scholarly journals Duckling mortality at a river weir

2019 ◽  
Vol 133 (2) ◽  
pp. 167
Author(s):  
Stewart B. Rood ◽  
Amber Willcocks
Keyword(s):  
Recirculation Zone ◽  
Anas Platyrhynchos ◽  
Prior Report ◽  
Low Head ◽  
Recirculation Zones

River weirs are low-head dams that dissipate energy by creating hydraulic recirculation zones at their base. These recirculation zones are a major cause of human drownings and have been referred to as “drowning machines”. We observed an event that allowed us to add ducklings to the list of weir victims. As a Mallard (Anas platyrhynchos) hen and her brood floated over the Calgary weir, the mother flew safely over the hydraulic recirculation. The ducklings drifted into the recirculation and three quickly passed through; four were stalled, repeatedly recirculated, and died. We observed other regional weirs where adult birds commonly flew over the hazard. We did not observe any other waterfowl drifting into recirculation zones, and we found no prior report of this lethal hazard. Although mortality might be rare at each weir, with hundreds of thousands of low-head dams worldwide, the collective hazard could be substantial. Weirs can be designed to eliminate the lethal recirculation zone, and the apparent hazard to ducklings could provide another motivation to redesign or modify these common structures.

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.

Numerical Investigation of Turbulence in Abdominal Aortic Aneurysms

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Digvijay S. Rawat ◽  
Mathieu Pourquie ◽  
Christian Poelma
Keyword(s):  
Vortex Ring ◽  
Recirculation Zone ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Transitional Flow ◽  
Recirculation Region ◽  
Abdominal Aortic ◽  
Recirculation Zones ◽  
Primary Focus ◽  
Small Change

Computational fluid dynamics (CFD) is a powerful method to investigate aneurysms. The primary focus of most investigations has been to compute various hemodynamic parameters to assess the risk posed by an aneurysm. Despite the occurrence of transitional flow in aneurysms, turbulence has not received much attention. In this article, we investigate turbulence in the context of abdominal aortic aneurysms (AAA). Since the clinical practice is to diagnose an AAA on the basis of its size, hypothetical axisymmetric geometries of various sizes are constructed. In general, just after the peak systole, a vortex ring is shed from the expansion region of an AAA. As the ring advects downstream, an azimuthal instability sets in and grows in amplitude thereby destabilizing the ring. The eventual breakdown of the vortex ring into smaller vortices leads to turbulent fluctuations. A residence time study is also done to identify blood recirculation zones, as a recirculation region can lead to degradation of the arterial wall. In some of the geometries simulated, the enhanced local mixing due to turbulence does not allow a recirculation zone to form, whereas in other geometries, turbulence had no effect on them. The location and consequence of a recirculation zone suggest that it could develop into an intraluminal thrombus (ILT). Finally, the possible impact of turbulence on the oscillatory shear index (OSI), a hemodynamic parameter, is explored. To conclude, this study highlights how a small change in the geometric aspects of an AAA can lead to a vastly different flow field.

Recirculation Flow of Nanofluid Through Periodic Nanotube with Hexagonal Cross-Section

2020 ◽  
Vol 12 (2) ◽  
pp. 147-155
Author(s):  
Md. Nazmul Hasan ◽  
Asif Mahmud ◽  
Md. Shakhaoath Khan ◽  
Md. Azmol Huda ◽  
Nazmul Islam
Keyword(s):  
Cross Section ◽  
Recirculation Zone ◽  
Geometric Parameters ◽  
Governing Equations ◽  
Throat Radius ◽  
Recirculation Flow ◽  
Hexagonal Cross Section ◽  
Recirculation Zones ◽  
Flow Through ◽  
Fortran 90

In this paper, we have investigated the recirculation flow of a nanofluid in the developed flow zones of an infinite periodic nanotube with a hexagonal cross-section. A numerical analysis is commenced to identify the existence of single and double recirculation zones for various geometric parameters. The boundary element method (BEM) has been formulated for an unbound interim nanotube for solving the governing equations. We have developed the codes for the BEM method in FORTRAN 90, and the graphs have been plotted in MATLAB 2016. We have various geometric parameters to inaugurate circumstances for the onset of recirculation. We have found recirculation flow through this type of periodic tube for a set of geometric parameters such as amplitude, wavelength and throat radius etc. Firstly recirculation flow in the expansion region of the nanotube is prophesied to arrive beyond a critical amplitude and second order recirculation zone is also predicted for still higher amplitudes. The recirculation flow has great importance in the application, for example, it can be used in the particle separation process.

