Three-Dimensional Flow Patterns in the Upper Human Airways

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Katrin Bauer ◽  
Alexander Rudert ◽  
Christoph Brücker
Keyword(s):  
Secondary Flow ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
Conventional Mechanical Ventilation ◽  
Flow Structures ◽  
Three Dimensional Model ◽  
Short Branch ◽  
Sixth Generation ◽  
Human Airways

Flow dynamics are studied for different ventilation conditions at a three-dimensional model of the human lung airways. The model is based on Horsfield and Weibel data and bifurcates down to the sixth generation. The flow is analyzed numerically and compared to experimental data received from exactly the same model. Numerical and experimental results agree well. Based on this agreement, flow behavior for conventional mechanical ventilation (CMV) as well as for high frequency oscillatory ventilation (HFOV) conditions can be analyzed. Velocity profiles as well as secondary flow structures are investigated during different phases of the unsteady flow. It is shown that the velocity profiles at peak inspiration and expiration are very similar for CMV and HFOV, probably due to too short branch lengths for the development of a frequency-dependent velocity profile. At the flow reversal times, characteristic zones of bidirectional mass flow emerge with increasing amplitude at higher frequencies. Furthermore, secondary flow structures are analyzed. This investigation reveals that the structures only depend on the local curvature and branch orientation, but are not influenced much by the nearby upper or lower branching generations.

Effects of Inclination Angle of Ribs on the Flow Behavior in Rectangular Ducts

2004 ◽  
Vol 126 (4) ◽  
pp. 692-699 ◽  
Author(s):  
Xiufang Gao ◽  
Bengt Sunde´n
Keyword(s):  
Velocity Component ◽  
Flow Direction ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Fluid Flows ◽  
Streamwise Velocity ◽  
Flow Structures ◽  
Local Flow ◽  
Flow Motion ◽  
Streamwise Velocity Component

The flow behavior in rib-roughened ducts is influenced by the inclination of ribs and the effect is investigated in the present study by Particle Image Velocimetry (PIV). The local flow structures between two adjacent ribs were measured. The Reynolds number was fixed at 5800. The flow field description was based on the PIV results in planes both parallel and perpendicular to the ribbed walls at various locations. The rib angle to the main flow direction was varied as 30 deg, 45 deg, 60 deg and 90 deg. The ribs induce three dimensional flow fields. The flow separation and reattachment between adjacent ribs are clearly observed. In addition, the inclined ribs are found to alter the spanwise distribution of the streamwise velocity component. The streamwise velocity component has its highest values at the upstream end of the ribs, and decreases continuously to its lowest values at the downstream end. Strong secondary flow motion occurs over the entire duct cross section for the inclined ribs. The flow structures between two consecutive ribs show that the fluid flows along the ribs from one end of the ribs to the other end, and then turns back at the transverse center. Downwash and upwash flows are observed at the upstream end and downstream end of the ribs, respectively.

Flow Characteristics Inside Circular Injection Holes Normally Oriented to a Crossflow: Part II—Three-Dimensional Flow Data and Aerodynamic Loss

2000 ◽  
Vol 123 (2) ◽  
pp. 274-280 ◽  
Author(s):  
Sang Woo Lee ◽  
Seong Kuk Joo ◽  
Joon Sik Lee
Keyword(s):  
Secondary Flow ◽  
Separation Bubble ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Windward Side ◽  
Leeward Side ◽  
Injection Hole ◽  
Potential Core ◽  
Aerodynamic Loss

Presented are three-dimensional mean velocity components and aerodynamic loss data inside circular injection holes. The holes are normally oriented to a crossflow and each hole has a sharp square-edged inlet. Because of their importance to flow behavior, three different blowing ratios, M=0.5, 1.0, and 2.0, and three hole length-to-diameter ratios, L/D=0.5, 1.0, and 2.0, are investigated. The entry flow is characterized by a separation bubble, and the exit flow is characterized by direct interaction with the crossflow. The uniform oncoming flow at the inlet undergoes a strong acceleration and a subsequent gradual deceleration along a converging–diverging flow passage formed by the inlet separation bubble. After passing the throat of the converging–diverging passage, the potential core flow, which is nearly axisymmetric, decelerates on the windward side, but tends to accelerate on the leeward side. The presence of the crossflow thus reduces the discharge of the injectant on the windward side, but enhances its efflux on the leeward side. This trend is greatly accentuated at M=0.5. In general, there are strong secondary flows in the inlet and exit planes of the injection hole. The secondary flow within the injection hole, on the other hand, is found to be relatively weak. The inlet secondary flow is characterized by a strong inward flow toward the injection-hole center. However, it is not completely directed inward since the crossflow effect is superimposed on it. Past the throat, secondary flow is observed such that the leeward velocity component induced by the crossflow is superimposed on the diverging flow. Short L/D usually results in an exit discharging flow with a steep velocity gradient as well as a strong deceleration on the windward side, as does low M. The aerodynamic loss inside the injection hole originates from the inlet separation bubble, wall friction and interaction of the injectant with the crossflow. The first one is considered as the most dominant source of loss, even in the case of L/D=2.0. At L/D=0.5, the first and third sources are strongly coupled with each other. Regardless of L/D, the mass-averaged aerodynamic loss coefficient has an increasing tendency with increasing M.

