scholarly journals HYSTERESIS AND VORTICES DYNAMICS IN A TURBULENT FLOW

2009 ◽  
Vol 19 (08) ◽  
pp. 2695-2703 ◽  
Author(s):  
JAVIER BURGUETE ◽  
ALBERTO DE LA TORRE
Keyword(s):  
Turbulent Flow ◽  
Additive Noise ◽  
Potential Model ◽  
Time Dependent ◽  
Small Range ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Bistable Regime ◽  
The Mean

Recent results about the slow dynamics present in a fully developed turbulent flow are reported. In a previous paper [de la Torre & Burguete, 2007] we showed that the mean velocity field in a turbulent flow bifurcates subcritically breaking some symmetries of the problem and becomes time-dependent because of equatorial vortices moving with a precession movement. This subcriticality produces a bistable regime, whose main characteristics were successfully reproduced using a three-well potential model with additive noise. In this paper we present the characterization of the hysteresis region, not previously observed, in this bifurcation. This hysteresis appears only for an extremely small range of parameters.

STEADY STATE HEAT TRANSFER TO FULLY DEVELOPED TURBULENT FLOW IN A CURVED CHANNEL

1957 ◽  
Vol 35 (4) ◽  
pp. 410-434
Author(s):  
A. W. Marris
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Curved Channel ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Angular Velocities ◽  
The Mean

A vorticity transfer analogy theory of turbulent heat transfer is developed first for the case of fully developed turbulent flow under zero transverse pressure and temperature gradients such as that in the annulus between concentric cylinders rotating with different angular velocities or in a "free vortex". The mean flow is assumed to be two-dimensional. The theory, which requires that the turbulence be statistically isotropic, yields a temperature distribution in agreement with experiment except in narrow regions immediately adjacent to the boundaries. An argument is given to show that the boundary layer thickness should be of the order of the reciprocal of the square root of the mean velocity, these boundaries are introduced, and Nusselt moduli are defined and their dependence on Reynolds and Prandtl numbers is investigated.The temperature distributions for the case of non-zero transverse temperature and pressure gradients, i.e. for the case of flow in a curved channel in which the fluid does not flow back into itself, are then obtained and the applicability of the simpler equations for zero transverse gradients to this case is investigated.

ON FULLY DEVELOPED TURBULENT FLOW IN CURVED CHANNELS

1956 ◽  
Vol 34 (11) ◽  
pp. 1134-1146 ◽  
Author(s):  
A. W. Marris
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Velocity Distribution ◽  
Radius Of Curvature ◽  
Mixing Length ◽  
Mean Velocity ◽  
Curved Channels ◽  
Fully Developed Turbulent Flow ◽  
The Mean ◽  
Theoretical Results

Formulae for the radial distribution of velocity and vorticity for the case of fully developed turbulent flow in the channel between concentric and infinitely long cylinders are developed on a similarity vorticity transfer theory, by postulating an Eulerian mixing length function dependent on both position and radius of curvature. The theoretical results obtained for the mean velocity distribution across the channel compare satisfactorily with existing experimental data when the curvature dependent parameters are given appropriate numerical values.

scholarly journals Turbulent flow in curved channels

2021 ◽  
Vol 931 ◽  
Author(s):  
Geert Brethouwer
Keyword(s):  
Turbulent Flow ◽  
Outer Region ◽  
Curvature Radius ◽  
Normal Velocity ◽  
Mean Velocity ◽  
Velocity Fluctuations ◽  
Turbulence Structures ◽  
Curvature Effects ◽  
Fully Developed Turbulent Flow ◽  
The Mean

Fully developed turbulent flow in channels with mild to strong longitudinal curvature is studied by direct numerical simulations. The Reynolds based on the bulk mean velocity and channel half-width $\delta$ is fixed at $20\,000$ , resulting in a friction Reynolds number of approximately 1000. Four cases are considered with curvature varying from $\gamma = 2\delta /r_c = 0.033$ to 0.333, where $r_c$ is the curvature radius at the channel centre. Substantial differences between the mean wall shear stress on the convex and concave walls are already observed for $\gamma = 0.033$ . A log-law region is absent and a region with nearly constant mean angular momentum develops in the channel centre for strong curvatures. Spanwise and wall-normal velocity fluctuations are strongly amplified by curvature in the outer region of the concave channel side. Only near the walls, where curvature effects are relatively weak, do the mean velocity and velocity fluctuation profiles approximately collapse when scaled by wall units based on the local friction velocity. Budgets of the streamwise and wall-normal Reynolds-stress equations are presented and turbulence structures are investigated through visualizations and spectra. In the case with strongest curvature, the flow relaminarizes locally near the convex wall. On the concave channel side, large elongated streamwise vortices reminiscent of Taylor–Görtler vortices develop for all curvatures considered. The maximum in the premultiplied two-dimensional wall-normal energy spectrum and co-spectrum shifts towards larger scales with increasing curvature. The large scales substantially contribute to the wall-normal velocity fluctuations and momentum transport on the concave channel side.