The Influence of Premixed Combustion Flame Stabilizer Geometry on Flame Stability and Emissions

1981 ◽  
Vol 103 (4) ◽  
pp. 749-758 ◽  
Author(s):  
N. A. Al Dabbagh ◽  
G. E. Andrews
Keyword(s):  
Gas Turbines ◽  
Recirculation Zone ◽  
Combustion Efficiency ◽  
Premixed Combustion ◽  
Major Influence ◽  
Flame Stability ◽  
Zone Size ◽  
Recirculation Zones ◽  
Combustion Systems ◽  
Ultimate Objective

Premixed combustion systems for gas turbines offer the possibility of low-pollution, high-combustion efficiency and good temperature distribution. They form a basis by which other well-mixed combustion systems may be assessed. The ultimate objective of this work is the development of nonpremixed rapid mixing combustion systems. Different geometries of baffle flame stabilizers are tested to study the influence of recirculation zone size and number of recirculation zones on flame stability, combustion efficiency and NOx. The results show that the flame stabilizer geometry has a major influence on combustion efficiency and flame stability but a lesser influence on NOx. Optimum equivalence ratios are identified for good combustion efficiency and low NOx at simulated low and high-power engine conditions.

scholarly journals Estimation on migration characteristics of leachate using analysis of hydraulic conductivity at bioreactor landfill

2019 ◽  
Vol 38 (1) ◽  
pp. 59-68
Author(s):  
Hyeong-Jin Choi ◽  
Yong Choi ◽  
Seung-Whee Rhee
Keyword(s):  
Hydraulic Conductivity ◽  
Moisture Content ◽  
Bulk Density ◽  
Recirculation Zone ◽  
Migration Time ◽  
Bioreactor Landfill ◽  
Leachate Recirculation ◽  
Factors Affecting ◽  
Recirculation Zones ◽  
The Relationship

In bioreactor landfill, moisture content is one of the most important factors affecting the migration of leachate. The migration characteristics of leachate in the Sudokwon landfill site was estimated by examining relationships among self-loading weight of waste (waste weight load), bulk density, hydraulic conductivity and moisture content of the landfilled waste. Experimental zones in the Sudokwon landfill were divided into leachate recirculation zones (3-C and 4-C zone) and reference zone (3-D zone). The volume of the leachate recirculation was 207 m3 d-1 for 12 months in the 3-C zone and 190 m3 d-1 for 3 months in the 4-C zone. A logarithmic graph can describe the relationship between waste weight load and bulk density by moisture content. However, both the relationship between bulk density and hydraulic conductivity and the relationship between hydraulic conductivity and waste weight load can be expressed by an exponential graph. Through these relationships, generalised equations for hydraulic conductivity were established using moisture content and waste weight load. The hydraulic conductivity calculated from the generalised equation in the leachate recirculation zone was estimated to be 6.27 × 10-4 cm s-1 in the 3-C zone and 4.43 × 10-4 cm s-1 in the 4-C zone. The migration time of leachate in the leachate recirculation zone was estimated to be 64.2 days in the 3-C zone and 94.5 days in the 4-C zone, respectively.

Flow Characteristics of a Servco Fume Cupboard

2013 ◽  
Vol 393 ◽  
pp. 753-758 ◽  
Author(s):  
Mohd Amal Asrol Omar ◽  
Wirachman Wisnoe ◽  
Azman Bakri
Keyword(s):  
Cross Sections ◽  
Recirculation Zone ◽  
Flow Characteristic ◽  
Cfd Simulation ◽  
Flow Characteristics ◽  
Shape Design ◽  
Breathing Zone ◽  
Working Chamber ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd

A fume cupboard is equipment used to carry out chemical reaction process in its working chamber. A suction fan takes air or gas from the working chamber and releases it outside. When the air or gas is flowing from the inlet to the outlet, some recirculation zones may be formed depending on the internal shape design of the fume cupboard. This recirculation zone may create back flow that can be the cause of leakage. Leakage happens when airborne contaminants escape through inlet of the fume cupboard to the user breathing zone and the surrounding air in the room. To have a good fume cupboard, the recirculation zone needs to be minimised. In this paper, the flow characteristic of a Servco fume cupboard will be presented as a result of computational fluid dynamics (CFD) simulation using κ-ω turbulence model. The results are presented in terms of velocity components at different cross sections of the fume cupboard.

