Steady Expiratory Flow in a Model Symmetric Bifurcation

1994 ◽  
Vol 116 (3) ◽  
pp. 318-323 ◽  
Author(s):  
Yao Zhao ◽  
Baruch B. Lieber
Keyword(s):  
Axial Flow ◽  
Reynolds Numbers ◽  
Small Region ◽  
Cross Sectional ◽  
Flow Divider ◽  
Velocity Peak ◽  
Branching Angle ◽  
Expiratory Flow ◽  
Junction Plane ◽  
Parent Tube

A model symmetric bifurcation was employed to simulate steady expiratory flow in the upper part of the human central airways. A two color, two component laser Doppler anemometer was used to measure both the axial flow and the secondary flow at three different Reynolds numbers of 518, 1036, and 2089, corresponding to Dean numbers of 98, 196, and 395. The test section is a symmetric bifurcation of constant cross-sectional area with a branching angle of 70 degrees. The flow rate into the two daughter branches was about the same. Results show that in the junction plane, velocity profiles in the daughter branches are skewed towards the inner walls. In the parent tube, just downstream of the flow divider, the velocity profile is biconcave with a dip at the center but this is rapidly transformed into a velocity peak. In a plane transverse to the bifurcation plane, parabolic velocity distribution was conserved through the daughter branches. In the parent tube, the transverse profiles became flat downstream of the flow divider and developed a defect at the center further downsteam towards the end of the parent tube part of the bifurcation. The velocity defect was confined to a small region in the vicinity of the centerline. Helical motion typified by symmetric vortices was observed in the daughter branches. In the parent tube, a set of four vortices induced by the turning of the flow was observed.

Steady Inspiratory Flow in a Model Symmetric Bifurcation

1994 ◽  
Vol 116 (4) ◽  
pp. 488-496 ◽  
Author(s):  
Yao Zhao ◽  
Baruch B. Lieber
Keyword(s):  
Test Section ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Axial Position ◽  
Flow Loop ◽  
Low Velocity ◽  
Cross Sectional ◽  
Branching Angle ◽  
Head Pressure ◽  
Constant Head

Flow in a bifurcating tube system typifying a major bronchial bifurcation is studied experimentally with a two color, two velocity component laser Doppler anemometer. The flow loop is composed of a pumping station, flow stratifiers and a constant head pressure tank; it can accommodate steady, pulsatile or oscillatory flow. The test section is a symmetric bifurcation of constant cross sectional area and has a branching angle of 70 deg. The test section is a cast of clear silicon rubber in a plexiglass mold that was milled on a numerically controlled milling machine. The flow division ratio from the parent to daughter branches is about unity. Steady flow results that model the inspiratory phase at Reynolds numbers of 518, 1036 and 2089, corresponding to Dean numbers of 98, 196 and 395, show that in the bifurcation plane velocity profiles in the daughter branches are skewed toward the inner wall. In the transverse plane, “m” shaped velocity profiles are found with low velocity at the center. Secondary flow patterns, which are responsible for such phenomena, are first observed at the axial position where the flow begins to turn. Flow separation was not observed at any point in the bifurcation.

scholarly journals Steady flow separation patterns in a 45 degree junction

2000 ◽  
Vol 411 ◽  
pp. 1-38 ◽  
Author(s):  
C. ROSS ETHIER ◽  
SUJATA PRAKASH ◽  
DAVID A. STEINMAN ◽  
RICHARD L. LEASK ◽  
GREGORY G. COUCH ◽  
...  
Keyword(s):  
Flow Separation ◽  
Stokes Equations ◽  
Bypass Graft ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Measured Velocity ◽  
Curved Tube

Numerical and experimental techniques were used to study the physics of flow separation for steady internal flow in a 45° junction geometry, such as that observed between two pipes or between the downstream end of a bypass graft and an artery. The three-dimensional Navier–Stokes equations were solved using a validated finite element code, and complementary experiments were performed using the photochromic dye tracer technique. Inlet Reynolds numbers in the range 250 to 1650 were considered. An adaptive mesh refinement approach was adopted to ensure grid-independent solutions. Good agreement was observed between the numerical results and the experimentally measured velocity fields; however, the wall shear stress agreement was less satisfactory. Just distal to the ‘toe’ of the junction, axial flow separation was observed for all Reynolds numbers greater than 250. Further downstream (approximately 1.3 diameters from the toe), the axial flow again separated for Re [ges ] 450. The location and structure of axial flow separation in this geometry is controlled by secondary flows, which at sufficiently high Re create free stagnation points on the model symmetry plane. In fact, separation in this flow is best explained by a secondary flow boundary layer collision model, analogous to that proposed for flow in the entry region of a curved tube. Novel features of this flow include axial flow separation at modest Re (as compared to flow in a curved tube, where separation occurs only at much higher Re), and the existence and interaction of two distinct three-dimensional separation zones.

