Yunhao Zheng, Yanjun Li, Fan Zhang, Shouqi Yuan, Xingye Zhu
The sharp decrease in the efficiency of a mixed flow pump within over-load flow rates presents a challenge for coastal drainage pumping stations. To address this issue, two different structures of advanced inlet guide vanes (AIGV), full-adjustable (FA) and half-adjustable (HA) structures, are designed to approach a better energy performance improvement strategy. Entropy production theory is applied into transient flow field to reveal their influence mechanism on the spatial distribution of energy dissipation. The primary findings are as follows: (1) AIGVs effectively solve the sharp decrease in the energy performance of mixed-flow pumps within the over-load flow rate range, broadening its efficient operation range. (2) The decrease in the axial velocity under the effect of AIGV explains the primary fluid physics of the increased efficiency. (3) The improvement in the match between the impeller inflow angle distribution and the impeller blades structure suppresses the generation and transmission of the flow separation on the pressure side, and reduce the near-wall energy dissipation. The novel HA-AIGV obtains a better flow control effect.
{"title":"Energy performance improvement for a mixed flow pump based on advanced inlet guide vanes","authors":"Yunhao Zheng, Yanjun Li, Fan Zhang, Shouqi Yuan, Xingye Zhu","doi":"10.1063/5.0223594","DOIUrl":"https://doi.org/10.1063/5.0223594","url":null,"abstract":"The sharp decrease in the efficiency of a mixed flow pump within over-load flow rates presents a challenge for coastal drainage pumping stations. To address this issue, two different structures of advanced inlet guide vanes (AIGV), full-adjustable (FA) and half-adjustable (HA) structures, are designed to approach a better energy performance improvement strategy. Entropy production theory is applied into transient flow field to reveal their influence mechanism on the spatial distribution of energy dissipation. The primary findings are as follows: (1) AIGVs effectively solve the sharp decrease in the energy performance of mixed-flow pumps within the over-load flow rate range, broadening its efficient operation range. (2) The decrease in the axial velocity under the effect of AIGV explains the primary fluid physics of the increased efficiency. (3) The improvement in the match between the impeller inflow angle distribution and the impeller blades structure suppresses the generation and transmission of the flow separation on the pressure side, and reduce the near-wall energy dissipation. The novel HA-AIGV obtains a better flow control effect.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"32 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258845","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}
Marine midges, tiny insects with a body size of 2 mm and a weight of 0.07 dyn, provide valuable insights into advanced locomotion techniques. Found in shallow reefs at Wanlitong, Kenting National Park, Taiwan, these midges can continuously traverse seawater surfaces for over 90 min at speeds around 340 body-lengths per second. Their flight relies on two primary mechanisms: wing sculling to utilize surface tension for thrust and wing retraction to generate aerodynamic lift. This study addresses the gap in understanding how marine midges generate the lift and thrust needed for prolonged flight. We investigated their unique locomotion by conducting experiments to measure their weight, speed, and wing frequency. These measurements informed 3D computational fluid dynamics (CFD) simulations to analyze the aerodynamic forces involved. The results highlight the critical role of the ground effect, where maintaining minimal gaps of 0.08 mm between the midge trunk and 0.055 mm at the wing tips is essential for lift. Additionally, a high wing-beat frequency exceeding 300 Hz is crucial for generating sufficient lift during wing retraction. Our findings emphasize that ground effect, forward speed (>60 cm/s), and wing-beat frequency are key factors enabling marine midges to sustain flight above the sea surface. This unique adaptation for water surface locomotion not only showcases the midge's remarkable flight capabilities but also offers valuable insights for the design of micro-air vehicles (MAVs).
