scholarly journals Mean flow, turbulence structure, and bed form superimposition across the ripple-dune transition

2006 ◽  
Vol 42 (5) ◽  
Author(s):  
Rocío Fernandez ◽  
Jim Best ◽  
Fabián López
Keyword(s):  
Turbulence Structure ◽  
Mean Flow ◽  
Bed Form ◽  
Flow Turbulence

Scaling laws for pipe-flow turbulence

1975 ◽  
Vol 67 (2) ◽  
pp. 257-271 ◽  
Author(s):  
A. E. Perry ◽  
C. J. Abell
Keyword(s):  
Pipe Flow ◽  
Scaling Laws ◽  
Dynamic Calibration ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Number Range ◽  
Static Calibration ◽  
Calibration Methods ◽  
The Mean ◽  
Flow Turbulence

Using hot-wire-anemometer dynamic-calibration methods, fully developed pipe-flow turbulence measurements have been taken in the Reynolds-number range 80 × 103 to 260 × 103. Comparisons are made with the results of previous workers, obtained using static-calibration methods. From the dynamic-calibration results, a consistent and systematic correlation for the distribution of turbulence quantities becomes evident, the resulting correlation scheme being similar to that which has previously been established for the mean flow. The correlations reported have been partly conjectured in the past by many workers but convincing experimental evidence has always been masked by the scatter in the results, no doubt caused by the difficulties associated with static-calibration methods, particularly the earlier ones. As for the mean flow, the turbulence intensity measurements appear to collapse to an inner and outer law with a region of overlap, from which deductions can be made using dimensional arguments. The long-suspected similarity of the turbulence structure and its consistency with the established mean-flow similarity appears to be confirmed by the measurements reported here.

An experimental study of the turbulence structure in smooth- and rough-wall boundary layers

1987 ◽  
Vol 177 ◽  
pp. 437-466 ◽  
Author(s):  
A. E. Perry ◽  
K. L. Lim ◽  
S. M. Henbest
Keyword(s):  
Boundary Layers ◽  
Wall Turbulence ◽  
Wall Region ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Mean Flow ◽  
Wavy Surfaces ◽  
The Mean ◽  
Flow Turbulence ◽  
Turbulent Wall

The turbulence structure in zero-pressure-gradient boundary layers above smooth, rough and wavy surfaces was investigated. The mean flow, turbulence intensity and spectral data for both smooth and rough surfaces show support for the attached eddy hypothesis of Townsend (1976), the model for wall turbulence proposed by Perry & Chong (1982) and the extended version developed by Perry, Henbest & Chong (1986). Anomalies in hot-wire behaviour when measuring in the turbulent wall region of the flow were discovered and some of these have been resolved.

scholarly journals Turbulence structure of non-uniform rough open channel flow

2018 ◽  
Vol 40 ◽  
pp. 05039
Author(s):  
Priscilla Williams ◽  
Vesselina Roussinova ◽  
Ram Balachandar
Keyword(s):  
Pressure Gradient ◽  
Channel Flow ◽  
Friction Velocity ◽  
Open Channel ◽  
Open Channel Flow ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Rough Bed ◽  
The Mean

This paper focuses on the turbulence structure in a non-uniform, gradually varied, sub-critical open channel flow (OCF) on a rough bed. The flow field is analysed under accelerating, near-uniform and decelerating conditions. Information for the flow and turbulence parameters was obtained at multiple sections and planes using two different techniques: two-component laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Different outer region velocity scaling methods were explored for evaluation of the local friction velocity. Analysis of the mean velocity profiles showed that the overlap layer exists for all flow cases. The outer layer of the decelerated velocity profile was strongly affected by the pressure gradient, where a large wake was noted. Due to the prevailing nature of the experimental setup it was found that the time-averaged flow quantities do not attained equilibrium conditions and the flow is spatially heterogeneous. The roughness generally increases the friction velocity and its effect was stronger than the effect of the pressure gradient. It was found that for the decelerated flow section over a rough bed, the mean flow and turbulence intensities were affected throughout the flow depth. The flow features presented in this study can be used to develop a model for simulating flow over a block ramp. The effect of the non-uniformity and roughness on turbulence intensities and Reynolds shear stresses was further investigated.

