Pub Date : 2023-10-01DOI: 10.1088/1873-7005/ad025e
Saeed ur Rahman, José Luis Díaz Palencia
Abstract This work provides a formulation of a fluid flow under a nonlinear diffusion based on a viscosity of Eyring–Powell type along with a degenerate semi-parabolic operator. The introduction of such a degenerate operator is significant as it allows us to explore a further general model not previously considered in the literature. Our aims are hence to provide analytical insights and numerical assessments to the mentioned flow model: firstly, some results are provided in connection with the regularity and uniqueness of weak solutions. The problem is converted into the travelling wave domain where solutions are obtained within an asymptotic expansion supported by the geometric perturbation theory. Finally, a numerical process is considered as the basis to ensure the validity of the analytical assessments presented. Such numerical process is performed for low Reynolds numbers given in classical porous media. As a main finding to highlight: we show that there exist exponential profiles of solutions for the velocity component. This result is not trivial for the non-linear viscosity terms considered.
{"title":"Insight into the Eyring–Powell fluid flow model using degenerate operator: geometric perturbation","authors":"Saeed ur Rahman, José Luis Díaz Palencia","doi":"10.1088/1873-7005/ad025e","DOIUrl":"https://doi.org/10.1088/1873-7005/ad025e","url":null,"abstract":"Abstract This work provides a formulation of a fluid flow under a nonlinear diffusion based on a viscosity of Eyring–Powell type along with a degenerate semi-parabolic operator. The introduction of such a degenerate operator is significant as it allows us to explore a further general model not previously considered in the literature. Our aims are hence to provide analytical insights and numerical assessments to the mentioned flow model: firstly, some results are provided in connection with the regularity and uniqueness of weak solutions. The problem is converted into the travelling wave domain where solutions are obtained within an asymptotic expansion supported by the geometric perturbation theory. Finally, a numerical process is considered as the basis to ensure the validity of the analytical assessments presented. Such numerical process is performed for low Reynolds numbers given in classical porous media. As a main finding to highlight: we show that there exist exponential profiles of solutions for the velocity component. This result is not trivial for the non-linear viscosity terms considered.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136093762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-25DOI: 10.1088/1873-7005/acf8ee
Jian Wu, Yakun Liu, Di Zhang, Ze Cao
Abstract To investigate the influence of structure’s oscillatory motion on flow, the present study employs the arbitrary Lagrangian–Eulerian method in k – ω shear stress transport (SST) turbulence model to simulate the flow past an oscillating rectangular cylinder at Re = 22 000. The cylinder undergoes reciprocating sinusoidal motion at a specified frequency f e , and the frequency ratio fr (defined as the ratio of cylinder oscillation frequency f e to the stationary cylinder vortex shedding frequency f 0 ), ranges from 0 to 4. The results demonstrate that, in the synchronization region (0.8 ⩽ fr ⩽ 1.2), the drag coefficient shows the most notable variation and reaches its maxima at fr = 1.1 and the root mean square ( r.m.s. ) of the lift coefficient is proportional to the square of fr ( Cl′=1.08∗fr2 , R 2 = 0.99). Moreover, the present study compares the similarities and differences of vortex shedding morphology between stationary and oscillating cylinders. With the increase of fr , the wake vortex gradually transforms from a single-row arrangement on the wake centerline to a parallel double-row arrangement, with the main vortex modes in the wake region observed as ‘2S’, ‘P + S’, ‘2P’ and ‘C’. Furthermore, spectral analysis, including amplitude spectrum analysis and wavelet analysis, in addition to probability density function statistical methods, are employed to comprehensively understand the velocity characteristics of the wake region. The results indicate that the oscillation of the cylinder reduces the correlation of the wake velocity. Those are beneficial in understanding the interaction between turbulence and structural fluid-induced motion.
