Experimental Investigation of Oscillatory Flow Through a Symmetrically Bifurcating Tube

1998 ◽  
Vol 120 (5) ◽  
pp. 584-593 ◽  
Author(s):  
R. A. Peattie ◽  
W. Schwarz
Keyword(s):  
Velocity Field ◽  
Axial Velocity ◽  
High Frequency ◽  
Oscillatory Flow ◽  
Low Frequency ◽  
High Frequency Ventilation ◽  
Dimensionless Frequency ◽  
Flow Through ◽  
Secondary Velocity ◽  
Parent Tube

To provide a quantitative description of the convection field of gas transport through the lung under both low and high-frequency ventilation conditions, volume-cycled, purely oscillatory flow has been investigated in a symmetrically bifurcating model bronchial bifurcation. Significant differences in the flow properties that developed as the Reynolds number varied from 750 to 950 and the dimensionless frequency varied from 3 to 12 are described. At low frequency, the axial velocity field was found to approximate closely that of a steady flow through a bifurcation. However, even at α = 3, secondary velocity fields were confined to within a few diameters of the bifurcation, with less than 10 percent of the magnitude of the axial velocity. At high frequency they were still slower and more limited. These secondary velocity observations are discussed in terms of a physical mechanism balancing inviscid centripetal acceleration with viscous retardation. As the dimensionless frequency increased but the flow amplitude decreased, the magnitude of the axial drift velocity field was found to decrease. In addition, a burst of high-frequency velocity fluctuations was detected in both the axial and secondary velocity measurements in the parent tube, in low-frequency flow, during the deceleration phase of expiration. The position and timing of this burst suggest that it derives from the free shear layer in the parent tube. Stability criteria for the flow were therefore evaluated.

Oscillatory flow in a tube of time-dependent curvature. Part 1. Perturbation to flow in a stationary curved tube

1999 ◽  
Vol 383 ◽  
pp. 327-352 ◽  
Author(s):  
S. L. WATERS ◽  
T. J. PEDLEY
Keyword(s):  
Pressure Gradient ◽  
Coronary Arteries ◽  
High Frequency ◽  
Low Frequency ◽  
Secondary Flows ◽  
Time Dependent ◽  
Dimensionless Frequency ◽  
Curved Tube ◽  
Power Series Expansions ◽  
Oscillatory Pressure

Motivated by the study of blood flow in the coronary arteries, this paper examines the flow of an incompressible Newtonian fluid in a tube of time-dependent curvature. The flow is driven by an oscillatory pressure gradient with the same dimensionless frequency, α, as the curvature variation. The dimensionless governing parameters of the flow are α, the curvature ratio δ0, a secondary streaming Reynolds number Rs and a parameter Rt representing the time-dependence of curvature. We consider the parameter regime δ0<Rt<1 (Rs and α remain O(1) initially) in which the effect of introducing time-dependent curvature is to perturb the flow driven by an oscillatory pressure gradient in a fixed curved tube. Flows driven by low- and high-frequency pressure gradients are then considered. At low frequency (δ0<Rt<α<1) the flow is determined by using a sequence of power series expansions (Rs=O(1)). At high frequency (δ0<Rt<1/α2<1) the solution is obtained using matched asymptotic expansions for the region near the wall (Stokes layer) and the region away from the wall in the interior of the pipe. The behaviour of the flow in the interior is then determined at both small and intermediate values of Rs. For both the low and high frequency cases, we find the principal corrections introduced by the time-varying curvature to the primary and secondary flows, and hence to the wall shear stress. The physiological application to flow in the coronary arteries is discussed.