Large-Eddy Simulation of Turbulent Flow in a Curved Pipe

1996 ◽  
Vol 118 (2) ◽  
pp. 248-254 ◽  
Author(s):  
B. J. Boersma ◽  
F. T. M. Nieuwstadt
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Mean Velocity ◽  
Curved Pipe ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Secondary Motion ◽  
Fully Developed Turbulent Flow ◽  
The Mean

In this paper, we use Large-Eddy Simulation (LES) to compute a fully-developed turbulent flow in a curved pipe. The results allow us to study how the curvature influences the mean velocity profile and also various turbulent statistics. We find reasonable agreement with the few experiments that are available. Our simulation also allows a detailed study of secondary motion in the cross section of the pipe which are caused by the centrifugal acceleration due to the pipe curvature. It is known that this secondary motion may consist of one, two, or three circulation cells. In our simulation results we find one circulation cell.

On Turbulent Flow Between Parallel Plates

1953 ◽  
Vol 20 (1) ◽  
pp. 109-114
Author(s):  
S. I. Pai
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
Poiseuille Flow ◽  
The Other ◽  
Turbulent Velocity ◽  
Parallel Plates ◽  
Mean Velocity ◽  
Reynolds Equations ◽  
Mean Pressure ◽  
The Mean

Abstract The Reynolds equations of motion of turbulent flow of incompressible fluid have been studied for turbulent flow between parallel plates. The number of these equations is finally reduced to two. One of these consists of mean velocity and correlation between transverse and longitudinal turbulent-velocity fluctuations u 1 ′ u 2 ′ ¯ only. The other consists of the mean pressure and transverse turbulent-velocity intensity. Some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. These equations are applied to two special cases: One is Poiseuille flow in which both plates are at rest and the other is Couette flow in which one plate is at rest and the other is moving with constant velocity. The mean velocity distribution and the correlation u 1 ′ u 2 ′ ¯ can be expressed in a form of polynomial of the co-ordinate in the direction perpendicular to the plates, with the ratio of shearing stress on the plate to that of the corresponding laminar flow of the same maximum velocity as a parameter. These expressions hold true all the way across the plates, i.e., both the turbulent region and viscous layer including the laminar sublayer. These expressions for Poiseuille flow have been checked with experimental data of Laufer fairly well. It also shows that the logarithmic mean velocity distribution is not a rigorous solution of Reynolds equations.

scholarly journals The Effect of Knee Flexion on Active and Passive Popliteal Venous Flow When Using Crutches or Knee Scooter While Immobilized

2020 ◽  
Vol 5 (4) ◽  
pp. 2473011420S0007
Author(s):  
Christopher W. Reb ◽  
Edward T. Haupt ◽  
Gregory C. Berlet
Keyword(s):  
Effect Size ◽  
Knee Flexion ◽  
Venous Return ◽  
Effect Sizes ◽  
Medium Effect ◽  
Small Range ◽  
Mean Velocity ◽  
Venous Flow ◽  
Flow Parameters ◽  
The Mean

Category: Trauma; Other Introduction/Purpose: Knee flexion has been demonstrated to impede popliteal venous return with large effect size among patients lying supine for surgery. Passive popliteal flow impedance has also been suggested to occur with knee scooter usage due to knee flexion. This study compared the effect of knee flexion angles on popliteal venous return between upright, crutch and knee scooter positioning when immobilized. Further, the countervailing effect of standardized hallux musculovenous pump activation was observed. Methods: This was an IRB approved study of young, healthy volunteers. Popliteal venous diameter and flow metrics were assessed with venous ultrasonography and compared between straight leg, crutch, and knee scooter positioning while wearing a walking boot and nonweightbearing. Flow was assessed with muscles at rest and with hallux musculovenous pump activation via active oscillation between hallux metatarsophalangeal joint extension and flexion at one motion per second (0.5 Hz) as paced by a metronome. Observer consistency was assessed. Paired-sample Student’s t-test and the Wilcoxon signed rank tests were used to assess within-subject differences for diameter and venous flow parameters, respectively. Knee flexion and musculovenous pump activation effects sizes were calculated. A priori sample size indicated 24 subjects were needed to achieve 80% power to detect a significant ( p < 0.006 ) difference in medial flow for any of 8 comparisons, assuming large effect sizes. Results: 16 of 24 (67%) subjects were female. Twelve limbs (50%) were right sided. The mean age was 21.9 years (SD 3.0 years) and the mean body mass index was 21.9 (SD 1.9). Observer consistencies were excellent (0.93 to 0.99). No significant differences in mean vessel diameter, time-averaged mean velocity, and total volume flow occurred. Corresponding knee flexion effect sizes were small (range -0.04 to -0.26). A significant decrease (-24%) in active median time-averaged peak velocity (TAPV) occurred between upright and crutch position (20.89 cm/s vs. 15.92 cm/s, p < 0.001) with a medium effect size (-0.51). Hallux musculovenous pump increased all flow parameters (all p< 0.001) and effect sizes were comparatively larger (>0.6) across all knee flexion positions. Conclusion: Compared to values reported for supine individuals, upright passive popliteal venous return was observed to be markedly diminished at all knee flexion angles. Knee flexion had minimal effect on diameter, a small effect in further diminishing TAMV and TVF and a medium effect on diminishing TAPV. Hallux musculovenous pump activiation had a large effect on increasing flow at all knee flexion angles. Patients may well be counseled to use toe motion to counter the negative effects of gravity, and to a lesser extent knee flexion, when using crutches and knee scooters while their ankle is immobilized.

