Pub Date : 2022-07-21DOI: 10.1088/1873-7005/ac830d
T. Fujikawa, Ryu Egashira, K. Hooman, Hisao Yaguchi, Hisashi Masubuti, Shigeo Fujikawa
Theory of dynamical cavitation threshold for vapor and non-condensable gas bubble nuclei is proposed based on a model equation constructed from Rayleigh–Plesset equation for glycerol, the liquid with viscosity higher than that of water by 1500 times, under a finite duration of strong tension. The model equation is ascertained to be valid in cases of strong tension under which cavitation occurs. Our model enables the study of dynamics of nuclei on the phase plane of the nucleus radius and the growth velocity, by which the full details of the threshold are revealed. We propose a dimensionless parameter to be used to classify the threshold of cavitation. Our model offers a simple mathematical expression to calculate the maximum radii attained, while under tension, for each of these three recognized patterns. For each observed pattern, we present unique predictive correlations for the radius of the nucleus growing for the tension duration. Moreover, we elucidate that the dynamics of the nuclei, grown up to certain sizes, is fully controlled by tension independent of the viscosity. The discrepancy between the dynamical threshold and the conventional Blake’s threshold is discussed. Finally, the utility of the theory presented here is demonstrated through numerical examples.
{"title":"Theory of dynamical cavitation threshold for diesel fuel atomization","authors":"T. Fujikawa, Ryu Egashira, K. Hooman, Hisao Yaguchi, Hisashi Masubuti, Shigeo Fujikawa","doi":"10.1088/1873-7005/ac830d","DOIUrl":"https://doi.org/10.1088/1873-7005/ac830d","url":null,"abstract":"Theory of dynamical cavitation threshold for vapor and non-condensable gas bubble nuclei is proposed based on a model equation constructed from Rayleigh–Plesset equation for glycerol, the liquid with viscosity higher than that of water by 1500 times, under a finite duration of strong tension. The model equation is ascertained to be valid in cases of strong tension under which cavitation occurs. Our model enables the study of dynamics of nuclei on the phase plane of the nucleus radius and the growth velocity, by which the full details of the threshold are revealed. We propose a dimensionless parameter to be used to classify the threshold of cavitation. Our model offers a simple mathematical expression to calculate the maximum radii attained, while under tension, for each of these three recognized patterns. For each observed pattern, we present unique predictive correlations for the radius of the nucleus growing for the tension duration. Moreover, we elucidate that the dynamics of the nuclei, grown up to certain sizes, is fully controlled by tension independent of the viscosity. The discrepancy between the dynamical threshold and the conventional Blake’s threshold is discussed. Finally, the utility of the theory presented here is demonstrated through numerical examples.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46838343","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 : 2022-07-14DOI: 10.1088/1873-7005/ac8118
M. Arora, Renu Bajaj
The stability of natural convection in thermally modulated inclined fluid layer is analyzed using linear instability analysis and generalized energy stability theory. A sufficient condition for the global stability of the fluid layer is obtained. The stability boundaries are found in terms of the Rayleigh number. Shooting method is used to find the stability limits numerically. Uncertain stability region is observed between the linear and the nonlinear stability boundaries. The onset of instability depends upon the frequency and the amplitude of modulation.
{"title":"Energy stability of thermally modulated inclined fluid layer","authors":"M. Arora, Renu Bajaj","doi":"10.1088/1873-7005/ac8118","DOIUrl":"https://doi.org/10.1088/1873-7005/ac8118","url":null,"abstract":"The stability of natural convection in thermally modulated inclined fluid layer is analyzed using linear instability analysis and generalized energy stability theory. A sufficient condition for the global stability of the fluid layer is obtained. The stability boundaries are found in terms of the Rayleigh number. Shooting method is used to find the stability limits numerically. Uncertain stability region is observed between the linear and the nonlinear stability boundaries. The onset of instability depends upon the frequency and the amplitude of modulation.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41632718","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 : 2022-06-27DOI: 10.1088/1873-7005/ac7c35
Alexander Baron
The object of this paper is to apply spectral geometry methods to predicting pressure losses in mildly curved pipes at high Reynolds numbers. The obtained formula for the pressure losses is theoretically justified and provides good agreement with the experimental results.
