Experiments on Flow About a Yawed Circular Cylinder

1972 ◽  
Vol 94 (4) ◽  
pp. 771-776 ◽  
Author(s):  
R. A. Smith ◽  
Woo Taik Moon ◽  
T. W. Kao
Keyword(s):  
Circular Cylinder ◽  
Normal Component ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Cylinder Pressure ◽  
Near Wake ◽  
Pressure Drag ◽  
Independence Principle ◽  
Angle Of Yaw ◽  
Yaw Angle

Experiments were performed to evaluate the influence of yaw angle on circular cylinder pressure drag and near wake characteristics in the range of Reynolds numbers 2000 to 10,000. It was found that the transition in the wake from laminar to turbulent motion was significantly promoted as the angle of yaw increased. As a result, wake properties such as base pressure and position of transition to turbulence do not obey the Independence Principle which requires that properties be dependent only on the normal component of the free-stream conditions.

scholarly journals The drag-adjoint field of a circular cylinder wake at Reynolds numbers 20, 100 and 500

2013 ◽  
Vol 730 ◽  
pp. 145-161 ◽  
Author(s):  
Qiqi Wang ◽  
Jun-Hui Gao
Keyword(s):  
Circular Cylinder ◽  
Flow Field ◽  
Unsteady Flow ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Adjoint Equations ◽  
Cylinder Wake ◽  
Near Wake ◽  
Navier Stokes Equation ◽  
D 20

AbstractThis paper analyses the adjoint solution of the Navier–Stokes equation. We focus on flow across a circular cylinder at three Reynolds numbers, ${\mathit{Re}}_{D} = 20, 100$ and $500$. The quantity of interest in the adjoint formulation is the drag on the cylinder. We use classical fluid mechanics approaches to analyse the adjoint solution, which is a vector field similar to a flow field. Production and dissipation of kinetic energy of the adjoint field is discussed. We also derive the evolution of circulation of the adjoint field along a closed material contour. These analytical results are used to explain three numerical solutions of the adjoint equations presented in this paper. The adjoint solution at ${\mathit{Re}}_{D} = 20$, a viscous steady state flow, exhibits a downstream suction and an upstream jet, the opposite of the expected behaviour of a flow field. The adjoint solution at ${\mathit{Re}}_{D} = 100$, a periodic two-dimensional unsteady flow, exhibits periodic, bean-shaped circulation in the near-wake region. The adjoint solution at ${\mathit{Re}}_{D} = 500$, a turbulent three-dimensional unsteady flow, has complex dynamics created by the shear layer in the near wake. The magnitude of the adjoint solution increases exponentially at the rate of the first Lyapunov exponent. These numerical results correlate well with the theoretical analysis presented in this paper.

Numerical investigation of near-wake characteristics of cavitating flow over a circular cylinder

2016 ◽  
Vol 790 ◽  
pp. 453-491 ◽  
Author(s):  
Aswin Gnanaskandan ◽  
Krishnan Mahesh
Keyword(s):  
Circular Cylinder ◽  
Single Phase ◽  
Three Dimensional ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Cavitating Flow ◽  
Cylinder Surface ◽  
Near Wake ◽  
Eddy Simulation ◽  
Wake Characteristics

A homogeneous mixture model is used to study cavitation over a circular cylinder at two different Reynolds numbers ($Re=200$ and 3900) and four different cavitation numbers (${\it\sigma}=2.0$, 1.0, 0.7 and 0.5). It is observed that the simulated cases fall into two different cavitation regimes: cyclic and transitional. Cavitation is seen to significantly influence the evolution of pressure, boundary layer and loads on the cylinder surface. The cavitated shear layer rolls up into vortices, which are then shed from the cylinder, similar to a single-phase flow. However, the Strouhal number corresponding to vortex shedding decreases as the flow cavitates, and vorticity dilatation is found to play an important role in this reduction. At lower cavitation numbers, the entire vapour cavity detaches from the cylinder, leaving the wake cavitation-free for a small period of time. This low-frequency cavity detachment is found to occur due to a propagating condensation front and is discussed in detail. The effect of initial void fraction is assessed. The speed of sound in the free stream is altered as a result and the associated changes in the wake characteristics are discussed in detail. Finally, a large-eddy simulation of cavitating flow at $Re=3900$ and ${\it\sigma}=1.0$ is studied and a higher mean cavity length is obtained when compared to the cavitating flow at $Re=200$ and ${\it\sigma}=1.0$. The wake characteristics are compared to the single-phase results at the same Reynolds number and it is observed that cavitation suppresses turbulence in the near wake and delays three-dimensional breakdown of the vortices.