OSCILLATORY FLOW OF HFV DISTRIBUTED IN LEFT AND RIGHT LUNGS: A MODEL-BASED EXPERIMENT AND INVESTIGATION

2014 ◽  
Vol 14 (06) ◽  
pp. 1440015
Author(s):  
YUEYANG YUAN ◽  
CHONGCHANG YANG ◽  
ZHE LI ◽  
ZHIXIN CAO ◽  
SIMON ZHANG ◽  
...  
Keyword(s):  
High Frequency ◽  
Oscillatory Flow ◽  
Flow Distribution ◽  
Lung Compliance ◽  
High Frequency Oscillation ◽  
High Frequency Ventilation ◽  
Signal Acquisition ◽  
Airflow Distribution ◽  
Frequency Ventilation ◽  
Left And Right

The human respiratory system is not entirely symmetric, and regional respiratory diseases can further enlarge this difference in most cases. Therefore, the lungs perform differently. This paper explored the possibilities of suppressing and enhancing the performance of a diseased lung with different high-frequency ventilation (HFV) frequencies by experimenting, as well as modeling, the oscillatory airflow distribution between the left and right lungs. The experimental setup mainly consisted of a physical respiratory model, a signal acquisition device, and a high-frequency oscillation ventilator. This ventilator outputs a positive sinusoidal air-pressure during inspiration. On these bases, a series of experiments were also conducted with different compliances and resistances in the left and the right lungs. The experiments demonstrated that the oscillatory flow distribution is primarily correlated with the oscillation frequency and the regional lung compliance.

A general dimensionless equation of gas transport by high-frequency ventilation

1986 ◽  
Vol 60 (3) ◽  
pp. 1025-1030 ◽  
Author(s):  
J. G. Venegas ◽  
C. A. Hales ◽  
D. J. Strieder
Keyword(s):  
High Frequency ◽  
Oscillatory Flow ◽  
Mammalian Species ◽  
Alveolar Ventilation ◽  
High Frequency Ventilation ◽  
Linear Regression Equation ◽  
Dimensionless Equation ◽  
Frequency Ventilation ◽  
Dimensionless Variables ◽  
Conducting Airways

To identify a general relationship between eucapnic oscillatory flow (Vosc) and frequency (f) in high-frequency ventilation (HFV), we searched the literature for eucapnic HFV data in different mammalian species. We found suitable results for rat, rabbit, monkey, dog, human, and horse, which we expressed in terms of two dimensionless variables, Q = Vosc/Va and F = f/(VA/VD), with VA the alveolar ventilation and VD the volume of the conducting airways. The experimental HFV data define the linear regression equation in Q = 0.54 In F + 0.92 (R = 0.94). Krogh's equation for conventional ventilation (CV), Vosc = VA + fVD, in dimensionless terms becomes Q = 1 + F, which is valid for low F. The intersection of the CV and HFV equations at F = 5.0 defines a transition frequency, ft = 5.0 (VA/VD). At that point the alveolar ventilation per breath, VA/f, represents 20% of VD, and tidal volume (VT) equals 1.20 VD. For eucapnia ft ranges from 5.9 Hz in the rat to 0.9 Hz in the dog. The dimensional form of our HFV equation, VA = 0.13 (VT/VD)1.2 (VTf) is very similar to other empirical equations reported for dogs in noneucapnic settings. Therefore the dimensionless equation should also be valid within a species at noneucapnic settings.

scholarly journals Exact and limiting solutions of fluid flow for axially oscillating cylindrical pipe and annulus

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
U. K. Sarkar ◽  
Nirmalendu Biswas
Keyword(s):  
Velocity Distribution ◽  
High Frequency ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Low Frequency ◽  
Navier Stokes ◽  
Cylindrical Pipe ◽  
Navier Stokes Equations ◽  
Cylindrical Annulus

AbstractThe Navier–Stokes equations have been solved to derive the expressions of the velocity distributions for two cases: (1) oscillatory flows inside and outside of an axially oscillating cylindrical pipe, and (2) oscillatory flow inside an axially oscillating cylindrical annulus. In both the cases, in addition to the exact expressions for the velocity profiles, particular emphasis has been given for the determination of approximate velocity distributions for the high frequency and low frequency or quasi-static limits. It is shown that, for sufficiently large value of an appropriate frequency parameter, the velocity distribution inside the axially or longitudinally oscillating cylindrical annulus can be approximated as a superposition of the velocity distribution inside an axially oscillating cylindrical pipe of radius $${\bar R_o}$$ R ¯ o and the velocity distribution outside an axially oscillating cylindrical pipe of radius $${\bar R_i}$$ R ¯ i , where $${\bar R_i}$$ R ¯ i and $${\bar R_o}$$ R ¯ o are the inner and outer radii of the axially oscillating annulus, respectively.

