic magnetic properties, and flow kinematics. Here, we present a first-principle-based theory delving into the morphology of a ferrofluid droplet under the combined influence of an external magnetic field and extensional flow. Unlike previous studies, we employ an asymptotic analysis that delves on the shape alterations by considering local magnetization as dependent on magnetic field intensity. Additionally, we develop a numerical model based on phase-field hydrodynamics to establish the practical applicability of the asymptotic solution and to explore large droplet-deformation regimes. The study demonstrates that increasing the magnetic field intensity, the saturation magnetization of the ferrofluid, and the initial magnetic susceptibility each independently improve droplet deformation. Additionally, we found that in a uniform magnetic field, the extensional viscosity of a ferrofluid emulsion is influenced by the strain rate, leading to strain-thickening behavior in the dilute emulsion. Our findings offer new insights into field-assisted manipulation of ferrofluid droplets, emphasizing their potential in applications ranging from process engineering to biomedical technology.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"10 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258844","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}
Huan Zhou, Jun Gao, Boqi Xiao, Lei Chen, Jiyin Cao, Gongbo Long, Jiacheng Zhang
The investigation of permeability in tree-like branching networks has attracted widespread attention. However, most studies about fractal models for predicting permeability in tree-like branching networks include empirical constants. This paper investigates the flow characteristics of power-law fluids in the dual porosity model of porous media in embedded tree-like branching networks. Considering the inherent properties of power-law fluids, non-Newtonian behavior effects, and fractal properties of porous media, a power-law fluids rheological equation is introduced based on the fractional-derivative theory and fractal theory. Then, an analytical formula for predicting the effective permeability of power-law fluids in dual porous media is derived. This analytical formula indicates the influences of fractal dimensions and structural parameters on permeability. With increasing length ratio, bifurcation series, and bifurcation angle, as well as decreasing power-law exponent and diameter ratio, the effective permeability decreases to varying degrees. The derived analytical model does not include empirical constants and is consistent with the non-Newtonian properties of power-law fluids, indicating that the model is an effective method for describing the flow process of complex non-Newtonian fluids in porous media in natural systems and engineering. Therefore, this study is of great significance to derive analytical solutions for the permeability of power-law fluids in embedded tree-like bifurcation networks.
{"title":"Fractal permeability model for power-law fluids in embedded tree-like branching networks based on the fractional-derivative theory","authors":"Huan Zhou, Jun Gao, Boqi Xiao, Lei Chen, Jiyin Cao, Gongbo Long, Jiacheng Zhang","doi":"10.1063/5.0231819","DOIUrl":"https://doi.org/10.1063/5.0231819","url":null,"abstract":"The investigation of permeability in tree-like branching networks has attracted widespread attention. However, most studies about fractal models for predicting permeability in tree-like branching networks include empirical constants. This paper investigates the flow characteristics of power-law fluids in the dual porosity model of porous media in embedded tree-like branching networks. Considering the inherent properties of power-law fluids, non-Newtonian behavior effects, and fractal properties of porous media, a power-law fluids rheological equation is introduced based on the fractional-derivative theory and fractal theory. Then, an analytical formula for predicting the effective permeability of power-law fluids in dual porous media is derived. This analytical formula indicates the influences of fractal dimensions and structural parameters on permeability. With increasing length ratio, bifurcation series, and bifurcation angle, as well as decreasing power-law exponent and diameter ratio, the effective permeability decreases to varying degrees. The derived analytical model does not include empirical constants and is consistent with the non-Newtonian properties of power-law fluids, indicating that the model is an effective method for describing the flow process of complex non-Newtonian fluids in porous media in natural systems and engineering. Therefore, this study is of great significance to derive analytical solutions for the permeability of power-law fluids in embedded tree-like bifurcation networks.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"14 13 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258847","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}
Huajie Xiong, Na Wang, Tao Zeng, Kairen Xu, Zhihong Zhou
The singularity issue arising from the phase fraction approaching zero in multiphase flow can significantly intensify the solution difficulty and lead to nonphysical results. By employing the conservative form of momentum equations in high-phase-fraction and discontinuity regions and the phase-intensive form of momentum equations in low-phase-fraction regions, computational reliability can be assured while avoiding the singularity issue. Regarding the proposed adaptive momentum equation method, the form of momentum equations for each cell is determined by a conversion bound and a phase fraction discontinuity detector. A comparative analysis is conducted on this method and other singularity-free methods. For discontinuities of dispersed phases, an error estimation method of the conversion bound is presented through theoretical analysis. Computational results demonstrate that the discontinuity detector accurately captures discontinuities in high-phase-fraction regions while disregarding pseudo-discontinuities in low-phase-fraction regions. Compared to the conservative form corrected by the terminal velocity method, the method yields higher-quality flow fields and potentially exhibits an efficiency improvement of over 10 times. Compared to the phase-intensive form, the method benefits from the physical quantity conservation, providing higher computational reliability. When encountering discontinuities, the expected error from the error estimation method aligns well with the actual error, indicating its effectiveness. When the conversion bound is below 1/10 000 of the inlet phase fraction, the errors of the adaptive method are essentially negligible.