{"title":"Mechanics of a marine midge water locomotion","authors":"Chih-Hua Wu, Keryea Soong, Bang-Fuh Chen","doi":"10.1063/5.0222806","DOIUrl":"https://doi.org/10.1063/5.0222806","url":null,"abstract":"Marine midges, tiny insects with a body size of 2 mm and a weight of 0.07 dyn, provide valuable insights into advanced locomotion techniques. Found in shallow reefs at Wanlitong, Kenting National Park, Taiwan, these midges can continuously traverse seawater surfaces for over 90 min at speeds around 340 body-lengths per second. Their flight relies on two primary mechanisms: wing sculling to utilize surface tension for thrust and wing retraction to generate aerodynamic lift. This study addresses the gap in understanding how marine midges generate the lift and thrust needed for prolonged flight. We investigated their unique locomotion by conducting experiments to measure their weight, speed, and wing frequency. These measurements informed 3D computational fluid dynamics (CFD) simulations to analyze the aerodynamic forces involved. The results highlight the critical role of the ground effect, where maintaining minimal gaps of 0.08 mm between the midge trunk and 0.055 mm at the wing tips is essential for lift. Additionally, a high wing-beat frequency exceeding 300 Hz is crucial for generating sufficient lift during wing retraction. Our findings emphasize that ground effect, forward speed (>60 cm/s), and wing-beat frequency are key factors enabling marine midges to sustain flight above the sea surface. This unique adaptation for water surface locomotion not only showcases the midge's remarkable flight capabilities but also offers valuable insights for the design of micro-air vehicles (MAVs).","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"17 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258833","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}
With the development of engineering applications and the increase in system complexity, some particular fields, such as liquid rocket engine turbopumps, aircraft engine fuel systems, and marine natural flow cooling systems, are increasingly focusing on the performance characteristics of pumps under natural flow conditions. The pump is in the form of resistance components under natural flow conditions without a power drive. The impeller undergoes passive rotation by the impact of inlet flow. Due to the specificity of its operating conditions and performance indicators, the pump's natural flow performance cannot be evaluated by regular methods. Therefore, this paper proposed a numerical prediction method for pump natural flow performance based on a coupled computational fluid dynamics coupled with six-degrees-of freedom model. The performance of a multistage pump with guide vanes was evaluated under different natural flow conditions, and the accuracy was verified by experimental measurements. The transient variation mode of pump performance parameters with time at the initial stage of natural flow impact was analyzed. The flow field's transient evolution characteristics and the wall shear stress variation during natural flow were investigated. It was found that the impeller's passive rotational speed increases linearly with the natural flow rate, while the hydraulic loss shows an exponentially increasing trend. Meanwhile, the natural flow loss coefficient shows an exponentially decreasing trend and gradually tends to a stable value. The high turbulent kinetic energy inside the impeller is mainly distributed in the flow separation region and large velocity gradients. The distribution of shear stresses is closely related to the flow behavior inside the pump and the geometrical features of the hydraulic components.
{"title":"Numerical prediction of passive speed and performance for multistage pump without power drive in natural flow process","authors":"Runze Zhou, Houlin Liu, Liang Dong, Kim Tiow Ooi, Shaopeng Kang, Zhiming Cheng","doi":"10.1063/5.0225798","DOIUrl":"https://doi.org/10.1063/5.0225798","url":null,"abstract":"With the development of engineering applications and the increase in system complexity, some particular fields, such as liquid rocket engine turbopumps, aircraft engine fuel systems, and marine natural flow cooling systems, are increasingly focusing on the performance characteristics of pumps under natural flow conditions. The pump is in the form of resistance components under natural flow conditions without a power drive. The impeller undergoes passive rotation by the impact of inlet flow. Due to the specificity of its operating conditions and performance indicators, the pump's natural flow performance cannot be evaluated by regular methods. Therefore, this paper proposed a numerical prediction method for pump natural flow performance based on a coupled computational fluid dynamics coupled with six-degrees-of freedom model. The performance of a multistage pump with guide vanes was evaluated under different natural flow conditions, and the accuracy was verified by experimental measurements. The transient variation mode of pump performance parameters with time at the initial stage of natural flow impact was analyzed. The flow field's transient evolution characteristics and the wall shear stress variation during natural flow were investigated. It was found that the impeller's passive rotational speed increases linearly with the natural flow rate, while the hydraulic loss shows an exponentially increasing trend. Meanwhile, the natural flow loss coefficient shows an exponentially decreasing trend and gradually tends to a stable value. The high turbulent kinetic energy inside the impeller is mainly distributed in the flow separation region and large velocity gradients. The distribution of shear stresses is closely related to the flow behavior inside the pump and the geometrical features of the hydraulic components.