Effect of the larynx on oscillatory flow in the central airways: a model study

1985 ◽  
Vol 59 (1) ◽  
pp. 160-169 ◽  
Author(s):  
A. S. Menon ◽  
M. E. Weber ◽  
H. K. Chang
Keyword(s):  
Oscillatory Flow ◽  
Flow Distribution ◽  
Maximum Flow ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Local Velocity ◽  
Mean Velocity ◽  
Model Study ◽  
Flow Cycle ◽  
The Mean

Measurements were made of the effect of the larynx on the oscillatory flow profiles in a 3:1 scale model of the human central airways. A fixed glottic aperture corresponding to the shape and size at midinspiration was used. Oscillatory airflows at peak Reynolds numbers, similar to those obtained during spontaneous breathing and panting, were studied. The flow distribution to the five lobar bronchi was maintained by distally placed linear resistors. A hot-wire anemometer probe was used to measure the local velocity along two perpendicular diameters at six stations distributed through the model. Near the proximal end of the trachea, the flat velocity profiles at the beginning of the flow cycle peaked at maximum flow because of the jet created by the glottic aperture. This peaked structure was conserved during the latter half of the inspiratory cycle. Close to the carina, the jet had almost dissipated and the entry conditions into the main bronchi corresponded to those in the absence of the laryngeal model. The effect of the glottic aperture on the mean velocity was not felt beyond the carina, and the characteristic skewed profiles seen in oscillatory flows, in the absence of the larynx, were present in the main and lobar bronchi.

Imbalanced flow changes of distal arteries: An important factor in process of delayed ipsilateral parenchymal hemorrhage after flow diversion in patients with cerebral aneurysms

2021 ◽  
pp. 159101992110091
Author(s):  
Wenqiang Li ◽  
Wei Zhu ◽  
Jian Liu ◽  
Xinjian Yang
Keyword(s):  
Blood Flow ◽  
Cerebral Artery ◽  
Cerebral Aneurysms ◽  
Flow Distribution ◽  
Maximum Flow ◽  
Flow Diverter ◽  
Control Group ◽  
Blood Flow Distribution ◽  
Mean Velocity ◽  
The Mean

Background and objective Hemodynamic forces may play a role in symptomatic delayed ipsilateral parenchymal hemorrhage (DIPH) of intracranial aneurysm (IA) after flow diverter placement. We aimed to investigate the hemodynamic risk factors in the postsurgical DIPH process. Methods Six patients with internal carotid artery (ICA) aneurysm developed to DIPH and 12 patients without DIPH (1:2 matched controls) after flow diverter were included between January 2015 to January 2019. Postsurgical hemodynamics of distal arteries (terminal ICA, middle cerebral artery (MCA), anterior cerebral artery (ACA)) were investigated using computational fluid dynamics, as well as the hemodynamic alteration between pre- and post-treatment. The DIPH related and unrelated distal arteries (either MCA or ACA) were discriminated and compared. Definition of imbalance index is the difference in increased velocity post-flow diverter between MCA and ACA and was used to evaluate the blood flow distribution of distal arteries. Results The mean and maximum flow velocities in the terminal ICA increased significantly after treatment in both groups. In DIPH group, the increase rate of mean velocity in the DIPH-related artery was significantly higher than that in DIPH-unrelated artery after the treatment (20.98 ± 15.38% vs −6.40 ± 7.74%; p = 0.028). Between the DIPH and control group, the baseline characteristics were well matched. However, a higher imbalance index of mean velocity was found in DIPH group (27.38 ± 13.03% vs 10.85 ± 14.12%; p = 0.031). Conclusion The mean velocity of DIPH related artery increased more, and the imbalance in increased blood flow distribution of distal arteries might play an important role in DIPH after flow diverter of IAs.