{"title":"Using spectral geometry to predict pressure losses in curved pipes at high Reynolds numbers","authors":"Alexander Baron","doi":"10.1088/1873-7005/ac7c35","DOIUrl":"https://doi.org/10.1088/1873-7005/ac7c35","url":null,"abstract":"The object of this paper is to apply spectral geometry methods to predicting pressure losses in mildly curved pipes at high Reynolds numbers. The obtained formula for the pressure losses is theoretically justified and provides good agreement with the experimental results.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45911774","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 : 2022-06-23DOI: 10.1088/1873-7005/ac7ba5
Tongbiao Guo, S. Zhong, D. Apsley, T. Craft
In this paper, an exact expression for the drag coefficient of a streamwise-periodic steady incompressible laminar channel and pipe flow with micro- or macro-scale wall roughness is derived, whereby the drag coefficient is decomposed into contributions from different components of the velocity gradient tensor in the flow field. It is shown through our theoretical analysis that drag reduction cannot be achieved by adding micro- or macro-scale spanwise-periodic/-symmetry wall roughness structures to the smooth inner walls of streamwise-periodic steady incompressible laminar channel/pipe flows while maintaining the same volumetric flow rate. It is also shown that wall roughness produces a higher drag due to two factors: (a) wall roughness induces other non-zero velocity gradient terms apart from the wall-normal/radial gradient of streamwise velocity that exists in a smooth channel/pipe flow; (b) the profile of streamwise velocity in the wall-normal/radial direction deviates from the parabolic profile that produces the minimum kinetic energy loss for a given volumetric flow rate. Finally, numerical simulations of laminar channel flow with longitudinal and transverse bars are conducted, and the numerical results confirm the theoretical finding.
{"title":"Theoretical drag analyses of laminar channel and pipe flows with wall roughness","authors":"Tongbiao Guo, S. Zhong, D. Apsley, T. Craft","doi":"10.1088/1873-7005/ac7ba5","DOIUrl":"https://doi.org/10.1088/1873-7005/ac7ba5","url":null,"abstract":"In this paper, an exact expression for the drag coefficient of a streamwise-periodic steady incompressible laminar channel and pipe flow with micro- or macro-scale wall roughness is derived, whereby the drag coefficient is decomposed into contributions from different components of the velocity gradient tensor in the flow field. It is shown through our theoretical analysis that drag reduction cannot be achieved by adding micro- or macro-scale spanwise-periodic/-symmetry wall roughness structures to the smooth inner walls of streamwise-periodic steady incompressible laminar channel/pipe flows while maintaining the same volumetric flow rate. It is also shown that wall roughness produces a higher drag due to two factors: (a) wall roughness induces other non-zero velocity gradient terms apart from the wall-normal/radial gradient of streamwise velocity that exists in a smooth channel/pipe flow; (b) the profile of streamwise velocity in the wall-normal/radial direction deviates from the parabolic profile that produces the minimum kinetic energy loss for a given volumetric flow rate. Finally, numerical simulations of laminar channel flow with longitudinal and transverse bars are conducted, and the numerical results confirm the theoretical finding.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44973218","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 : 2022-06-16DOI: 10.1088/1873-7005/ac796f
L. M. Lin
The initially generated pure mode A, as a transitional stage, is investigated in the three-dimensional wake transition of a circular cylinder. Direct numerical simulations are carried out over a range of Reynolds numbers from 100 to 210. According to the different dynamic behaviors of hydrodynamic parameters and similar features in the spatiotemporal evolution of vorticity in the near wake, two stages are identified. The first, investigated here, is the initial generation of pure mode A at Reynolds numbers less than 195, while the second, already reported, is the full development of pure mode A at Reynolds numbers greater than 195. The relationship between the volume-RMS (root-mean-square) vorticity and Reynolds number indicates two critical Reynolds numbers, 145 and 195 (at most). The first critical Reynolds number denotes the initial appearance of three-dimensional instability. The second critical Reynolds number indicates the transition of pure mode A from the initially generated state to the fully developed state in the near wake. After the first critical Reynolds number, the evolution of the vorticity in the near wake and on the rear surface of the cylinder clearly shows that the appearance of pure mode A is a gradual process, rather than a sudden process accompanied by a jump in vortex shedding frequency. In particular, as the Reynolds number increases, the streamwise vorticity first appears on and near the cylinder surface, then in the shear layers, and finally in the shedding primary vortices, instead of appearing instantaneously in the shedding vortices after the instability of primary vortex cores.