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"17 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258834","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 extraction and time evolution of optimal perturbation (OP) offers abundant physical insights in fluid dynamics. Nonlinear OP (NLOP) analysis provides an approach for obtaining the trajectory to induce the maximum changes in the flow field. In an extension into unsteady flow field, we tracked the changes of trajectory by an application of initial perturbation field in the compressible Navier–Stokes equation, and we focused on the entropy production (EP) to characterize the trajectory. We proposed entropy production-based NLOP (EP-NLOP) analysis for compressible flows and investigated the effect of evaluation function on the extracted Ops using the subsonic flow around an airfoil. Compared with the conventional disturbance energy (DE-) based NLOP (DE-NLOP) analysis, we demonstrated that the OPs with different spatial wavelength and concentration regions were successfully extracted due to the different spatial sensitivity of evaluation function. In the EP-NLOP analysis, the spatial distribution of OP extracted the larger energy dissipation upstream of the separation points for the short evaluation time. For the long evaluation time, EP-NLOP analysis extracted the transient-time evolution of interacting separation vortices, attributing the multiple wavelengths of OPs. These differences in the OPs offer promising insights into fluid dynamics.
{"title":"Entropy production-based nonlinear optimal perturbation for subsonic flows around an airfoil","authors":"Nobutaka Taniguchi, Yuya Ohmichi, Kojiro Suzuki","doi":"10.1063/5.0220442","DOIUrl":"https://doi.org/10.1063/5.0220442","url":null,"abstract":"The extraction and time evolution of optimal perturbation (OP) offers abundant physical insights in fluid dynamics. Nonlinear OP (NLOP) analysis provides an approach for obtaining the trajectory to induce the maximum changes in the flow field. In an extension into unsteady flow field, we tracked the changes of trajectory by an application of initial perturbation field in the compressible Navier–Stokes equation, and we focused on the entropy production (EP) to characterize the trajectory. We proposed entropy production-based NLOP (EP-NLOP) analysis for compressible flows and investigated the effect of evaluation function on the extracted Ops using the subsonic flow around an airfoil. Compared with the conventional disturbance energy (DE-) based NLOP (DE-NLOP) analysis, we demonstrated that the OPs with different spatial wavelength and concentration regions were successfully extracted due to the different spatial sensitivity of evaluation function. In the EP-NLOP analysis, the spatial distribution of OP extracted the larger energy dissipation upstream of the separation points for the short evaluation time. For the long evaluation time, EP-NLOP analysis extracted the transient-time evolution of interacting separation vortices, attributing the multiple wavelengths of OPs. These differences in the OPs offer promising insights into fluid dynamics.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"16 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258837","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 explores the solitary wave solutions of a generalized Hirota–Satsuma Coupled Korteweg–de Vries (HSCKdV) equation. The HSCKdV equation is a mathematical model that describes certain types of long waves, particularly those found in shallow water. The generalized HSCKdV equation is solved exactly using the Homotopy Perturbation Transform Method (HPTM). By applying this technique, the authors obtain solutions in the form of a convergent power series. These solutions offer an understanding of the characteristics of solitary waves within the domain of shallow water waves. The HSCKdV equation has been solved using the adomian decomposition method, and the results have been compared with those obtained from the HPTM. This comparison demonstrates the effectiveness of the HPTM in solving such nonlinear equations. Further, the HSCKdV equation is extended to a fuzzy version considering the initial condition as a fuzzy parameter. Uncertainty in the initial condition is addressed by representing it using triangular and trapezoidal fuzzy numbers. The generalized fuzzy HSCKdV equation is subsequently tackled using the fuzzy HPTM (FHPTM) providing fuzzy bound solutions. Using the FHPTM, we explain the fuzzy results, highlighting how the solitary wave splits into two solitary waves and noting that the lower and upper bound solutions are interchanged due to negative fuzzy results.
