scholarly journals Flow Separation Dynamics in Three-Dimensional Asymmetric Diffusers

2021 ◽  
Author(s):  
Arthur Hajaali ◽  
Thorsten Stoesser
Keyword(s):  
Experimental Data ◽  
Flow Separation ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Quadrant Analysis ◽  
Spectra Analysis ◽  
Instantaneous Flow ◽  
Reversal Flow ◽  
The Mean ◽  
Similar Area

AbstractThe mean and instantaneous flow separation of two different three-dimensional asymmetric diffusers is analysed using the data of large-eddy simulations. The geometry of both diffusers under investigation is based on the experimental configuration of Cherry et al. (Int J Heat Fluid Flow 29(3):803–811, 2008). The two diffusers feature similar area ratios of $$\mathrm{AR}=4.8$$ AR = 4.8 and $$\mathrm{AR}=4.5$$ AR = 4.5 while exhibiting differing asymmetric expansion ratios of $$\mathrm{AER}=4.5$$ AER = 4.5 or $$\mathrm{AER}=2.0$$ AER = 2.0 , respectively. The Reynolds number based on the averaged inlet velocity and height of the inlet duct is approximately $${\textit{Re}}=10{,}000$$ Re = 10 , 000 . The time-averaged flow in both diffusers in terms of streamwise velocity profiles or the size and location of the mean backflow region are validated using experimental data. In general good agreement of simulated results with the experimental data is found. Further quantification of the flow separation behaviour and unsteadiness using the backflow coefficient reveals the volume portion in which the instantaneous reversal flow evolves. This new approach investigates the cumulative fractional volume occupied by the instantaneous backflow throughout the simulation, a power density spectra analysis of their time series reveals the periodicity of the growth and reduction phases of the flow separation within the diffusers. The dominating turbulent events responsible for the formation of the energy-containing motions including ejection and sweep are examined using the quadrant analysis at various locations. Finally, isourfaces of the Q-criterion visualise the instantaneous flow and the origin and fate of coherent structures in both diffusers.

scholarly journals Flow Kinematics in Variable-Height Rotating Cylinder Arrays

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Anna E. Craig ◽  
John O. Dabiri ◽  
Jeffrey R. Koseff
Keyword(s):  
Power Output ◽  
Rotation Rate ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Streamwise Velocity ◽  
Vertical Flow ◽  
Mean Flow ◽  
Freestream Velocity ◽  
Cylinder Arrays ◽  
The Mean

Experimental data are presented for large arrays of rotating, variable-height cylinders in order to study the dependence of the three-dimensional mean flows on the height heterogeneity of the array. Elements in the examined arrays were spatially arranged in the same staggered paired configuration, and the heights of each element pair varied up to ±37.5% from the mean height (kept constant across all arrays), such that the arrays were vertically structured. Four vertical structuring configurations were examined at a nominal Reynolds number (based on freestream velocity and cylinder diameter) of 600 and nominal tip-speed ratios of 0, 2, and 4. It was found that the vertical structuring of the array could significantly alter the mean flow patterns. Most notably, a net vertical flow into the array from above was observed, which was augmented by the arrays' vertical structuring, showing a 75% increase from the lowest to highest vertical flows (as evaluated at the maximum element height, at a single rotation rate). This vertical flow into the arrays is of particular interest as it represents an additional mechanism by which high streamwise momentum can be transported from above the array down into the array. An evaluation of the streamwise momentum resource within the array indicates up to a 56% increase in the incoming streamwise velocity to the elements (from the lowest to highest ranking arrays, at a single rotation rate). These arrays of rotating cylinders may provide insight into the flow kinematics of arrays of vertical axis wind turbines (VAWTs). In a physical VAWT array, an increase in incoming streamwise flow velocity to a turbine corresponds to a (cubic) increase in the power output of the turbine. Thus, these results suggest a promising approach to increasing the power output of a VAWT array.

