A visual study of the flow around an oscillating circular cylinder at low Keulegan–Carpenter numbers and low Stokes numbers

1990 ◽  
Vol 211 ◽  
pp. 157-182 ◽  
Author(s):  
M. Tatsuno ◽  
P. W. Bearman
Keyword(s):  
Circular Cylinder ◽  
Flow Visualization ◽  
Flow Separation ◽  
Three Dimensional ◽  
Stokes Number ◽  
Flow Patterns ◽  
Half Cycle ◽  
Visual Study ◽  
Sinusoidal Oscillations ◽  
Dimensional Instability

The structures of the flow induced by a circular cylinder performing sinusoidal oscillations in a fluid at rest are investigated by means of flow visualization. The experiments are carried out at Keulegan–Carpenter numbers between 1.6 and 15 and at Stokes numbers between 5 and 160. Above a certain value of Keulegan–Carpenter number, depending on the Stokes number, some asymmetry appears in the flow separation and the associated vortex development behind the cylinder. The two vortices that are developed in a half cycle differ in strength and may be convected in different directions. This results in a fascinating set of flow patterns. Eight different regimes of flow can be identified within the ranges of Keulegan–Carpenter number and Stokes number studied. Furthermore, most of the resulting flows show a three-dimensional instability along the axis of the cylinder. Measurements of the wavelength of these disturbances are presented.

Experimental Study on the Stability of the Flow Behind an Accelerating Circular Cylinder

2007 ◽  
Author(s):  
A. Inasawa ◽  
K. Toda ◽  
M. Asai
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Cylinder Wake ◽  
Global Instability ◽  
The Stability ◽  
Dimensional Instability ◽  
Wake Oscillation

Disturbance growth in the wake of a circular cylinder moving at a constant acceleration is examined experimentally. The cylinder is installed on a carriage moving in the still air. The results show that the critical Reynolds number for the onset of the global instability leading to a self-sustained wake oscillation increases with the magnitude of acceleration, while the Strouhal number of the growing disturbance at the critical Reynolds number is not strongly dependent on the magnitude of acceleration. It is also found that with increasing the acceleration, the Ka´rma´n vortex street remains two-dimensional even at the Reynolds numbers around 200 where the three-dimensional instability occurs to lead to the vortex dislocation in the case of cylinder moving at constant velocity or in the case of cylinder wake in the steady oncoming flow.

Interference Between a Square and a Circular Cylinder

2015 ◽  
Author(s):  
Nithin S. Kumar ◽  
R. Ajith Kumar ◽  
Jayalakshmi Mohan
Keyword(s):  
Circular Cylinder ◽  
Flow Visualization ◽  
Shear Layer ◽  
Flow Pattern ◽  
Water Channel ◽  
Flow Patterns ◽  
Observation Time ◽  
Square Cylinder ◽  
Circulating Water ◽  
Layer Flow

The flow visualization studies around a square cylinder (upstream) and a circular cylinder arranged in tandem configuration is studied experimentally to identify the interference flow patterns. Flow visualization studies are carried out in a re-circulating water channel. The investigations are carried out for tandem arrangement varying the center-to-center distance (L) between the cylinders; L/B ratio is varied from 1 to 5 where B is the characteristic length. Experiments were conduct at a Reynolds number of 2100 (based on B). The results are also obtained for two tandem square cylinder configuration. The flow patterns observed are: Alternate Shear Layer Reattachment with and without gap flow, Simultanous shear layer reattachment and detached shear layer flow pattern. The time of persistence (in percentage) for each flow pattern is estimated over a sufficiently long period of observation time to identify the most influential, predominant flow pattern. Though these patterns are identical for square-square and square-circular tandem configurations, their order of predominance is different for both the configurations.

A Study of the Flow Patterns Between Two Corrugated Plates With an Egg-Carton Configuration

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Benjamin Giron-Palomares ◽  
Abel Hernandez-Guerrero ◽  
Ricardo Romero-Mendez ◽  
Qiang He
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Numerical Models ◽  
Average Distance ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Secondary Flows ◽  
3D Interaction ◽  
Corrugated Plates ◽  
Phase Angles