{"title":"Fuzzy uncertainty modeling of generalized Hirota–Satsuma coupled Korteweg–de Vries equation","authors":"Rambabu Vana, Perumandla Karunakar","doi":"10.1063/5.0226445","DOIUrl":"https://doi.org/10.1063/5.0226445","url":null,"abstract":"This article explores the solitary wave solutions of a generalized Hirota–Satsuma Coupled Korteweg–de Vries (HSCKdV) equation. The HSCKdV equation is a mathematical model that describes certain types of long waves, particularly those found in shallow water. The generalized HSCKdV equation is solved exactly using the Homotopy Perturbation Transform Method (HPTM). By applying this technique, the authors obtain solutions in the form of a convergent power series. These solutions offer an understanding of the characteristics of solitary waves within the domain of shallow water waves. The HSCKdV equation has been solved using the adomian decomposition method, and the results have been compared with those obtained from the HPTM. This comparison demonstrates the effectiveness of the HPTM in solving such nonlinear equations. Further, the HSCKdV equation is extended to a fuzzy version considering the initial condition as a fuzzy parameter. Uncertainty in the initial condition is addressed by representing it using triangular and trapezoidal fuzzy numbers. The generalized fuzzy HSCKdV equation is subsequently tackled using the fuzzy HPTM (FHPTM) providing fuzzy bound solutions. Using the FHPTM, we explain the fuzzy results, highlighting how the solitary wave splits into two solitary waves and noting that the lower and upper bound solutions are interchanged due to negative fuzzy results.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"21 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258842","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}
Head-on collision of the two small-amplitude electron-acoustic (EA) solitons is studied in an unmagnetized collisionless plasma in the presence of superthermal (hot) trapped electrons. For this purpose, using a well-known extended Poincare–Lighthill–Kuo (PLK) method, a pair of the trapped Korteweg–de Vries (tKdV) equations is derived to investigate the soliton trajectories and phase shifts. The latter are found dependent on amplitudes of the interacting solitons, effectively altering with hot-electron superthermality and plasma parameters. Typical parameters for the electron diffusion region (EDR) and day-side auroral zone have been selected to examine the impact of hot-electron superthermality, trapping parameter, hot-to-cold electron number density ratio, and cold-to-hot electron temperature ratio on the profiles of potential excitations and phase shifts of interacting solitons. It is found that phase speed of the EA waves becomes altered by varying the κ–parameter, strongly modifying the nonlinearity and dispersive coefficients in a superthermal trapped plasma. However, particle trapping phenomenon does not affect the linear phase speed but introduces a fractional nonlinearity in the tKdV equations of two interacting solitons. The impact of the adiabatic and isothermal pressures is also highlighted to show new modifications in the propagation characteristics of two interacting solitons.
