Fluid Dynamics Research最新文献

{"title":"Algebraic stability modes in rotational shear flow","authors":"T. Gebler, D. Plümacher, J. Kahle, M. Oberlack","doi":"10.1088/1873-7005/ac44f9","DOIUrl":"https://doi.org/10.1088/1873-7005/ac44f9","url":null,"abstract":"We investigate the two-dimensional (2D) stability of rotational shear flows in an unbounded domain. The eigenvalue problem is formulated by using a novel algebraic mode decomposition distinct from the normal modes with temporal evolution exp(ωt) . Based on the work of Nold and Oberlack (2013 Phys. Fluids 25 104101), we show how these new modes can be constructed from the symmetries of the linearized stability equation. For the azimuthal base flow velocity V(r)=r−1 an additional symmetry exists, such that a mode with algebraic temporal evolution t s is found. s refers to an eigenvalue for the algebraic growth or decay of the kinetic energy of the perturbations. An eigenvalue problem for the viscous and inviscid stability using algebraic modes is formulated on an infinite domain with r→∞ . An asymptotic analysis of the eigenfunctions shows that the flow is linearly stable under 2D perturbations. We find stable modes with the algebraic mode ansatz, which can not be obtained by a normal mode analysis. The stability results are in line with Rayleigh’s inflection point theorem.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41683775","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}

{"title":"Determination of hydraulic resistance of channels using spectral geometry methods","authors":"Alexander Baron","doi":"10.1088/1873-7005/ac44fa","DOIUrl":"https://doi.org/10.1088/1873-7005/ac44fa","url":null,"abstract":"In this paper, we propose a new method for calculation of hydraulic resistance of channels with constant cross-section. The method is based on the obtained estimates for the average energy dissipation rate in a turbulent flow. The first part of the paper is devoted to theoretical justification of the method. The second part is devoted to calculation of hydraulic resistance of various channels using the above-mentioned method and comparison of these values with the known results. The proposed method allows for calculation of hydraulic resistance of various channels with sufficiently high accuracy and is based only on the information about the channel geometry.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46715463","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}

{"title":"New single vortex generation method for flame/vortex interaction using flow behind a rotating cylinder","authors":"Soufyane Hazel, Yong Huang, Mokhtar Ait Amirat","doi":"10.1088/1873-7005/ac4385","DOIUrl":"https://doi.org/10.1088/1873-7005/ac4385","url":null,"abstract":"\u0000 This paper investigates a new experimental method to generate a single two-dimensional translated vortex for flame/vortex interaction studies. A rotating cylinder is immersed in a uniform flow and, its rotating speed is impulsively reduced. This sudden action triggers the generation of a single vortex when both the initial and the final rotation speeds are in the range of a steady-state regime. Flow visualization allows confirming the applicability of this method, while a complementary two-dimensional numerical simulation is conducted to understand the vortex formation process. A vorticity layer is detached from the cylinder, initiating a feeding process and gradual growth of a single leading vortex. The feeding process is saturated at a specific distance from the cylinder and, vortex separation from the vorticity layer is observed. At the final stage of the formation process, the generated vortex is advected away and, a steady-state regime is again established behind the cylinder. The vortex characteristics appear to be related to the normalized reduction in the rotation rate ∆α, defined as the initial and final rotation rates difference normalized by the initial rotation rate. Several combinations of initial and final rotation rates corresponding to different normalized reductions are investigated experimentally and numerically. The results allow understanding the effect of this parameter; a higher normalized reduction generates a stronger, more rapidly growing vortex. However, its trajectory is related to the wake deviation corresponding to the final rotation rate.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"1 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43186015","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}

{"title":"Qualitative assessment of the complexity of the Karman vortex in the flow past double cylinders based on Shannon entropy","authors":"T. Jia, Sen Zhang, D. Gao","doi":"10.1088/1873-7005/ac408b","DOIUrl":"https://doi.org/10.1088/1873-7005/ac408b","url":null,"abstract":"\u0000 Numerical simulations of flows past double cylinders under the conditions of different inlet velocities are carried out based on finite element methods. The phenomenon of Karman vortex is observed in the numerical study. Shannon entropy of the velocity field is calculated to quantify the complexity of the velocity field, and the time-evolution of the Shannon entropy data is analyzed by time series models of ARMA (autoregressive moving average) and GARCH (generalized autoregressive conditional heteroskedasticity).","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44460061","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}

