An experimental investigation of an asymmetrical turbulent wake

1972 ◽  
Vol 53 (4) ◽  
pp. 593-610 ◽  
Author(s):  
M. D. Palmer ◽  
J. F. Keffer
Keyword(s):  
Diffusion Mechanism ◽  
Small Diameter ◽  
Flow Characteristics ◽  
Turbulent Energy ◽  
Turbulent Wake ◽  
The Other ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Spread Rate ◽  
Mean Velocity

Experiments on the two-dimensional turbulent wake generated by pairs of cylinders of unequal diameter have revealed some interesting flow characteristics. The wake width grew asymmetrically in the downstream direction, spread rate and entrainment coefficients proving larger on the small diameter cylinder side. Mean velocity profiles were also skewed to this side while maximum values of Reynolds stresses were larger on the other. Close to the cylinder, a region or turbulent ‘energy reversal’ was measured. The level of turbulence and the diffusion mechanism were high at this point and some comments are made concerning the structure of the flow under these conditions.

Experimental sensitivity analysis of the global properties of a two-dimensional turbulent wake

2012 ◽  
Vol 693 ◽  
pp. 115-149 ◽  
Author(s):  
Vladimir Parezanović ◽  
Olivier Cadot
Keyword(s):  
Turbulent Wake ◽  
Base Pressure ◽  
Recirculation Region ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Recirculation Bubble ◽  
Global Properties ◽  
Bubble Length ◽  
The Impact ◽  
Control Cylinder

AbstractThe sensitivity of the global properties of a two-dimensional turbulent wake produced by the separated flow of a ‘D’-shaped cylinder at $\mathit{Re}= 13\hspace{0.167em} 000$ is investigated experimentally using a small circular control cylinder as a local disturbance. The height of the main cylinder is $D= 25~\mathrm{mm} $ and control cylinders are of diameters $d= 0. 04D$ and $d= 0. 12D$, the former being smaller than the shear layer thickness detaching from the main cylinder, while the latter is larger. In both cases, the control cylinder is able to modify the global frequency, base pressure and spanwise velocity correlation. The results are presented as sensitivity maps. Reynolds stresses spatial structure and the recirculation bubble length are examined in detail when the control cylinder is displaced vertically across the wake at a fixed downstream location. It is found that the increase of the recirculation bubble length is accompanied by a damping of Reynolds stresses with a downstream shift of their spatial structures together with the base pressure increase. The global frequency can be either decreased or increased independently of the bubble length modification. The sensitivity of these global properties is interpreted on the basis of the ability of the control cylinder to change the size of the formation region of the Kármán vortex street by interacting with the primary detached shear layers. The corresponding physical mechanisms are discussed. The impact of a two-dimensional control cylinder on the three-dimensional properties of the wake is examined through spanwise correlation. This is found to be improved whenever the control cylinder is placed inside the recirculation region of the main cylinder wake.

The Prediction of Turbulent, Supersonic, Two-Dimensional, Boundary-Layer Flows

1971 ◽  
Vol 22 (3) ◽  
pp. 274-294 ◽  
Author(s):  
S. Sivasegaram ◽  
J. H. Whitelaw
Keyword(s):  
Experimental Data ◽  
Turbulent Energy ◽  
Two Dimensional ◽  
Boundary Layer Flows ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Wide Range ◽  
Two Dimensional Flow ◽  
Dimensional Boundary ◽  
Flow Configurations

SummaryThe prediction procedures of Bradshaw and Ferriss and Spalding and Patankar are compared with a wide range of experimental data obtained in turbulent, supersonic, two-dimensional flow. Both procedures are shown to result in satisfactory predictions of mean velocity profiles and wall shear stress in adiabatic-wall situations: in addition, the procedure of Spalding and Patankar is shown to be satisfactory in heat transfer situations. The Bradshaw and Ferriss procedure employs a turbulent energy hypothesis in contrast to the mixing-length assumptions used in the present version of the Spalding and Patankar procedure. The close agreement between the predictions of the two procedures indicates a lack of experimental data obtained in flow configurations with suddenly imposed or relaxed pressure gradients.