{"title":"Soliton interaction in a two-temperature electron plasma with trapping and superthermality effects","authors":"Usama H. Malik, S. Ali, R. Jahangir, Majid Khan","doi":"10.1063/5.0223332","DOIUrl":"https://doi.org/10.1063/5.0223332","url":null,"abstract":"Head-on collision of the two small-amplitude electron-acoustic (EA) solitons is studied in an unmagnetized collisionless plasma in the presence of superthermal (hot) trapped electrons. For this purpose, using a well-known extended Poincare–Lighthill–Kuo (PLK) method, a pair of the trapped Korteweg–de Vries (tKdV) equations is derived to investigate the soliton trajectories and phase shifts. The latter are found dependent on amplitudes of the interacting solitons, effectively altering with hot-electron superthermality and plasma parameters. Typical parameters for the electron diffusion region (EDR) and day-side auroral zone have been selected to examine the impact of hot-electron superthermality, trapping parameter, hot-to-cold electron number density ratio, and cold-to-hot electron temperature ratio on the profiles of potential excitations and phase shifts of interacting solitons. It is found that phase speed of the EA waves becomes altered by varying the κ–parameter, strongly modifying the nonlinearity and dispersive coefficients in a superthermal trapped plasma. However, particle trapping phenomenon does not affect the linear phase speed but introduces a fractional nonlinearity in the tKdV equations of two interacting solitons. The impact of the adiabatic and isothermal pressures is also highlighted to show new modifications in the propagation characteristics of two interacting solitons.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"28 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258846","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}
Yan Liu, Zhengdao Tang, Lei Huang, Thorsten Stoesser, Hongwei Fang
In this paper, the results of numerical simulations of open-channel flow through boulder arrays at varying Froude numbers are reported. The simulations aim at clarifying the role of the Froude number on flow, turbulence, and hyporheic exchange. At low and intermediate Fr, the boulder top is above the water surface, and time-averaged streamwise flow velocity, Reynolds shear stresses, and the turbulent kinetic energy (TKE) are relatively low in the wake of boulders. Conversely, at high Fr values, the boulders are submerged, hence the flow separates at the boulder crest, creates vertical recirculation, and reattaches on the bed downstream, resulting in an area of elevated Reynolds shear stresses and TKE downstream of the boulders. Two dominant turbulence structures are observed: (i) flapping of boulder wakes with a characteristic length of 2.1 times the boulder diameter (D) at low and intermediate Fr and (ii) an upstream oriented hairpin vortex with a length scale of 1.0D at high Fr. These turbulence structures influence hyporheic exchange downstream of boulders within a limited region of x/D<2.0. In other locations, hyporheic flow is driven by downwelling flow immediately upstream of boulders with a wavelength larger than 2.9D. Finally, the normalized time-averaged hyporheic flux increases with increasing Fr, but it decreases at higher Fr values once the overtopping flow disrupts the formation of the boulder wake.
{"title":"On the role of the Froude number on flow, turbulence, and hyporheic exchange in open-channel flow through boulder arrays","authors":"Yan Liu, Zhengdao Tang, Lei Huang, Thorsten Stoesser, Hongwei Fang","doi":"10.1063/5.0222673","DOIUrl":"https://doi.org/10.1063/5.0222673","url":null,"abstract":"In this paper, the results of numerical simulations of open-channel flow through boulder arrays at varying Froude numbers are reported. The simulations aim at clarifying the role of the Froude number on flow, turbulence, and hyporheic exchange. At low and intermediate Fr, the boulder top is above the water surface, and time-averaged streamwise flow velocity, Reynolds shear stresses, and the turbulent kinetic energy (TKE) are relatively low in the wake of boulders. Conversely, at high Fr values, the boulders are submerged, hence the flow separates at the boulder crest, creates vertical recirculation, and reattaches on the bed downstream, resulting in an area of elevated Reynolds shear stresses and TKE downstream of the boulders. Two dominant turbulence structures are observed: (i) flapping of boulder wakes with a characteristic length of 2.1 times the boulder diameter (D) at low and intermediate Fr and (ii) an upstream oriented hairpin vortex with a length scale of 1.0D at high Fr. These turbulence structures influence hyporheic exchange downstream of boulders within a limited region of x/D&lt;2.0. In other locations, hyporheic flow is driven by downwelling flow immediately upstream of boulders with a wavelength larger than 2.9D. Finally, the normalized time-averaged hyporheic flux increases with increasing Fr, but it decreases at higher Fr values once the overtopping flow disrupts the formation of the boulder wake.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"208 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269346","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}
Zengshuang Chen, Xiankai Li, Ming Ma, Yang Zhang, Xueguang Meng
Aerodynamic interference occurs at the wingtips when flying organisms fly in a V formation. In this paper, the wingtip aerodynamic interference of two flapping wings on opposite sides at low Reynolds numbers (Re) is numerically investigated. The effects of streamwise spacing (L1), spanwise spacing (L2), and phase angle (γ) on aerodynamic performance are considered. The results show that, compared to a single wing, a favorable combination of L1 and L2 can improve the overall thrust by 24% while keeping the overall lift essentially unchanged. In an unfavorable case, overall lift and thrust decrease by 18% and 20%, respectively. The overall aerodynamic forces are dominated by the rear wing. Analyzing the essential flow characteristics reveals the double-edged role of downwash and upwash in force generation. Moreover, it is found that the rear wing can realize the upwash/downwash exploitation by flap phasing, turning an unfavorable situation into a favorable one. The key flow physics behind this transformation lies in the relationship between the direction of wing motion and the direction of fluid velocity induced by vortices. These findings provide valuable insights into the understanding of biological phenomena and the design of new flapping wing vehicles.