Axisymmetric internal waves generated by a travelling oscillating body

1969 ◽  
Vol 35 (2) ◽  
pp. 219-224 ◽  
Author(s):  
T. N. Stevenson
Keyword(s):  
Internal Waves ◽  
Salt Solution ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
Dispersive Waves ◽  
The Mean ◽  
Oscillating Sphere

Experiments are presented in which axisymmetric internal waves are generated by an oscillating sphere moving vertically in a stably stratified salt solution. The Reynolds numbers for the sphere based on the diameter and the mean velocity are between 10 and 200. Lighthill's theory for dispersive waves is used to calculate the phase configuration of the internal waves. The agreement between experiment and theory is reasonably good.

scholarly journals Natural logarithms

2013 ◽  
Vol 718 ◽  
pp. 1-4 ◽  
Author(s):  
B. J. McKeon
Keyword(s):  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Wall Turbulence ◽  
Significant Advance ◽  
Mean Velocity ◽  
Velocity Fluctuations ◽  
Logarithmic Scaling ◽  
The Mean ◽  
High Reynolds

AbstractMarusic et al. (J. Fluid Mech., vol. 716, 2013, R3) show the first clear evidence of universal logarithmic scaling emerging naturally (and simultaneously) in the mean velocity and the intensity of the streamwise velocity fluctuations about that mean in canonical turbulent flows near walls. These observations represent a significant advance in understanding of the behaviour of wall turbulence at high Reynolds number, but perhaps the most exciting implication of the experimental results lies in the agreement with the predictions of such scaling from a model introduced by Townsend (J. Fluid Mech., vol. 11, 1961, pp. 97–120), commonly termed the attached eddy hypothesis. The elegantly simple, yet powerful, study by Marusic et al. should spark further investigation of the behaviour of all fluctuating velocity components at high Reynolds numbers and the outstanding predictions of the attached eddy hypothesis.

LDV and PIV Velocity Results in a Thermosiphon

2003 ◽  
Author(s):  
J. Kulman ◽  
D. Gray ◽  
S. Sivanagere ◽  
S. Guffey
Keyword(s):  
Large Scale ◽  
Single Phase ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Laser Doppler Velocimeter ◽  
Mean Velocity ◽  
Developed Turbulence ◽  
The Mean ◽  
Good Agreement

Heat transfer and flow characteristics have been determined for a single-phase rectangular loop thermosiphon. The plane of the loop was vertical, and tests were performed with in-plane tilt angles ranging from 3.6° CW to 4.2° CCW. Velocity profiles were measured in one vertical leg of the loop using both a single-component Laser Doppler Velocimeter (LDV), and a commercial Particle Image Velocimeter (PIV) system. The LDV data and PIV data were found to be in good agreement. The measured average velocities were approximately 2–2.5 cm/s at an average heating rate of 70 W, and were independent of tilt angle. Significant RMS fluctuations of 10–20% of the mean velocity were observed in the test section, in spite of the laminar or transitional Reynolds numbers (order of 700, based on the hydraulic diameter). These fluctuations have been attributed to vortex shedding from the upstream temperature probes and mitre bends, rather than to fully developed turbulence. Animations of the PIV data clearly show these large scale unsteady flow patterns. Multiple steady state flow patterns were not observed.

Free Span Vibrations of Submarine Pipelines in Steady Flows—Effect of Free-Stream Turbulence on Mean Drag Coefficients

1985 ◽  
Vol 107 (4) ◽  
pp. 415-420 ◽  
Author(s):  
A. To̸rum ◽  
N. M. Anand
Keyword(s):  
Free Stream ◽  
Fluid Flows ◽  
Reynolds Numbers ◽  
Steady Flows ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
The Mean ◽  
Elastically Supported ◽  
Wave Induced ◽  
Rigid Smooth

In this paper part of the results of a laboratory study related to free span vibrations of submarine pipelines in steady and wave-induced fluid flows are summarized. Tests have been carried out using an elastically supported rigid smooth circular cylinder close to a plane smooth boundary in steady flows with turbulence intensities of 3.4, 5.5, and 9.5 percent for four cylinder gap to diameter ratios, G/D equal to 0.5, 0.75, 1.0, and 3.0. The range of Reynolds numbers based on mean velocity of flow and cylinder diameter was 0.65·104 to 0.35·105. Effect of turbulence intensity on the mean drag force and vibration amplitudes are discussed.

scholarly journals Model-based scaling of the streamwise energy density in high-Reynolds-number turbulent channels