The two-dimensional mixing region

1970 ◽  
Vol 41 (2) ◽  
pp. 327-361 ◽  
Author(s):  
I. Wygnanski ◽  
H. E. Fiedler
Keyword(s):  
Velocity Profile ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Outer Part ◽  
Eddy Diffusivity ◽  
Turbulent Energy ◽  
Two Dimensional ◽  
Low Velocity ◽  
Mean Velocity ◽  
Axial Velocity Profile

The two-dimensional incompressible mixing layer was investigated by using constant-temperature, linearized hot wire anemometers. The measurements were divided into three categories: (1) the conventional average measurements; (2) time-average measurements in the turbulent and the non-turbulent zones; (3) ensemble average measurements conditioned to a specific location of the interface. The turbulent energy balance was constructed twice, once using the conventional results and again using the turbulent zone results. Some differences emerged between the two sets of results. It appears that the mixing region can be divided into two regions, one on the high velocity side which resembles the outer part of a wake and the other on the low velocity side which resembles a jet. The binding turbulent–non-turbulent interfaces seem to move independently of each other. There is a strong connexion between the instantaneous location of the interface and the axial velocity profile. Indeed the well known exponential mean velocity profile never actually exists at any given instant. In spite of the complexity of the flow the simple concepts of eddy viscosity and eddy diffusivity appear to be valid within the turbulent zone.

Two-Component Phase-Averaged Turbulence Statistics Downstream of a Rotating Spoked-Wheel Wake Generator

1989 ◽  
Vol 111 (4) ◽  
pp. 475-482 ◽  
Author(s):  
J. E. O’Brien ◽  
S. P. Capp
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Guide Vane ◽  
Turbulent Transport ◽  
Turbulent Energy ◽  
Tangential Component ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Velocity Probability ◽  
Probability Density Distributions

Measurements of the axial and tangential components of the unsteady turbulent flow downstream of a rotating spoked-wheel wake generator have been obtained. The results of this study have implications for the use of this type of wake generator to produce simulated turbine guide vane wakes. Instantaneous velocity information was phase averaged based on a signal synchronized with the bar-passing frequency. Mean velocity profiles and phase-averaged Reynolds stress results were found to be consistent with measurements obtained behind a stationary cylinder. Reynolds stresses were significantly higher than corresponding measurements obtained in large-scale research turbomachines, however. Phase-averaged triple velocity correlations, also calculated from the digital velocity records, reveal the sign and magnitude of skewness in the velocity probability density distributions for the two components. Large crossflow gradients observed in the triple correlations in the wake indicate the importance of the tangential-component fluctuations in the net turbulent transport of turbulent energy across the wake. Streamwise-component wake velocity spectra for low values of reduced bar-passing frequency include a peak associated with vortex shedding from the cylindrical wake-generating bars at a shedding Strouhal number of 0.2. For higher bar-passing frequencies, the energy associated with vortex shedding is shifted to lower frequencies and becomes broadband from the stationary reference frame viewpoint.

Wake characteristics of two-dimensional perforated plates normal to an air-stream

1971 ◽  
Vol 46 (3) ◽  
pp. 599-609 ◽  
Author(s):  
I. P. Castro
Keyword(s):  
Reynolds Number ◽  
The Other ◽  
Turbulent Intensity ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Perforated Plates ◽  
Number Range ◽  
Air Stream ◽  
The Mean ◽  
Shedding Frequency

The flow in the wakes behind two-dimensional perforated plates has been investigated in the Reynolds number range 2·5 × 104 to 9·0 × 104.Measurements of drag and shedding frequency were made and a pulsed hotwire anemometer was used to measure the mean velocity and turbulent intensity variations in the highly turbulent regions immediately behind the plates.The results indicate the existence of two distinct types of flows: one appropriate to high and the other to low values of plate porosity.

scholarly journals Measurements in the turbulent wake of a cylinder

1947 ◽  
Vol 190 (1023) ◽  
pp. 551-561 ◽  
Keyword(s):  
Experimental Study ◽  
Reynolds Numbers ◽  
Turbulent Energy ◽  
Turbulent Wake ◽  
Mean Velocity ◽  
Dissipation Of Energy ◽  
Air Stream ◽  
The Mean ◽  
And Diffusion ◽  
Three Components

An experimental study has been made of the conditions in the turbulent' wake behind a cylinder in an air stream at cylinder Reynolds numbers between 100 and 7000. The measurements include the mean velocity distribution, the distribution of the three components of turbulence, the statistical distribution in time of the turbulent velocity components, and the correlation derivatives in the downstream direction for both the longitudinal and transverse correlations. It is shown that the intensities of the three components of turbulent velocities are nearly equal except at the centre of the wake, where the balance between viscous decay and diffusion from the regions of shear results in a considerably greater intensity for the component at right angles to the direction of flow and also to the axis of the cylinder, i.e. in the direction of diffusion of turbulent energy. An analysis of the energy in the wake proves that complete dynamical similarity in the wake, if it is ever attained, does not occur closer to the cylinder than 1000 diameters, and that the viscous dissipation of energy can be described in terms of a length parameter, nearly constant over the width of the wake and approximately equal to the measured value of Taylor’s scale of micro-turbulence.

