scholarly journals Computational and Experimental Study of Turbulent Flow Past an Array of Bluff Bodies Aligned Along the Channel Axis

1997 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shih-Hui Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Channel Height ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Height Ratio ◽  
Channel Axis ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Phase Cycle

Computations and measurements of time mean velocities, total fluctuation intensities, and Reynolds stresses are presented for spatially periodic flows past an array of bluff bodies aligned along the channel axis. The Reynolds number based on the channel hydraulic diameter and cross-sectional bulk mean velocity, the pitch to rib-height ratio, and the rib-height to channel-height ratio were 2 × 104, 10, and 0.133, respectively. The unsteady phase-averaged Navier-Stokes equations were solved using a Reynolds stress model with wall function and wall-related pressure strain treatment to reveal the feature of examined unsteady vortex shedding flow. Laser Doppler velocimetry measurements were performed to measure the velocity filed. Code verifications were performed through comparisons with others’ measured developing single-rib flow and our measured fully developed rib-array flow. The computed results and measured data are found in reasonable agreement, which justifies the turbulence model adopted. The calculated phase-averaged flow field clearly displays the vortex shedding behind the rib and is characterized in terms of shedding Strouhal number, vortex trajectory, vortex celerity, and vortex travelling distance in a phase cycle. Furthermore, the difference between the computed developing single-rib flow and fully developed rib-array flow is addressed.

Turbulent Flow Past an Array of Bluff Bodies Aligned Along the Channel Axis

1998 ◽  
Vol 120 (3) ◽  
pp. 520-530 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shih-Hui Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Channel Height ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Height Ratio ◽  
Channel Axis ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Phase Cycle

Computations and measurements of time mean velocities, total fluctuation intensities, and Reynolds stresses are presented for spatially periodic flows past an array of bluff bodies aligned along the channel axis. The Reynolds number based on the channel hydraulic diameter and cross-sectional bulk mean velocity, the pitch to rib-height ratio, and the rib-height to channel-height ratio were 2 × 104, 10, and 0.13, respectively. The unsteady phase-averaged Navier-Stokes equations were solved using a Reynolds stress model with wall function and wall-related pressure strain treatment to reveal the feature of examined unsteady vortex shedding flow. Laser Doppler velocimetry measurements were performed to measure the velocity field. Code verifications were performed through comparisons with others’ measured developing single-rib flow and our measured fully developed rib-array flow. The possible causes for the differences between the experiments and computations are discussed. The calculated phase-averaged flow field clearly displays the vortex shedding behind the rib and is characterized in terms of shedding Strouhal number, vortex trajectory, vortex celerity, and vortex travelling distance in a phase cycle. Furthermore, the difference between the computed developing single-rib flow and fully developed rib-array flow is addressed.

LDV Measurements of Spatially Periodic Flows Over a Detached Solid-Rib Array

1997 ◽  
Vol 119 (2) ◽  
pp. 383-389 ◽  
Author(s):  
Tong-Miin Liou ◽  
Chih-Ping Yang ◽  
Hsin-Li Lee
Keyword(s):  
Fluid Dynamic ◽  
Turbulent Shear ◽  
Parameter Distribution ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Height Ratio ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Periodic Flows ◽  
Spatially Periodic

Measurements of mean velocities, turbulence intensities, and Reynolds stresses are presented for spatially periodic flows in a duct of width-to-height ratio 2 with a detached solid-rib array. The Reynolds number based on the duct hydraulic diameter and cross-sectional bulk mean velocity (Ub), the pitch to rib-height ratio, and the rib-height to duct-height ratio were 2 × 104, 10, and 0.133, respectively. The rib-detached-distance to rib-height ratio was varied from 0 to 3.25 (duct axis) to study its effect on wake length and asymmetry, convective velocity and turbulent kinetic energy immediately behind the rib, maximum turbulent shear stress, and turbulence anisotropy. The results showed that the dominant fluid dynamic factors responsible for the reported peak values of local Nusselt number around the detached rib could be identified. Moreover, the turbulence structure parameter distribution and anisotropy were analyzed to examine the basic assumptions embedded in the turbulence models. Furthermore, the secondary-flow mean velocities were found to be one to two order of magnitude smaller than Ub.

Numerical Investigation of Flow Around Bluff Bodies

1998 ◽  
Vol 14 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Chou-Jiu Tsai ◽  
Ger-Jyh Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Near Wake ◽  
Navier Stokes Equations ◽  
Physical Description ◽  
Geometrical Shapes ◽  
Flow Phenomena ◽  
Volume Method

ABSTRACTIn this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.

scholarly journals Coherent structures in the linearized impulse response of turbulent channel flow

2019 ◽  
Vol 863 ◽  
pp. 1190-1203 ◽  
Author(s):  
Sabarish B. Vadarevu ◽  
Sean Symon ◽  
Simon J. Illingworth ◽  
Ivan Marusic
Keyword(s):  
Channel Flow ◽  
Coherent Structures ◽  
Large Scale ◽  
Body Force ◽  
Stokes Equations ◽  
Turbulent Channel Flow ◽  
Kinetic Energy Density ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Velocity Fluctuations

We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at $Re_{\unicode[STIX]{x1D70F}}=10\,000$. Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices; some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.

