Effect of Channel Inlet Blockage on the Wake Structure of a Rotationally Oscillating Cylinder

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
S. Kumar
Keyword(s):  
Mode Shape ◽  
Channel Wall ◽  
Shape Change ◽  
Vortex Street ◽  
Channel Width ◽  
Channel Inlet ◽  
Oscillating Cylinder ◽  
Wake Structure ◽  
Freestream Velocity ◽  
Cylinder Diameter

This paper investigates, experimentally for the first time, the effect of channel inlet blockage induced by bringing the channel inlet walls closer together on the wake structure of a rotationally oscillating cylinder. The cylinder is placed symmetrically inside the channel inlet. The Reynolds number (based on constant upstream channel inlet freestream velocity) is 185, and three channel wall spacings of two, four, and eight cylinder diameters are used. Cylinder oscillation amplitudes vary from π/8 to π, and normalized forcing frequencies vary from 0 to 5. The diagnostics is done using hydrogen-bubble flow visualization, hot-wire anemometry, and particle image velocimetry (PIV). It is found that rotational oscillations induce inverted-vortex-street formation at channel width of two cylinder diameter where there is no shedding in unforced case. The channel wall boundary layers at this spacing undergo vortex-induced instability due to vortex shedding from cylinders and influence the mechanism of inverted-vortex-street formation near the cylinder. At channel width of four cylinder diameter, the inverted-vortex-street is still present but the mode shape change seen at normalized forcing frequency of 1.0 in the absence of channel walls is delayed due to the presence of nearby walls. The wake structure is observed to resemble the wake structure in unbounded domain case at channel width of eight cylinder diameter with some effect of channel walls on forcing parameters where mode shape change occurs. The lock-on diagram is influenced by the closeness of the channel walls, with low-frequency boundary moving to lower frequencies at smallest channel width.

scholarly journals The Natural Oscillations of an Ice-Covered Channel

1984 ◽  
Vol 30 (106) ◽  
pp. 313-320
Author(s):  
Theodore Green
Keyword(s):  
Dispersion Relation ◽  
Mode Shape ◽  
Channel Wall ◽  
Natural Oscillations ◽  
Natural Modes ◽  
Hydrostatic Approximation

AbstractThe natural modes of oscillation of an infinitely long, ice covered channel are considered, using the hydrostatic approximation, and assuming the ice to behave elastically. The dispersion relation, mode shape, and associated force on the channel wall are found for the lowest three modes. Special attention is paid to the limitations associated with the hydrostatic and elastic approximations.

scholarly journals The Natural Oscillations of an Ice-Covered Channel

1984 ◽  
Vol 30 (106) ◽  
pp. 313-320 ◽  
Author(s):  
Theodore Green
Keyword(s):  
Dispersion Relation ◽  
Mode Shape ◽  
Channel Wall ◽  
Natural Oscillations ◽  
Natural Modes ◽  
Hydrostatic Approximation

Abstract The natural modes of oscillation of an infinitely long, ice covered channel are considered, using the hydrostatic approximation, and assuming the ice to behave elastically. The dispersion relation, mode shape, and associated force on the channel wall are found for the lowest three modes. Special attention is paid to the limitations associated with the hydrostatic and elastic approximations.

scholarly journals Configuration and Optimization of a Minichannel Using Water–Alumina Nanofluid by Non-Dominated Sorting Genetic Algorithm and Response Surface Method

Nanomaterials ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 901 ◽  
Author(s):  
Ali Akbar Ahmadi ◽  
Masoud Arabbeiki ◽  
Hafiz Muhammad Ali ◽  
Marjan Goodarzi ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Response Surface ◽  
Channel Width ◽  
Pumping Power ◽  
Nsga Ii ◽  
Square Channel ◽  
Cylinder Diameter ◽  
Input Variables ◽  
Volume Method

Nanofluids in minichannels with various configurations are applied as cooling and heating fluids. Therefore, it is essential to have an optimal design of minichannels. For this purpose, a square channel with a cylinder in the center connected to wavy fins at various concentrations of an Al2O3 nanofluid is simulated using the finite volume method (FVM). Moreover, central composite design (CCD) is used as a method of design of experiment (DOE) to study the effects of three input variables, namely the cylinder diameter, channel width, and fin radius on the convective heat transfer and pumping power. The impacts of the linear term, together with those of the square and interactive on the response variables are determined using Pareto and main effects plots by an ANOVA. The non-dominated sorting genetic algorithm-II (NSGA-II), along with the response surface methodology (RSM) is applied to achieve the optimal configuration and nanofluid concentration. The results indicate that the effect of the channel width and cylinder diameter enhances about 21% and 18% by increasing the concentration from 0% to 5%. On the other hand, the pumping power response is not sensitive to the nanofluid concentration. Besides, the channel width has the highest and lowest effect on the heat transfer coefficient (HTC) and pumping power, respectively. The optimization for a concentration of 3% indicates that in Re = 500 when the geometry is optimized, the HTC enhances by almost 9%, while the pumping power increases by about 18%. In contrast, by increasing the concentration from 1% to 3%, merely an 8% enhancement in HTC is obtained, while the pumping power intensifies around 60%.