Study on Grain Topology with Potts Model Monte Carlo Simulation

2014 ◽  
Vol 926-930 ◽  
pp. 1538-1541
Author(s):  
Hao Wang ◽  
Guo Quan Liu
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Potts Model ◽  
Three Dimensional ◽  
Wide Range ◽  
The Mean ◽  
Simulation Results ◽  
Number Of Faces ◽  
Grain Topology ◽  
Range Of Values

Three-dimensional normal grain growth has been simulated in scale 300×300×300 using the generally accepted Potts model Monte Carlo method. The studies of the topology of grains indicate that the mean number of faces in the grain network <f>=13.91 is similar to other simulation results, but higher than most of the experimental data which containing a wide range of values, i.e., <f>=11.16~13.93. The three-dimensional AboavWeaire law and Liu-Yu law are observed to hold, but the fit coefficient is different from the theory models.

Computation of Three-Dimensional Compressible Flow From a Rectangular Nozzle With Delta Tabs

1999 ◽  
Vol 121 (2) ◽  
pp. 235-242 ◽  
Author(s):  
D. R. Reddy ◽  
C. J. Steffen ◽  
K. B. M. Q. Zaman
Keyword(s):  
Experimental Data ◽  
Nozzle Exit ◽  
Flow Analysis ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Navier Stokes ◽  
Rectangular Nozzle ◽  
Flow Configurations ◽  
Subsonic Jet

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration, which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics is examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.

scholarly journals Numerical Simulation of the DLR-F4 Wing/Body Configuration With Wall Functions

2002 ◽  
Author(s):  
Eric Goncalves ◽  
Robert Houdeville
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Transport Equation ◽  
Flow Separation ◽  
Transonic Flow ◽  
Multigrid Method ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Three Dimensional Flow ◽  
Wall Functions

This paper deals with the three-dimensional RANS computations of the transonic flow around the DLR-F4 wing-body configuration with a wall law approach. A study of the behaviour of different transport-equation turbulence models is given with comparisons to experimental data. The structure of the three-dimensional flow separation predicted by the computations is described and its topological coherence is checked. Moreover, to drastically reduce the CPU cost, a computation with a multigrid method coupled to wall functions has been tested.

scholarly journals Comparison of projection of distance techniques for genetic diversity studies

2019 ◽  
Vol 42 ◽  
pp. e42483
Author(s):  
Isabela de Castro Sant'Anna ◽  
Gabi Nunes Silva ◽  
Vinicius Quintão Carneiro ◽  
Daiana Salles Pontes ◽  
Moyses Nascimento ◽  
...  
Keyword(s):  
Experimental Data ◽  
Genetic Diversity ◽  
Three Dimensional ◽  
Principal Component ◽  
Dispersion Analysis ◽  
Principal Coordinate Analysis ◽  
Projection Technique ◽  
Analysis Techniques ◽  
The Mean ◽  
Diversity Studies

The objective of this study was to compare different graphical dispersion analysis techniques in two- or three-dimensional planes. In this study, the data from different published works were used in order to determine the best methodology for analyzing the genetic diversity of different species. In this study, efficiency is measured by the amount of original distance absorbed by the projection of distances technique, which in the case of major components is equal to the amount of total variation originally available and retained by the principal components used for dispersion purposes. The projection of dissimilarity measurement technique, principal component analysis (PCA), and principal coordinate analysis (PCoA) were used. Considering the analysis by means of three orthogonal axes, the graphical dispersion efficiency was 82.22 for PCA, 87.22 for PCoA, and 85.25 for the projection of distances technique. For the 2D analysis, considering the two main axes, the mean dispersion efficiency was 69.90 for the PCA, 75.06 for the projection technique, and 78.16 for PCoA. Considering the studies carried out with experimental data of six different species, it is concluded that the principal coordinate analysis is superior.