{"title":"Numerical simulation of flow past an 8:1 oscillating rectangular cylinder at Re=22000","authors":"Jian Wu, Yakun Liu, Di Zhang, Ze Cao","doi":"10.1088/1873-7005/acf8ee","DOIUrl":"https://doi.org/10.1088/1873-7005/acf8ee","url":null,"abstract":"Abstract To investigate the influence of structure’s oscillatory motion on flow, the present study employs the arbitrary Lagrangian–Eulerian method in k – ω shear stress transport (SST) turbulence model to simulate the flow past an oscillating rectangular cylinder at Re = 22 000. The cylinder undergoes reciprocating sinusoidal motion at a specified frequency f e , and the frequency ratio fr (defined as the ratio of cylinder oscillation frequency f e to the stationary cylinder vortex shedding frequency f 0 ), ranges from 0 to 4. The results demonstrate that, in the synchronization region (0.8 ⩽ fr ⩽ 1.2), the drag coefficient shows the most notable variation and reaches its maxima at fr = 1.1 and the root mean square ( r.m.s. ) of the lift coefficient is proportional to the square of fr ( <?CDATA $C_l^{prime}=1.08*{fr}^2$?> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:msubsup> <mml:mi>C</mml:mi> <mml:mi>l</mml:mi> <mml:mi mathvariant=\"normal\">′</mml:mi> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>1.08</mml:mn> <mml:mo>∗</mml:mo> <mml:msup> <mml:mrow> <mml:mi>f</mml:mi> <mml:mi>r</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:math> , R 2 = 0.99). Moreover, the present study compares the similarities and differences of vortex shedding morphology between stationary and oscillating cylinders. With the increase of fr , the wake vortex gradually transforms from a single-row arrangement on the wake centerline to a parallel double-row arrangement, with the main vortex modes in the wake region observed as ‘2S’, ‘P + S’, ‘2P’ and ‘C’. Furthermore, spectral analysis, including amplitude spectrum analysis and wavelet analysis, in addition to probability density function statistical methods, are employed to comprehensively understand the velocity characteristics of the wake region. The results indicate that the oscillation of the cylinder reduces the correlation of the wake velocity. Those are beneficial in understanding the interaction between turbulence and structural fluid-induced motion.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769448","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-21DOI: 10.1088/1873-7005/acf59f
Genta Kawahara
Objective identification of complex and apparently chaotic structures appearing in turbulent flows without arbitrariness is a crucial step toward understanding turbulent phenomena. Various identification criteria have been proposed, particularly, for vortical structures, which undergo less non-local effects of pressure (compared to rate of strain) so that their temporal evolution may be discussed locally. Typical kinematic criteria are based on the invariants of the velocity gradient tensor. Among them, the identificationmethod proposed byHunt et al (1988) is one of themost widely known. In theirmethod, vortical structures are extracted from incompressible turbulent flows as regions with a positive value of the second invariant of the velocity gradient tensor (meaning the dominance of rotation over deformation). For two-dimensional flows, the same criterion has independently been proposed by Okubo (1970) and Weiss (1991) long before Hunt et al (1988). This criterion, currently called the Okubo-Weiss criterion, is often used for the identification of vortical structures in two-dimensional turbulent flows. The above prize-winning paper has provided an interesting theoretical discussion on the Okubo-Weiss criterion. The Okubo-Weiss criterion is expressed in terms of the square of the eigenvalue of the (two-dimensional) velocity gradient tensor,Q referred to as the Okubo-Weiss parameter (a positive value of which corresponds to a negative value of the second invariant). If the Okubo-Weiss parameter Q is negative (or positive), rotation (or deformation) is dominant, i.e., streamlines are elliptic (or hyperbolic). For two-dimensional incompressible Euler flows, the Lagrangian derivative of the divorticity vector is equal to the product of the velocity gradient tensor and the divorticity vector, implying that the divorticity vector will be frozen in the fluid, where the divorticity vector is defined as the rotation of the vorticity and is tangential to iso-contours of the vorticity. This paper has discussed the relation betweenQ and the Gaussian curvature of the vorticity distribution under the condition (a kind of the Beltrami condition) that the divorticity vector and the velocity vector are parallel to each other, and has demonstrated that the Gaussian curvature of the vorticity distribution is negative at points where deformation is dominant and thus Q is positive, indicating that the vorticity field has a saddle point. This is an interesting result that can characterise the two-dimensional flow field under the Beltrami condition in terms of the Gaussian curvature of the vorticity field. The authors have also given an expression of the Okubo-Weiss parameter in a plane polar coordinate system, and using the given expression they have identified the flow fields associated with the Lamb-Oseen vortex and the (three-dimensional axisymmetric) Burgers vortex as elliptic (or hyperbolic) near (or far from) the vortex. Furthermore, the authors have extended t