Study of the Cold Flow Field of a Multi-Injection Combustor

2009 ◽  
Author(s):  
F. Wang ◽  
Y. Huang ◽  
T. Deng
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Gas Turbine ◽  
Recirculation Zone ◽  
Turbulent Model ◽  
Gas Turbine Combustor ◽  
Cold Flow ◽  
Basic Work ◽  
Lining Structure ◽  
Recirculation Zones

Multi-injection combustor (MIC) could extend the steady working range of the whole combustor and reduce emissions therefore, so it is one of the Gas Turbine Combustor (GTC) design direction of future. The cold flow character of MIC is the basic work for MIC designers. Because of the low cost nowadays, the CFD method is a very suitable tool for it. Thus, firstly realizable k-epsilon turbulent model (RKE) and Reynolds stress turbulent model (RSM) were used to simulate the downstream flow field of a double radial swirl-cup amongst a simple tube, and the prediction results are compared with the experimental data which are gained by another researcher in Beihang University. The comparison between the experimental data and the CFD prediction results are shown that in most regions, the prediction results quite agree with the experimental data, and the max error of RKE model and RSM model is about 5% and 3% respectively. So the RKE model can be used for swirl-cup combustor simulation for its low computing cost. Then the RKE model is applied in a single swirl-cup gas turbine combustor and two kinds of multi-injection GTC flow field simulation. In the comparison between one single swirl-cup and nine arranged swirl-cups which all are in the same lining structure, each swirl-cup in MIC has a recirculation zone after its exit. Gradually, the recirculation zones mixed and united together in the downstream region. Finally, the recirculation zones structure turns to be similar to the structure in the single swirl-cup GTC after the primary combustion holes. In the other comparison between two kinds of lining structures which all are fixed with the same multi-injection head, the primary combustion holes affect flow field obviously. All the recirculation zones finished before the former primary combustion holes of the MIC without the primary combustion holes, and the separated recirculation zones form a new recirculation zone close to the primary holes for the MIC with primary holes. So the MIC design should combine with the real combustor lining structure to make a high performance for the whole combustor.

Effects of Back-Pressure in a Lean Blowout Research Combustor

1993 ◽  
Vol 115 (3) ◽  
pp. 486-498 ◽  
Author(s):  
G. J. Sturgess ◽  
S. P. Heneghan ◽  
M. D. Vangsness ◽  
D. R. Ballal ◽  
A. L. Lesmerises ◽  
...  
Keyword(s):  
Temperature Profile ◽  
Recirculation Zone ◽  
Shear Layers ◽  
Experimental Information ◽  
Back Pressure ◽  
Gaseous Fuel ◽  
Lean Blowout ◽  
Recirculation Zones ◽  
Flame Behavior

Experimental information is presented on the effects of back-pressure on flame-holding in a gaseous fuel research combustor. Data for wall temperatures and static pressures are used to infer behavior of the major recirculation zones, as a supplement to some velocity and temperature profile measurements using LDV and CARS systems. Observations of flame behavior are also included. Lean blowout is improved by exit blockage, with strongest sensitivity at high combustor loadings. It is concluded that exit blockage exerts its influence through effects on the jet and recirculation zone shear layers.

scholarly journals An Investigation of the Establishment of a Recirculation Zone by Swirling Flows Within a Conical Duct

1983 ◽  
Author(s):  
P. Rama Mohan ◽  
C. M. Vara Prasad
Keyword(s):  
Experimental Data ◽  
Recirculation Zone ◽  
Cone Angle ◽  
Swirling Flows ◽  
Short Length ◽  
Maximum Pressure ◽  
Swirl Number ◽  
Curve Fit ◽  
Inlet Swirl ◽  
Recirculation Zones

This paper reports an investigation carried out on the recirculation zones established in conical chambers with radial vaned inlet swirlers. The boundaries of the recirculation zones established in various conical chambers of different cone angles are presented for different inlet swirl numbers and an optimum cone angle which gives a reasonably short length of the recirculation zone with maximum pressure recovery is suggested. The inlet swirl number is also optimized for a fairly high swirl strength within the recirculation zone and the inlet swirl number for which the recirculation completely disappears is also estimated. In addition to this, an equation is curve-fit to the experimental data which correlates the length of the recirculation zone for any given cone angle and inlet swirl number.

scholarly journals CFD predictions of Swirl burner aerodynamics with variable outlet configurations

2019 ◽  
pp. 31-43 ◽  
Author(s):  
Hesham Baej
Keyword(s):  
Recirculation Zone ◽  
Chemical Species ◽  
Swirl Burner ◽  
Low Velocity ◽  
Lean Premixed Combustion ◽  
Active Chemical ◽  
Lean Premixed ◽  
Swirling Flame ◽  
Recirculation Zones ◽  
Reduction Of Nox

Swirl stabilised combustion is one of the most widely used techniques for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using several gaseous blends at a constant power output. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by the blend and infer that it is governed by both the shear layer surrounding the Central Recirculation Zones (CRZ) and the gas composition.

Sign in / Sign up

Export Citation Format

Share Document