Coherent structures in coflowing jets and wakes

1978 ◽  
Vol 88 (3) ◽  
pp. 451-463 ◽  
Author(s):  
A. E. Perry ◽  
T. T. Lim
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Glass Tube ◽  
Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Naturally Occurring ◽  
Number Flow ◽  
High Reynolds ◽  
Scale Motion

By applying small lateral oscillations to a glass tube from which smoke was issuing, perfectly periodic coflowing jets and wake structures were produced at Reynolds numbers of order 300-1000. These structures remained coherent over long streamwise distances and appeared to be perfectly frozen when viewed under stroboscopic light which was synchronized with the disturbing oscillation. By the use of strobing laser beams, longitudinal sections of the structures were photographed and an account of the geometry of these structures is reported.When the tube was unforced, similar structures occurred but they modulated in scale and frequency, and their orientation was random.A classification of structures is presented and examples are demonstrated in naturally occurring situations such as smoke from a cigarette, the wake behind a three-dimensional blunt body, and the high Reynolds number flow in a plume from a chimney. It is suggested that an examination of these structures may give some insight into the large-scale motion in fully turbulent flow.

Turbulent flow between counter-rotating concentric cylinders: a direct numerical simulation study

2008 ◽  
Vol 615 ◽  
pp. 371-399 ◽  
Author(s):  
S. DONG
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Outer Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Taylor Vortex ◽  
Small Scale ◽  
Mean Flow ◽  
Concentric Cylinders ◽  
High Reynolds

We report three-dimensional direct numerical simulations of the turbulent flow between counter-rotating concentric cylinders with a radius ratio 0.5. The inner- and outer-cylinder Reynolds numbers have the same magnitude, which ranges from 500 to 4000 in the simulations. We show that with the increase of Reynolds number, the prevailing structures in the flow are azimuthal vortices with scales much smaller than the cylinder gap. At high Reynolds numbers, while the instantaneous small-scale vortices permeate the entire domain, the large-scale Taylor vortex motions manifested by the time-averaged field do not penetrate a layer of fluid near the outer cylinder. Comparisons between the standard Taylor–Couette system (rotating inner cylinder, fixed outer cylinder) and the counter-rotating system demonstrate the profound effects of the Coriolis force on the mean flow and other statistical quantities. The dynamical and statistical features of the flow have been investigated in detail.

Vortex Suppression Efficiency of Discontinuous Helicoidal Fins

2007 ◽  
Author(s):  
Antonio Pinto ◽  
Riccardo Broglia ◽  
Elena Ciappi ◽  
Andrea Di Mascio ◽  
Emilio F. Campana ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Computational Time ◽  
Reynolds Number Flow ◽  
Flow Past A Cylinder ◽  
Helical Strakes ◽  
Unsteady Rans ◽  
Number Flow ◽  
Offshore Industry ◽  
Good Trade ◽  
High Reynolds

Vortex-Induced Vibration (VIV) is one of the most demanding areas in the offshore industry, and detailed investigation of the fluid-structure interaction is becoming fundamental for designing new structures able to reduce VIV phenomenon. To carry on such analysis, and get reliable results in term of global coefficients, the correct modelling of turbulence, boundary layer, and separated flows is required. Nonetheless, the more accurate is the simulation, the more costly is the computation. Unsteady RANS simulations provide a good trade-off between numerical accuracy and computational time. This paper presents the analysis of the flow past a cylinder with several three-dimensional helical fins at high Reynolds number. Flow field, vortical structures, and response frequency patterns are analysed. Spectral analysis of data is performed to identify carrier frequencies, deemed to be critical due to the induced vibration of the whole structure. Finally, helical strakes efficiency in reducing the riser vibrations is also addressed, through direct consideration on the carrier shedding frequency.