{"title":"The 16th FDR prize","authors":"Genta Kawahara","doi":"10.1088/1873-7005/acf59f","DOIUrl":"https://doi.org/10.1088/1873-7005/acf59f","url":null,"abstract":"Objective identification of complex and apparently chaotic structures appearing in turbulent flows without arbitrariness is a crucial step toward understanding turbulent phenomena. Various identification criteria have been proposed, particularly, for vortical structures, which undergo less non-local effects of pressure (compared to rate of strain) so that their temporal evolution may be discussed locally. Typical kinematic criteria are based on the invariants of the velocity gradient tensor. Among them, the identificationmethod proposed byHunt et al (1988) is one of themost widely known. In theirmethod, vortical structures are extracted from incompressible turbulent flows as regions with a positive value of the second invariant of the velocity gradient tensor (meaning the dominance of rotation over deformation). For two-dimensional flows, the same criterion has independently been proposed by Okubo (1970) and Weiss (1991) long before Hunt et al (1988). This criterion, currently called the Okubo-Weiss criterion, is often used for the identification of vortical structures in two-dimensional turbulent flows. The above prize-winning paper has provided an interesting theoretical discussion on the Okubo-Weiss criterion. The Okubo-Weiss criterion is expressed in terms of the square of the eigenvalue of the (two-dimensional) velocity gradient tensor,Q referred to as the Okubo-Weiss parameter (a positive value of which corresponds to a negative value of the second invariant). If the Okubo-Weiss parameter Q is negative (or positive), rotation (or deformation) is dominant, i.e., streamlines are elliptic (or hyperbolic). For two-dimensional incompressible Euler flows, the Lagrangian derivative of the divorticity vector is equal to the product of the velocity gradient tensor and the divorticity vector, implying that the divorticity vector will be frozen in the fluid, where the divorticity vector is defined as the rotation of the vorticity and is tangential to iso-contours of the vorticity. This paper has discussed the relation betweenQ and the Gaussian curvature of the vorticity distribution under the condition (a kind of the Beltrami condition) that the divorticity vector and the velocity vector are parallel to each other, and has demonstrated that the Gaussian curvature of the vorticity distribution is negative at points where deformation is dominant and thus Q is positive, indicating that the vorticity field has a saddle point. This is an interesting result that can characterise the two-dimensional flow field under the Beltrami condition in terms of the Gaussian curvature of the vorticity field. The authors have also given an expression of the Okubo-Weiss parameter in a plane polar coordinate system, and using the given expression they have identified the flow fields associated with the Lamb-Oseen vortex and the (three-dimensional axisymmetric) Burgers vortex as elliptic (or hyperbolic) near (or far from) the vortex. Furthermore, the authors have extended t","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136235655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-05DOI: 10.1088/1873-7005/acf6de
Zhaoyu Qu, N. Yang, Xiongliang Yao, Wenhua Wu, Guihui Ma
The hydrodynamic characteristics of underwater vehicles are significantly affected by the ventilated cavity covered by the vehicle surface. In this paper, the unsteady flow characteristics of this ventilated cavity are studied using experimental and numerical methods, and the unsteady entrainment behaviour of the ventilated air mass is emphasised. The flow pattern of the ventilated air mass is recorded using a high-speed camera. The large eddy simulation turbulence model is employed for the numerical simulations, and a good agreement is observed between the experimental and numerical results. In the early stage of the formation of the ventilated air mass, the internal structure exhibits a symmetric kidney vortex system, while the ventilated cavity below the vent hole has a continuous hairpin vortex structure. The ventilated air mass experiences a growth stage, an entrainment stage, and a shedding stage. The entrainment behaviour enables the ventilated air mass to quickly fill the ventilated cavity and modifies the surface pressure distribution of the vehicle. As the cavitation number decreases, the radial size of the ventilated cavity increases, and the contact area between the cavity and the water body increases, thus enhancing the vertical drag coefficient of the vehicle.