Study On the Applicability of URANS, LES and Hybrid LES/RANS Models for Prediction of Hydrodynamics of Cyclone Separator

2021 ◽  
Author(s):  
Sai Guruprasad Jakkala ◽  
S Vengadesan
Keyword(s):  
Fluid Flow ◽  
Flow Characteristics ◽  
Mesh Size ◽  
Turbulent Energy ◽  
Computational Time ◽  
Detached Eddy Simulation ◽  
Reynolds Stresses ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Rans Models

Abstract Cyclone separators are an integral part of many industrial processes. A good understanding of the flow features is paramount to efficiently use them. The turbulent fluid flow characteristics are modelled using URANS, LES and hybrid LES/RANS turbulent models. The hybrid LES/RANS approaches, namely DES (Detached Eddy Simulation), DDES (Delayed Detached Eddy Simulation) and IDDES (Improved Delayed Detached Eddy Simulation) based on the k - $\omega$ SST RANS approaches are explored. The study is carried out for three different inlet velocities (v = 8, 16:1, and 32 m=s). The results from hybrid LES/RANS models are shown to be in good agreement with the experimental data available in the literature. Reduction in computational time and mesh size are the two main benefits of using hybrid LES/RANS models over the traditional LES methods. The Reynolds stresses are observed in order to understand the redistribution of turbulent energy in the flow field. The velocity profiles and vorticity quantities are explored to obtain a better understanding of the behaviour of fluid flow in cyclone separators.

Evaluation of RANS and LES turbulence models for simulating a steady 2-D plane wall jet

2018 ◽  
Vol 35 (1) ◽  
pp. 211-234
Author(s):  
Zhitao Yan ◽  
Yongli Zhong ◽  
William E. Lin ◽  
Eric Savory ◽  
Yi You
Keyword(s):  
Flow Characteristics ◽  
Turbulence Models ◽  
Velocity Profiles ◽  
Plane Wall ◽  
Wall Jet ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Content Type ◽  
Rectangular Slot ◽  
Law Of The Wall

PurposeThis paper examines various turbulence models for numerical simulation of a steady, two-dimensional (2-D) plane wall jet without co-flow using the commercial CFD software (ANSYS FLUENT 14.5). The purpose of this paper is to decide the most suitable and most economical method for steady, 2-D plane wall jet simulation.Design/methodology/approachSeven Reynolds-averaged Navier–Stokes (RANS) turbulence models were evaluated with respect to typical jet scaling parameters such as the jet half-height and the decay of maximum jet velocity, as well as coefficients from the law of the wall and for skin friction. Then, a plane wall jet generating from a rectangular slot of 1:6 aspect ratio located adjacent to the wall was investigated in a three-dimensional (3-D) model using large eddy simulation (LES) and the Stress-omega Reynolds stress model (SWRSM), with the results compared to experimental measurements.FindingsThe comparisons of these simulated flow characteristics indicated that the SWRSM was the best of the seven RANS models for simulating the turbulent wall jet. When scaled with outer variables, LES and SWRSM gave generally indistinguishable mean velocity profiles. However, SWRSM performed better for near-wall mean velocity profiles when scaled with inner variables. In general, the results show that LES performed reasonably well when predicting the Reynolds stresses.Originality/valueThe main contribution of this article is in determining the capabilities of different RANS turbulence closures and LES for the prediction of the 2-D steady wall jet flow to identify the best modelling approach.

Three-Dimensional Reconstruction of Two Forms of the Chaperonin GRO EL

1990 ◽  
Vol 48 (1) ◽  
pp. 258-259
Author(s):  
J.L. Carrascosa ◽  
G. Abella ◽  
S. Marco ◽  
M. Muyal ◽  
J.M. Carazo
Keyword(s):  
Three Dimensional ◽  
The Other ◽  
Two Dimensional ◽  
Series Method ◽  
Three Dimensional Reconstruction ◽  
Structural Components ◽  
E Coli ◽  
Dimensional Reconstruction ◽  
Morphogenetic Factors ◽  
Tilt Series

Chaperonins are a class of proteins characterized by their role as morphogenetic factors. They trantsiently interact with the structural components of certain biological aggregates (viruses, enzymes etc), promoting their correct folding, assembly and, eventually transport. The groEL factor from E. coli is a conspicuous member of the chaperonins, as it promotes the assembly and morphogenesis of bacterial oligomers and/viral structures.We have studied groEL-like factors from two different bacteria:E. coli and B.subtilis. These factors share common morphological features , showing two different views: one is 6-fold, while the other shows 7 morphological units. There is also a correlation between the presence of a dominant 6-fold view and the fact of both bacteria been grown at low temperature (32°C), while the 7-fold is the main view at higher temperatures (42°C). As the two-dimensional projections of groEL were difficult to interprete, we studied their three-dimensional reconstruction by the random conical tilt series method from negatively stained particles.

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