{"title":"Initially generated pure mode A in the three-dimensional wake transition of a circular cylinder","authors":"L. M. Lin","doi":"10.1088/1873-7005/ac796f","DOIUrl":"https://doi.org/10.1088/1873-7005/ac796f","url":null,"abstract":"The initially generated pure mode A, as a transitional stage, is investigated in the three-dimensional wake transition of a circular cylinder. Direct numerical simulations are carried out over a range of Reynolds numbers from 100 to 210. According to the different dynamic behaviors of hydrodynamic parameters and similar features in the spatiotemporal evolution of vorticity in the near wake, two stages are identified. The first, investigated here, is the initial generation of pure mode A at Reynolds numbers less than 195, while the second, already reported, is the full development of pure mode A at Reynolds numbers greater than 195. The relationship between the volume-RMS (root-mean-square) vorticity and Reynolds number indicates two critical Reynolds numbers, 145 and 195 (at most). The first critical Reynolds number denotes the initial appearance of three-dimensional instability. The second critical Reynolds number indicates the transition of pure mode A from the initially generated state to the fully developed state in the near wake. After the first critical Reynolds number, the evolution of the vorticity in the near wake and on the rear surface of the cylinder clearly shows that the appearance of pure mode A is a gradual process, rather than a sudden process accompanied by a jump in vortex shedding frequency. In particular, as the Reynolds number increases, the streamwise vorticity first appears on and near the cylinder surface, then in the shear layers, and finally in the shedding primary vortices, instead of appearing instantaneously in the shedding vortices after the instability of primary vortex cores.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43547530","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 : 2022-06-01DOI: 10.1088/1873-7005/ac6e02
Michael J McPhail, Michael H Krane
This article presents an extension of Liepmann's characterization of an aeroacoustic source in terms of the motion of a bounding surface containing the source region. Rather than using an arbitrary surface, we express the problem in terms of bounding material surfaces, identified by Lagrangian Coherent Structures (LCS), which demarcate flow into regions with distinct dynamics. The sound generation of the flow is written in terms of the motion of these material surfaces using the Kirchhoff integral equation, so that the flow noise problem now appears like that of a deforming body. This approach provides a natural connection between the flow topology, as revealed through LCS analysis, and sound generation mechanisms. As examples, we examine two-dimensional cases of co-rotating vortices and leap-frogging vortex pairs and compare estimated sound sources to vortex sound theory.
{"title":"Aeroacoustic source prediction using material surfaces bounding the flow.","authors":"Michael J McPhail, Michael H Krane","doi":"10.1088/1873-7005/ac6e02","DOIUrl":"https://doi.org/10.1088/1873-7005/ac6e02","url":null,"abstract":"<p><p>This article presents an extension of Liepmann's characterization of an aeroacoustic source in terms of the motion of a bounding surface containing the source region. Rather than using an arbitrary surface, we express the problem in terms of bounding material surfaces, identified by Lagrangian Coherent Structures (LCS), which demarcate flow into regions with distinct dynamics. The sound generation of the flow is written in terms of the motion of these material surfaces using the Kirchhoff integral equation, so that the flow noise problem now appears like that of a deforming body. This approach provides a natural connection between the flow topology, as revealed through LCS analysis, and sound generation mechanisms. As examples, we examine two-dimensional cases of co-rotating vortices and leap-frogging vortex pairs and compare estimated sound sources to vortex sound theory.</p>","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"54 3","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10275497/pdf/nihms-1818263.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"9762403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-25DOI: 10.1088/1873-7005/ac734c
J. Liao, H. Keh
The steady creeping flow of an incompressible Newtonian fluid around a slip spherical particle rotating about its diameter perpendicular to one or two slip plane walls is analyzed. To satisfy the Stokes equation for fluid velocity, the general solution consists of the sum of the essential solutions in spherical and cylindrical coordinates. Boundary conditions are implemented first on the plane walls by means of the Hankel transforms and then on the particle surface through a collocation method. The hydrodynamic torque exerted on the particle is obtained with excellent convergence for various values of the pertinent geometrical and stick-slip parameters, and the effect of the slip planes on the rotational motion of the slip particle is interesting. The torque increases with an increase in the stickiness of the walls from the limit of full slip to the limit of no slip. When the stick parameters of the plane walls are larger than some critical values, the hydrodynamic torque is more than that on an identical particle in the unbounded fluid and an increasing function of the stickiness of the particle surface and ratio of the particle radius to distance from the walls. When the stick parameters of the plane walls are smaller than the critical values, on the contrary, the torque is less than that on the particle in the unbounded fluid and a decreasing function of the surface stickiness and relative radius of the particle.