Effects of channel width on film condensation in a top-closed vertical channel

2008 ◽  
Vol 222 (9) ◽  
pp. 1763-1771
Author(s):  
T B Chang ◽  
F J Wang
Keyword(s):  
Shear Stress ◽  
Channel Wall ◽  
Vertical Channel ◽  
Transformation Method ◽  
Channel Width ◽  
Film Condensation ◽  
Governing Equations ◽  
Apparent Effect ◽  
Saturated Vapour ◽  
Condensate Layer

This article conducts a theoretical investigation into the condensation of a saturated vapour within a top-closed, vertical isothermal channel. The theoretical model takes account of the inertia and convection effects in a condensate layer and the shear stress at the liquid—vapour interface. Using a dimensionless transformation method, the complex partial differential governing equations are transformed into a corresponding system of ordinary differential equations, which are then solved using the forward Runge—Kutta shooting scheme. Numerical results indicate that the condensate flowrate decreases and the negative shear stress at the liquid—vapour interface increases as the channel width is reduced. Conversely, a larger channel width increases the shear stress at the channel wall, but has no apparent effect on the temperature profile within the condensate layer.

Flow past a rotationally oscillating cylinder with an attached flexible filament

2021 ◽  
Vol 930 ◽  
Author(s):  
Puja Sunil ◽  
Sanjay Kumar ◽  
Kamal Poddar
Keyword(s):  
Control Volume ◽  
Transverse Velocity ◽  
Experimental Studies ◽  
Vortex Street ◽  
Oscillating Cylinder ◽  
Karman Vortex Street ◽  
Flexible Filament ◽  
Flow Past ◽  
Kármán Vortex Street ◽  
Karman Vortex

Experimental studies are conducted on a rotationally oscillating cylinder with an attached flexible filament at a Reynolds number of 150. Parametric studies are carried out to investigate the effect of cylinder forcing parameters and filament stiffness on the resultant wake structure. The diagnostics are flow visualization using the laser-induced fluorescence technique, frequency measurement using a hot film, and characterization of the velocity and vorticity field using planar particle image velocimetry. The streamwise force and power are estimated through control volume analysis, using a modified formulation, which considers the streamwise and transverse velocity fluctuations in the wake. These terms become important in a flow field where asymmetric wakes are observed. An attached filament significantly modifies the flow past a rotationally oscillating cylinder from a Bénard–Kármán vortex street to a reverse Bénard–Kármán vortex street, albeit over a certain range of Strouhal number, $St_{A} \sim 0.25\text {--}0.5$ , encountered in nature in flapping flight/fish locomotion and in the flow past pitching airfoils. The transition from a Kármán vortex street to a reverse Kármán vortex street precedes the drag-to-thrust transition. The mechanism of unsteady thrust generation is discussed. Maximum thrust is generated at the instants when vortices are shed in the wake from the filament tip. At $St_{A} > 0.4$ , a deflected wake associated with the shedding of an asymmetric vortex street is observed. Filament flexibility delays the formation of an asymmetric wake. Wake symmetry is governed by the time instant at which a vortex pair is shed in the wake from the filament tip.

scholarly journals Determining the effects of surface elasticity and surface stress by measuring the shifts of resonant frequencies

2013 ◽  
Vol 469 (2159) ◽  
pp. 20130449 ◽  
Author(s):  
Y. Zhang ◽  
L. J. Zhuo ◽  
H. S. Zhao
Keyword(s):  
Resonant Frequency ◽  
Mode Shape ◽  
Surface Stress ◽  
Atomistic Simulation ◽  
Shape Change ◽  
Surface Elasticity ◽  
Axial Loading ◽  
Practical Method ◽  
Resonant Frequencies

Both surface elasticity and surface stress can result in changes of resonant frequencies of a micro/nanostructure. There are infinite combinations of surface elasticity and surface stress that can cause the same variation for one resonant frequency. However, as shown in this study, there is only one combination resulting in the same variations for two resonant frequencies, which thus provides an efficient and practical method of determining the effects of both surface elasticity and surface stress other than an atomistic simulation. The errors caused by the different models of surface stress and mode shape change due to axial loading are also discussed.

Damage Detection of Cantilever Beams Based on Derivatives of Mode Shapes

2014 ◽  
Vol 488-489 ◽  
pp. 817-820
Author(s):  
Jin Quan Guo ◽  
Fen Lan Ou ◽  
Jian Feng Zhong ◽  
Shun Cong Zhong ◽  
Xiao Xiang Yang ◽  
...  
Keyword(s):  
Mode Shape ◽  
Crack Detection ◽  
Shape Change ◽  
Approximation Error ◽  
Mode Shapes ◽  
Difference Approximation ◽  
Cantilever Beams ◽  
Crack Location ◽  
Displacement Mode ◽  
Derivatives Of

For the small crack detection (crack ration less than 5%), the derivatives of mode shapes of cantilever beams were used for crack detection in the beams. These derivatives consist of the slope, curvature and rate of curvature, which are the first, second and third derivatives of the displacement mode shape respectively. The presence of a crack results in a slight change in the mode shape of a structure which is manifested as a small discontinuity in the response at the crack location. It is hard to detect small cracks in beams using the direct data of mode shape change. But when the first, second and third derivatives of the displacement mode shape, that is the slope, curvature and rate of curvature, respectively, of the cracked cantilever beam provide a progressively better indication of the presence of a crack. However, `noise' effects due to the difference approximation error also begin to be magnified at higher derivatives so that it is not advantageous to go beyond the third derivatives of mode shapes. For the intact beam, these derivatives are smooth curves. So the local peaks or discontinuity on the slope, curvature and rate of curvature modal curves can be used to indicate abnormal mode shape changes at those positions. In this way, these local peak positions can be used to detect and locate cracks in the structure. The modal responses of the damaged and intact cantilever beams used were computed using the finite element method.

Formation of a vortex street behind an oscillating cylinder

1995 ◽  
Vol 30 (1) ◽  
pp. 40-44 ◽  
Author(s):  
Ya. D. Afanasyev ◽  
I. A. Filippov
Keyword(s):  
Vortex Street ◽  
Oscillating Cylinder
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