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.

LDV Measurements of Periodic Fully Developed Main and Secondary Flows in a Channel With Rib-Disturbed Walls

1993 ◽  
Vol 115 (1) ◽  
pp. 109-114 ◽  
Author(s):  
T.-M. Liou ◽  
Y.-Y. Wu ◽  
Y. Chang
Keyword(s):  
Kinetic Energy ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Parameter Distribution ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Production Term ◽  
Basic Assumptions

Laser-Doppler velocimeter measurements of mean velocities, turbulence intensities, and Reynolds stresses are presented for periodic fully developed flows in a channel with square rib-disturbed walls on two opposite sides. Quantities such as the vorticity thickness and turbulent kinetic energy are used to characterize the flow. The investigated flow was periodic in space. The Reynolds number based on the channel hydraulic diameter was 3.3×104. The ratios of pitch to rib-height and rib-height to chamber-height were 10 and 0.133, respectively. Regions where maximum and minimum Reynolds stress and turbulent kinetic energy occurred were identified from the results. The growth rate of the shear layers of the present study was compared with that of a backward-facing step. The measured turbulence anisotropy and structure parameter distribution were used to examine the basic assumptions embedded in the k–ε and k–ε–A models. For a given axial station, the peak axial mean-velocity was found not to occur at the center point. The secondary flow was determined to be Prandtl’s secondary flow of the second kind according to the measured streamwise mean vorticity and its production term.

Aerodynamic Characteristics of Asymmetric Bluff Bodies

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
J. C. Hu ◽  
Y. Zhou
Keyword(s):  
Bluff Body ◽  
Laser Doppler Anemometry ◽  
Vortex Formation ◽  
Aerodynamic Characteristics ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Freestream Velocity ◽  
Drag And Lift ◽  
Particle Imaging ◽  
Visualization Techniques

The wake of asymmetric bluff bodies was experimentally measured using particle imaging velocimetry, laser Doppler anemometry, load cell, hotwire, and flow visualization techniques at Re=2600–8500 based on the freestream velocity and the characteristic height of the bluff bodies. Asymmetry is produced by rounding some corners of a square cylinder and leaving others unrounded. It is found that, with increasing corner radius, the flow reversal region is expanded, and the vortex formation length is prolonged. Accordingly, the vortex shedding frequency increases and the base pressure rises, resulting in a reduction in the mean drag as well as the fluctuating drag and lift. It is further found that, while the asymmetric cross section of the cylinder causes the wake centerline to shift toward the sharp corner side of the bluff body, the wake remains globally symmetric about the shifted centerline. The near wake of asymmetric bluff bodies is characterized in detail, including the Reynolds stresses, characteristic velocity, and length scale, and is further compared with that of the symmetric ones.

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.

Evaluation of Turbulence Models for Predicting Buoyant Flows

1990 ◽  
Vol 112 (4) ◽  
pp. 945-951 ◽  
Author(s):  
A. Shabbir ◽  
D. B. Taulbee
Keyword(s):  
Experimental Data ◽  
Kinetic Energy ◽  
Turbulent Transport ◽  
Turbulence Models ◽  
Heat Fluxes ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Buoyant Flows ◽  
Model Equations ◽  
Stress Models

Experimental data for the buoyant axisymmetric plume are used to validate certain closure hypotheses employed in turbulence model equations for calculating buoyant flows. Closure formulations for the turbulent transport of momentum, thermal energy, kinetic energy, and squared temperature used in the k–ε and algebraic stress models are investigated. Experimental data for the mean velocity, mean temperature, and kinetic energy are used in the closure formulation to obtain Reynolds stresses, heat fluxes, etc., which are then compared with their measured values.

Measurements of Losses and Reynolds Stresses in the Secondary Flow Downstream of a Low-Speed Linear Turbine Cascade

2010 ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander ◽  
T. J. Praisner
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Hole Pressure ◽  
The Mean

Experimental measurements of the mean and turbulent flow field were preformed downstream of a low-speed linear turbine cascade. The influence of turbulence on the production of secondary losses is examined. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Each probe was traversed downstream of the cascade along planes positioned at three axial locations: 100%, 120% and 140% of the axial chord (Cx) downstream of the leading edge. The seven-hole pressure probe was used to determine the local total and static pressure as well as the three mean velocity components. The rotatable x-type hotwire probe, in addition to the mean velocity components, provided the local Reynolds stresses and the turbulent kinetic energy. The axial development of the secondary losses is examined in relation to the rate at which mean kinetic energy is transferred to turbulent kinetic energy. In general, losses are generated as a result of the mean flow dissipating kinetic energy through the action of viscosity. The production of turbulence can be considered a preliminary step in this process. The measured total pressure contours from the three axial locations (1.00, 1.20 and 1.40Cx) demonstrate the development of the secondary losses. The peak loss core in each plane consists mainly of low momentum fluid that originates from the inlet endwall boundary layer. There are, however, additional losses generated as the flow mixes with downstream distance. These losses have been found to relate to the turbulent Reynolds stresses. An examination of the turbulent deformation work term demonstrates a mechanism of loss generation in the secondary flow region. The importance of the Reynolds shear stress to this process is explored in detail.