{"title":"Adaptive momentum equation method for overcoming singularities of dispersed phases","authors":"Huajie Xiong, Na Wang, Tao Zeng, Kairen Xu, Zhihong Zhou","doi":"10.1063/5.0225332","DOIUrl":"https://doi.org/10.1063/5.0225332","url":null,"abstract":"The singularity issue arising from the phase fraction approaching zero in multiphase flow can significantly intensify the solution difficulty and lead to nonphysical results. By employing the conservative form of momentum equations in high-phase-fraction and discontinuity regions and the phase-intensive form of momentum equations in low-phase-fraction regions, computational reliability can be assured while avoiding the singularity issue. Regarding the proposed adaptive momentum equation method, the form of momentum equations for each cell is determined by a conversion bound and a phase fraction discontinuity detector. A comparative analysis is conducted on this method and other singularity-free methods. For discontinuities of dispersed phases, an error estimation method of the conversion bound is presented through theoretical analysis. Computational results demonstrate that the discontinuity detector accurately captures discontinuities in high-phase-fraction regions while disregarding pseudo-discontinuities in low-phase-fraction regions. Compared to the conservative form corrected by the terminal velocity method, the method yields higher-quality flow fields and potentially exhibits an efficiency improvement of over 10 times. Compared to the phase-intensive form, the method benefits from the physical quantity conservation, providing higher computational reliability. When encountering discontinuities, the expected error from the error estimation method aligns well with the actual error, indicating its effectiveness. When the conversion bound is below 1/10 000 of the inlet phase fraction, the errors of the adaptive method are essentially negligible.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"9 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258839","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}
Anil Pasam, Daniel Tudball Smith, David Burton, Mark C. Thompson
This study investigates the flow behavior over roughened inline cylinders for postcritical flow, a parameter space with relatively little prior scrutiny. Two cylinders of the same relative surface roughness, ks/D=1.9×10−3, separated by a pitch (i.e., L, distance between the centers of two cylinders) between 1.175≤L/D≤10 are studied at Reynolds numbers from 3×105 to 6×105 using unsteady surface pressure measurements. As pitch ratio is increased from L/D=1.175, CD of the downstream cylinder increases sharply at (L/D)c=3.25. This critical pitch ratio (L/D)c is toward the lower end of the reported range for subcritical smooth cylinders. Asymmetric mean gap flow along with alternating reattachment is found for 1.5≤L/D<2.25 (i.e., two asymmetric modes in the gap, mode 1 and mode 2, that are the reflections of each other), and symmetric gap flow with a continuous reattachment is found for 2.25<L/D≤3. The gap flow is also symmetric for the closest pitch ratio tested of L/D=1.175. While the change in upstream cylinder drag coefficient with Reynolds number broadly follows that of an isolated cylinder, for the downstream cylinder, it is approximately independent. The critical separation is also insensitive to Reynolds number within 3×105≤Re≤6×105. Transitions between the reattachment and the co-shedding flow are predominantly continuous over the spanwise planes tested. On the other hand, alternating reattachment occurs in spanwise cells, where one sectional measurement exhibits the asymmetric mode 1 while a spanwise-adjacent section exhibits the asymmetric mode 2 or even symmetric flow. Previously reported maxima in the fluctuating lift and drag coefficients of the downstream cylinder at L/D≈2.4 at subcritical Reynolds numbers are absent in the current investigation.