scholarly journals Effects of Waterpipe Tobacco Smoking on the Spirometric Profile of University Students in Palestine: A Cross-Sectional Study

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Zaher Nazzal ◽  
Deema Odeh ◽  
Fatima Azahraa Haddad ◽  
Mohammad Berawi ◽  
Belal Rahhal ◽  
...  
Keyword(s):  
Young Adults ◽  
University Students ◽  
Respiratory Health ◽  
Cross Sectional Study ◽  
Forced Expiratory Volume ◽  
Waterpipe Smoking ◽  
Sectional Study ◽  
Cross Sectional ◽  
Lung Functions ◽  
Expiratory Flow

Background. Waterpipe smoking in young individuals is increasing with limited studies addressing its respiratory health effects. The aim of the study was to determine the effect of waterpipe smoking on young adults’ lung functions. Spirometric parameters were compared between waterpipe smokers and nonsmokers. Methods. A comparative cross-sectional study of university students, including males and females, was conducted. An interviewer-administered questionnaire was used to record students’ characteristics. The spirometry test was performed to assess students’ lung functions; we recorded the forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), FEV1/FVC ratio, peak expiratory flow (PEF), and forced expiratory flow between 25 and 75% of FVC (FEF25–75%). Results. A total of 300 apparently healthy students (150 waterpipe smokers and 150 nonsmokers) were included in the study. Waterpipe smokers showed significantly lower values in FEV1, FEV1/FVC ratio, PEF, and FEF25–75% compared to the nonsmoker group (P<0.05 to P<0.001). The subgroup analysis on female students (50 WP smokers and 50 nonsmokers) showed a significant decrease in FEV1/FVC ratio, PEF, and FEF25–75% parameters (P<0.001). Conclusion. Waterpipe smoking is associated with reduced spirometric parameters in healthy young adults with relatively limited smoking years.

scholarly journals Viscoelasticity of the trachea and its effects on flow limitation

2006 ◽  
Vol 100 (2) ◽  
pp. 384-389 ◽  
Author(s):  
Nikolai Aljuri ◽  
Jose G. Venegas ◽  
Lutz Freitag
Keyword(s):  
Wave Speed ◽  
Mathematical Representation ◽  
Forced Expiration ◽  
Flow Limitation ◽  
Time Dependency ◽  
Cross Sectional ◽  
Elastic Tubes ◽  
Forced Expiratory Flow ◽  
Expiratory Flow ◽  
The Relationship

To test the hypothesis that peak expiratory flow is determined by the wave-speed-limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area [the tube law (TL)] of six excised human tracheae under controlled conditions of static (no flow) and forced expiratory flow. We found that TLs of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro (Shapiro AH. J Biomech Eng 99: 126–147, 1977) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow was significantly stiffer than the static TL. As a result, the stiffer TL measured at the onset of forced expiratory flow predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant static TL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and “supramaximal” expiratory flows seen at the onset of forced expiration.

scholarly journals Viscous effects in the absolute–convective instability of the Batchelor vortex

2002 ◽  
Vol 459 ◽  
pp. 371-396 ◽  
Author(s):  
C. OLENDRARU ◽  
A. SELLIER
Keyword(s):  
Reynolds Number ◽  
Convective Instability ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Absolute Instability ◽  
Viscous Effects ◽  
Swirling Jets ◽  
Bending Mode ◽  
Transitional Mode ◽  
The Absolute