Measurements with a pulsed-wire and a hot-wire anemometer in the highly turbulent wake of a normal flat plate

1976 ◽  
Vol 77 (3) ◽  
pp. 473-497 ◽  
Author(s):  
L. J. S. Bradbury
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Flow Direction ◽  
Operating Conditions ◽  
Turbulent Intensity ◽  
Hot Wire ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
Better Than

This paper describes an investigation into the response of both the pulsed-wire anemometer and the hot-wire anemometer in a highly turbulent flow. The first part of the paper is concerned with a theoretical study of some aspects of the response of these instruments in a highly turbulent flow. It is shown that, under normal operating conditions, the pulsed-wire anemometer should give mean velocity and longitudinal turbulent intensity estimates to an accuracy of better than 10% without any restriction on turbulence level. However, to attain this accuracy in measurements of turbulent intensities normal to the mean flow direction, there is a lower limit on the turbulent intensity of about 50%. An analysis is then carried out of the behaviour of the hot-wire anemometer in a highly turbulent flow. It is found that the large errors that are known to develop are very sensitive to the precise structure of the turbulence, so that even qualitative use of hot-wire data in such flows is not feasible. Some brief comments on the possibility of improving the accuracy of the hot-wire anemometer are then given.The second half of the paper describes some comparative measurements in the highly turbulent flow immediately downstream of a normal flat plate. It is shown that, although it is not possible to interpret the hot-wire results on their own, it is possible to calculate the hot-wire response with a surprising degree of accuracy using the results from the pulsed-wire anemometer. This provides a rather indirect but none the less welcome check on the accuracy of the pulsed-wire results, which, in this very highly turbulent flow, have a certain interest in their own right.

Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids

1982 ◽  
Vol 119 ◽  
pp. 423-441 ◽  
Author(s):  
M. A. Goldshtik ◽  
V. V. Zametalin ◽  
V. N. Shtern
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Outer Boundary ◽  
Viscous Sublayer ◽  
Viscous Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
The Mean ◽  
Near Wall

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.

Investigations of Tripping Effect on the Friction Factor in Turbulent Pipe Flows

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
A. Al-Salaymeh ◽  
O. A. Bayoumi
Keyword(s):  
Friction Factor ◽  
Reynolds Numbers ◽  
Original Data ◽  
Turbulent Pipe Flow ◽  
Wall Friction ◽  
Mean Flow ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
The Mean ◽  
The Difference

Tripping devices are usually installed at the entrance of laboratory-scale pipe test sections to obtain a fully developed turbulent flow sooner. The tripping of laminar flow to induce turbulence can be carried out in different ways, such as using cylindrical wires, sand papers, well-organized tape elements, fences, etc. Claims of tripping effects have been made since the classical experiments of Nikuradse (1932, Gesetzmässigkeit der turbulenten Strömung in glatten Rohren, Forschungsheft 356, Ausgabe B, Vol. 3, VDI-Verlag, Berlin), which covered a significant range of Reynolds numbers. Nikuradse’s data have become the metric by which theories are established and have also been the subject of intense scrutiny. Several subsequent experiments reported friction factors as much as 5% lower than those measured by Nikuradse, and the authors of those reports attributed the difference to tripping effects, e.g., work of Durst et al. (2003, “Investigation of the Mean-Flow Scaling and Tripping Effect on Fully Developed Turbulent Pipe Flow,” J. Hydrodynam., 15(1), pp. 14–22). In the present study, measurements with and without ring tripping devices of different blocking areas of 10%, 20%, 30%, and 40% have been carried out to determine the effect of entrance condition on the developing flow field in pipes. Along with pressure drop measurements to compute the skin friction, both the Pitot tube and hot-wire anemometry measurements have been used to accurately determine the mean velocity profile over the working test section at different Reynolds numbers based on the mean velocity and pipe diameter in the range of 1.0×105–4.5×105. The results we obtained suggest that the tripping technique has an insignificant effect on the wall friction factor, in agreement with Nikuradse’s original data.

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