{"title":"Minimal model of quasi-cyclic behaviour in turbulence driven by Taylor–Green forcing","authors":"R. Araki, W. Bos, S. Goto","doi":"10.1088/1873-7005/acdff7","DOIUrl":"https://doi.org/10.1088/1873-7005/acdff7","url":null,"abstract":"We attempt to formulate the simplest possible model mimicking turbulent dynamics, such as quasi-cyclic behaviour (QCB), using only three variables. To this end, we first conduct direct numerical simulations of three-dimensional flow driven by the steady Taylor–Green forcing to find a similarity between a stable periodic orbit (SPO) at a small Reynolds number (Re) and turbulent QCB at higher Re. A close examination of the SPO allows the heuristic formulation of a three-equation model, representing the evolution of Fourier modes in three distinct scales. The model reproduces the continuous bifurcation from SPO to turbulence with QCB when Re is varied. We also demonstrate that, by changing model parameters, the proposed model exhibits a discontinuous transition from steady to chaotic solutions without going through an SPO.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"55 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41600674","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}

{"title":"Slow axisymmetric rotation of a sphere in a circular tube with slip surfaces","authors":"Ming-Chang Lee, H. Keh","doi":"10.1088/1873-7005/ac39f9","DOIUrl":"https://doi.org/10.1088/1873-7005/ac39f9","url":null,"abstract":"The steady rotation of a slip spherical particle about a diameter lying along the longitudinal axis of a slip circular tube filled with an incompressible Newtonian fluid at low Reynolds numbers is analyzed. To solve the Stokes equations for the fluid flow, the solution is constituted by the summation of general solutions in both cylindrical and spherical coordinates. The boundary conditions are implemented first along the tube wall via the Fourier cosine transform and then over the particle surface through a collocation method. Results of the resisting torque acting on the particle are obtained for various values of the relevant dimensionless parameters. The effect of the confining tube on the axisymmetric rotation of the particle with slip surfaces is interesting. The torque increases monotonically with an increase in the stickiness of the tube wall, keeping the other parameters unchanged. When the stickiness of the tube wall is greater than a critical value, the torque is greater than that on the particle in an unbounded identical fluid and increases with increases in the stickiness of the particle surface and particle-to-tube radius ratio. When the stickiness of the tube wall is less than the critical value, conversely, the torque is smaller than that on the unconfined particle and decreases with increases in the particle stickiness and radius ratio.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41737818","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}

{"title":"Wind tunnel tests of aerodynamic interference effects on two iced vertical circular cylinders in a tandem arrangement","authors":"Shengli Li, Ruiqing Han, P. Guo, Xidong Wang, Yajie Chu","doi":"10.1088/1873-7005/ac3b36","DOIUrl":"https://doi.org/10.1088/1873-7005/ac3b36","url":null,"abstract":"The aerodynamic characteristics of the two iced vertical circular cylinders in a tandem arrangement, due to the shape change by icing, are complex, and lack systematical investigation. Therefore, a set of wind tunnel tests were carried out to study the aerodynamic characteristics of the leeward vertical cylinder, with ice shape, icing thickness, cylinder spacing, and icing relative position of cylinders varied in the subcritical Reynolds number range in this study. Results show that the icing thicknesses had a greater impact on the lift coefficients of D-shaped ice leeward cylinder at the same angle of attack. The aerodynamic characteristics of the iced leeward cylinder were stable when the ratio (L/D) of cylinder spacing was within the range of 4.8–6.2. The change of flow field should be considered in the stability analysis of two circular vertical cylinders. The drag coefficients of the iced leeward cylinder varied significantly due to the shielding effects, especially within the range of 9° attack angle and L< 6.2D. The results of this work can provide an experimental reference for future research on wind resistance of two circular cylindrical structures in engineering practice.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42992189","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}