Direct simulations of low-Reynolds-number turbulent flow in a rotating channel

1993 ◽  
Vol 256 ◽  
pp. 163-197 ◽  
Author(s):  
Reidar Kristoffersen ◽  
Helge I. Andersson
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Complete Suppression ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Computational Mesh ◽  
Developed Pressure ◽  
Rotating Channel

Direct numerical simulations of fully developed pressure-driven turbulent flow in a rotating channel have been performed. The unsteady Navier–Stokes equations were written for flow in a constantly rotating frame of reference and solved numerically by means of a finite-difference technique on a 128 × 128 × 128 computational mesh. The Reynolds number, based on the bulk mean velocity Um and the channel half-width h, was about 2900, while the rotation number Ro = 2|Ω|h/Um varied from 0 to 0.5. Without system rotation, results of the simulation were in good agreement with the accurate reference simulation of Kim, Moin & Moser (1987) and available experimental data. The simulated flow fields subject to rotation revealed fascinating effects exerted by the Coriolis force on channel flow turbulence. With weak rotation (Ro = 0.01) the turbulence statistics across the channel varied only slightly compared with the nonrotating case, and opposite effects were observed near the pressure and suction sides of the channel. With increasing rotation the augmentation and damping of the turbulence along the pressure and suction sides, respectively, became more significant, resulting in highly asymmetric profiles of mean velocity and turbulent Reynolds stresses. In accordance with the experimental observations of Johnston, Halleen & Lezius (1972), the mean velocity profile exhibited an appreciable region with slope 2Ω. At Ro = 0.50 the Reynolds stresses vanished in the vicinity of the stabilized side, and the nearly complete suppression of the turbulent agitation was confirmed by marker particle trackings and two-point velocity correlations. Rotational-induced Taylor-Görtler-like counter-rotating streamwise vortices have been identified, and the simulations suggest that the vortices are shifted slightly towards the pressure side with increasing rotation rates, and the number of vortex pairs therefore tend to increase with Ro.

Particle Image Velocimetry Measurements in a Two-Pass 90 Degree Ribbed-Wall Parallelogram Channel

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Tong-Miin Liou ◽  
Shyy-Woei Chang ◽  
Shu-Po Chan ◽  
Yu-Shuai Liu
Keyword(s):  
Particle Image Velocimetry ◽  
Secondary Flow ◽  
Particle Image ◽  
Separation Bubble ◽  
Channel Height ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Local Flow ◽  
Image Velocimetry ◽  
Sharp Turn

A parallelogram channel has drawn very little or no attention in the open literature although it appears as a cross-sectional configuration of some gas turbine rotor blades. Particle image velocimetry (PIV) is presented of local flow structure in a two-pass 90 deg ribbed-wall parallelogram channel with a 180 deg sharp turn. The channel has a cross-sectional equal length, 45.5 mm, of adjacent sides and two pairs of opposite angles are 45 deg and 135 deg. The rib height to channel height ratio is 0.1. All the measurements were performed at a fixed Reynolds number, characterized by channel hydraulic diameter of 32.17 mm and cross-sectional bulk mean velocity, of 10,000 and a null rotating number. Results are discussed in terms of the distributions of streamwise and secondary-flow mean velocity vector, turbulent intensity, Reynolds stress, and turbulent kinetic energy of the cooling air. It is found that the flow is not periodically fully developed in pitchwise direction through the inline 90 deg ribbed straight inlet and outlet leg. Pitchwise variation of reattachment length is revealed, and comparison with reported values in square channels is made. Whether the 180 deg sharp turn induced separation bubble exists in the ribbed parallelogram channel is also documented. Moreover, the measured secondary flow results inside the turn are successively used to explain previous heat transfer trends.

Vortex shedding and lock-on of a circular cylinder in oscillatory flow

1986 ◽  
Vol 170 ◽  
pp. 527-544 ◽  
Author(s):  
C. Barbi ◽  
D. P. Favier ◽  
C. A. Maresca ◽  
D. P. Telionis
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Published Data ◽  
Bluff Bodies ◽  
Driving Frequency ◽  
Frequency Limit ◽  
Mean Velocity ◽  
Shedding Frequency ◽  
Friction Measurements

An experimental study has been made of a circular cylinder in steady and oscillatory flow with non-zero mean velocity up to a Reynolds number of 40000. The results for the stationary cylinder are in close agreement with previously published data. Skin-friction measurements revealed the amplitude of fluctuation of the boundary layer for different angular locations. It has been universally accepted that bluff bodies shed vortices at their natural frequency of shedding (Strouhal frequency), or, when synchronized with an external unsteadiness, at the frequency of the disturbance or half of it, depending of the direction of the unsteadiness. Our findings, instead, indicate that the shedding frequency may vary smoothly with the driving frequency before locking on its subharmonic. Moreover, the present results indicate that, at the lowest frequency limit of lock-on, vortices are shed simultaneously on both sides of the model. A more traditional alternate pattern of vortex shedding is then recovered at higher driving frequencies.