2013 ◽  
Vol 734 ◽  
pp. 275-316 ◽  
Author(s):  
Rashad Moarref ◽  
Ati S. Sharma ◽  
Joel A. Tropp ◽  
Beverley J. McKeon
Keyword(s):  
Reynolds Number ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Low Rank ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Navier Stokes Equations ◽  
Self Similar ◽  
The Mean ◽  
High Reynolds

AbstractWe study the Reynolds-number scaling and the geometric self-similarity of a gain-based, low-rank approximation to turbulent channel flows, determined by the resolvent formulation of McKeon & Sharma (J. Fluid Mech., vol. 658, 2010, pp. 336–382), in order to obtain a description of the streamwise turbulence intensity from direct consideration of the Navier–Stokes equations. Under this formulation, the velocity field is decomposed into propagating waves (with single streamwise and spanwise wavelengths and wave speed) whose wall-normal shapes are determined from the principal singular function of the corresponding resolvent operator. Using the accepted scalings of the mean velocity in wall-bounded turbulent flows, we establish that the resolvent operator admits three classes of wave parameters that induce universal behaviour with Reynolds number in the low-rank model, and which are consistent with scalings proposed throughout the wall turbulence literature. In addition, it is shown that a necessary condition for geometrically self-similar resolvent modes is the presence of a logarithmic turbulent mean velocity. Under the practical assumption that the mean velocity consists of a logarithmic region, we identify the scalings that constitute hierarchies of self-similar modes that are parameterized by the critical wall-normal location where the speed of the mode equals the local turbulent mean velocity. For the rank-1 model subject to broadband forcing, the integrated streamwise energy density takes a universal form which is consistent with the dominant near-wall turbulent motions. When the shape of the forcing is optimized to enforce matching with results from direct numerical simulations at low turbulent Reynolds numbers, further similarity appears. Representation of these weight functions using similarity laws enables prediction of the Reynolds number and wall-normal variations of the streamwise energy intensity at high Reynolds numbers (${Re}_{\tau } \approx 1{0}^{3} {\unicode{x2013}} 1{0}^{10} $). Results from this low-rank model of the Navier–Stokes equations compare favourably with experimental results in the literature.

Large Eddy Simulation of Fully Developed Turbulent Pipe Flow

2004 ◽  
Author(s):  
Sowjanya Vijiapurapu ◽  
Jie Cui
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Reynolds Numbers ◽  
Grid Resolution ◽  
Turbulent Pipe Flow ◽  
Scale Model ◽  
Subgrid Scale ◽  
Mean Velocity ◽  
Fine Mesh ◽  
Large Eddy

Fully developed turbulent pipe flow is investigated by large eddy simulations (LES). The three-dimensional, unsteady, incompressible, filtered continuity and Navier-Stokes equations in cylindrical coordinates are discretized by a finite difference method. The spatial derivatives are approximated by second order conservative schemes. This scheme eliminates the numerical generation or dissipation of energy. The pressure Poisson equation is solved by FFT method and time is advanced through a third order Runge-Kutta method. The commonly used subgrid scale (SGS) models — the Smagorinsky model and the dynamic model are implemented and simulations are performed for fully developed turbulent pipe flow at two different Reynolds numbers. The flow features in terms of mean velocity as well as higher order turbulence intensities and correlations are presented and compared to experimental and DNS data available in literature. Extensive comparisons are made for cases using different grid resolution, different streamwise domain dimension, different sub-grid scale model, and, at two different Reynolds number. For two Reynolds numbers (5,000 and 30,000) tested in this study, the fine mesh (64 × 96 × 64, circumferential × radial × longitudinal) produces better results than the coarse mesh (32 × 48 × 32), indicating the significance of the grid resolution, especially near the pipe surface. On the fine mesh for the two Reynolds numbers, the results exhibit a slight Reynolds number effect, indicating the mesh needs to be further refined at higher Reynolds number. Simulations were performed for two domain sizes, namely 6D and 12D, where D is the pipe diameter. When the streamwise grid resolution remains unchanged, the two simulations show negligible difference. This ensures that a 6D domain is adequate to include the largest eddies in a fully developed turbulent pipe flow at the current Reynolds number. When the fine mesh is used, the subgrid scale models (Smagorinsky and Dynamic) provide limited contribution to the total turbulent kinetic energy. Although the current results agree quite well with other published LES simulations, when compared with the Law of the wall, benchmark experiments and DNS results, the simulated mean velocity in the log region is higher than the experimental and DNS data. Overall, it was observed that the numerical methods work satisfactorily well for turbulent pipe flows at low and high Reynolds numbers, and, the method has capability to be used in the simulation of flows with practical interest.

