Numerical and Experimental Investigation of an Annular Jet Flow With Large Blockage

2004 ◽  
Vol 126 (3) ◽  
pp. 375-384 ◽  
Author(s):  
Christian Del Taglia ◽  
Lars Blum ◽  
Ju¨rg Gass ◽  
Yiannis Ventikos ◽  
Dimos Poulikakos
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Large Scale ◽  
Recirculation Zone ◽  
Blockage Ratio ◽  
Flow Conditions ◽  
Preferential Direction ◽  
Vortical Structures ◽  
Annular Jet ◽  
Unsteady Simulation

Unsteady 3-D numerical simulations and 3-D LDA measurements of an annular jet with a blockage ratio of 0.89 and Reynolds number 4400 are presented. At these flow conditions, the flow inside of the recirculation zone is asymmetric, with a preferential direction. Very good predictions of the velocity fluctuation values are achieved with the unsteady simulation technique in the same region, as the fluctuations are mainly large scale, structure dominated. A frequency near to 10 Hz is identified in the simulations, which is attributed to the principal shedding behavior of the vortical structures.

Spontaneous Break of Symmetry in Unconfined Laminar Annular Jets

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Christian Del Taglia ◽  
Alfred Moser ◽  
Lars Blum
Keyword(s):  
Reynolds Number ◽  
Preferential Flow ◽  
Flow Direction ◽  
Blockage Ratio ◽  
Steady Regime ◽  
Single Plane ◽  
Flow Asymmetry ◽  
Annular Jet ◽  
Annular Jets ◽  
Flow Symmetry

Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow.

Experimental Investigation of Free Stream Turbulence Effects on Flow Separation

2003 ◽  
Author(s):  
Mahmoud Ardebili ◽  
Yiannis Andreopoulos
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Flow Separation ◽  
Large Scale ◽  
Free Stream ◽  
Pressure Coefficient ◽  
Free Stream Turbulence ◽  
Vorticity Flux

An experimental investigation of a separated boundary layer flow has been attempted which has been created by perturbing a flat plate flow with a favorable pressure gradient immediately followed by an adverse pressure gradient. The aim of the research program is possible control of flow separation by means of free stream turbulence. The flow is configured in a large-scale low speed wind tunnel where measurements of turbulence can be obtained with high spatial and temporal resolution. A model has been designed by using CFD analysis. Mean wall pressure and vorticity flux measurements are reported in this paper. Twelve experiments with three different mesh size grids at three different Reynolds numbers have been carried out. Three bulk flow parameters seem to characterize the flow: The Reynolds number of the boundary layer, Re+, the Reynolds number of the flow through the grid, ReM, and the solidity of the grid. It was found that the pressure coefficient depends weakly on the solidity of the grids. Vorticity flux also depends on the grid used to generate free stream turbulence. The location of maximum or minimum vorticity flux moves upstream at higher ReM.

Large scales in the developing mixing layer

1976 ◽  
Vol 76 (1) ◽  
pp. 127-144 ◽  
Author(s):  
F. K. Browand ◽  
P. D. Weidman
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Vortical Structure ◽  
Mixing Layer ◽  
Two Dimensional ◽  
Conditional Sampling ◽  
Pairing Interaction ◽  
Vortical Structures ◽  
Developing Flow ◽  
Moderate Reynolds Number

A new experimental technique is described for the study of the interactions between the large-scale vortical features in the two-dimensional mixing layer. Detector probes above and below the mixing layer are used to monitor the large-scale structure. Conditional sampling is performed in a moderate Reynolds number developing flow, by using phase and amplitude information from these detector probes. It is shown that significant Reynolds-stress production is associated with the pairing interaction in which two vortical structures combine to form a single, larger vortical structure.