{"title":"The 14th FDR prize","authors":"Y. Fukumoto","doi":"10.1088/1873-7005/ac2ef2","DOIUrl":"https://doi.org/10.1088/1873-7005/ac2ef2","url":null,"abstract":"Steady flow in a rapidly rotating spheroid with weak precession: I Shigeo Kida Vol. 52, No. 1, 015513 (2020) The flow in a rotating spheroidal container that executes precession has long attracted attention as a model for pursuing the origin of the dynamos of celestial bodies including the geodynamo. In recent years, research has been made from the viewpoint of generating a compact turbulence and utilizing it for efficient mixer (Goto et al 2007). The first key result is a steady inviscid solution heuristically derived by Poincaré (1910), which is a uniform vorticity state with the velocity field linear in coordinates; a spheroidal container filled with an inviscid fluid rapidly rotating around the axis of symmetry (referred to as the x axis) precesses around another axis (referred to as the z axis) perpendicular to the symmetric axis. The vorticity, relative to the spinning spheroid, is parallel to the z axis for an oblate spheroid but is antiparallel for a prolate spheroid. In between, there is no special direction for a spherical container, for which the magnitude of the vorticity diverges. To rescue this difficulty, Busse (1968) made an attempt at incorporating the effect of the boundary layer on the vessel by using the integral balance of torque, but his treatment turned out to be incomplete. This paper has resolved the problem of singularity by making a precise perturbation analysis of the boundary layer. There are three parameters in this problem, the aspect ratio c= b/a of the spheroid with the axis length 2 b and the equatorial length a, the Poincaré number Po=Ωp/Ωs, being the ratio of the precession angular velocity Ωp to the angular velocity Ωs of the main spin, and the Reynolds number Re= aΩs/ν, with ν being the kinematic viscosity of fluid. For a spheroid close to a sphere |c− 1| ≪ 1, a boundary-layer solution is constructed in the region of Po≪Max(Re−1/2, |c− 1|) (the obtained solution requests |c− 1| ≪ Re−1/2). Introducing ellipsoidal coordinates in the ‘rigidly rotating system’ with the X axis parallel to the full angular velocity vector ω̄, a solution is constructed in the form of perturbations in powers of a small parameter ε̄, a measure of the magnitude of the deviation flow, in such a way that the boundary-layer solution smoothly matches to the solution in the inviscid region. Unknown parameters are the three components of the perturbation of the angular velocity due to precession. For the spherical case (c= 1), these remain undetermined. The balance of the total torque is invoked, consisting of the integrals of the pressure, the precession-induced Coriolis force, and the viscous stress. Busse (1968) carried out this procedure to O(ε̄), which is insufficient for obtaining the correction term c̄ of the x component of the angular velocity. This paper has gained the axisymmetric component c̄ for the first time by including, in the torque, the circumferential average of the nonlinear boundary-layer solution of O(ε̄2). Without this","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45238489","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}

{"title":"The deformation and breakup of a droplet under the combined influence of electric field and shear flow","authors":"Yanyan Chen, Yusheng Liang, Mengyuan Chen","doi":"10.1088/1873-7005/ac3893","DOIUrl":"https://doi.org/10.1088/1873-7005/ac3893","url":null,"abstract":"A lattice Boltzmann and finite-difference hybrid method is used to simulate the droplet deformation and breakup under the combined action of shear flow and electric field. The hybrid method is first used to validate for the droplet deformation in the combined action of shear flow and electric field. It is then used to simulate the droplet deformation and breakup in two different electric systems. Results of prolate droplets show that the droplet height and deformation both increase with increasing electric capillary number ( CaE ). In addition, for the breakup mode of prolate droplets, increasing CaE makes the long axis of the droplet incline more towards the wall electrodes and droplet breaks up into more daughter droplets. Results of oblate droplets show that the droplet height decreases with increasing CaE . However, the droplet deformation first decreases and then increases with increasing CaE , and its minima occurs at CaE=0.01 . For the breakup mode of oblate droplets, the droplet deforms into a more oblate shape with a longer neck and finally breakup into more daughter droplets with increasing CaE .","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42524634","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}

{"title":"Predictability and benefits of coupled Eulerian-Lagrangian approach over Eulerian characterization of droplet annular flow","authors":"Digvijay Singh, A. Das","doi":"10.1088/1873-7005/ac34ec","DOIUrl":"https://doi.org/10.1088/1873-7005/ac34ec","url":null,"abstract":"Wavy annular flow and subsequent droplet dispersion in air-water two-phase flow has been studied numerically using conventional Eulerian volume of fluid (VOF) solver and coupled Eulerian-Lagrangian approach. The VOF based investigation has been reported to highlights the formation of droplet swarm and its population dynamics. Coupled Eulerian-Lagrangian method has also been shown to replicate similar features with lesser computational effort. Entrainment, deposition, fragmentation and unification are traced from the numerical simulation, which ultimately predicts the volume filling behavior of the droplets inside the tube. Flow kinematics around droplet is critically assessed numerically for finding out reasons behind deposition, fragmentation and unification. A comparative behavior between different velocity ratios of gas and liquid flow rates are presented which clearly shows higher entrainment rate as shear between annular liquid and gaseous core increases. An assessment of the droplet population in coupled Eulerian-Lagrangian method shows the generation of the smaller sized spherical droplet by entrainment and fragmentation route.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":" ","pages":""},"PeriodicalIF":1.5,"publicationDate":"2021-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43178653","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}