scholarly journals Effect of recirculation zones on the ventilation of a public washroom

2021 ◽  
Vol 33 (11) ◽  
pp. 117101
Author(s):  
Krishnendu Sinha ◽  
Mani Shankar Yadav ◽  
Utkarsh Verma ◽  
Janani Srree Murallidharan ◽  
Vivek Kumar
Keyword(s):  
Recirculation Zones

Numerical Simulation of Blood Flow in Patient-Specific Stenotic Carotid Bifurcation Geometries

2009 ◽  
Author(s):  
Megan Cummins ◽  
Jenn S. Rossmann
Keyword(s):  
Vortex Shedding ◽  
Carotid Bifurcation ◽  
Secondary Flows ◽  
Patient Specific ◽  
Mechanical Forces ◽  
Plaque Vulnerability ◽  
Governing Equations ◽  
Unstable Plaque ◽  
Recirculation Zones ◽  
Insight Into

The hemodynamics and fluid mechanical forces in blood vessels have long been implicated in the deposition and growth of atherosclerotic plaque. Detailed information about the hemodynamics in vessels affected by significant plaque deposits can provide insight into the mechanisms and likelihood of plaque weakening and rupture. In the current study, the governing equations are solved in their finite volume formulation in several patient-specific geometries. Recirculation zones, vortex shedding, and secondary flows are captured. The forces on vessel walls are shown to correlate with unstable plaque deposits. The results of these simulations suggest morphological features that may usefully supplement percent stenosis as a predictor of plaque vulnerability.

Flow recirculation zone length and shear rate are differentially affected by stenosis severity in human coronary arteries

2013 ◽  
Vol 304 (4) ◽  
pp. H559-H566 ◽  
Author(s):  
Ashkan Javadzadegan ◽  
Andy S. C. Yong ◽  
Michael Chang ◽  
Austin C. C. Ng ◽  
John Yiannikas ◽  
...  
Keyword(s):  
Shear Rate ◽  
Coronary Arteries ◽  
Recirculation Zone ◽  
Fluid Dynamic ◽  
Zone Length ◽  
Flow Recirculation ◽  
Stenosis Severity ◽  
Recirculation Zones ◽  
The Relationship

Flow recirculation zones and shear rate are associated with distinct pathogenic biological pathways relevant to thrombosis and atherogenesis. The interaction between stenosis severity and lesion eccentricity in determining the length of flow recirculation zones and peak shear rate in human coronary arteries in vivo is unclear. Computational fluid dynamic simulations were performed under resting and hyperemic conditions on computer-generated models and three-dimensional (3-D) reconstructions of coronary arteriograms of 25 patients. Boundary conditions for 3-D reconstructions simulations were obtained by direct measurements using a pressure-temperature sensor guidewire. In the computer-generated models, stenosis severity and lesion eccentricity were strongly associated with recirculation zone length and maximum shear rate. In the 3-D reconstructions, eccentricity increased recirculation zone length and shear rate when lesions of the same stenosis severity were compared. However, across the whole population of coronary lesions, eccentricity did not correlate with recirculation zone length or shear rate ( P = not signficant for both), whereas stenosis severity correlated strongly with both parameters ( r = 0.97, P < 0.001, and r = 0.96, P < 0.001, respectively). Nonlinear regression analyses demonstrated that the relationship between stenosis severity and peak shear was exponential, whereas the relationship between stenosis severity and recirculation zone length was sigmoidal, with an apparent threshold effect, demonstrating a steep increase in recirculation zone length between 40% and 60% diameter stenosis. Increasing stenosis severity and lesion eccentricity can both increase flow recirculation and shear rate in human coronary arteries. Flow recirculation is much more sensitive to mild changes in the severity of intermediate stenoses than is peak shear.