The effects of viscosity on the instability properties of the Batchelor vortex are investigated. The characteristics of spatially amplified branches are first documented in the convectively unstable regime for different values of the swirl parameter q and the co-flow parameter a at several Reynolds numbers Re. The absolute–convective instability transition curves, determined by the Briggs–Bers zero-group velocity criterion, are delineated in the (a, q)-parameter plane as a function of Re. The azimuthal wavenumber m of the critical transitional mode is found to depend on the magnitude of the swirl q and on the jet (a > −0.5) or wake (a < −0.5) nature of the axial flow. At large Reynolds numbers, the inviscid results of Olendraru et al. (1999) are recovered. As the Reynolds number decreases, the pocket of absolute instability in the (a, q)-plane is found to shrink gradually. At Re = 667; the critical transitional modes for swirling jets are m = −2 or m = −3 and absolute instability prevails at moderate swirl values even in the absence of counterflow. For higher swirl levels, the bending mode m = −1 becomes critical. The results are in good overall agreement with those obtained by Delbende et al. (1998) at the same Reynolds number. However, a bending (m = +1) viscous mode is found to partake in the outer absolute–convective instability transition for jets at very low positive levels of swirl. This asymmetric branch is the spatial counterpart of the temporal viscous mode isolated by Khorrami (1991) and Mayer & Powell (1992). At Re = 100, the critical transitional mode for swirling jets is m = −2 at moderate and high swirl values and, in order to trigger an absolute instability, a slight counterflow is always required. A bending (m = +1) viscous mode again becomes critical at very low swirl values. For wakes (a < −0.5) the critical transitional mode is always found to be the bending mode m = −1, whatever the Reynolds number. However, above q = 1.5, near-neutral centre modes are found to define a tongue of weak absolute instability in the (a, q)-plane. Such modes had been analytically predicted by Stewartson & Brown (1985) in a strictly temporal inviscid framework.

scholarly journals Associations between cardiac function and retinal microvascular geometry among Chinese adults

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Lihua Huang ◽  
Wei-Qing Chen ◽  
Izzuddin M. Aris ◽  
Louis L. Y. Teo ◽  
Tien Yin Wong ◽  
...  
Keyword(s):  
Cardiac Function ◽  
Cross Sectional Study ◽  
Chinese Adults ◽  
Cross Sectional ◽  
Atrial Contraction ◽  
Retinal Microvasculature ◽  
Velocity Flow ◽  
Retinal Vascular Caliber ◽  
Unit Increase ◽  
Branching Angle

Abstract Abnormal retinal microvascular geometry has been associated with cardiac remodeling and heart failure. However, its relation to cardiac function, prior to clinical disease has not been explored. In this cross-sectional study, 50 participants (mean age 62.5 ± 11.7 years) without cardiovascular disease (CVD) were recruited from the Cardiac Ageing Study. Transthoracic echocardiography imaging was performed to measure cardiac function indices, and retinal imaging was used to measure retinal vascular caliber and retinal vascular geometric indices. Multiple linear regressions were applied to examine associations between indices of cardiac function and retinal microvasculature, adjusting for age, sex, body mass index, mean blood pressure and comorbidity (i.e. hypertension, diabetes and dyslipidemia). After adjusting for confounders, each unit decrease in peak systolic septal mitral annular velocity (Septal S′) indicating poorer left function was associated with smaller retinal venular branching angle (β: − 2.69°; 95% CI − 4.92, − 0.46). Furthermore, each unit increase in peak velocity flow in late diastole by atrial contraction (MV A Peak) indicating poorer left atrial function was associated with lower retinal venular fractal dimension (− 0.13Df; − 0.25, − 0.004). Our findings suggested a relationship between poorer cardiac function and suboptimal retinal microvascular geometry, among Chinese without CVD.

Visualization of flow over a thick airfoil with circular cross-sectional riblets at low Reynolds numbers

2019 ◽  
Vol 22 (5) ◽  
pp. 877-888 ◽  
Author(s):  
Mehrdad Nafar-Sefiddashti ◽  
Mahdi Nili-Ahmadabadi ◽  
Behnam Saeedi-Rizi ◽  
Jalal Pourhoseini
Keyword(s):  
Reynolds Numbers ◽  
Cross Sectional ◽  
Low Reynolds Numbers ◽  
Thick Airfoil ◽  
Low Reynolds

Flow Regimes in Two-Phase Hexane/Water Semibatch Vertical Taylor Vortex Flow

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Charlton Campbell ◽  
Michael G. Olsen ◽  
R. Dennis Vigil
Keyword(s):  
Vortex Flow ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Water Phase ◽  
Taylor Vortex ◽  
Two Phase ◽  
Annular Gap ◽  
Taylor Vortex Flow ◽  
Regime Map