Numerical Study of the Winter-Kennedy Method—A Sensitivity Analysis

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Binaya Baidar ◽  
Jonathan Nicolle ◽  
Chirag Trivedi ◽  
Michel J. Cervantes
Keyword(s):  
Boundary Conditions ◽  
Secondary Flow ◽  
Numerical Study ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Local Flow ◽  
Spiral Case ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Changes

The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ=30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

scholarly journals Experimental and Computational Study of the Unsteady Flow in a 1.5 Stage Axial Turbine With Emphasis on the Secondary Flow in the Second Stator

1998 ◽  
Author(s):  
Ralf E. Walraevens ◽  
Heinz E. Gallus ◽  
Alexander R. Jung ◽  
Jürgen F. Mayer ◽  
Heinz Stetter
Keyword(s):  
Unsteady Flow ◽  
Secondary Flow ◽  
Computational Study ◽  
Three Dimensional ◽  
Cross Flow ◽  
Axial Flow ◽  
Time Dependent ◽  
Flow Structures ◽  
Mean Flow ◽  
Dependent Flow

A study of the unsteady flow in an axial flow turbine stage with a second stator blade row is presented. The low aspect ratio blades give way to a highly three-dimensional flow which is dominated by secondary flow structures. Detailed steady and unsteady measurements throughout the machine and unsteady flow simulations which include all blade rows have been carried out. The presented results focus on the second stator flow. Secondary flow structures and their origins are identified and tracked on their way through the passage. The results of the time-dependent secondary velocity vectors as well as flow angles and Mach number distributions as perturbation from the time-mean flow field are shown in cross-flow sections and azimuthal cuts throughout the domain of the second stator. At each location the experimental and numerical results are compared and discussed. A good overall agreement in the time-dependent flow behaviour as well as in the secondary flow structures is stated.

Numerical Investigations of Forced Convection From Rectangular Coiled Pipes

2007 ◽  
Author(s):  
Ibrahima Conte´ ◽  
Xiao-Feng Peng ◽  
Zhen Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Secondary Flow ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Heat Transfer Process ◽  
Single Vortex ◽  
Staggered Arrangement ◽  
Inclination Angles ◽  
Turbulent Air Flow

Investigations are done to numerically study forced convective heat transfer from the flow inside a rectangular coiled pipe, as micro-scale heat exchange device with staggered arrangement, to the external flow around the pipe. The commercial CFD software Fluent 6.0 is used as the solver. The problems considered were three-dimensional laminar flow of the refrigerant R141B through the tube and turbulent air flow exterior to the tube. The studied coiled pipe was composed of four rows among which two rows were encompassed in a large rectangular coil and the other two were in an inner smaller rectangular coil. The results showed remarkable differences in the flow behavior and heat transfer for different rows of tubes. The secondary flow in the tubes bends of the larger rectangular coil is very weak compared to that of the inner rectangular coil. Better heat transfer process occurred through the tubes of the second row where the higher values of the fluid temperatures were observed in the pipe. The results showed the effects of the straight tubes inclination angle on the flow behavior in rectangular coiled pipes. The shape of the secondary flow is changed from a couple of vortices in the case of smaller angle (α = 9°) to a single vortex in the case of larger angle (α = 45°). The results also showed the rotation of the maximum axial velocity due to the increase in the straight tubes inclination angles. The results are in good agreement with previous numerical and experimental works on laminar flow in helical coil pipe.

Secondary Flow in a Strong Curved Converging Channel

2005 ◽  
Vol 9 (3) ◽  
pp. 58-63
Author(s):  
L.X. L.X. ◽  
B. Wang ◽  
F.H. She
Keyword(s):  
Secondary Flow ◽  
Mesh Generation ◽  
Flow Characteristic ◽  
Three Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Rotor Spinning ◽  
Converging Channel ◽  
Transfer Channel ◽  
High Reynolds

A three-dimensional model is developed to evaluate the effect of secondary flow generated from strongly bent duct profiles and turbulent flow of high Reynolds number on fibre movement in a bent channel. The fibre configuration is more complex in a three-dimensional model with the introduction of secondary flow. The strategies of mesh generation for threedimensional problems are discussed. The flow characteristic in the transfer-channel of a rotor spinning machine is predicted.