Measurement of Velocity Profiles of Laminar to Turbulent Water Flows in a Tube Using Particle Image Velocimetry

2004 ◽  
Author(s):  
Meredith R. Martin
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Glass Tube ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Reynolds Number Flow ◽  
Image Velocimetry ◽  
Dye Visualization ◽  
Number Flow

The transition from laminar to turbulent in-tube flow is studied in this paper. Water flow in a glass tube with an inside diameter of 21.7 mm was investigated by two methods. First, a dye visualization test using a setup similar to the 1883 experiment of Osborne Reynolds was conducted. For the dye visualization, Reynolds numbers ranging from approximately 1000 to 3500 were tested and the transition from laminar to turbulent flow was observed between Reynolds numbers of 2500 and 3500. For the second method, a particle image velocimetry (PIV) system was used to measure the velocity profiles of flow in the same glass tube at Reynolds numbers ranging from approximately 500 to 9000. The resulting velocity profiles were compared to theoretical laminar profiles and empirical turbulent power-law profiles. Good agreement was found between the lower Reynolds number flow and the laminar profile, and between the higher Reynolds number flow and turbulent power-law profile. In between the flow appeared to be in a transition region and deviated some between the two profiles.

Three-Dimensional Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibrations

2006 ◽  
Author(s):  
Juan P. Pontaza ◽  
Hamn-Ching Chen
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Time Step ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
High Reynolds ◽  
Two Degree Of Freedom

In an effort to gain a better understanding of the VIV phenomena, we present three-dimensional numerical simulations of VIV of circular cylinders. We consider operating conditions that correspond to high Reynolds number flow, low structural damping, and allow for two-degree of freedom motion. The numerical implementation makes use of overset (Chimera) grids, in a multiple block environment where the workload associated with the blocks is distributed among multiple processors working in parallel. The three-dimensional grids around the cylinder are allowed to undergo arbitrary motions with respect to fixed background grids, eliminating the need for tedious grid regeneration at every time step.

scholarly journals Laminar and turbulent comparisons for channel flow and flow control

2007 ◽  
Vol 570 ◽  
pp. 467-477 ◽  
Author(s):  
IVAN MARUSIC ◽  
D. D. JOSEPH ◽  
KRISHNAN MAHESH
Keyword(s):  
Pressure Gradient ◽  
Flow Control ◽  
Turbulent Flows ◽  
Control Strategies ◽  
Reynolds Numbers ◽  
Volume Flux ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
High Reynolds ◽  
Strategy Design

A formula is derived that shows exactly how much the discrepancy between the volume flux in laminar and in turbulent flow at the same pressure gradient increases as the pressure gradient is increased. We compare laminar and turbulent flows in channels with and without flow control. For the related problem of a fixed bulk-Reynolds-number flow, we seek the theoretical lowest bound for skin-friction drag for control schemes that use surface blowing and suction with zero-net volume-flux addition. For one such case, using a crossflow approach, we show that sustained drag below that of the laminar-Poiseuille-flow case is not possible. For more general control strategies we derive a criterion for achieving sublaminar drag and use this to consider the implications for control strategy design and the limitations at high Reynolds numbers.

Study on Spacer Grid Span Pressure Loss Under High Reynolds Number Flow Condition

2009 ◽  
Author(s):  
Kazuo Ikeda ◽  
Yasunao Yamaguchi ◽  
Juntaro Shimizu ◽  
Kaoru Okamoto
Keyword(s):  
Reynolds Number ◽  
Flow Condition ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Cfd Model ◽  
Spacer Grid ◽  
Reynolds Number Flow ◽  
Rod Bundle ◽  
Number Flow ◽  
High Reynolds

