Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
40
2
2013
Experimental Investigation of Vortical Structures in the Near Field of an Axisymmetric Jet by Time-Series Analysis
91-105
Yassine
Zaouali
Metrology and Energetic Systems (UR11ES59) School of Engineering of Monastir Monastir, Tunisia
Habib Ben
Aissia
Unit of Metrology and Energy Systems, National Engineering School of Monastir, University
of Monastir, Tunisia
Jacques
Jay
Thermal Science Centre of Lyon (CETHIL - UMR CNRS 5008) National Institute of Applied Sciences of Lyon Lyon, France
Amina
Meslem
LaSIE, University of La Rochelle Pole Sciences et Technologie La Rochelle, France
The study herein focuses on the spatio-temporal evolution of a free natural air jet discharging from a round nozzle in stagnant air. Five Reynolds numbers extending from 1300 to 1700 are considered. The jet behavior related to its vortical structures is investigated in the first 6 diameters downstream from the nozzle via high-speed flow visualization and time-series analysis. It has been observed a transition from helical to axisymmetric vortical structures mode in the shear layer of the jet for a Reynolds number of 1500. Additionally, the spatio-temporal visualization of the traces that vortical structures design on parallel and horizontal lines to the jet axis permits to determine their convection velocity, life duration and axial progression before breaking-up. Particular attention is paid to the axial variation of the vortical structures frequency and the jet Strouhal number as function of the Reynolds number.
On a Closed-Form Solution of Prandtl's System of Equations
106-114
J.
Venetis
School of Applied Mathematics and Physical Sciences NTUA, Section
of Mechanics, 5 Heroes of Polytechnion Ave., GR—15773 Athens, Greece
Emilio
Sideridis
School of Applied Mathematics and Physical Sciences NTUA, Section of Mechanics, 5 Heroes of Polytechnion Ave., GR—15773 Athens, Greece
In this paper, we will attempt to obtain a closed form solution of Prandtl's system of equations which describe the boundary layer of a two-dimensional steady and incompressible viscous flow over a curved surface. Specifically, we will obtain a direct integration of these equations resulting step by step to a closed-form expression for velocity profile taking also into account the corresponding boundary conditions which complete the known from literature Prandtl's simplified assumptions concerning boundary layer flows.
An Incompressible Multi-Relaxation-Time Lattice Boltzmann Method for Large Eddy Simulation of Two-Dimensional Turbulent Flows
115-132
Ahmad Reza
Rahmati
Department of Mechanical Engineering, University of Kashan, Kashan, Iran
Mahmud
Ashrafizaadeh
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran
Ebrahim
Shirani
Foolad Institute of Technology, Fooladshahr, Isfahan, 8491663763, Iran
In this article, an incompressible Multiple-Relaxation-Time Lattice Boltzmann Equation (MRT-LBE) model for Large-Eddy Simulation (LES) of incompressible turbulent flows is considered. The implementation is discussed in the context of D2Q9 MRT-LBE model in conjunction with the Smagorinsky subgrid closure model. The MRT-LBE LES is applied to a two-dimensional driven cavity flow and double shear flow for studying the dynamics of flow structures. The combination of the LBE method with the subgrid model allows us to simulate the cavity flow up to a Reynolds number of 1000000. The MRT-LBE LES results are compared with (single-relaxation-time) SRT-LBE LES results and existing CFD simulations. Reasonable agreement between the presented numerical results and those of existing CFD simulations demonstrate that the MRT-LBE method is a potentially viable tool for LES of turbulence.
Interactions between Rigid Particles
133-147
Samireh
Vahid
Kingston University River House, 53-57, High Street, Kingston upon Thames, Surrey KT1 1LQ, United Kingdom
This paper is concerned with the migration of particles in a dense slurry flow, which is a mixture, consisting of more or less spherical particles immersed in a Newtonian fluid. The particles are rough, and we study their interaction in the lubrication limit, both analytically and in a numerical simulation. The analytical results are replicated in the simulation: structures form in the low shear rate region when the particle interaction does not involve a substantial repulsive element, they disappear when a repulsive elastic interaction is implemented.
Inviscid Flow Arrangements in Fluid Dynamics
148-158
Allan
Runstedtler
Natural Resources Canada
It is common knowledge that, as the Reynolds number increases, flows lose their ability to damp out disturbances and they are increasingly composed of swirling eddies or vortices. This work proposes that the formation of inviscid flow arrangements is the mechanism that is responsible for these observations. Inviscid flow arrangements are flows of viscous fluids in which viscous forces vanish, not to be confused with inviscid fluids which have zero viscosity. The presentation begins with analysis of the viscous terms in the Navier−Stokes equation, showing that it is possible to arrange the flow of a viscous fluid so that viscous forces vanish, that these arrangements are vortex-like, and that inviscid arrangements are most likely to form in flow conditions corresponding to high Reynolds number. The author proposes that hurricanes, tornadoes, sink drain vortices, and turbulence are among the possible consequences. To the author's knowledge, this concept has not been presented in the scientific literature. A numerical study is then presented of laminar pipe flow subjected to a disturbance to determine if inviscid flow arrangements form and to study their behavior. An important emphasis is the inclusion of the disturbance in the Reynolds number. Using a novel method to visualize the deviation from laminar flow, inviscid flow arrangements are found to increasingly form as the Reynolds number increases. If it is true that inviscid flow arrangements play a key role in turbulence, then it is ironic that the phenomenon which increases the effective viscosity of a flow is actually a result of the tendency to eliminate the viscous force.
Flow past an Impulsively Started Horizontal Cylinder in a Rotating Fluid
159-167
Rudra Kanta
Deka
Department of Mathematics, Gauhati University, Guwahati-781014, Assam, India
Ashish
Paul
Department of Mathematics, Cotton University, Guwahati-781001, Assam, India
This paper presents an exact solution to the flow of a viscous incompressible fluid past an impulsively started horizontal cylinder in a rotating fluid. Dimensionless governing equations are solved by Laplace transform technique. Expressions of axial and transverse components of velocity, skin friction are derived using Laplace transform technique and effects of rotation parameter and time on these components are shown in graphs. It is demonstrated that the rotation leads to oscillatory motion solely due to rotation for smaller time, while the flow approaches steady state at larger time.
Near Wake Structure of Wall-Mounted Finite Cylinders in Shallow Open Channel Flow
168-183
Martin
Agelin-Chaab
Automotive, Mechanical and Manufacturing Engineering Department, University of Ontario Institute of Technology Oshawa, ON, L1H 7K4, Canada
S. S.
Paul
CG Power Systems Canada Inc. Winnipeg MB, Canada
This paper reports an experimental investigation of the structure of the flow field around wall-mounted finite circular and square cylinders in an open water channel. A particle image velocimetry technique was used to conduct detailed velocity measurements in the streamwise-transverse and streamwise-spanwise planes. From these measurements, the iso-contours and profiles of the mean velocities and turbulent quantities were obtained at selected streamwise locations to document the salient flow features. The wake half-width of the square cylinder is 23 % higher than that of the circular cylinder but their spanwise spread rates are both linear and similar. The square cylinder generates more turbulence at its free end than the circular cylinder which is evidenced by the higher turbulent quantities. The proper orthogonal decomposition (POD) analysis revealed that for each cylinder type there are more energetic structures in the streamwise-spanwise plane than in the streamwise-transverse plane. There are also more energetic structures in the square cylinder than the circular cylinder.