Analysis of the Flow in the Combustor—Transition Piece Considering the Variation in the Fuel Composition

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
J. Arturo Alfaro-Ayala ◽  
A. Gallegos-Muñoz ◽  
J. Manuel Riesco-Ávila ◽  
M. Flores-López ◽  
A. Campos-Amezcua ◽  
...  
Keyword(s):  
Radial Direction ◽  
Combustion Process ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
Maximum Temperature ◽  
Fuel Composition ◽  
Temperature Profiles ◽  
Three Dimensional Model ◽  
Order Polynomial ◽  
Transition Piece

An analysis of the flow that depends on the fuel composition (natural gas) in the combustor–transition piece system, applying computational fluid dynamics, is presented. The study defines the velocity and temperature profiles at the exit of the transition piece and the hot streak along the system. The variation of the composition in the fuel depends of the amount of N2 contained in the fuel, and the hot track influences on the temperature distribution at the input of the first stage of vanes and blades of the gas turbine. The study takes place in a three-dimensional model in steady state using FLUENT® 6.3.26, applying the k-ε turbulence model and chemical equilibrium to the combustion process. The results show the influence of the transition piece geometry over the velocity and temperature profiles, principally, in the radial direction. The velocity profiles on the radial direction can be represented by six order polynomial and the temperature profile by third order polynomial. The temperature and velocity profiles keep a symmetry profile and they can be represented by six order polynomial at the circumferential direction. Knowing these profiles, it is possible to compute a more exact study of the heat transfer at vanes and blades of the first stage of the turbine to evaluate the performance and life of them. On the other hand, considering from 2% to 10% of N2 in the fuel composition, the maximum temperature is reduced in the combustion process and consequently the NOx emissions too.

Analysis of the Flow in the Combustor-Transition Piece Considering the Variation in the Fuel Composition

2010 ◽  
Author(s):  
J. Arturo Alfaro Ayala ◽  
Armando Gallegos Mun˜oz ◽  
J. Manuel Riesco A´vila ◽  
Marco Polo Flores Lo´pez ◽  
Alfonso Campos Amezcua ◽  
...  
Keyword(s):  
Radial Direction ◽  
Combustion Process ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
Maximum Temperature ◽  
Fuel Composition ◽  
Temperature Profiles ◽  
Three Dimensional Model ◽  
Order Polynomial ◽  
Transition Piece

An analysis of the flow that depends of the fuel composition (natural gas) in the combustor-transition piece system, applying Computational Fluid Dynamics, is presented. The study defines the velocity and temperature profiles at the exit of the transition piece and the hot streak along the system. The variation of the composition in the fuel depends of the amount of N2 contained in the fuel, and the hot track influences on the temperature distribution at the input of the first stage of vanes and blades of the gas turbine. The study takes place in a three-dimensional model in steady state using FLUENT ® 6.3.26, applying the k-ε turbulence model and chemical equilibrium to the combustion process. The results show the influence of the transition piece geometry over the velocity and temperature profiles, principally, in the radial direction. The velocity profiles on the radial direction can be represented by six order polynomial and the temperature profile by third order polynomial. The temperature and velocity profiles keep a symmetry profile and they can be represented by six order polynomial at the circumferential direction. Knowing these profiles, it is possible to compute a more exact study of the heat transfer at vanes and blades of the first stage of the turbine to evaluate the performance and life of them. On the other hand, considering from 5% to 10% of N2 in the fuel composition, the maximum temperature is reduced in the combustion process and consequently the NOx emissions too.

Impact of Hub Clearance on Endwall Flow in a Highly Loaded Axial Compressor Stator

2013 ◽  
Author(s):  
Christian Beselt ◽  
Dieter Peitsch ◽  
Ruben van Rennings ◽  
Frank Thiele
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Flow Structures ◽  
Blade Loading ◽  
Numerical Predictions ◽  
Clearance Flow ◽  
Flow Features ◽  
Rotating Instability

Within the present paper the development and interaction of secondary flow structures at different hub clearance gaps at high blade loadings are investigated. Three-dimensional numerical computations were carried out at three levels of hub clearance, ranging from zero to 3% of blade chord. Experimental results at 1% and 3% chord hub clearance were obtained to asses the validity of the numerical predictions. The experimentally and numerically obtained results provide a detailed picture of the development, the interaction of secondary flow structures and the influence of clearance flow for high blade loading. Therefore the time averaged flow features obtained from the experimental test rig and from numerical simulations are compared. In addition this investigation tends to explain the phenomenon of rotating instability for this compressor stator at a specific operating point and different hub clearance gaps by analyzing the secondary flow structures in the leading edge region at the hub.

scholarly journals Numerical Analysis on Flow Behavior of Molten Iron and Slag in Main Trough of Blast Furnace during Tapping Process

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Li Wang ◽  
Chien-Nan Pan ◽  
Wen-Tung Cheng
Keyword(s):  
Blast Furnace ◽  
Separation Efficiency ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Molten Iron ◽  
Three Dimensional Model ◽  
Operation Conditions ◽  
Main Trough ◽  
Iron Losses ◽  
Volume Method

The three-dimensional model was developed according to number 4 of the main trough of blast furnace at China Steel Co. (CSC BF4). The k-ε equations and volume of fluid (VOF) were used for describing the turbulent flow at the impinging zone of trough, indicating fluids of liquid iron, molten slag, and air in the governing equation, respectively, in this paper. The pressure field and velocity profile were then obtained by the finite volume method (FVM) and the pressure implicit with splitting of operators (PISO), respectively, followed by calculating the wall shear stress through Newton’s law of viscosity for validation. Then, the operation conditions and the main trough geometry were numerically examined for the separation efficiency of iron from slag stream. As shown in the results, the molten iron losses associated with the slag can be reduced by increasing the height difference between the slag and iron ports, reducing the tapping rate, and increasing the height of the opening under the skimmer.

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