{"title":"Flow over two inline rough cylinders in the postcritical regime","authors":"Anil Pasam, Daniel Tudball Smith, David Burton, Mark C. Thompson","doi":"10.1063/5.0221390","DOIUrl":"https://doi.org/10.1063/5.0221390","url":null,"abstract":"This study investigates the flow behavior over roughened inline cylinders for postcritical flow, a parameter space with relatively little prior scrutiny. Two cylinders of the same relative surface roughness, ks/D=1.9×10−3, separated by a pitch (i.e., L, distance between the centers of two cylinders) between 1.175≤L/D≤10 are studied at Reynolds numbers from 3×105 to 6×105 using unsteady surface pressure measurements. As pitch ratio is increased from L/D=1.175, CD of the downstream cylinder increases sharply at (L/D)c=3.25. This critical pitch ratio (L/D)c is toward the lower end of the reported range for subcritical smooth cylinders. Asymmetric mean gap flow along with alternating reattachment is found for 1.5≤L/D&lt;2.25 (i.e., two asymmetric modes in the gap, mode 1 and mode 2, that are the reflections of each other), and symmetric gap flow with a continuous reattachment is found for 2.25&lt;L/D≤3. The gap flow is also symmetric for the closest pitch ratio tested of L/D=1.175. While the change in upstream cylinder drag coefficient with Reynolds number broadly follows that of an isolated cylinder, for the downstream cylinder, it is approximately independent. The critical separation is also insensitive to Reynolds number within 3×105≤Re≤6×105. Transitions between the reattachment and the co-shedding flow are predominantly continuous over the spanwise planes tested. On the other hand, alternating reattachment occurs in spanwise cells, where one sectional measurement exhibits the asymmetric mode 1 while a spanwise-adjacent section exhibits the asymmetric mode 2 or even symmetric flow. Previously reported maxima in the fluctuating lift and drag coefficients of the downstream cylinder at L/D≈2.4 at subcritical Reynolds numbers are absent in the current investigation.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"68 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258788","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}
Conventional micro aerial vehicles (MAVs) have primarily relied on complex, flapping-wing mechanisms for propulsion, often exhibiting limitations in terms of reliability and efficiency. To overcome these challenges, this study explores the potential of electroaerodynamic (EAD) thrusters as a novel propulsion system. By accelerating air molecules through ion collisions, EAD jet flow generates thrust, offering advantages such as noiseless operation and zero emissions due to its moving-part-free design. This research presents a comprehensive experimental and numerical investigation of a wire-to-two-drop thruster configuration to elucidate its electromechanical performance, plasma flow dynamics, and EAD jet characteristics. Experimental measurements of key parameters, including current, thrust, power, and effectiveness, were correlated with numerical simulations, demonstrating excellent agreement with a maximum error below 5%. These findings align strongly with established theoretical frameworks, revealing an inverse square root relationship between effectiveness and thrust. To optimize thruster performance, optimal operating voltages were identified at approximately 8.2, 9.4, and 11.6 kV for inter-electrode gap distances of 10, 15, and 20 mm, respectively, achieving a balanced trade-off between thrust and effectiveness. Detailed numerical visualizations of the plasma flow field, including velocity distribution, jet morphology, potential distribution, and electric field lines, provided valuable insights into the thruster's operation. Building upon these insights, a proof-of-concept EAD flier was constructed and tested, incorporating a serrated emitter electrode and lightweight materials. This flier achieved a mass of 0.5 g and generated a thrust of 0.77 g at 15 kV, resulting in a thrust-to-weight ratio of 1.54 and successful liftoff. This demonstration highlights the potential of EAD propulsion for practical MAV applications.
{"title":"Wire-to-two-drop plasma thruster: Experimental and numerical investigation of electroaerodynamic jet flow for micro aerial vehicle propulsion","authors":"Mahdy Ahangar, Narges Alebrahim","doi":"10.1063/5.0222640","DOIUrl":"https://doi.org/10.1063/5.0222640","url":null,"abstract":"Conventional micro aerial vehicles (MAVs) have primarily relied on complex, flapping-wing mechanisms for propulsion, often exhibiting limitations in terms of reliability and efficiency. To overcome these challenges, this study explores the potential of electroaerodynamic (EAD) thrusters as a novel propulsion system. By accelerating air molecules through ion collisions, EAD jet flow generates thrust, offering advantages such as noiseless operation and zero emissions due to its moving-part-free design. This research presents a comprehensive experimental and numerical investigation of a wire-to-two-drop thruster configuration to elucidate its electromechanical performance, plasma flow dynamics, and EAD jet characteristics. Experimental measurements of key parameters, including current, thrust, power, and effectiveness, were correlated with numerical simulations, demonstrating excellent agreement with a maximum error below 5%. These findings align strongly with established theoretical frameworks, revealing an inverse square root relationship between effectiveness and thrust. To optimize thruster performance, optimal operating voltages were identified at approximately 8.2, 9.4, and 11.6 kV for inter-electrode gap distances of 10, 15, and 20 mm, respectively, achieving a balanced trade-off between thrust and effectiveness. Detailed numerical visualizations of the plasma flow field, including velocity distribution, jet morphology, potential distribution, and electric field lines, provided valuable insights into the thruster's operation. Building upon these insights, a proof-of-concept EAD flier was constructed and tested, incorporating a serrated emitter electrode and lightweight materials. This flier achieved a mass of 0.5 g and generated a thrust of 0.77 g at 15 kV, resulting in a thrust-to-weight ratio of 1.54 and successful liftoff. This demonstration highlights the potential of EAD propulsion for practical MAV applications.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"23 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258841","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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