Three-dimensional dynamics and transition to turbulence in the wake of bluff objects

1992 ◽  
Vol 238 ◽  
pp. 1-30 ◽  
Author(s):  
George Em Karniadakis ◽  
George S. Triantafyllou
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Period Doubling ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Two Dimensional ◽  
Near Wake ◽  
Vortex Filaments ◽  
Average Flow ◽  
Time Average

The wakes of bluff objects and in particular of circular cylinders are known to undergo a ‘fast’ transition, from a laminar two-dimensional state at Reynolds number 200 to a turbulent state at Reynolds number 400. The process has been documented in several experimental investigations, but the underlying physical mechanisms have remained largely unknown so far. In this paper, the transition process is investigated numerically, through direct simulation of the Navier—Stokes equations at representative Reynolds numbers, up to 500. A high-order time-accurate, mixed spectral/spectral element technique is used. It is shown that the wake first becomes three-dimensional, as a result of a secondary instability of the two-dimensional vortex street. This secondary instability appears at a Reynolds number close to 200. For slightly supercritical Reynolds numbers, a harmonic state develops, in which the flow oscillates at its fundamental frequency (Strouhal number) around a spanwise modulated time-average flow. In the near wake the modulation wavelength of the time-average flow is half of the spanwise wavelength of the perturbation flow, consistently with linear instability theory. The vortex filaments have a spanwise wavy shape in the near wake, and form rib-like structures further downstream. At higher Reynolds numbers the three-dimensional flow oscillation undergoes a period-doubling bifurcation, in which the flow alternates between two different states. Phase-space analysis of the flow shows that the basic limit cycle has branched into two connected limit cycles. In physical space the period doubling appears as the shedding of two distinct types of vortex filaments.Further increases of the Reynolds number result in a cascade of period-doubling bifurcations, which create a chaotic state in the flow at a Reynolds number of about 500. The flow is characterized by broadband power spectra, and the appearance of intermittent phenomena. It is concluded that the wake undergoes transition to turbulence following the period-doubling route.

On a circular cylinder in a steady wind at transition Reynolds numbers

1960 ◽  
Vol 9 (4) ◽  
pp. 603-612 ◽  
Author(s):  
John S. Humphreys
Keyword(s):  
Experimental Investigation ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Subsonic Flow ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Cylinder Surface ◽  
Visualization Technique ◽  
Cell Pattern ◽  
Critical Range

Some results of an experimental investigation of forces associated with the subsonic flow of air around a circular cylinder in a wind tunnel are presented. The oscillating forces due to the downstream vortex street are studied for Reynolds numbers in the ‘critical’ range 4 × 104 to 6 × 105. Of particular interest is the observation, at the onset of transition to turbulence, of a spanwise wave or cell pattern near the cylinder surface, which is stabilized in a striking manner by the use of the fine threads as a visualization technique.

Laminar flow of an incompressible fluid past a bluff body: the separation, reattachment, eddy properties and drag

1979 ◽  
Vol 92 (1) ◽  
pp. 171-205 ◽  
Author(s):  
F. T. Smith
Keyword(s):  
Circular Cylinder ◽  
Large Scale ◽  
Bluff Body ◽  
Reynolds Numbers ◽  
The Body ◽  
Navier Stokes ◽  
Pressure Drag ◽  
Body Scale ◽  
Flow Situation ◽  
Large Scale Flow

The asymptotic theory for the laminar, incompressible, separating and reattaching flow past the bluff body is based on an extension of Kirchhoff's (1869) free-streamline solution. The flow field (only the upper half of which is discussed since we consider a symmetric body and flow) consists of two basic parts. The first is the flow on the body scalel*, which is described to leading order by the Kirchhoff solution with smooth inviscid separation, but with an$O(Re^{-\frac{1}{16}})$modification to explain fully the viscous separation (hereRe([Gt ] 1) is the Reynolds number). The influence of this$O(Re^{-\frac{1}{16}})$modification is determined for the circular cylinder. The second part is the large-scale flow, comprising mainly the eddy and the ultimate wake. The eddy has length scaleO(Rel*), widthO(Re½l*) and is of elliptical shape to keep the eddy pressure almost uniform. The ultimate wake is determined numerically and fixes the eddy length. The (asymptotically small) back pressure from the eddy acts (on the body scale) both in the free stream and in the eddy, and it has a marked effect at moderate Reynolds numbers; combined with the Kirchhoff solution, it predicts the pressure drag on a circular cylinder accurately, to within 10% whenRe= 5 and to within 4% whenRe= 50. Other predictions, for the eddy length and width, the front pressure and the eddy pressure, also show encouraging agreement with experiments and Navier-Stokes solutions at moderate Reynolds numbers (of about 30), both for the circular cylinder and the normal flat plate. Finally, an analysis in the appendix indicates that, in wind-tunnel experiments, the tunnel walls (even if widely spaced) can exert considerable influence on the eddy properties, eventually forcing an upper bound on the eddy width asReincreases instead of theO(l*Re½) growth appropriate to the unbounded flow situation.