{"title":"Experimental and numerical study on unsteady entrainment behaviour of ventilated air mass in underwater vehicles","authors":"Zhaoyu Qu, N. Yang, Xiongliang Yao, Wenhua Wu, Guihui Ma","doi":"10.1088/1873-7005/acf6de","DOIUrl":"https://doi.org/10.1088/1873-7005/acf6de","url":null,"abstract":"The hydrodynamic characteristics of underwater vehicles are significantly affected by the ventilated cavity covered by the vehicle surface. In this paper, the unsteady flow characteristics of this ventilated cavity are studied using experimental and numerical methods, and the unsteady entrainment behaviour of the ventilated air mass is emphasised. The flow pattern of the ventilated air mass is recorded using a high-speed camera. The large eddy simulation turbulence model is employed for the numerical simulations, and a good agreement is observed between the experimental and numerical results. In the early stage of the formation of the ventilated air mass, the internal structure exhibits a symmetric kidney vortex system, while the ventilated cavity below the vent hole has a continuous hairpin vortex structure. The ventilated air mass experiences a growth stage, an entrainment stage, and a shedding stage. The entrainment behaviour enables the ventilated air mass to quickly fill the ventilated cavity and modifies the surface pressure distribution of the vehicle. As the cavitation number decreases, the radial size of the ventilated cavity increases, and the contact area between the cavity and the water body increases, thus enhancing the vertical drag coefficient of the vehicle.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46493248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-11DOI: 10.1088/1873-7005/acef58
Chen Wang, Zhenguo Tian, Shengdong Li, Yi Hao
The study of plasma flow under the thermal protection magnetic field of reentry vehicle is helpful to verify the magnetic control thermal protection technology and further understand its flow law. By solving hypersonic magnetohydrodynamics equations and combining with dipole magnetic field conditions, the plasma flow mechanism of radio attenuation measurement (RAM)-CII (RAM Experiment) spacecraft at 61 km altitude is analyzed and compared with orbital reentry experiment (OREX) spacecraft under the same conditions. The results show that the plasma flow of RAM-CII is more complex than that of OREX, and there are several regions with different Lorentz force directions near the aircraft, which play the role of plasma ejection and adsorption. Under the action of Lorentz force, the side flow of the aircraft will be separated and reattached, and the fluid stagnation zone will be generated. The results show that for different shapes of aircraft, the flow laws caused by magnetic thermal protection technology are different, and the side flow may be greatly affected.
