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.

Temperature Ratio Effects on Bluff-Body Wake Dynamics Using Large Eddy Simulation and Proper Orthogonal Decomposition

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Ryan Blanchard ◽  
Wing Ng ◽  
Uri Vandsburger
Keyword(s):  
Large Eddy Simulation ◽  
Heat Release ◽  
Proper Orthogonal Decomposition ◽  
Gas Turbines ◽  
Bluff Body ◽  
Orthogonal Decomposition ◽  
Combustion Dynamics ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Proper Orthogonal

In this article, we describe the use of proper orthogonal decomposition (POD) to investigate how the dominant wake structures of a bluff-body-stabilized turbulent premixed flame are affected by the heat released by the flame itself. The investigation uses a validated large eddy simulation (LES) to simulate the dynamics of the bluff-body's wake (Blanchard et al., 2014, “Simulating Bluff-Body Flameholders: On the Use of Proper Orthogonal Decomposition for Wake Dynamics Validation,” ASME J. Eng. Gas Turbines Power, 136(12), p. 122603; Blanchard et al., 2014, “Simulating Bluff-Body Flameholders: On the Use of Proper Orthogonal Decomposition for Combustion Dynamics Validation,” ASME J. Eng. Gas Turbines Power, 136(12), p. 121504). The numerical simulations allow the effect of heat release, shown as the ratio of the burned to unburned temperatures, to be varied independently from the Damköhler number. Five simulations are reported with varying fractions of the heat release ranging from 0% to 100% of the value of the baseline experiment. The results indicate similar trends reported qualitatively by others, but by using POD to isolate the dominant heat release modes of each simulation, the decomposed data can clearly show how the previously reported flow structures transition from asymmetric shedding in the case of zero heat-release to a much weaker, but fully symmetric shedding mode in the case of full heat release with a much more elongated and stable wake.

scholarly journals Adaptation of Phase-Lagged Boundary Conditions to Large Eddy Simulation in Turbomachinery Configurations

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Gaelle Mouret ◽  
Nicolas Gourdain ◽  
Lionel Castillon
Keyword(s):  
Large Eddy Simulation ◽  
Industrial Applications ◽  
Orthogonal Decomposition ◽  
Navier Stokes ◽  
Compression Method ◽  
Promising Technique ◽  
Computing Power ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Proper Orthogonal

With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of turbomachinery flow predictions. However, these simulations are very expensive for industrial applications, especially when a 360  deg configuration should be considered. The objective of this paper is thus to adapt the well-known phase-lagged conditions to the LES approach by replacing the traditional Fourier series decomposition (FSD) with a compression method that does not make any assumptions on the spectrum of the flow. Several methods are reviewed, and the proper orthogonal decomposition (POD) is retained. This new method is first validated on a flow around a circular cylinder with rotating downstream blocks. The results show significant improvements with respect to the FSD. It is then applied to unsteady Reynolds-averaged Navier–Stokes (URANS) simulations of a single-stage compressor in 2.5D and 3D as a first validation step toward single-passage LES of turbomachinery configuration.

Three-dimensional study of separated flow over a square cylinder by large eddy simulation

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
M Farhadi ◽  
M Rahnama
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Mean Flow ◽  
Central Difference ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy

Large eddy simulation of flow over a square cylinder in a channel is performed at Reynolds numbers of 22 000 and 21 400. The selective structure function (SSF) modelling of the subgrid-scale stress terms is used and the convective terms are discretized using quadratic upstream interpolation for convective kinematics (QUICK) and central difference (CD) schemes. A series of time-averaged velocities, turbulent stresses, and some global flow parameters such as lift and drag coefficients and their fluctuations are computed and compared with experimental data. The suitability of SSF model has been shown by comparing the computed mean flow velocities and turbulent quantities with experiments. Results show negligible variation in the flow parameters for the two Reynolds numbers used in the present computations. It was observed that both QUICK and CD schemes are capable of obtaining results close to those of the experiments with some minor differences.

Large-eddy simulation of passive scalar dispersion in an urban-like canopy

2013 ◽  
Vol 723 ◽  
pp. 404-428 ◽  
Author(s):  
D. A. Philips ◽  
R. Rossi ◽  
G. Iaccarino
Keyword(s):  
Three Dimensional ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Computational Domain ◽  
Mean Flow ◽  
Scalar Dispersion ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Building Array ◽  
The Impact

AbstractResults from large-eddy simulations of short-range dispersion of a passive scalar from a point source release in an urban-like canopy are presented. The computational domain is that of a variable height array of buildings immersed in a pressure-driven, turbulent flow with a roughness Reynolds number ${\mathit{Re}}_{\tau } = 433$. A comparative study of several cases shows the changes in plume behaviour for different mean flow directions and source locations. The analysis of the results focuses on utilizing the high-fidelity datasets to examine the three-dimensional flow field and scalar plume structure. The detailed solution of the flow and scalar fields within the canopy allows for a direct assessment of the impact of local features of the building array geometry. The staggered, skewed and aligned arrangements of the buildings with respect to the oncoming flow were shown to affect plume development. Additional post-processing quantified this development through parameters fundamental to reduced-order Gaussian dispersion models. The parameters include measures of concentration decay with distance from the source as well as plume trajectory and spread. The horizontal plume trajectory and width were found to be more sensitive to source location variations, and hence local geometric features, than vertical plume parameters.

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