A K—ε—γ equation turbulence model

1992 ◽  
Vol 237 ◽  
pp. 301-322 ◽  
Author(s):  
Ji Ryong Cho ◽  
Myung Kyoon Chung
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulence Model ◽  
Mixing Layer ◽  
Spreading Rate ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Model Equations ◽  
Entrainment Effect ◽  
Intermittency Factor

By considering the entrainment effect on the intermittency in the free boundary of shear layers, a set of turbulence model equations for the turbulent kinetic energy k, the dissipation rate ε, and the intermittency factor γ is proposed. This enables us to incorporate explicitly the intermittency effect in the conventional K–ε turbulence model equations. The eddy viscosity νt is estimated by a function of K, ε and γ. In contrast to the closure schemes of previous intermittency modelling which employ conditional zone averaged moments, the present model equations are based on the conventional Reynolds averaged moments. This method is more economical in the sense that it halves the number of partial differential equations to be solved. The proposed K–ε–γ model has been applied to compute a plane jet, a round jet, a plane far wake and a plane mixing layer. The computational results of the model show considerable improvement over previous models for all these shear flows. In particular, the spreading rate, the centreline mean velocity and the profiles of Reynolds stresses and turbulent kinetic energy are calculated with significantly improved accuracy.

Large-scale vortex structures in turbulent wakes behind bluff bodies. Part 2. Far-wake structures

1987 ◽  
Vol 174 ◽  
pp. 271-298 ◽  
Author(s):  
T. R. Steiner ◽  
A. E. Perry
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Mean Velocity ◽  
Wake Flows ◽  
Wake Patterns ◽  
Large Scale Vortex ◽  
High Reynolds ◽  
Far Wake

An investigation of a selection of high-Reynolds-number bluff-body flows was conducted. Here in Part 2 phase-averaged velocity-field results will be presented for several far-wake flows generated by nominally two-dimensional and three-dimensional bodies. In these far-wake flows the shed vortices have approached a nearly constant convection velocity. Some mean velocity and phase-averaged and global Reynoldsstress measurements are also presented. The turbulent wake of a lift-producing three-dimensional body has been examined. Also included are the phase-averaged wake patterns behind a flapping flag and a windmill. The topological structure of these patterns is discussed and a preliminary classification of wake patterns is presented.

Laboratory studies of the velocity field over deep-water waves

1970 ◽  
Vol 42 (4) ◽  
pp. 733-754 ◽  
Author(s):  
Robert H. Stewart
Keyword(s):  
Velocity Field ◽  
Deep Water ◽  
Water Waves ◽  
Numerical Solutions ◽  
Viscous Sublayer ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Measured Velocity ◽  
The Mean ◽  
Deep Water Waves

The mean-velocity field over monochromatic, 1·96 Hz, deep-water waves was measured by means of hot-wire anemometers for a range of wind speeds (relative to wave speed) of 0·4 to 3·0. The mean-velocity profile, over waves 0·64 cm in amplitude, was the same as that over a rough plate; that is, the mean velocity varied as the logarithm of the height above the mean-water level, except very close to the water, where the effect of the viscous sublayer became important. The wave-induced perturbation-velocity field and its associated Reynolds stresses were also measured and compared with numerical solutions of various linear equations governing shearing flow over a wavy boundary. The comparison showed that the measured velocity field was not well predicted by these theories.

Reynolds Stresses and Dissipation Mechanisms Downstream of a Turbine Cascade

1987 ◽  
Vol 109 (2) ◽  
pp. 258-267 ◽  
Author(s):  
J. Moore ◽  
D. M. Shaffer ◽  
J. G. Moore
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Redundant Data ◽  
Fitting Procedures

An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10 percent of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The measured Reynolds stresses are combined with measured distributions of velocity to show how and where losses are being produced. The mechanisms for the dissipation of mean kinetic energy in this swirling three-dimensional flow are revealed.

An Experimental and Numerical Study of the Isothermal Flowfield Behind a Bluff Body Flameholder

1997 ◽  
Vol 119 (2) ◽  
pp. 328-339 ◽  
Author(s):  
C. N. Raffoul ◽  
A. S. Nejad ◽  
R. D. Gould ◽  
S. A. Spring
Keyword(s):  
Steady State ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Steady State Solution ◽  
Accurate Solution ◽  
State Solution ◽  
Laser Doppler Velocimeter ◽  
Two Dimensional ◽  
Reynolds Stresses

An experimental and numerical investigation was conducted to study the turbulent velocities and stresses behind a two-dimensional bluff body. Simultaneous three-component laser-Doppler velocimeter (LDV) measurements were made in the isothermal incompressible turbulent flowfield downstream of a bluff body placed at midstream in a rectangular test section. Mean velocities and Reynolds stresses were measured at various axial positions. Spanwise velocity measurements indicated that the flow is three dimensional in the recirculation zone of the bluff body. Confidence in the accuracy of the data was gained by calculating the mass fluxes at each axial station. These were found to agree with each other to within ±3 percent. A parallel Computational Fluid Dynamics (CFD) study was initiated to gage the predictive accuracy of currently available CFD techniques. Three solutions were computed: a two-dimensional steady-state solution using the standard k-ε model, a two-dimensional time-accurate solution using the standard k-ε model, and a two-dimensional time-accurate solution using a Renormalized-Group (RNG) k-ε turbulence model. The steady-state solution matched poorly with the data, severely underpredicting the Reynolds stresses in the recirculation zone. The time-accurate solutions captured the unsteady vortex shedding from the base of the bluff body, providing a source for the higher Reynolds stresses. The RNG k-ε solution provided the best match to the data.

Sign in / Sign up

Export Citation Format

Share Document