Pressure loss coefficient of spacer grid is used as a key parameter for PWR core thermal hydraulic design. It has been obtained by single-phase hydraulic testing for many years. However, it is necessary to develop design tool for precise estimation of pressure loss of spacer grids as well as hydraulic tests to meet the needs of the worldwide nuclear fuel market. Recently, Computational Fluid Dynamics (CFD) analysis has been applied for estimation of flow field in a fuel rod bundle. In this study, the numerical simulation in a range of bare rod Reynolds numbers of the reactor flow condition is performed to examine the applicability of the CFD model for estimating spacer grid span pressure loss. For verification of the numerical estimation, the span pressure loss of 5×5 rod bundle with spacer grid is measured in Nuclear Development Corporation (NDC) hydraulic test facility up to bare rod Reynolds number as high as 500,000. The simulation shows good agreement with experimental data in the range of Reynolds numbers. The CFD model is also utilized to investigate the pressure loss as a function of distance from last passed spacer grid and to discuss the turbulent flow characteristics in the rod bundle with spacer grid under high Reynolds number flow condition.

High Reynolds number flow between torsionally oscillating disks

1970 ◽  
Vol 2 (1) ◽  
pp. 55-79
Author(s):  
K.G. Smith ◽  
A.F. Pillow
Keyword(s):  
Boundary Layers ◽  
Viscous Incompressible Fluid ◽  
Reynolds Numbers ◽  
Main Body ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
High Reynolds Numbers ◽  
Number Flow ◽  
High Reynolds ◽  
Steady Convection

In this paper the problem solved is that of unsteady flow of a viscous incompressible fluid between two parallel infinite disks, which are performing torsional oscillations about a common axis. The solution is restricted to high Reynolds numbers, and thus extends an earlier solution by Rosenblat for low Reynolds numbers.The solution is obtained by the method of matched asymptotic expansions. In the main body of the fluid the flow is inviscid, but may be rotational, and in the boundary layers adjacent to the disks the non-linear convection terms are small. These two regions do not overlap, and it is found that in order to match the solutions a third region is required in which viscous diffusion is balanced by steady convection. The angular velocity is found to be non-zero only in the boundary layers adjacent to the disks.

Pressure and Vortex Shedding Patterns Around a Low Aspect Ratio Cylinder in a Sheared Flow at Transitional Reynolds Numbers

1981 ◽  
Vol 103 (1) ◽  
pp. 88-95 ◽  
Author(s):  
D. M. Rooney ◽  
R. D. Peltzer
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Pressure Measurements ◽  
Reynolds Number Flow ◽  
Sheared Flow ◽  
Number Flow ◽  
High Reynolds ◽  
First Time ◽  
Upstream Flow

Model tests were performed in a wind tunnel to determine vortex shedding patterns induced around a circular cylinder by spanwise shear in transitional Reynolds number flow. In addition, mean and fluctuating pressure measurements were obtained. The introduction of shear in the upstream flow generated two distinct cells of vortex frequencies behind the cylinder in the transcritical regime, thereby documenting for the first time that the re-established high Reynolds number shedding closely parallels patterns already observed in subcritical flow. The two cell pattern did not permit any correlation between shear level and cell length to be found.

The interacting boundary-layer flow due to a vortex approaching a cylinder

1997 ◽  
Vol 346 ◽  
pp. 319-343 ◽  
Author(s):  
Z. XIAO ◽  
O. R. BURGGRAF ◽  
A. T. CONLISK
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Two Dimensions ◽  
Unsteady Boundary Layer ◽  
Reynolds Number Flow ◽  
Boundary Layer Equations ◽  
Number Flow ◽  
Layer Flow ◽  
High Reynolds

In this paper the solution to the three-dimensional and unsteady interacting boundary-layer equations for a vortex approaching a cylinder is calculated. The flow is three-dimensional and unsteady. The purpose of this paper is to enhance the understanding of the structure in three-dimensional unsteady boundary-layer separation commonly observed in a high-Reynolds-number flow. The short length scales associated with the boundary-layer eruption process are resolved through an efficient and effective moving adaptive grid procedure. The results of this work suggest that like its two-dimensional counterpart, the three-dimensional unsteady interacting boundary layer also terminates in a singularity at a finite time. Furthermore, the numerical calculations confirm the theoretical analysis of the singular structure in two dimensions for the interacting boundary layer due to Smith (1988).

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