scholarly journals Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

2021 ◽  
Vol 42 (9) ◽  
pp. 1297-1310
Author(s):  
Y. Zhang ◽  
M. Vanierschot
Keyword(s):  
Kinetic Energy ◽  
Proper Orthogonal Decomposition ◽  
Turbulent Kinetic Energy ◽  
Three Dimensional ◽  
Orthogonal Decomposition ◽  
Wake Flow ◽  
Recirculation Region ◽  
Mean Flow ◽  
Annular Jet ◽  
Proper Orthogonal

AbstractA three-dimensional incompressible annular jet is simulated by the large eddy simulation (LES) method at a Reynolds number Re = 8 500. The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric. The proper orthogonal decomposition (POD) analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow. The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1% of the turbulent kinetic energy, and hence their impact on the wake dynamics is studied. The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point. The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction. In addition, the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.

Single Orifice Diesel Injector Flow Characterization and the Impact of Needle Lift Using Large Eddy Simulation and Proper Orthogonal Decomposition

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Mohamed Chouak ◽  
Louis Dufresne ◽  
Patrice Seers
Keyword(s):  
Large Eddy Simulation ◽  
Proper Orthogonal Decomposition ◽  
Three Dimensional ◽  
Orthogonal Decomposition ◽  
Wall Turbulence ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Proper Orthogonal ◽  
The Impact

The flow in the injector's sac volume has been reported to influence diesel-injector nozzle flow, but few studies have characterized sac volume. Our study modeled flow in the sac volume using a large Eddy simulation (LES) approach to gain better insight into the complexity of the flow dynamics. It focused on the effect of fixed needle lifts on sac-volume internal flow of a single-hole injector with emphasis on large-scale unsteadiness; three-dimensional proper orthogonal decomposition (POD) was used to analyze the flow. The near-wall turbulence resolution of the elaborated computational fluid dynamics (CFD) model has been validated with direct numerical simulation (DNS) results in the canonical case of fully developed channel flow. The main findings are: (1) an enlarging flow jet entering the sac volume with decreasing small scales of turbulence was observed as needle lift increased. (2) three-dimensional POD revealed that the mean flow energy was nearly constant at low needle lifts (6%, 8%, and 10%) and decreased twofold at the higher needle lift of 31%. (3) The analysis of fluctuating modes revealed that flow restructuring occurred with increasing needle lift as three different energy distributions were observed with the lowest (6%), intermediary (8%, 10%, and 16%), and highest needle lifts (31%). (4) Finally, the analysis of the POD-reduced-order model has shown that the lowest frequency of mode 1, which carries the highest fluctuating energy, is responsible for the oscillation of the main rotating structure within the sac volume that causes fuel-jet enlarging/narrowing with time. This oscillation of the main structure was found to decrease with increased needle lift.

Flow Around a Leading Edge Slat: Part II — Cove Flow Dynamics via Snapshot POD

2014 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Patrick R. Richard ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Proper Orthogonal Decomposition ◽  
Shear Layer ◽  
Turbulent Kinetic Energy ◽  
Leading Edge ◽  
Orthogonal Decomposition ◽  
Flow Dynamics ◽  
Dipole Source ◽  
Proper Orthogonal

The dynamics of flow within the cove of a leading edge slat has been investigated using Proper Orthogonal Decomposition by the method of snapshots. The shear-layer that originates from the slat cusp contains a large proportion of the turbulent kinetic energy within the flow. Reconstructions performed with the first 10 POD eigenmodes illustrates that several smaller regions of vorticity persist within the shear-layer. Depending on the Reynolds number and the angle of attack, the shear-layer can impinge upon the leading edge of the main wing element, roll up within the slat cove, or be ejected through the gap between the slat trailing edge and the leading edge of the wing. This unsteady impingement of both the shear-layer, and the smaller features within the shear-layer could result in a very strong acoustic dipole source.

A Comparison of Classic and Snapshot Proper Orthogonal Decomposition on the Three Dimensional Wall Jet Flow Field

2014 ◽  
Author(s):  
Mahdi Hosseinali ◽  
Stephen Wilkins ◽  
Lhendup Namgyal ◽  
Joseph Hall
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Energy Content ◽  
Near Field ◽  
Three Dimensional ◽  
Orthogonal Decomposition ◽  
Wall Jet ◽  
Polar Coordinate ◽  
Wall Jet Flow ◽  
Turbulent Wall ◽  
Proper Orthogonal

In this paper, classic Proper Orthogonal Decomposition (POD) on a polar coordinate and snapshot POD on a Cartesian grid will be applied separately in the near field of a turbulent wall jet. Three-component stereoscopic PIV measurements are performed in the transverse plane of a wall jet formed using a round contoured nozzle with a Reynolds number of 250,000. Eigenfunctions and energy distributions of the two methods are compared. Reconstructions using same number of modes and same content of energy have been compared. The effect of grid resolution on the energy content of the classic method has also been studied.

Sign in / Sign up

Export Citation Format

Share Document