Laminar flow through slots

1988 ◽  
Vol 190 ◽  
pp. 179-200 ◽  
Author(s):  
E. G. Tulapurkara ◽  
B. H. Lakshmana Gowda ◽  
N. Balachandran
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Flow Visualization ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Computer Code ◽  
Channel Height ◽  
Visualization Technique ◽  
Recirculating Flow ◽  
Flow Through

Laminar flow through slots is investigated using a flow-visualization technique and the numerical solution of the Navier-Stokes equations for steady flow. In the flow situation studied here, the fluid enters an upper channel blocked at the rear end and leaves through a lower channel blocked at the front end. The two channels are interconnected by one, two and three slots. The flow-visualization technique effectively brings out the various features of the flow through slot(s). The ratio of the slot width to the channel height w/h is varied between 0.5 to 4.0 and the Reynolds number Re, based on the velocity at the entry to the channel and the height of the channel, is varied between 300 and 2000. Both w/h and Re influence the flow in general and the extent of the regions of recirculating flow in particular. The Reynolds number at which the vortex shedding begins depends on w/h. Computations are carried out using the computer code 2/E/FIX of Pun & Spalding (1977). The computed flow patterns closely resemble the observed patterns at various Reynolds numbers investigated except around the Reynolds number where the vortex shedding begins.

Velocity characteristics in the turbulent near wakes of confined axisymmetric bluff bodies

1984 ◽  
Vol 139 ◽  
pp. 391-416 ◽  
Author(s):  
A. M. K. P. Taylor ◽  
J. H. Whitelaw
Keyword(s):  
Kinetic Energy ◽  
Bluff Body ◽  
Numerical Solutions ◽  
Equations Of Motion ◽  
Laser Doppler Velocimeter ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Recirculation Length ◽  
Annular Jets

Measurements of the velocity characteristics and wall pressure are reported for the axisymmetric turbulent flow downstream of three bluff bodies (disks of 25% and 50% area blockage and a cone of 25% blockage) confined by a long pipe. The dimensions of the recirculation regions were found from the mean-velocity components, which were determined by a laser-Doppler velocimeter: the corresponding components of Reynolds stress were also recorded. The lengths and maximum widths of the recirculation bubbles (in bluff-body diameters), recirculating mass-flow rates (normalized by the average velocity in the plane of the baffle, U0, and the baffle diameter) and maximum turbulent kinetic energy (normalized by U02) were as follows: cone 1.55, 0.55, 0.19, 0.11; disk (25% blockage) 1.75, 0.62, 0.31, 0.19; disk (50% blockage) 2.20, 0.55, 0.26, 0.16. The increase in recirculation length with blockage is opposite to the trend in unconfined, annular jets. The distribution of Reynolds stresses is strongly dependent on blockage: for the smaller blockage both the disk and the cone have the maximum value of kinetic energy near the rear stagnation point. It is proposed that this is because the generation of turbulence by normal stresses is more important in the flow consequent on the smaller blockage.The measurements include profiles of the velocity characteristics at, as well as upstream of, the trailing edges of the baffles for use as boundary conditions in numerical solutions of the equations of motion.

Fluid Flow Inside a Rectangular Duct With Two Opposite Walls Roughened by Deepened Scales

2009 ◽  
Author(s):  
T. M. Liou ◽  
S. W. Chang ◽  
J. S. Chen ◽  
C. Y. Chan
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Flow Visualization ◽  
Laser Sheet ◽  
Rectangular Channel ◽  
Laminar Flows ◽  
Maximum Depth ◽  
Channel Height ◽  
Mean Velocity ◽  
Cross Sectional

Laser-Doppler velocimetry (LDV) measurements supplemented by numerical simulation and flow visualization were performed to study flow characteristics and explain the reported heat transfer features in a rectangular channel with two opposite walls roughened by deepened scales. The study is lacking in the published literature. Ratios of scale print diameter to channel height, scale maximum depth to channel height and scale pitch to scale maximum depth were 1.0, −0.1, and 10 respectively. The scale-roughened section had a cross-sectional width to height ratio of 8. All measurements were undertaken at a fixed Reynolds number, based on hydraulic diameter and cross-sectional bulk mean velocity, of 10000 with air flows directed forward and downward. Results are documented in terms of distributions of mean velocity components, mean velocity vector field, fluctuation components, and turbulent kinetic energy. The distances attaining periodic fully developed flow condition are identified. Both LDV measurements and laser-sheet flow visualization unravel the presence of near-wall secondary vortex arrays in the cross-sectional planes. The fluid flow results are subsequently used to explain previously published heat transfer trends. The dominant flow dynamic factors are recognized to provide the logic for the differences in heat transfer enhancements attained by the forward and downward channel flows over the scaled walls. A comparison of the computed sizes of cavity trapped vortex illustrates the reported difference in heat transfer augmented by the scale and dimple roughened surfaces as well as by the turbulent and laminar flows.

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