Optical-based experiments were carried out using the immiscible pair of liquids hexane and water in a vertically oriented Taylor–Couette reactor operated in a semibatch mode. The dispersed droplet phase (hexane) was continually fed and removed from the reactor in a closed loop setup. The continuous water phase did not enter or exit the annular gap. Four distinct flow patterns were observed including (1) a pseudo-homogenous dispersion, (2) a weakly banded regime, (3) a horizontally banded dispersion, and (4) a helical flow regime. These flow patterns can be organized into a two-dimensional regime map using the azimuthal and axial Reynolds numbers as axes. In addition, the dispersed phase holdup was found to increase monotonically with both the azimuthal and axial Reynolds numbers. The experimental observations can be explained in the context of a competition between the buoyancy-driven axial flow of hexane droplets and the wall-driven vortex flow of the continuous water phase.

scholarly journals Peak expiratory flow rate among smokers and non-smokers working in Kathmandu Medical College

2020 ◽  
Vol 10 (2) ◽  
pp. 33-35
Author(s):  
Preetu Gurung
Keyword(s):  
Cigarette Smoking ◽  
Peak Expiratory Flow ◽  
Flow Rate ◽  
Peak Expiratory Flow Rate ◽  
Cross Sectional Study ◽  
P Value ◽  
Cross Sectional ◽  
Medical College ◽  
Significant Difference ◽  
Expiratory Flow

Background: Cigarette smoking has remained a popular habit since ages. Most people are well aware of the deleterious effects of cigarette smoking yet continue to give a blind eye which dete­riorates overall public health. The purpose of the present study was to assess Peak Expiratory Flow Rate among smoking and nonsmoking staffs who work in Kathmandu Medical College. Methods: In this comparative cross-sectional study Peak Expiratory Flow Rate was obtained using Mini Wright’s Peak Flow Meter of 108 smokers and 108 nonsmokers in the age group ranging from 25-45 years. Those who never smoked or who have quit smoking for the past 2 years were grouped as nonsmokers and the smokers with history of smoking at least five or more cigarettes per day for at least two years were included in the study for measuring their Peak Expiratory Flow Rate. Data was collected, compiled and analyzed by using Statistical Package of Social Science (SPSS) software version16. Student ‘t’ test was used for group comparison. Results: The Peak Expiratory Flow Rate value was significantly reduced in the smokers (p value< 0.05). Mean Peak Expiratory Flow Rate was reduced with increasing age of the smokers. However, no significant difference was observed in Peak Expiratory Flow Rate with increase in the number of cigarettes smoked (p value> 0.05). Conclusions: In the study Peak Expiratory Flow Rate among smokers (367.13 ± 74.182) was lower than nonsmokers (471.39±60.842), which was statistically significant proving that cigarette smok­ing reduced peak expiratory flow rate.

Numerical Investigation on Turbulence Statistics and Heat Transfer of a Circular Jet Impinging on a Roughened Flat Plate

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
Abdulrahman Alenezi ◽  
Abdulrahman Almutairi ◽  
Hamad Alhajeri ◽  
Abdulaziz Gamil ◽  
Faisal Alshammari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Roughness Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Cross Sectional ◽  
Flow Physics ◽  
Baseline Case

Abstract A detailed heat transfer numerical study of a three-dimensional impinging jet on a roughened isothermal surface is presented and is investigated from flow physics vantage point under the influence of different parameters. The effects of the Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer parameters are studied. Additionally, the relations between average heat transfer coefficient (AHTC) and flow physics including pressure, wall shear and flow vortices with thermodynamic nonequilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of square cross-sectional continuous ribs to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three different radial locations (R/D) = 1, 1.5, and 2 and at each location its height (i.e., width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study used a jet angle (α) of 90 deg, jet-to-target distance (H/D = 6), and Re ranges from 10,000 to 50,000, where H is the vertical distance between the target plate and jet exit. The results show that the AHTC can be significantly affected by changing the geometry and dimensions of the roughness element. This variation can be either an augmentation of, or decrease in, the (HTC) when compared with the baseline case. An enhancement of 12.9% in the AHTC was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. However, a diminution between 10% and 30% in (AHTC) was attained by the use of rib height e = 1 mm at Re = 50k. The variation of both rib location and height showed better contribution in increasing heat transfer for low-range Reynolds numbers.

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