{"title":"Numerical investigation of wingtip aerodynamic interference of two flapping wings on opposite sides","authors":"Zengshuang Chen, Xiankai Li, Ming Ma, Yang Zhang, Xueguang Meng","doi":"10.1063/5.0226399","DOIUrl":"https://doi.org/10.1063/5.0226399","url":null,"abstract":"Aerodynamic interference occurs at the wingtips when flying organisms fly in a V formation. In this paper, the wingtip aerodynamic interference of two flapping wings on opposite sides at low Reynolds numbers (Re) is numerically investigated. The effects of streamwise spacing (L1), spanwise spacing (L2), and phase angle (γ) on aerodynamic performance are considered. The results show that, compared to a single wing, a favorable combination of L1 and L2 can improve the overall thrust by 24% while keeping the overall lift essentially unchanged. In an unfavorable case, overall lift and thrust decrease by 18% and 20%, respectively. The overall aerodynamic forces are dominated by the rear wing. Analyzing the essential flow characteristics reveals the double-edged role of downwash and upwash in force generation. Moreover, it is found that the rear wing can realize the upwash/downwash exploitation by flap phasing, turning an unfavorable situation into a favorable one. The key flow physics behind this transformation lies in the relationship between the direction of wing motion and the direction of fluid velocity induced by vortices. These findings provide valuable insights into the understanding of biological phenomena and the design of new flapping wing vehicles.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"11 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258843","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}
Recirculation gyres adjacent to western boundary currents (WBCs) in the ocean enhance the poleward transport of these currents. While it is well-established that the WBC in a barotropic ocean strengthens with increase in basin's aspect ratio (the meridional-to-zonal extent ratio), how intensity of the recirculation through the western boundary layer varies with this parameter remains unexplored. I address this using the non-dimensional form of the nonlinear, wind-driven Stommel–Munk model of westward intensification that comprises three parameters—the aspect ratio (δ), the damping coefficient (ϵ), and the β-Rossby number (Rβ). Here, ϵ is set by the ratio of Rayleigh friction coefficient (or eddy viscosity) to the meridional gradient of the Coriolis frequency and the basin's zonal dimension, while Rβ is proportional to wind stress amplitude and quantifies the strength of nonlinearity. In the weak-to-moderate nonlinearity limit (Rβ<∼ϵ), perturbation analysis reveals that recirculation varies concavely with aspect ratio, suggesting existence of an optimal aspect ratio (δopt) for which the recirculation is maximum and for typical values of ϵ (10−3−10−2), δopt follows the power-law relation δopt=4.3ϵ. Numerical simulations further validate the existence of δopt. For large ϵ (>5×10−3), the power-law predicts δopt for the numerical solutions rather accurately, but does not hold for smaller ϵ (2×10−3) due to increased importance of nonlinear terms. Nevertheless, the nonlinear variation in recirculation through the western boundary layer with aspect ratio is observed for all ϵ values and may contribute to the heterogeneous increase in the WBC's transport across different ocean basins in a warming climate.