{"title":"Side plasma flow and stagnation of a conical blunt body vehicle under an axial dipole magnetic field","authors":"Chen Wang, Zhenguo Tian, Shengdong Li, Yi Hao","doi":"10.1088/1873-7005/acef58","DOIUrl":"https://doi.org/10.1088/1873-7005/acef58","url":null,"abstract":"The study of plasma flow under the thermal protection magnetic field of reentry vehicle is helpful to verify the magnetic control thermal protection technology and further understand its flow law. By solving hypersonic magnetohydrodynamics equations and combining with dipole magnetic field conditions, the plasma flow mechanism of radio attenuation measurement (RAM)-CII (RAM Experiment) spacecraft at 61 km altitude is analyzed and compared with orbital reentry experiment (OREX) spacecraft under the same conditions. The results show that the plasma flow of RAM-CII is more complex than that of OREX, and there are several regions with different Lorentz force directions near the aircraft, which play the role of plasma ejection and adsorption. Under the action of Lorentz force, the side flow of the aircraft will be separated and reattached, and the fluid stagnation zone will be generated. The results show that for different shapes of aircraft, the flow laws caused by magnetic thermal protection technology are different, and the side flow may be greatly affected.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44457891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-26DOI: 10.1088/1873-7005/aceaa3
Dongrong Zhang
At the ocean surface, the wind shear stress not only drives the ocean currents, but also generates waves and breaks waves. The turbulence in the ocean surface layer (OSL) is much enhanced due to wave breaking. A typical field measurement of this enhanced turbulence is the dissipation of turbulent kinetic energy (TKE) ɛ at a depth y below the ocean surface, which scales as ε∝y−a . However, there is significant uncertainty as to the value of this power law exponent a in different field measurements. Here we consider the dissipation of TKE in the OSL by adding the wave breaking influence into the theoretical framework of the spectral link, originally proposed in sheared flows with no waves (Gioia et al 2010 Phys. Rev. Lett. 105 184501). The expanded theory recovers the power law of ɛ and sheds light on the uncertainty of the power law exponent a by relating it to the variation of the turbulent Prandtl number. In addition, we also apply this theory to oscillating-grid turbulence.
{"title":"Spectral link and wave breaking enhanced dissipation of turbulent kinetic energy","authors":"Dongrong Zhang","doi":"10.1088/1873-7005/aceaa3","DOIUrl":"https://doi.org/10.1088/1873-7005/aceaa3","url":null,"abstract":"At the ocean surface, the wind shear stress not only drives the ocean currents, but also generates waves and breaks waves. The turbulence in the ocean surface layer (OSL) is much enhanced due to wave breaking. A typical field measurement of this enhanced turbulence is the dissipation of turbulent kinetic energy (TKE) ɛ at a depth y below the ocean surface, which scales as ε∝y−a . However, there is significant uncertainty as to the value of this power law exponent a in different field measurements. Here we consider the dissipation of TKE in the OSL by adding the wave breaking influence into the theoretical framework of the spectral link, originally proposed in sheared flows with no waves (Gioia et al 2010 Phys. Rev. Lett. 105 184501). The expanded theory recovers the power law of ɛ and sheds light on the uncertainty of the power law exponent a by relating it to the variation of the turbulent Prandtl number. In addition, we also apply this theory to oscillating-grid turbulence.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44137716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-18DOI: 10.1088/1873-7005/ace846
Yuki Yagi, K. Yabushita, Hiroyoshi Suzuki
We study an analytical solution of steady, laminar, and incompressible flow past a sphere in the region of intermediate Reynolds number. The flow is governed by the Navier–Stokes (N–S) equation and the continuity equation. By applying a simple perturbation method to solve the equations, a second-order approximation cannot be obtained, as well-known (Whitehead’s paradox). Many analytical studies, such as Oseen approximation, matching technique, the homotopy analysis method, etc, have been conducted to resolve the paradox. The drag coefficients of these solutions are valid in the region of Reynolds number Rd<30 (R d is the diameter-based Reynolds number) However, the solution cannot express the flow separation behind a sphere observed in experiments. We also develop a perturbation technique to construct a solution of the N–S equation asymptotically to solve the paradox. The solution consists of power series of Rdh , where h is an arbitrary constant (0