{"title":"Slow rotation of a sphere about its diameter normal to two planes with slip surfaces","authors":"J. Liao, H. Keh","doi":"10.1088/1873-7005/ac734c","DOIUrl":"https://doi.org/10.1088/1873-7005/ac734c","url":null,"abstract":"The steady creeping flow of an incompressible Newtonian fluid around a slip spherical particle rotating about its diameter perpendicular to one or two slip plane walls is analyzed. To satisfy the Stokes equation for fluid velocity, the general solution consists of the sum of the essential solutions in spherical and cylindrical coordinates. Boundary conditions are implemented first on the plane walls by means of the Hankel transforms and then on the particle surface through a collocation method. The hydrodynamic torque exerted on the particle is obtained with excellent convergence for various values of the pertinent geometrical and stick-slip parameters, and the effect of the slip planes on the rotational motion of the slip particle is interesting. The torque increases with an increase in the stickiness of the walls from the limit of full slip to the limit of no slip. When the stick parameters of the plane walls are larger than some critical values, the hydrodynamic torque is more than that on an identical particle in the unbounded fluid and an increasing function of the stickiness of the particle surface and ratio of the particle radius to distance from the walls. When the stick parameters of the plane walls are smaller than the critical values, on the contrary, the torque is less than that on the particle in the unbounded fluid and a decreasing function of the surface stickiness and relative radius of the particle.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48825812","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 : 2022-04-22DOI: 10.1088/1873-7005/ac6978
Wenbo Wu
The fish can be driven by the sarcomere at different locations of the body. To study the hydrodynamic performance of the fish in this process, the self-propulsion of a composite plate driving on two points was investigated. It is supposed that the forces were exerted on the junction point to maintain a given pitch motion of the rigid portion, and an additional external moment was exerted at a point on the flexible plate. The ratio between the lengths of the rigid portion and the flexible portion was fixed as 1/9, which was reasonable for a real fish. The acting point and phase angle of the additional external moment was varying to study the cooperation of the forces on different points. It was found that the additional external moment was not always promoting the propulsion velocity and efficiency of the composite plate. The additional external moment near the joint point was most suitable for improve the propulsive velocity and efficiency of the composite plate. The anti-phase additional external moment was prejudicing the propulsion of the plate. The additional external moment could change the vibration shape of the flexible plate and the flow structure around it. As ϕ = π, the amplitude and the gradient of the deformation was largely reduced, and the wake became long and narrow. The hydrodynamic forces at the head and tail portion of the flexible plate were hindering the propulsion of the plate, while the thrust was mainly produced on the intermediate portion. It was expected that our investigation can be helpful for the design of the soft robotic fish.
{"title":"Study on the propulsion of the rigid-flexible composite plate driven on two points","authors":"Wenbo Wu","doi":"10.1088/1873-7005/ac6978","DOIUrl":"https://doi.org/10.1088/1873-7005/ac6978","url":null,"abstract":"The fish can be driven by the sarcomere at different locations of the body. To study the hydrodynamic performance of the fish in this process, the self-propulsion of a composite plate driving on two points was investigated. It is supposed that the forces were exerted on the junction point to maintain a given pitch motion of the rigid portion, and an additional external moment was exerted at a point on the flexible plate. The ratio between the lengths of the rigid portion and the flexible portion was fixed as 1/9, which was reasonable for a real fish. The acting point and phase angle of the additional external moment was varying to study the cooperation of the forces on different points. It was found that the additional external moment was not always promoting the propulsion velocity and efficiency of the composite plate. The additional external moment near the joint point was most suitable for improve the propulsive velocity and efficiency of the composite plate. The anti-phase additional external moment was prejudicing the propulsion of the plate. The additional external moment could change the vibration shape of the flexible plate and the flow structure around it. As ϕ = π, the amplitude and the gradient of the deformation was largely reduced, and the wake became long and narrow. The hydrodynamic forces at the head and tail portion of the flexible plate were hindering the propulsion of the plate, while the thrust was mainly produced on the intermediate portion. It was expected that our investigation can be helpful for the design of the soft robotic fish.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43309489","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 : 2022-04-12DOI: 10.1088/1873-7005/ac6690
Hossein Sayyari, M. Peiravi, J. Alinejad
In this study, droplet impact on a solid surface with obstacles occurring in many technological processes was numerically analyzed. The simulation of the hollow droplet impact on to solid surface used the volume of fluid method. A hollow droplet consists of a liquid shell enclosing an air cavity. The hollow droplet impact onto the surface has an obstacle with a different ratio of D/h and diameter of obstacle at three different speeds. It is found that the obstacle made dual jet in some cases. The length of the counter jet decreased with increased the dimension of the obstacle that the maximum and minimum length of the jet is been in case 1 at impact velocity 10 m s−1 and case 3 in V = 5 m s−1. Spread factor (f) increased 34.61% and 44.31% when impact velocity changed 1 m s−1–5 m s−1 and 10 m s−1 respectively.