The Near-Wake of a Circular Cylinder in Crossflow

1968 ◽  
Vol 90 (4) ◽  
pp. 476-483 ◽  
Author(s):  
F. B. Hanson ◽  
P. D. Richardson
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Digital Computer ◽  
Large Body ◽  
Reynolds Numbers ◽  
Hot Wire ◽  
Near Wake ◽  
Random Data ◽  
Hot Wire Anemometry

The flow in the near-wake of a circular cylinder was measured with hot-wire anemometry. Processing of the large body of data on unsteady features of the flow was aided with a digital computer. The major sets of results are for Reynolds numbers of 10,600 and 53,000. The results are presented in several complementary forms. In discussion of the results it is shown how they relate to the generation and maintenance of the Strouhal frequency, the existence and discussion of velocity spikes, the control of heat transfer, and to greater irregularity at lower Reynolds numbers. Some issues are raised in the processing of nonstationary random data.

On the Organization of Flow and Heat Transfer in the Near Wake of a Circular Cylinder in Steady and Pulsed Flow

1992 ◽  
Vol 114 (3) ◽  
pp. 348-355 ◽  
Author(s):  
D. P. Telionis ◽  
M. Gundappa ◽  
T. E. Diller
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Skin Friction ◽  
Power Spectra ◽  
Reynolds Numbers ◽  
Driving Frequency ◽  
Near Wake ◽  
Flow And Heat Transfer ◽  
Pulsed Flow ◽  
Oncoming Stream

Skin friction, pressure, and heat transfer gages are employed to monitor the flow and heat transfer field along the periphery of a circular cylinder in steady and pulsed flow at Reynolds numbers, Re = 23,000 to 50,000. Averaged distributions, RMS, and power spectra of all measurements are displayed. Special attention is directed at the organization of the near wake, as detected by the three types of surface gages. The response of the wake to pulsing of the oncoming stream is also examined. It is found that when the wake is locked on the driving frequency, the basic character of the flow is not changed, but the organized motion stands out more clearly. Moreover, the signals become cleaner and background noise in the spectra is reduced. Skin friction and heat transfer gages are shown to respond to local variations of the corresponding quantities, whereas pressure gages respond to global characteristics of the flow.

The Flow Around an Impulsively Started Square Prism

2010 ◽  
Author(s):  
Nelson Tonui ◽  
David Sumner
Keyword(s):  
Circular Cylinder ◽  
Recirculation Zone ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Temporal Development ◽  
Near Wake ◽  
Towing Tank ◽  
Streamwise Location ◽  
Square Prism ◽  
Image Velocimetry

The flow around a square prism impulsively set into motion was studied experimentally using particle image velocimetry (PIV). The experiments were conducted in an X-Y towing tank for Reynolds numbers from Re = 200 to 1000 and dimensionless acceleration parameters from a* = 0.5 to 10. The temporal development of the near-wake recirculation zone, and its pair of primary eddies, was examined from the initial start until the wake became asymmetric. When considering the time elapsed from the start of motion, the temporal development of the wake was sensitive the initial acceleration. “Impulsively started” conditions were effectively attained for a* ≥ 3. However, when considering the distance traveled from the start of motion, the wake parameters were sensibly independent of a* for a* ≥ 0.5. Concerning the temporal development of the recirculation zone, the length of the recirculation zone, the streamwise location of the primary eddies, and the strength of the primary eddies increased with time following the impulsive start, while the cross-stream spacing of the eddy centres remained nearly constant. The recirculation zone of the square prism was longer than that of the impulsively started circular cylinder but shorter than an impulsively started flat plate. For t* > 2, the primary eddy strength, maximum vorticity, and cross-stream spacing of the primary eddies were the same for both the square prism and circular cylinder.

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