An Investigation of the Wake Structure and Aerodynamic Characteristics of a Finite Circular Cylinder. 2nd Report. Organized Fluctuating Surface Pressures and Fluctuating Fluid Forces acting on Finite Cylinders with Various Aspect Ratios.

Recent advancement of LES (Large Eddy Simulation) technique for turbulent wake has made it possible to numerically investigate the turbulence effects on aerodynamic characteristics of a bluff body. Here we carry out LES of wake flows past a circular cylinder in the subcritical Reynolds number regime. For inflow boundary condition, homogeneous turbulence generated statistically is given time-sequentially. We bring into focus the interaction between the oncoming turbulence and the shear layer separated from a circular cylinder. Shear layer instability easily occurs under such a stimulation and details of its behavior are visualized. Turbulence effects on unsteady flows in the cylinder wake are discussed. The resulting aerodynamic characteristics and their physical mechanism are clarified.

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The Hydrodynamic Forces Acting on a Long Flexible Circular Cylinder Responding to VIV

Volume 9: 6th FSI, AE and FIV and N Symposium ◽

10.1115/pvp2006-icpvt-11-93896 ◽

2006 ◽

Cited By ~ 3

Author(s):

P. W. Bearman ◽

F. J. Huera Huarte ◽

J. R. Chaplin

Keyword(s):

Circular Cylinder ◽

Cross Flow ◽

Element Model ◽

Transverse Force ◽

Diameter Ratio ◽

Mass Ratio ◽

Force Coefficients ◽

Fluid Forces ◽

Maximum Value ◽

Vibration Prediction

Distributions of the fluid forces acting along a long flexible circular cylinder free to respond in-line and transverse to a stepped current are presented. Forces are calculated using a finite element model of the cylinder with measured responses providing the input. The length to diameter ratio of the model used was 469, the mass ratio was 3 and the Reynolds number could be varied up to maximum value of approximately 2.6 · 104. Fluid force coefficients for two cases are presented: in the first, the dominant modes are the 2nd cross-flow and the 4th in line. For the second case the leading modes are the 7th and 12th respectively. In general, transverse force coefficients and in-line drag coefficients are found to be larger than those measured for short sections of cylinder undergoing free and forced one and two-dimensional motions. It is anticipated that the results will be of value to developers of vortex-induced vibration prediction methods.

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Effect of Selectively Applied Surface Roughness and Wake Splitter Plate on the Aerodynamic Characteristics of a Circular Cylinder

Lecture Notes in Mechanical Engineering - Advances in Fluid and Thermal Engineering ◽

10.1007/978-981-13-6416-7_65 ◽

2019 ◽

pp. 697-705

Author(s):

Shruthi Sivadas ◽

K. Arun Kumar ◽

R. Ajith Kumar

Keyword(s):

Surface Roughness ◽

Circular Cylinder ◽

Aerodynamic Characteristics ◽

Splitter Plate

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Three-dimensional instabilities in oscillatory flow past elliptic cylinders

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.319 ◽

2016 ◽

Vol 798 ◽

pp. 371-397 ◽

Cited By ~ 1

Author(s):

José P. Gallardo ◽

Helge I. Andersson ◽

Bjørnar Pettersen

Keyword(s):

Circular Cylinder ◽

Flow Direction ◽

Three Dimensional ◽

Circular Cylinders ◽

Flow Structures ◽

Three Dimensional Flow ◽

Elliptical Cross ◽

Dimensional Flow ◽

Aspect Ratios ◽

Flow Past

We investigate the early development of instabilities in the oscillatory viscous flow past cylinders with elliptic cross-sections using three-dimensional direct numerical simulations. This is a classical hydrodynamic problem for circular cylinders, but other configurations have received only marginal attention. Computed results for some different aspect ratios ${\it\Lambda}$ from 1 : 1 to 1 : 3, all with the major axis of the ellipse aligned in the main flow direction, show good qualitative agreement with Hall’s stability theory (J. Fluid Mech., vol. 146, 1984, pp. 347–367), which predicts a cusp-shaped curve for the onset of the primary instability. The three-dimensional flow structures for aspect ratios larger than 2 : 3 resemble those of a circular cylinder, whereas the elliptical cross-section with the lowest aspect ratio of 1 : 3 exhibits oblate rather than tubular three-dimensional flow structures as well as a pair of counter-rotating spanwise vortices which emerges near the tips of the ellipse. Contrary to a circular cylinder, instabilities for an elliptic cylinder with sufficiently high eccentricity emerge from four rather than two different locations in accordance with the Hall theory.

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Vibration analysis of a rotor supported on magnetorheological squeeze film damper with short bearing approximation: A contrast between short and long bearing approximations

Journal of Vibration and Control ◽

10.1177/1077546315601298 ◽

2015 ◽

Vol 23 (11) ◽

pp. 1792-1808 ◽

Cited By ~ 6

Author(s):

Mostafa Irannejad ◽

Abdolreza Ohadi

Keyword(s):

Dynamic Behavior ◽

Electrical Current ◽

Magnetorheological Fluid ◽

Squeeze Film ◽

Fluid Viscosity ◽

Squeeze Film Damper ◽

Fluid Forces ◽

Rotating Systems ◽

Aspect Ratios ◽

Variable Damping

Squeeze film dampers are widely used to reduce the vibration of rotating systems. Using magnetorheological fluid in these dampers can lead to a variable-damping damper called Magnetorheological Squeeze Film Damper (MRSFD). Magnetorheological fluid viscosity alter under different values of magnetic field. The previous research have widely used long bearing approximation to derive the equations governing the hydrodynamic behavior of MRSFDs. In this paper, the behavior of MRSFDs has been studied using short bearing approximation. Next, the effects of MRSFDs on the dynamic behavior of a flexible rotor have been studied, using finite element method (FEM). Synchronous whirl motion has not been imposed on the system behavior, as an external assumption. Damper pressure distribution and forces, dynamic trajectories, eccentricity and the frequency response of the rotor are tools used to analyze the dynamic behavior of MRSFDs and rotor system. As the results show, it seems to be more precise to use short bearing approximation to analyze dampers with aspect ratios lower than a limit (especially L/D < 1). Furthermore, by controlling electrical current one can control the dynamic behavior of a rotor, to avoid failure and damage. Finally, the whirl motion of the rotor was observed to remain synchronous, even when fluid forces are present.

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