Wind tunnel investigation on the retention of air pollutants in three-dimensional recirculation zones in urban areas

2007 ◽  
Vol 41 (23) ◽  
pp. 4949-4961 ◽  
Author(s):  
Marcos Sebastião de Paula Gomes ◽  
André Augusto Isnard ◽  
José Maurício do Carmo Pinto
Keyword(s):  
Wind Tunnel ◽  
Urban Areas ◽  
Air Pollutants ◽  
Three Dimensional ◽  
Recirculation Zones

scholarly journals Detailed Examination of a Modified Two-Stage Micro Gas Turbine Combustor

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Andreas Schwärzle ◽  
Thomas O. Monz ◽  
Andreas Huber ◽  
Manfred Aigner
Keyword(s):  
Gas Turbine ◽  
Detailed Examination ◽  
Flame Stabilization ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Two Stage ◽  
Micro Gas Turbine ◽  
Previous Design ◽  
Recirculation Zones ◽  
Asme Paper

Jet-stabilized combustion is a promising technology for fuel flexible, reliable, highly efficient combustion systems. The aim of this work is a reduction of NOx emissions of a previously published two-stage micro gas turbine (MGT) combustor (Zanger et al., 2015, “Experimental Investigation of the Combustion Characteristics of a Double-Staged FLOX-Based Combustor on an Atmospheric and a Micro Gas Turbine Test Rig,” ASME Paper No. GT2015-42313 and Schwärzle et al., 2016, “Detailed Examination of Two-Stage Micro Gas Turbine Combustor,” ASME Paper No. GT2016-57730), where the pilot stage (PS) of the combustor was identified as the main contributor to NOx emissions. The geometry optimization was carried out regarding the shape of the pilot dome and the interface between PS and main stage (MS) in order to prevent the formation of high-temperature recirculation zones. Both stages have been run separately to allow a detailed understanding of the flame stabilization within the combustor, its range of stable combustion, the interaction between both stages, and the influence of the modified geometry. All experiments were conducted at atmospheric pressure and an air preheat temperature of 650  °C. The flame was analyzed in terms of shape, length, and lift-off height, using OH* chemiluminescence (OH-CL) images. Emission measurements for NOx, CO, and unburned hydrocarbons (UHC) emissions were carried out. At a global air number of λ = 2, a fuel split variation was carried out from 0 (only PS) to 1 (only MS). The modification of the geometry leads to a decrease in NOx and CO emissions throughout the fuel split variation in comparison with the previous design. Regarding CO emissions, the PS operations are beneficial for a fuel split above 0.8. The local maximum in NOx emissions observed for the previous combustor design at a fuel split of 0.78 was not apparent for the modified design. NOx emissions were increasing, when the local air number of the PS was below the global air number. In order to evaluate the influence of the modified design on the flow field and identify the origin of the emission reduction compared to the previous design, unsteady Reynolds-averaged Navier–Stokes simulations were carried out for both geometries at fuel splits of 0.93 and 0.78, respectively, using the DLR (German Aerospace Center) in-house code turbulent heat release extension of the tau code (theta) with the k–ω shear stress transport turbulence model and the DRM22 (Kazakov and Frenklach, 1995, “DRM22,” University of California at Berkeley, Berkeley, CA, accessed Sept. 21, 2017, http://www.me.berkeley.edu/drm/) detailed reaction mechanism. The numerical results showed a strong influence of the recirculation zones on the PS reaction zone.

Analysis of the Motion and Deformation of a Bubble Rising in a Viscoelastic Fluid

2006 ◽  
Author(s):  
Shriram Pillapakkam ◽  
Pushpendra Singh ◽  
Denis L. Blackmore ◽  
Nadine Aubry
Keyword(s):  
Velocity Field ◽  
Newtonian Fluid ◽  
Viscoelastic Fluid ◽  
Bubble Radius ◽  
Polymer Concentration ◽  
Deborah Number ◽  
Two Phase ◽  
Bubble Volume ◽  
Recirculation Zones ◽  
Bubble Rising