在本研究中，数值分析了在许多工艺过程中液滴对有障碍物的固体表面的撞击。采用流体体积法模拟空心液滴对固体表面的冲击。一个中空的液滴由一个包裹着空腔的液体外壳组成。在三种不同的速度下，空心液滴撞击表面形成了D/h比和直径不同的障碍物。研究发现，在某些情况下，障碍物会产生双射流。反射流长度随障碍物尺寸的增大而减小，在冲击速度为10 m s−1时，情形1的射流长度最大，最小;在V = 5 m s−1时，情形3的射流长度最小。当冲击速度变化1 m s−1 ~ 5 m s−1和10 m s−1时，扩散系数(f)分别增大34.61%和44.31%。
{"title":"Impinging hollow droplet of glycerin in spray coating influence of mutable obstacle and dynamic contact angle","authors":"Hossein Sayyari, M. Peiravi, J. Alinejad","doi":"10.1088/1873-7005/ac6690","DOIUrl":"https://doi.org/10.1088/1873-7005/ac6690","url":null,"abstract":"In this study, droplet impact on a solid surface with obstacles occurring in many technological processes was numerically analyzed. The simulation of the hollow droplet impact on to solid surface used the volume of fluid method. A hollow droplet consists of a liquid shell enclosing an air cavity. The hollow droplet impact onto the surface has an obstacle with a different ratio of D/h and diameter of obstacle at three different speeds. It is found that the obstacle made dual jet in some cases. The length of the counter jet decreased with increased the dimension of the obstacle that the maximum and minimum length of the jet is been in case 1 at impact velocity 10 m s−1 and case 3 in V = 5 m s−1. Spread factor (f) increased 34.61% and 44.31% when impact velocity changed 1 m s−1–5 m s−1 and 10 m s−1 respectively.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46871275","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 : 2022-04-05DOI: 10.1088/1873-7005/ac6419
S. Izawa, T. Oku, Y. Nishio, Y. Fukunishi
This study numerically investigates an early stage of nonlinear interaction for the better understanding of the onset of nonlinear behaviors. Two-dimensional shear flow is chosen as a canonical flow. When two disturbances of different wavenumbers satisfying no resonance condition are initially given, new components appear one after another while the original disturbances grow. The vorticity budget analysis shows that the beat of the two exciting modes plays an essential role in forming the sum and difference nonlinear components, namely the secondary modes. For the nonlinear interaction mechanism, the high vorticity around the center of the shear layer is locally transported in the transverse direction at specific streamwise sections where the amplitude of the vertical velocity fluctuation becomes relatively larger compared to other sections. The distance between these specific sections corresponds to the wavelength of the beat. The vertically dispersed vorticity will then be convected in the horizontal directions by the mean flow. As a result, several regions of concentrated vorticity appear which eventually develop into vortices. The amplification mechanism is found to be the same for both the primary and secondary modes, though the secondary modes arise from the additional perturbation deriving from the initial perturbation.
{"title":"Onset of nonlinearity in a two-dimensional thin shear layer","authors":"S. Izawa, T. Oku, Y. Nishio, Y. Fukunishi","doi":"10.1088/1873-7005/ac6419","DOIUrl":"https://doi.org/10.1088/1873-7005/ac6419","url":null,"abstract":"This study numerically investigates an early stage of nonlinear interaction for the better understanding of the onset of nonlinear behaviors. Two-dimensional shear flow is chosen as a canonical flow. When two disturbances of different wavenumbers satisfying no resonance condition are initially given, new components appear one after another while the original disturbances grow. The vorticity budget analysis shows that the beat of the two exciting modes plays an essential role in forming the sum and difference nonlinear components, namely the secondary modes. For the nonlinear interaction mechanism, the high vorticity around the center of the shear layer is locally transported in the transverse direction at specific streamwise sections where the amplitude of the vertical velocity fluctuation becomes relatively larger compared to other sections. The distance between these specific sections corresponds to the wavelength of the beat. The vertically dispersed vorticity will then be convected in the horizontal directions by the mean flow. As a result, several regions of concentrated vorticity appear which eventually develop into vortices. The amplification mechanism is found to be the same for both the primary and secondary modes, though the secondary modes arise from the additional perturbation deriving from the initial perturbation.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42480816","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：