Computation of 3-D Compressible Flow From a Rectangular Nozzle With Delta Tabs

1997 ◽  
Author(s):  
Dhanireddy R. Reddy ◽  
Christopher J. Steffen ◽  
Khairul B. M. Q. Zaman
Keyword(s):  
Experimental Data ◽  
Nozzle Exit ◽  
Flow Analysis ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Navier Stokes ◽  
Rectangular Nozzle ◽  
Flow Configurations ◽  
Subsonic Jet

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics are examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.

The three-dimensional structure of momentum transfer in turbulent channels

2012 ◽  
Vol 694 ◽  
pp. 100-130 ◽  
Author(s):  
Adrián Lozano-Durán ◽  
Oscar Flores ◽  
Javier Jiménez
Keyword(s):  
Large Scale ◽  
Layer Structure ◽  
Three Dimensional ◽  
Fractal Dimensions ◽  
Dimensional Structure ◽  
Quadrant Analysis ◽  
Reynolds Stresses ◽  
The Mean ◽  
Logarithmic Layer ◽  
Attached Eddies

AbstractThe quadrant analysis of the intense tangential Reynolds stress in plane turbulent channels is generalized to three-dimensional structures (Qs), with special emphasis on the logarithmic and outer layers. Wall-detached Qs are background stress fluctuations. They are small and isotropically oriented, and their contributions to the mean stress cancel. Wall-attached Qs are larger, and carry most of the mean Reynolds stresses. They form a family of roughly self-similar objects that become increasingly complex away from the wall, resembling the vortex clusters in del Álamo et al. (J. Fluid Mech., vol. 561, 2006, pp. 329–358). Individual Qs have fractal dimensions of the order of $D= 2$, slightly fuller than the clusters. They can be described as ‘sponges of flakes’, while vortex clusters are ‘sponges of strings’. The number of attached Qs decays away from the wall, but the fraction of the stress that they carry is independent of their sizes. A substantial fraction of the stress resides in a few large objects extending beyond the centreline, reminiscent of the very large structures of several authors. The predominant logarithmic-layer structure is a side-by-side pair of a sweep (Q4) and an ejection (Q2), with an associated cluster, and shares dimensions and stresses with the conjectured attached eddies of Townsend (J. Fluid Mech., vol. 11, 1961, pp. 97–120). Those attached eddies tend to be aligned streamwise from each other, located near the side walls between the low- and high-velocity large-scale streaks, but that organization does not extend far enough to explain the very long structures in the centre of the channel.

Comparison of Numerical and Experimental Results for a Turbulent Flow Field With a Longitudinal Vortex Pair

1993 ◽  
Vol 115 (2) ◽  
pp. 270-274 ◽  
Author(s):  
J. X. Zhu ◽  
M. Fiebig ◽  
N. K. Mitra
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Streamwise Velocity ◽  
Longitudinal Vortex ◽  
Mean Velocity ◽  
Average Deviation ◽  
Longitudinal Vortices

A numerical simulation of a three-dimensional turbulent flow with longitudinal vortices embedded in the boundary layer on a channel wall is presented. The flow is described by the unsteady incompressible Reynolds averaged Navier-Stokes equations and the standard k–ε turbulence model. A finite difference scheme based on the SOLA-algorithm is developed for the numerical solution of the governing equations. Comparison with the experimental data of Pauley and Eaton (1988 a, b) shows that the numerical computations predict the general characteristics of the flow correctly. Agreement to within 13 percent is obtained for the worst location in mean velocity fields. The average deviation of predicted mean streamwise velocity from the experimental data is 3.6 percent.

Electron Holographic Nano-Characterization of Gold Catalyst at Interface

2002 ◽  
Vol 727 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
M. Okumura ◽  
M. Haruta ◽  
K. Tanaka
Keyword(s):  
Contact Angle ◽  
Titanium Oxide ◽  
Gold Catalyst ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Electron Holography ◽  
Gold Particles ◽  
Oxide Support ◽  
The Mean ◽  
A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

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