Enhancing mixing in heat exchangers for low Re regimes is vital. A better mixing may be achieved by using corrugated plates. In this work, the flow patterns between corrugated plates with a novel egg-carton geometry were studied. Three-dimensional (3D) numerical models were developed for the steady laminar flow between two corrugated plates having 180 deg or 0 deg phase angles. The Reynolds number (Re ≤ 600) was defined as a function of the average distance between the corrugated plates. The numerical models were strictly developed and corroborated to achieve global convergence, local convergence, and grid-size independence. For both phase angles, it was determined that “close recirculations” decrease in size downstream and finally disappear becoming “open recirculations” due to the flow developing characteristics; the secondary flow regions were found to grow downstream; interestingly, increments on the Reynolds number favor recirculation growth and early flow detachment; the behavior and geometry of the recirculation were in line with previous flow visualization results. The recirculations were determined to be z-symmetric with respect to the channel center only for the 180 deg model. The recirculations in the 0 deg model were smaller and became “open recirculations” earlier than in the 180 deg model. Convex geometries on the transversal direction were found to favor detachment, while concave geometries inhibit it. The capability of the numerical methods to track flow paths in any direction showed a complex three-dimensional flow causing 3D-interaction among secondary flows and the main flow not reported before for these channels and just hinted by previous flow visualization studies.

scholarly journals The Performance & Flow Visualization Studies of Three dimensional (3-D) Wind Turbine Blade Models

2016 ◽  
Vol 10 (5) ◽  
pp. 132 ◽  
Author(s):  
Sutrisno . ◽  
Prajitno . ◽  
Purnomo . ◽  
B.W. Setyawan
Keyword(s):  
Flow Visualization ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Wind Turbine Blade ◽  
Wind Turbine Blades ◽  
Rotating Blade ◽  
Wind Turbine System

<p>The researches on the design of 3-D wind turbine blades have been received less attention so far even though 3-D blade products are widely sold. In the opposite, advanced researches in 3-D helicopter blade have been studied rigorously. Researches in wind turbine blade modeling are mostly assumed that blade span wise sections behaves as independent two dimensional (2-D) airfoils, implying that there is no exchange of momentum in the span wise direction. Further more flow visualization experiments are infrequently conducted.</p><p>The purpose of this study is to investigate the performance of 3-D wind turbine blade models with backward-forward swept and verify the flow patterns using flow visualization. In this research, the blade models are constructed based on the twist and chord distributions following Schmitz’s formula. Forward and backward swept are added to the wind turbine blades. It is hoped that the additional swept would enhance or diminish outward flow disturbance or stall development propagation on the span wise blade surfaces to give better blade design.</p><p>The performance of the 3-D wind turbine system models are measured by a torque meter, employing Prony’s braking system, and the 3-D flow patterns around the rotating blade models are investigated applying “tuft-visualization technique”, to study the appearance of laminar, separated and boundary layer flow patterns surrounding the 3-dimentional blade system.</p>For low speed wind turbines, Dumitrescu and Cardos (2011) have identified that stall spreads from the root of the rotating blade. In this study, it is found that for blades with (i) forward swept tip and backward swept root, the initial stall at the blade bottom would be amplified by concurrent strengthening flow due to  the backward swept root to create strong stall spreading outward, and therefore the blades gives lower performance. For blades with (ii) backward swept tip and forward swept root, the initial stall at the blade bottom would be weakened by opposite weakening flow due to the forward swept root, generate weak stall that tend to deteriorate. These blades have better performance.

Effects of Endplates on Secondary Streaming of Oscillating Flows Past a Circular Cylinder

2008 ◽  
Author(s):  
C. T. Hsu ◽  
Yan Su
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Stokes Number ◽  
Fluid Particle ◽  
Navier Stokes ◽  
Oscillating Flows ◽  
Navier Stokes Equations ◽  
Stagnation Points ◽  
Streaming Flows

The effects of parallel endplates on the secondary streaming of oscillating flows past a circular cylinder are studied by solving the Navier-Stokes equations numerically with Direct Numerical Simulation (DNS) method. A fractional-step scheme was implemented with the incorporation of the spectral method applied along the circumferential direction in solving a set of 2-D Poisson equations. The structure of the secondary streaming flows is presented with three-dimensional fluid particle traces (streak lines) and vorticity distributions. Unlike the traditional secondary streaming of two dimensional oscillating flows that exhibits 8 closed re-circulation zones (two in each quadrant), the mean secondary streaming flows in this study are three-dimensional without closed recirculation. The fluid particle traces show that there are three-dimensional spirals in each quadrant. Fluid particles near the endplates are attracted into the spirals toward the mid-plane of the two endplates. The trace trajectories in the flow domains never interest except at the stagnation points. The effects of cylinder aspect ratio, Keulegan-Carpenter number, and Stokes number on the secondary streaming patterns are also studied. The oscillatory drag and lift coefficients are also computed and discussed. The comparison of flow patterns obtained from this study with the results of experimental visualization shows qualitative agreement.

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