{"title":"Recirculation through western boundary currents varies nonlinearly with the ocean basin's aspect ratio","authors":"Kaushal Gianchandani","doi":"10.1063/5.0226883","DOIUrl":"https://doi.org/10.1063/5.0226883","url":null,"abstract":"Recirculation gyres adjacent to western boundary currents (WBCs) in the ocean enhance the poleward transport of these currents. While it is well-established that the WBC in a barotropic ocean strengthens with increase in basin's aspect ratio (the meridional-to-zonal extent ratio), how intensity of the recirculation through the western boundary layer varies with this parameter remains unexplored. I address this using the non-dimensional form of the nonlinear, wind-driven Stommel–Munk model of westward intensification that comprises three parameters—the aspect ratio (δ), the damping coefficient (ϵ), and the β-Rossby number (Rβ). Here, ϵ is set by the ratio of Rayleigh friction coefficient (or eddy viscosity) to the meridional gradient of the Coriolis frequency and the basin's zonal dimension, while Rβ is proportional to wind stress amplitude and quantifies the strength of nonlinearity. In the weak-to-moderate nonlinearity limit (Rβ&lt;∼ϵ), perturbation analysis reveals that recirculation varies concavely with aspect ratio, suggesting existence of an optimal aspect ratio (δopt) for which the recirculation is maximum and for typical values of ϵ (10−3−10−2), δopt follows the power-law relation δopt=4.3ϵ. Numerical simulations further validate the existence of δopt. For large ϵ (&gt;5×10−3), the power-law predicts δopt for the numerical solutions rather accurately, but does not hold for smaller ϵ (2×10−3) due to increased importance of nonlinear terms. Nevertheless, the nonlinear variation in recirculation through the western boundary layer with aspect ratio is observed for all ϵ values and may contribute to the heterogeneous increase in the WBC's transport across different ocean basins in a warming climate.","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":"142258899","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}
Rundi Qiu, Haosen Dong, Jingzhu Wang, Chun Fan, Yiwei Wang
The physics-informed neural networks (PINNs) have shown great potential in solving a variety of high-dimensional partial differential equations (PDEs), but the complexity of a realistic problem still restricts the practical application of the PINNs for solving most complicated PDEs. In this paper, we propose a parallel framework for PINNs that is capable of modeling two-phase flows with complicated interface evolution. The proposed framework divides the problem into several simplified subproblems and solves them through training several PINNs on corresponding subdomains simultaneously. To enhance the accuracy of the parallel training framework in two-phase flow, the overlapping domain decomposition method is adopted. The optimal subnetwork sizes and partitioned method are systematically discussed, and a series of cases including a bubble rising, droplet splashing, and the Rayleigh–Taylor instability are applied for quantitative validation. The maximum relative error of quantitative values in these cases is 0.1319. Our results show that the proposed framework not only can accelerate the training procedure of PINNs, but also can capture the spatiotemporal evolution of the interface between various phases. This framework overcomes the difficulties of training PINNs to solve a forward problem in two-phase flow, and it is expected to model more realistic dynamic systems in nature.
{"title":"Modeling two-phase flows with complicated interface evolution using parallel physics-informed neural networks","authors":"Rundi Qiu, Haosen Dong, Jingzhu Wang, Chun Fan, Yiwei Wang","doi":"10.1063/5.0216609","DOIUrl":"https://doi.org/10.1063/5.0216609","url":null,"abstract":"The physics-informed neural networks (PINNs) have shown great potential in solving a variety of high-dimensional partial differential equations (PDEs), but the complexity of a realistic problem still restricts the practical application of the PINNs for solving most complicated PDEs. In this paper, we propose a parallel framework for PINNs that is capable of modeling two-phase flows with complicated interface evolution. The proposed framework divides the problem into several simplified subproblems and solves them through training several PINNs on corresponding subdomains simultaneously. To enhance the accuracy of the parallel training framework in two-phase flow, the overlapping domain decomposition method is adopted. The optimal subnetwork sizes and partitioned method are systematically discussed, and a series of cases including a bubble rising, droplet splashing, and the Rayleigh–Taylor instability are applied for quantitative validation. The maximum relative error of quantitative values in these cases is 0.1319. Our results show that the proposed framework not only can accelerate the training procedure of PINNs, but also can capture the spatiotemporal evolution of the interface between various phases. This framework overcomes the difficulties of training PINNs to solve a forward problem in two-phase flow, and it is expected to model more realistic dynamic systems in nature.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":"206 1","pages":""},"PeriodicalIF":4.6,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258836","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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