{"title":"An analytic solution of Navier–Stokes flow past a sphere in the region of intermediate Reynolds number","authors":"Yuki Yagi, K. Yabushita, Hiroyoshi Suzuki","doi":"10.1088/1873-7005/ace846","DOIUrl":"https://doi.org/10.1088/1873-7005/ace846","url":null,"abstract":"We study an analytical solution of steady, laminar, and incompressible flow past a sphere in the region of intermediate Reynolds number. The flow is governed by the Navier–Stokes (N–S) equation and the continuity equation. By applying a simple perturbation method to solve the equations, a second-order approximation cannot be obtained, as well-known (Whitehead’s paradox). Many analytical studies, such as Oseen approximation, matching technique, the homotopy analysis method, etc, have been conducted to resolve the paradox. The drag coefficients of these solutions are valid in the region of Reynolds number Rd<30 (R d is the diameter-based Reynolds number) However, the solution cannot express the flow separation behind a sphere observed in experiments. We also develop a perturbation technique to construct a solution of the N–S equation asymptotically to solve the paradox. The solution consists of power series of Rdh , where h is an arbitrary constant (0<h⩽1) . By setting the value of h to avoid divergence of the solution in the all-region where steady flow exists, the solution expresses the flow separation behind a sphere, coinciding with experiments in the region of intermediate Reynolds number ( Rd<130 ), although the existing analytical solutions could not express. Also, the present solution gives the drag coefficient which agrees with experimental and numerical values in the region of Rd<30 .","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42462952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-12DOI: 10.1088/1873-7005/ace6cf
Shenshu Zhang, N. Gui, Xingtuan Yang, J. Tu, Shengyao Jiang
Even with modern measurement techniques and data from direct numerical simulation (DNS), it is very difficult to identify the individual attached eddies and understand their dynamical behavior due to the multi-scale nature of the eddies in wall-bounded flows, which puts these issues at the center of the current debate. However, Liutex vector ( L for short), a rotational vector field with information on both the rotation axis and swirling strength, has recently been developed by Prof. Liu’s group as a more accurate and clear definition of a vortex. Combining conventional and L methods may provide more detailed information about the complex flow structures as well as insights into the flow’s mixing and transport features. We simulated the channel flow in large eddy simulation by implementing an inflow condition based on the box turbulence. After validating the results with DNS data, we used L isosurfaces and their vector profiles to track ordered flow structures in wall-bounded turbulence. Based on the data, we observe numerous turbulent phenomena that have been described in other works with different visualization techniques. Moreover, the shear contamination on the wall is the most severe while all the root-mean-square L component variations are negligible. Due to the presence of background shear, the peak location of vorticity fluctuation is closer to the wall than the corresponding L fluctuation, and the displacement of peak location brought on by shear contamination is greatest for the spanwise component (z-component) of the vorticity fluctuation. According to the two-point correlation of L components, the streamwise size of turbulent structures does not vary considerably with y+ , however, the spanwise size of turbulent structures increases gradually as y+ increases.
{"title":"Rotational vector-based analysis of turbulent structures in channel flow using large eddy simulation simulation","authors":"Shenshu Zhang, N. Gui, Xingtuan Yang, J. Tu, Shengyao Jiang","doi":"10.1088/1873-7005/ace6cf","DOIUrl":"https://doi.org/10.1088/1873-7005/ace6cf","url":null,"abstract":"Even with modern measurement techniques and data from direct numerical simulation (DNS), it is very difficult to identify the individual attached eddies and understand their dynamical behavior due to the multi-scale nature of the eddies in wall-bounded flows, which puts these issues at the center of the current debate. However, Liutex vector ( L for short), a rotational vector field with information on both the rotation axis and swirling strength, has recently been developed by Prof. Liu’s group as a more accurate and clear definition of a