scholarly journals Functional responses of Daphnia magna to zero-mean flow turbulence

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Teresa Serra ◽  
Mara F. Müller ◽  
Jordi Colomer
Keyword(s):  
Daphnia Magna ◽  
Mean Flow ◽  
Functional Responses ◽  
Flow Turbulence

The structure of a shear layer bounding a separation region. Part 2. Effects of free-stream turbulence

1988 ◽  
Vol 192 ◽  
pp. 577-595 ◽  
Author(s):  
I. P. Castro ◽  
A. Haque
Keyword(s):  
Shear Layer ◽  
Free Stream ◽  
Layer Structure ◽  
Low Frequency ◽  
Flow Region ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Turbulence Data ◽  
Upstream Flow

Detailed measurements throughout the separated region behind a flat plate placed normal to a turbulent stream are reported. A long, central, downstream splitter plate prevented vortex shedding and led to a relatively extensive reversed flow region. Mean flow and turbulence data are compared with results obtained in the (nominal) absence of free-stream turbulence, and attention is concentrated on the changes in the shear-layer structure resulting from the different nature of the upstream flow.Many aspects of the results confirm those obtained recently by other workers. Free-stream turbulence enhances shear-layer entrainment rates, reduces the distance to reattachment and modifies the relatively low-frequency ‘flapping’ motion of the shear layer. In addition, however, extensive use of pulsed wire anemometry has allowed detailed measurements of the turbulence structure throughout the flow and it is shown that this is also modified significantly by the stream turbulence.

scholarly journals Energy-consistent entrainment relations for jets and plumes

2015 ◽  
Vol 782 ◽  
pp. 333-355 ◽  
Author(s):  
Maarten van Reeuwijk ◽  
John Craske
Keyword(s):  
Kinetic Energy ◽  
Richardson Number ◽  
Turbulence Kinetic Energy ◽  
Mean Flow ◽  
Unified Framework ◽  
First Order ◽  
Entrainment Coefficient ◽  
The Mean ◽  
Flow Turbulence ◽  
Pure Plume

We discuss energetic restrictions on the entrainment coefficient${\it\alpha}$for axisymmetric jets and plumes. The resulting entrainment relation includes contributions from the mean flow, turbulence and pressure, fundamentally linking${\it\alpha}$to the production of turbulence kinetic energy, the plume Richardson number$\mathit{Ri}$and the profile coefficients associated with the shape of the buoyancy and velocity profiles. This entrainment relation generalises the work by Kaminskiet al. (J. Fluid Mech., vol. 526, 2005, pp. 361–376) and Fox (J. Geophys. Res., vol. 75, 1970, pp. 6818–6835). The energetic viewpoint provides a unified framework with which to analyse the classical entrainment models implied by the plume theories of Mortonet al.(Proc. R. Soc. Lond.A, vol. 234, 1955, pp. 1–23) and Priestley & Ball (Q. J. R. Meteorol. Soc., vol. 81, 1954, pp. 144–157). Data for pure jets and plumes in unstratified environments indicate that to first order the physics is captured by the Priestley and Ball entrainment model, implying that (1) the profile coefficient associated with the production of turbulence kinetic energy has approximately the same value for pure plumes and jets, (2) the value of${\it\alpha}$for a pure plume is roughly a factor of$5/3$larger than for a jet and (3) the enhanced entrainment coefficient in plumes is primarily associated with the behaviour of the mean flow and not with buoyancy-enhanced turbulence. Theoretical suggestions are made on how entrainment can be systematically studied by creating constant-$\mathit{Ri}$flows in a numerical simulation or laboratory experiment.

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