Effect of Upstream Flow Processes on Hydrodynamic Development in a Duct

1977 ◽  
Vol 99 (3) ◽  
pp. 556-560 ◽  
Author(s):  
E. M. Sparrow ◽  
C. E. Anderson
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Center Line ◽  
Viscous Effects ◽  
Mean Velocity ◽  
Inertia Effects ◽  
Reynolds Number Flow ◽  
Compact Size ◽  
Number Flow ◽  
The Mean

Consideration is given to the developing laminar flow in a parallel plate channel, with the fluid being drawn from a large upstream space. The flow fields upstream and downstream of the channel inlet were solved simultaneously. A finite-difference technique was employed which was facilitated by a coordinate transformation that telescoped the broadly extended flow domain into a more compact size. For the solutions, the Reynolds number was assigned values from 1 to 1000, covering the range from viscous-dominated flows to those where both viscous and inertia effects are relevant. Streamline maps indicate that whereas a low Reynolds number flow glides smoothly into the channel, a high Reynolds number flow has to turn sharply to enter the channel, with the result that the sharply turning fluid tends to overshoot at first and then readjust. A significant amount of upstream predevelopment occurs at low and intermediate Reynolds numbers. Thus, for example, at Re = 1 and 100, the center-line velocities at inlet are, respectively, 1.37 and 1.13 times the mean velocity (the fully developed center-line velocity is 1.5 times the mean). The upstream pressure drop, measured in terms of the velocity head, is substantially increased by viscous effects at low and intermediate Reynolds numbers.

Comparison of turbulent boundary layers over smooth and rough surfaces up to high Reynolds numbers

2016 ◽  
Vol 795 ◽  
pp. 210-240 ◽  
Author(s):  
D. T. Squire ◽  
C. Morrill-Winter ◽  
N. Hutchins ◽  
M. P. Schultz ◽  
J. C. Klewicki ◽  
...  
Keyword(s):  
Outer Region ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Rough Wall ◽  
Turbulent Shear ◽  
Smooth Wall ◽  
Mean Velocity ◽  
Wide Range ◽  
Velocity Variance ◽  
The Mean

Turbulent boundary layer measurements above a smooth wall and sandpaper roughness are presented across a wide range of friction Reynolds numbers, ${\it\delta}_{99}^{+}$, and equivalent sand grain roughness Reynolds numbers, $k_{s}^{+}$ (smooth wall: $2020\leqslant {\it\delta}_{99}^{+}\leqslant 21\,430$, rough wall: $2890\leqslant {\it\delta}_{99}^{+}\leqslant 29\,900$; $22\leqslant k_{s}^{+}\leqslant 155$; and $28\leqslant {\it\delta}_{99}^{+}/k_{s}^{+}\leqslant 199$). For the rough-wall measurements, the mean wall shear stress is determined using a floating element drag balance. All smooth- and rough-wall data exhibit, over an inertial sublayer, regions of logarithmic dependence in the mean velocity and streamwise velocity variance. These logarithmic slopes are apparently the same between smooth and rough walls, indicating similar dynamics are present in this region. The streamwise mean velocity defect and skewness profiles each show convincing collapse in the outer region of the flow, suggesting that Townsend’s (The Structure of Turbulent Shear Flow, vol. 1, 1956, Cambridge University Press.) wall-similarity hypothesis is a good approximation for these statistics even at these finite friction Reynolds numbers. Outer-layer collapse is also observed in the rough-wall streamwise velocity variance, but only for flows with ${\it\delta}_{99}^{+}\gtrsim 14\,000$. At Reynolds numbers lower than this, profile invariance is only apparent when the flow is fully rough. In transitionally rough flows at low ${\it\delta}_{99}^{+}$, the outer region of the inner-normalised streamwise velocity variance indicates a dependence on $k_{s}^{+}$ for the present rough surface.

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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