vortex. Combining conventional and L methods may provide more detailed information about the complex flow structures as well as insights into the flow’s mixing and transport features. We simulated the channel flow in large eddy simulation by implementing an inflow condition based on the box turbulence. After validating the results with DNS data, we used L isosurfaces and their vector profiles to track ordered flow structures in wall-bounded turbulence. Based on the data, we observe numerous turbulent phenomena that have been described in other works with different visualization techniques. Moreover, the shear contamination on the wall is the most severe while all the root-mean-square L component variations are negligible. Due to the presence of background shear, the peak location of vorticity fluctuation is closer to the wall than the corresponding L fluctuation, and the displacement of peak location brought on by shear contamination is greatest for the spanwise component (z-component) of the vorticity fluctuation. According to the two-point correlation of L components, the streamwise size of turbulent structures does not vary considerably with y+ , however, the spanwise size of turbulent structures increases gradually as y+ increases.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46868376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-10DOI: 10.1088/1873-7005/ace5d0
Azeddine Rachik, S. Aniss
A linear and a non-linear analysis are carried out for the instability of the free surface of a liquid layer contained in a Hele-Shaw cell subjected to periodic vertical oscillation. The linear stability analysis shows that for certain ranges of the oscillation frequency, the depth of the liquid layer and the surface tension can have a substantial effect on the selection of the wavenumbers and on the critical forcing amplitude. This results in a new dispersion relation, relating the critical wavenumber and the frequency of oscillation, which is in excellent agreement with recent experimental results by Li et al (2018 Phys. Fluids 30 102103). On the other hand, for low frequencies, the thresholds can be either harmonic or subharmonic with the existence of a series of bicritical points where these two types of thresholds can coexist. Weakly nonlinear analysis is performed in the vicinity of the first subharmonic resonance that occurs in the high frequency limit. Thus, using the multiscale technique, for low dissipation and forcing, we derive a free surface amplitude equation, involving a new nonlinear term coefficient, χ, that includes finite depth and surface tension. For infinite depth, Rajchenbach et al (2011 Phys. Rev. Lett. 107 024502), and Li et al (2019 J. Fluid Mech. 871 694–716) showed that hysteresis can only occur if the response frequency is lower than the natural frequency. However in the present work, it turns out that the coefficient χ can be either positive or negative depending on the depth and surface tension of the fluid. Thus, if χ is positive, hysteresis is found when the response frequency is greater than the natural frequency. Furthermore, the infinite depth approximation, where the short wavelengths dominate, is valid when the depth and wavenumber satisfy kh > 5, whereas for kh < 5, where long wavelengths dominate, the finite depth should be considered.
本文对Hele-Shaw槽内液体层自由表面在周期性垂直振荡作用下的不稳定性进行了线性和非线性分析。线性稳定性分析表明，在一定的振荡频率范围内，液层深度和表面张力对波数的选择和临界强迫幅值有很大的影响。这导致了一种新的色散关系，将临界波数与振荡频率联系起来，这与Li等人(2018 Phys)最近的实验结果非常吻合。液体30 102103)。另一方面，对于低频，阈值可以是谐波或次谐波，存在一系列双临界点，这两种阈值可以共存。在高频极限发生的第一次谐波谐振附近进行弱非线性分析。因此，使用多尺度技术，对于低耗散和强迫，我们导出了一个自由表面振幅方程，涉及一个新的非线性项系数χ，它包括有限深度和表面张力。对于无限深度，Rajchenbach等人(2011年物理。Rev. Lett. 107 024502)和Li et al . (2019 J. Fluid Mech. 871 694-716)研究表明，只有当响应频率低于固有频率时才会发生迟滞。然而，在目前的工作中，事实证明，系数χ可以是正的或负的，这取决于流体的深度和表面张力。因此，如果χ为正，则在响应频率大于固有频率时发现迟滞。此外，当深度和波数满足kh > 5时，短波长的无限深度近似是有效的，而当kh < 5时，长波占主导地位，则应考虑有限深度。
{"title":"Effects of finite depth and surface tension on the linear and weakly non-linear stability of Faraday waves in Hele-Shaw cell","authors":"Azeddine Rachik, S. Aniss","doi":"10.1088/1873-7005/ace5d0","DOIUrl":"https://doi.org/10.1088/1873-7005/ace5d0","url":null,"abstract":"A linear and a non-linear analysis are carried out for the instability of the free surface of a liquid layer contained in a Hele-Shaw cell subjected to periodic vertical oscillation. The linear stability analysis shows that for certain ranges of the oscillation frequency, the depth of the liquid layer and the surface tension can have a substantial effect on the selection of the wavenumbers and on the critical forcing amplitude. This results in a new dispersion relation, relating the critical wavenumber and the frequency of oscillation, which