Fluid Dynamics of a Conical Flame Stabilizer

1989 ◽  
Vol 111 (1) ◽  
pp. 97-102 ◽  
Author(s):  
D. R. Ballal ◽  
T. H. Chen ◽  
W. J. Schmoll
Keyword(s):  
Large Scale ◽  
Recirculation Zone ◽  
Axial Direction ◽  
Combustible Mixture ◽  
High Shear ◽  
Blockage Ratio ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Two Component ◽  
Skewness And Kurtosis

Turbulence measurements were performed on a 45 deg conical flame stabilizer with a 31 percent blockage ratio, mounted coaxially at the mouth of a circular pipe and supplied with a turbulent premixed methane-air mixture at a Reynolds number of 2.85 × 104. A two-component LDA system was used in the measurement of mean velocities, turbulence intensities, Reynolds stresses, skewness, and kurtosis. It was found that combustion accelerates mean-flow velocities but damps turbulence intensity via the processes of turbulent dilatation and viscous dissipation due to heat release. Measurements in the axial direction showed that the length of the recirculation zone was nearly doubled as a result of combustion. Also, the region around the downstream stagnation point where streamlines meet and velocities change direction was found to be highly turbulent. Skewness and kurtosis data indicated that large-scale eddies carrying fresh combustible mixture are entrained into the high-shear region surrounding the recirculation zone. Finally, a discussion of turbulence-combustion interaction is presented to explain these experimental results.

Experimental Investigation of the Stability Mechanism and Emissions of a Lifted Swirl Nonpremixed Flame

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Paris A. Fokaides ◽  
Plamen Kasabov ◽  
Nikolaos Zarzalis
Keyword(s):  
Experimental Investigation ◽  
Large Scale ◽  
Recirculation Zone ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Measurement Techniques ◽  
Turbulence Structure ◽  
Ignition Process ◽  
Nonpremixed Flame

We report on the experimental investigation of a confined lifted swirl nonpremixed flame by applying a novel Airblast nozzle (Zarzalis, N., et al., 2005, Fuel Injection Apparatus, Patent No. DE 10 2005 022 772.4, EP 06 009 563.5). 3D-laser doppler anemometry, a nonintrusive, laser-based measurement technique, is adapted for the measurement of all three mean velocity components and of the six Reynolds stress components. The determination of the temperature and mixture field occurs by employing in-flame measurement techniques. Valuable information concerning the mixing procedure, the temperature distribution, the turbulence level, and the velocity field of the flame is provided. The results demonstrate that there is sufficient residence time in the precombustion area of the lifted flame in order to achieve spatial and temporal uniformity of the mixture, leading to a quasi-premixed state. It was also found that hot reaction products, carried upstream by an annular zone of reverse flow, react with fresh unburnt mixture in a re-ignition process. The determination of the flow pattern revealed the presence of an inner weak recirculation zone in the nozzle vicinity and a dominant external recirculation zone. The examination of the probability density function of the velocity measurements was also found to be a very useful tool in terms of the analysis of the turbulence structure of the flow. The bimodal distribution in the shear layer between the downstream flow and the recirculated gases yields the existence of large scale eddies. Finally, the significant reduced NOx emissions in the lean area were also shown by means of emission measurements for elevated pressure conditions.

scholarly journals Margination of white blood cells: a computational approach by a hydrodynamic phase field model

2016 ◽  
Vol 790 ◽  
pp. 389-406 ◽  
Author(s):  
Wieland Marth ◽  
Sebastian Aland ◽  
Axel Voigt
Keyword(s):  
Reynolds Number ◽  
Blood Cells ◽  
Large Scale ◽  
Field Model ◽  
Single Cells ◽  
White Blood Cells ◽  
Phase Field Model ◽  
Type Model ◽  
Flow Conditions ◽  
Inertia Effects

We numerically investigate margination of white blood cells and demonstrate the dependency on a number of conditions including haematocrit, the deformability of the cells and the Reynolds number. The approach, which is based on a mesoscopic hydrodynamic Helfrich-type model, reproduces previous results, e.g. a decreasing tendency for margination with increasing deformability and a non-monotonic dependency on haematocrit. The consideration of inertia effects, which may be of relevance in various parts of the cardiovascular system, indicates a decreasing tendency for margination with increasing Reynolds number. The effect is discussed by analysing inertial and non-inertial lift forces for single cells under different flow conditions and large-scale two-dimensional simulations of interacting red blood cells and white blood cells in an idealized blood vessel.

Experimental Investigation on Blunt-Edged UTM Delta Wing VFE-2 Configurations at Low Reynolds Number

2018 ◽  
Vol 12 (3) ◽  
pp. 255
Author(s):  
Muhammad Zal Aminullah Daman Huri ◽  
Shabudin Bin Mat ◽  
Mazuriah Said ◽  
Shuhaimi Mansor ◽  
Md. Nizam Dahalan ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Delta Wing ◽  
Low Reynolds Number ◽  
Low Reynolds
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