Phase-Average Mean Flow and Turbulence Structure in a Staggered Cylinder Array Subjected to Pulsating Cross-Flow

2004 ◽  
Vol 126 (3) ◽  
pp. 323-336 ◽  
Author(s):  
E. Konstantinidis ◽  
S. Balabani ◽  
M. Yianneskis
Keyword(s):  
Vortex Shedding ◽  
Laser Doppler Anemometry ◽  
Cross Flow ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Phase Average ◽  
Cylinder Array ◽  
Pulsation Cycle ◽  
Insight Into

The unsteady turbulent flow field in a staggered array of cylinders with streamwise and transverse spacing to diameter ratios of 2.1 and 3.6, respectively, was studied experimentally by means of laser-Doppler anemometry for a Reynolds number of 2300. Flow pulsations in the streamwise direction were employed to control the frequency of vortex shedding in the array as has been previously demonstrated in Konstantinidis et al. [1]. Under these conditions, it was possible to obtain velocity measurements and for each velocity sample assign the phase-angle with respect to the pulsation cycle. This methodology allowed reconstruction of the unsteady (periodic) mean flow and random turbulence fields over an average vortex shedding cycle. The experimental data obtained are analyzed and the results offer a unique insight into the flow processes that take place inside the cylinder array.

An Experimental Study of the Mean Flow and Turbulence Structure Of Cross-Flow Over Tube Bundles

1996 ◽  
Vol 210 (4) ◽  
pp. 317-331 ◽  
Author(s):  
S Balabani ◽  
M Yianneskis
Keyword(s):  
Pressure Drop ◽  
Laser Doppler Anemometry ◽  
Cross Flow ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Time Resolved ◽  
Numerical Predictions ◽  
Dissipation Rates ◽  
Tube Bundles ◽  
The Mean

The velocity characteristics of cross-flow over tube bundles were investigated in a water tunnel. Three tube arrays with a transverse pitch ratio of 3.6 were studied: an in-line and two staggered arrays with longitudinal pitch ratios of 2.1, 1.6 and 2.1 respectively. The mean velocities, turbulence levels, spectra, time and length scales and dissipation rates were determined from ensemble-averaged and time-resolved laser Doppler anemometry (LDA) measurements. The pressure drop across the bundles was also measured. The staggered arrays were found to generate higher levels of turbulence and a higher pressure drop. Turbulence kinetic energy reaches a maximum downstream of the second row in staggered arrays. The wake regions in both geometries are anisotropic with transverse r.m.s. velocities being higher than axial ones. Increasing the longitudinal spacing in the staggered configuration results in lower r.m.s. levels in the wakes and alteration of the recirculation characteristics. A discrete periodicity with a Strouhal number of 0.26 was identified in the 3.6 times 1.6 staggered array which is associated with vortex shedding. Turbulence scales and dissipation rates were estimated and compared with numerical predictions.

scholarly journals The Development of the Mean Flow and Turbulence Structure in an Annular S-Shaped Duct

1994 ◽  
Author(s):  
K. M. Britchford ◽  
J. F. Carrotte ◽  
S. J. Stevens ◽  
J. J. McGuirk
Keyword(s):  
Reynolds Stress ◽  
Laser Doppler Anemometry ◽  
Reynolds Shear Stress ◽  
Turbulence Models ◽  
Test Facility ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Mean Velocity ◽  
Curvature Effects ◽  
The Mean

This paper describes an investigation of the mean and fluctuating flow field within an annular S-shaped duct which is representative of that used to connect the compressor spools of aircraft gas turbine engines. Data was obtained from a fully annular test facility using a 3-component Laser Doppler Anemometry (LDA) system. The measurements indicate that development of the flow within the duct is complex and significantly influenced by the combined effects of streamwise pressure gradients and flow curvature. In addition CFD predictions of the flow, using both the k-ε and Reynolds stress transport equation turbulence models, are compared with the experimental data. Whereas curvature effects are not described properly by the k-ε model, such effects are captured more accurately by the Reynolds stress model leading to a better prediction of the Reynolds shear stress distribution. This, in turn, leads to a more accurate prediction of the mean velocity profiles, as reflected by the boundary layer shape parameters, particularly in the critical regions of the duct where flow separation is most likely to occur.