is in excellent agreement with recent experimental results by Li et al (2018 Phys. Fluids 30 102103). On the other hand, for low frequencies, the thresholds can be either harmonic or subharmonic with the existence of a series of bicritical points where these two types of thresholds can coexist. Weakly nonlinear analysis is performed in the vicinity of the first subharmonic resonance that occurs in the high frequency limit. Thus, using the multiscale technique, for low dissipation and forcing, we derive a free surface amplitude equation, involving a new nonlinear term coefficient, χ, that includes finite depth and surface tension. For infinite depth, Rajchenbach et al (2011 Phys. Rev. Lett. 107 024502), and Li et al (2019 J. Fluid Mech. 871 694–716) showed that hysteresis can only occur if the response frequency is lower than the natural frequency. However in the present work, it turns out that the coefficient χ can be either positive or negative depending on the depth and surface tension of the fluid. Thus, if χ is positive, hysteresis is found when the response frequency is greater than the natural frequency. Furthermore, the infinite depth approximation, where the short wavelengths dominate, is valid when the depth and wavenumber satisfy kh > 5, whereas for kh < 5, where long wavelengths dominate, the finite depth should be considered.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42742682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-04DOI: 10.1088/1873-7005/ace3f0
Sanjalee Maheshwari, Y. D. Sharma, O. P. Yadav
The primary objective of this study is to investigate non-linear Bénard convection in a single-walled carbon nanotube suspension saturated in a rotating porous medium with an internal heat sink/source. The modified Buongiorno model is utilized to formulate the governing equations for the flow. Both linear and weak non-linear stability analyses are conducted in this investigation. The linear stability analysis employs the truncated Fourier series transformation, while the weakly non-linear stability analysis utilizes the Lorenz model, assuming weak thermophoresis, porous friction, and small-scale convective motion. The cubic Ginzburg–Landau equation is formulated and subsequently solved to derive the expression for the amplitude. The influence of various parameters, such as the Taylor number, heat sink/source parameter, and viscosity parameter, is discussed in relation to the threshold criteria of convection, as well as heat and mass transport rates. Based on the linear stability analysis, it is determined that the introduction of a rotating frame of reference delays the initiation of convection, whereas the energy supplied to the system accelerates the onset of convection. The heat transfer rate increases by 22% when the nanofluidic system is placed in the rotating frame of reference under the presence of an internal heat source.
{"title":"The linear and non-linear study of effect of rotation and internal heat source/sink on Bénard convection","authors":"Sanjalee Maheshwari, Y. D. Sharma, O. P. Yadav","doi":"10.1088/1873-7005/ace3f0","DOIUrl":"https://doi.org/10.1088/1873-7005/ace3f0","url":null,"abstract":"The primary objective of this study is to investigate non-linear Bénard convection in a single-walled carbon nanotube suspension saturated in a rotating porous medium with an internal heat sink/source. The modified Buongiorno model is utilized to formulate the governing equations for the flow. Both linear and weak non-linear stability analyses are conducted in this investigation. The linear stability analysis employs the truncated Fourier series transformation, while the weakly non-linear stability analysis utilizes the Lorenz model, assuming weak thermophoresis, porous friction, and small-scale convective motion. The cubic Ginzburg–Landau equation is formulated and subsequently solved to derive the expression for the amplitude. The influence of various parameters, such as the Taylor number, heat sink/source parameter, and viscosity parameter, is discussed in relation to the threshold criteria of convection, as well as heat and mass transport rates. Based on the linear stability analysis, it is determined that the introduction of a rotating frame of reference delays the initiation of convection, whereas the energy supplied to the system accelerates the onset of convection. The heat transfer rate increases by 22% when the nanofluidic system is placed in the rotating frame of reference under the presence of an internal heat source.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46014935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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