Laminar flow instability in a rectangular channel with a cylindrical core

2006 ◽  
Vol 18 (4) ◽  
pp. 044108 ◽  
Author(s):  
A. Gosset ◽  
S. Tavoularis
Keyword(s):  
Laminar Flow ◽  
Flow Instability ◽  
Rectangular Channel

scholarly journals Numerical Analysis of Unsteady Laminar Flow past a Pentagonal Obstacle

2021 ◽  
Vol 10 (2) ◽  
pp. 968-974
Keyword(s):  
Laminar Flow ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Time Frame ◽  
Two Dimensional ◽  
Fluid Inertia ◽  
Time Step ◽  
The Face ◽  
Computational Fluid Dynamics Cfd ◽  
Current Article

The current article dispenses the numerical investigation of a two dimensional unsteady laminar flow of incompressible fluid passing a regular pentagonal obstacle in an open rectangular channel. The centre of attention of this work is the comparison of drag coefficients estimated for two distinct cases based on the orientation of face and corner of an obstacle against the flow direction. The numerical results shows that the corner – oriented obstacle bring about 42% larger value of drag coefficient at Re = 500 than face – oriented obstacle. The substantial growth in the expanse of vortex behind obstacle (presented as a function of fluid inertia 25 < Re < 500) is analyzed through the contours and streamline patterns of velocity field. The two eddies in the downstream become entirely unsymmetrical at Re = 500 for both the cases, whereas; the flow separation phenomena occurs a bit earlier in the face – oriented case at Re = 250. Two dimensional Pressure – Based – Segregated solver is employed to model the governing equations written in velocity and pressure fields. The numerical simulations of unsteady flow are presented for 50 seconds time frame with time step 0.01 by using one of the best available commercial based Computational Fluid Dynamics (CFD) software, ANSYS 15.0.

The wake instability in viscoelastic flow past confined circular cylinders

1993 ◽  
Vol 344 (1671) ◽  
pp. 265-304 ◽  
Keyword(s):  
Velocity Field ◽  
Flow Visualization ◽  
Cellular Structure ◽  
Flow Instability ◽  
Rectangular Channel ◽  
Extensional Flow ◽  
Viscoelastic Flow ◽  
Circular Cylinders ◽  
Flow Transition ◽  
Wake Instability

Laser Doppler velocimetry (LDV) and video flow visualization are used to investigate the creeping motion of a highly elastic, constant-viscosity fluid flowing past a cylinder mounted centrally in a rectangular channel. A sequence of viscoelastic flow transitions are documented as the volumetric flow rate past the cylinder is increased and elastic effects in the fluid become increasingly important. Velocity profiles clearly show that elasticity has almost no effect on the kinematics upstream of the cylinder, but that the streamlines in the wake of the cylinder are gradually shifted further downstream . Finite element calculations with a nonlinear constitutive model closely reproduce the evolution of the steady two-dimensional velocity field. However, at a well defined set of flow conditions the steady planar stagnation ow in the downstream wake is experimentally observed to become unstable to a steady, three-dimensional cellular structure. The Reynolds number at the onset of the flow instability is less than 0.05 and inertia plays little role in the flow transition, LDV measurements in the wake close to the cylinder reveal large spatially periodic fluctuations of the streamwise velocity that extend along the length of the cylinder and more than five cylinder radii downstream of the cylinder. Fourier analysis shows that the characteristic spatial wavelength of these flow perturbations scales closely with the cylinder radius R . Flow visualization combined with LDV measurements also indicates that the perturbations in the velocity field are confined to the narrow region of strongly extensional flow near the downstream stagnation point. A second flow transition is observed at higher flow rates that leads to steady translation of the cellular structure along the length of the cylinder and time-dependent velocity oscillations in the wake. Measurements of the flow instability are presented for a range of cylinder sizes, and a stability diagram is constructed which shows that the onset point of the wake instability depends on both the extensional deformation of the fluid in the stagnation flow and the shearing flow between the cylinder and the channel.

The pulsating laminar flow in a rectangular channel

2015 ◽  
Vol 22 (6) ◽  
pp. 733-744 ◽  
Author(s):  
E. P. Valueva ◽  
M. S. Purdin
Keyword(s):  
Laminar Flow ◽  
Rectangular Channel

Theoretical Research on Two-Phase Flow Instability in Parallel Rectangular Channels Under Periodic Perturbation

2020 ◽  
Author(s):  
Libo Qian ◽  
Jian Deng ◽  
Tao Huang ◽  
Rong Cai
Keyword(s):  
Pressure Drop ◽  
Channel Model ◽  
Flow Instability ◽  
Rectangular Channel ◽  
Static Condition ◽  
Periodic Perturbation ◽  
Theoretical Research ◽  
Threshold Power ◽  
Additional Pressure ◽  
Rectangular Channels

Abstract A theoretical model for Density Wave Oscillations (DWOs) flow instability in parallel rectangular channels under periodic heaving motion is established with a lumped mathematical model based on homogenous hypothesis. The parallel rectangular channels comprise of the entrance section, the heating section, the riser section and the upper- and lower plenums, which guarantee the isobaric pressure drop condition between channels and the model consists of boiling channel model, pressure drop model, parallel channel model, additional pressure drop model generated by heaving motions, the constitutive and numerical models. The effect of periodic perturbation is introduced through additional pressure drop in the momentum equation. The model is validated with experimental data of a twin-rectangular-channel flow instability experiment under static condition. Then the flow instability in parallel-rectangular-channel system is studied under periodic perturbation and the margin of flow instability and the threshold power of the system under static condition is calculated as basis condition for comparison. The effect of the amplitude and period of perturbation is analyzed analytically and the results show that the amplitude and period of perturbation shows little effect on flow instability. While when the additional pressure difference introduced by heaving motion is comparable with that under static condition, the effect of amplitude becomes stronger. And the period of perturbation strongly effects the threshold power when it is identical to that of natural period of the system, which can be explained by resonance between the perturbation and the system. And this effect is even stronger when the asymmetric heating condition is introduced.

Hydrodynamics of slug flow in a vertical narrow rectangular channel under laminar flow condition

2014 ◽  
Vol 73 ◽  
pp. 465-477 ◽  
Author(s):  
Yang Wang ◽  
Changqi Yan ◽  
Xiaxin Cao ◽  
Licheng Sun ◽  
Chaoxing Yan ◽  
...  
Keyword(s):  
Laminar Flow ◽  
Flow Condition ◽  
Slug Flow ◽  
Rectangular Channel
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