Velocity measurements in a high-Reynolds-number, momentum-conserving, axisymmetric, turbulent jet

1994 ◽  
Vol 258 ◽  
pp. 31-75 ◽  
Author(s):  
Hussein J. Hussein ◽  
Steven P. Capp ◽  
William K. George
Keyword(s):  
Reynolds Number ◽  
Laser Doppler Anemometry ◽  
Cross Flow ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Third Order ◽  
Burst Mode ◽  
High Turbulence ◽  
High Reynolds ◽  
Velocity Moments

The turbulent flow resulting from a top-hat jet exhausting into a large room was investigated. The Reynolds number based on exit conditions was approximately 105. Velocity moments to third order were obtained using flying and stationary hot-wire and burst-mode laser-Doppler anemometry (LDA) techniques. The entire room was fully seeded for the LDA measurements. The measurements are shown to satisfy the differential and integral momentum equations for a round jet in an infinite environment.The results differ substantially from those reported by some earlier investigators, both in the level and shape of the profiles. These differences are attributed to the smaller enclosures used in the earlier works and the recirculation within them. Also, the flying hot-wire and burst-mode LDA measurements made here differ from the stationary wire measurements, especially the higher moments and away from the flow centreline. These differences are attributed to the cross-flow and rectification errors on the latter at the high turbulence intensities present in this flow (30% minimum at centreline). The measurements are used, together with recent dissipation measurements, to compute the energy balance for the jet, and an attempt is made to estimate the pressure-velocity and pressure-strain rate correlations.

Flow in the Wake of Surface-Mounted Pyramids

2002 ◽  
Author(s):  
Mazen AbuOmar ◽  
Robert J. Martinuzzi
Keyword(s):  
Boundary Layers ◽  
Vortex Shedding ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Reattachment Point ◽  
Flow Surface ◽  
Surface Patterns ◽  
The Mean ◽  
Shedding Frequency ◽  
Pressure And Velocity Measurements

The flow around square-based, wall-mounted pyramids in thin and thick boundary layer was experimentally investigated as a function of the pyramid apex angle, ζ, and, angle of attack, α, based on mean flow surface patterns, pressure and velocity measurements. For thin boundary layers, wake periodicity is observed. For slender pyramids (20° < ζ < 75°), periodic shedding of vortices is observed. The shedding frequency scales with the frontal (projected) width. For broad pyramids, wake periodicity cannot be related to vortex shedding. Vortex shedding appears related to the existence of a double vortex-structure along the side faces of the slender pyramids. For thick boundary layers, no wake periodicity is observed and the mean flow structure resembles that of broad pyramids. In all cases, the separation and reattachment point upstream and downstream of the obstacle scales with the projected frontal area.

CFD Performance Analysis of a Flowmaker

2006 ◽  
Author(s):  
Lasse A. Rosendahl ◽  
Xiaopeng Wang ◽  
Christian B. Jacobsen
Keyword(s):  
Cfd Simulation ◽  
Laser Doppler Anemometry ◽  
Near Field ◽  
Proximity Effects ◽  
Scale Model ◽  
Valuable Insight ◽  
Mean Flow ◽  
Multiple Frame ◽  
Wall Proximity ◽  
Insight Into

In the present work, the mean flow field in a stirred tank equipped with a scale model of a commercially available Grundfos AFG.40.230.35 flowmaker is investigated using CFD simulation and Laser Doppler Anemometry (LDA), in order to provide information on the interaction between flow, propeller and wall proximity. The propeller is placed at a specified location in the tank, and measurements are taken at various locations in the tank to provide as detailed a representation of the resulting flow as possible as well as insight into the near-field of the flowmaker. The simulation, carried out with Ansys CFX 10, used a multiple frame of reference (MFR) approach to include a full representation of the flowmaker blade and motor geometry, to fully include the effects of the blade shape and variable pitch. The reported results are based on a k-e model using a second order discretization scheme. The results show good agreement on downstream axial velocities immediately after the flowmaker, although the numerical results exhibit symmetry to a greater extent than the experimental data, which is believed to be due to a combination of wall proximity effects in the latter and the turbulence model in the latter. However, the results provide valuable insight into the performance of CFD analysis on this type of flow maker, and highlight aspects for future work.

Numerical Simulation of Blood Flow in Patient-Specific Stenotic Carotid Bifurcation Geometries

2009 ◽  
Author(s):  
Megan Cummins ◽  
Jenn S. Rossmann
Keyword(s):  
Vortex Shedding ◽  
Carotid Bifurcation ◽  
Secondary Flows ◽  
Patient Specific ◽  
Mechanical Forces ◽  
Plaque Vulnerability ◽  
Governing Equations ◽  
Unstable Plaque ◽  
Recirculation Zones ◽  
Insight Into

The hemodynamics and fluid mechanical forces in blood vessels have long been implicated in the deposition and growth of atherosclerotic plaque. Detailed information about the hemodynamics in vessels affected by significant plaque deposits can provide insight into the mechanisms and likelihood of plaque weakening and rupture. In the current study, the governing equations are solved in their finite volume formulation in several patient-specific geometries. Recirculation zones, vortex shedding, and secondary flows are captured. The forces on vessel walls are shown to correlate with unstable plaque deposits. The results of these simulations suggest morphological features that may usefully supplement percent stenosis as a predictor of plaque vulnerability.

scholarly journals Vortex-induced vibrations of a long flexible cylinder in shear flow

2011 ◽  
Vol 677 ◽  
pp. 342-382 ◽  
Author(s):  
REMI BOURGUET ◽  
GEORGE E. KARNIADAKIS ◽  
MICHAEL S. TRIANTAFYLLOU
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Transition To Turbulence ◽  
Wave Component ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

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