Effect of Fuel Distribution on Spray Dynamics in a Two-Staged Multi-Injection Burner

2011 ◽  
Author(s):  
T. Providakis ◽  
L. Zimmer ◽  
P. Scouflaire ◽  
S. Ducruix
Keyword(s):  
Velocity Field ◽  
High Frequency ◽  
Gas Turbines ◽  
Low Frequency ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Reactive Flow ◽  
Mean Values ◽  
Fuel Distribution ◽  
Flame Dynamics

Burners operating in lean premixed prevaporized (LPP) regimes are considered as good candidates to reduce pollutant emissions from gas turbines. Lean combustion regimes result in lower burnt gas temperatures and therefore a reduction on the NOx emissions, one of the main pollutant species. However, these burners usually show strong flame dynamics, making them prone to various stabilization problems (combustion instabilities, flashback, flame extinction). To face this issue, multi-injection staged combustion can be envisaged. Staging procedures enable fuel distribution control, while multipoint injections can lead to a fast and efficient mixing. A laboratory-scale staged multipoint combustor is developed in the present study, in the framework of LPP combustion, with an injection device close to the industrial one. Using a staging procedure between the primary pilot stage and the secondary multipoint one, droplet and velocity field distributions can be varied in the spray that is formed at the entrance of the combustion chamber. Non-reactive and reactive flows are characterized through an extensive Phase Doppler Anemometry (PDA) campaign. Three staging values, corresponding to three different flame stabilization processes, are analyzed, while power is kept constant. It is shown that mean values and droplet distributions are affected by the staging procedure in the non-reactive as in the reactive situations. Using adequate post-processing, it is also possible to study non-reactive and reactive flow/flame dynamics. Spectral analysis shows that the non-reactive flow is strongly structured by a high frequency rotating structure that can clearly be associated with a precessing vortex core (PVC), while the reactive situation encounters a strong acoustic-flame coupling leading to a low frequency oscillation of both the velocity field and the spray droplet distribution. In this last situation, high frequency phenomena, which may be due to PVC, are still visible.

Interaction of oscillatory and unidirectional flows in straight tubes and an airway cast

1982 ◽  
Vol 52 (4) ◽  
pp. 1097-1105 ◽  
Author(s):  
H. L. Dorkin ◽  
A. C. Jackson ◽  
D. J. Strieder ◽  
S. V. Dawson
Keyword(s):  
Boundary Layer ◽  
Frequency Dependence ◽  
High Frequency ◽  
Airway Pressure ◽  
Oscillatory Flow ◽  
Low Frequency ◽  
Tidal Breathing ◽  
Unidirectional Flow ◽  
Pressure Changes ◽  
Central Airway

Because oscillatory resistance of the respiratory system is often measured during tidal breathing, we studied the interaction between simultaneous oscillatory and unidirectional flows in three straight tubes (radius ranging from 0.3025 to 0.679 cm and length either 30.7 or 173 cm) and a central airway cast (tracheal radius 0.685 cm). Oscillatory flow was generated by a loudspeaker, airway pressure was measured with a transducer, and flow was calculated from pressure changes in an airtight enclosure mounted behind the flow source (loudspeaker plethysmograph). Oscillatory resistance, i.e., the real part of impedance, was determined from 2 to 64 Hz. In the absence of unidirectional flow, frequency dependence of resistance was observed for the two 30.7-cm-long tubes to match previously published theory. Frequency dependence of resistance for the airway cast was similar to that of the tube of comparable inlet radius. In the presence of unidirectional flow, oscillatory resistance at low frequency was independent of frequency and determined by the magnitude of the unidirectional flow. Oscillatory resistance at high frequency was frequency dependent but still influenced by the magnitude of the unidirectional flow. Our results indicate that the presence of unidirectional flow alters the oscillatory resistance of tubes and the cast at any given frequency, presumably by changing the shape of the boundary layer.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

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