A finite element code based on the level set method is developed for performing two and three dimensional direct numerical simulations (DNS) of viscoelastic two-phase flow problems. The Oldroyd-B constitutive equation is used to model the viscoelastic liquid and both transient and steady state shapes of bubbles in viscoelastic buoyancy driven flows are studied. The influence of the governing dimensionless parameters, namely the Capillary number (Ca), the Deborah Number (De) and the polymer concentration parameter c, on the deformation of the bubble is also analyzed. Our simulations demonstrate that the rise velocity oscillates before reaching a steady value. The shape of the bubble, the magnitude of velocity overshoot and the amount of damping depend mainly on the parameter c and the bubble radius. Simulations also show that there is a critical bubble volume at which there is a sharp increase in the bubble terminal velocity as the increasing bubble volume increases, similar to the behavior observed in experiments. The structure of the wake of a bubble rising in a Newtonian fluid is strikingly different from that of a bubble rising in a viscoelastic fluid. In addition to the two recirculation zones at the equator of the bubble rising in a Newtonian fluid, two more recirculation zones exist in the wake of a bubble rising in viscoelastic fluids which influence the shape of a rising bubble. Interestingly, the direction of motion of the fluid a short distance below the trailing edge of a bubble rising in a viscoelastic fluid is in the opposite direction to the direction of the motion of the bubble, thus creating a “negative wake”. In this paper, the velocity field in the wake of the bubble, the effect of the parameters on the velocity field and their influence on the shape of the bubble are also investigated.

Natural Convection from a Horizontal Cylinder—Laminar Regime

1981 ◽  
Vol 103 (3) ◽  
pp. 522-527 ◽  
Author(s):  
B. Farouk ◽  
S. I˙. Gu¨c¸eri
Keyword(s):  
Natural Convection ◽  
Horizontal Cylinder ◽  
Heat Transfer Characteristics ◽  
Convective Flows ◽  
Finite Difference Numerical Method ◽  
Temperature Boundary ◽  
Recirculation Zones ◽  
Boussinesq Fluid ◽  
Temperature Boundary Condition ◽  
Good Agreement

A finite-difference numerical method has been adopted to generate flow patterns and heat transfer characteristics for laminar, steady-state, two-dimensional natural convection around a circular cylinder submerged in an unbounded Boussinesq fluid. The approach allows the use of nonuniform as well as uniform specified temperature and heat flux distributions over the cylindrical surface. Part of the results are generated for reverse convective flows with recirculation zones which occur when part of the cylinder is below the ambient temperature while the remaining part is above. The results for uniform temperature boundary condition are in good agreement with the experimental data and other solutions available in literature.

Numerical Simulation of Flow Field in Burnt Lime Hydrator

2011 ◽  
Vol 383-390 ◽  
pp. 2206-2210
Author(s):  
Ming Hua Bai ◽  
Yu Zhang ◽  
Qiu Fang Wang
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Flow Field ◽  
Velocity Gradient ◽  
Rotational Speed ◽  
Fugitive Dust ◽  
Work Condition ◽  
Burnt Lime ◽  
Stirring Effect ◽  
Recirculation Zones

The flow field distribution in burnt lime hydrator has been investigated by a software FLUENT, with k-ε turbulence model and MRF method. The simulation result shows that when four blades deflect 30°, the whole velocity gradient of flow reduces and the recirculation zones also diminish; when the rotational speed is 75r/min, the turbulence kinetic energy of stir zone between two axes becomes larger, which can raise stirring effect and reduce fugitive dust, so it is easy to achieve the purpose of improving the environment of work condition.

Flow structures in meander bends with recirculation zones: implications for bend movements

2004 ◽  
pp. 49-57 ◽  
Author(s):  
D Parsons ◽  
R Ferguson ◽  
S Lane ◽  
R Hardy
Keyword(s):  
Flow Structures ◽  
Recirculation Zones ◽  
Meander Bends
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