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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

RANS and Large Eddy Simulation of Internal Combustion Engine Flows—A Comparative Study

[+] Author and Article Information
Xiaofeng Yang

e-mail: Xiaofeng.yang@gm.com

Venkatesh Gopalakrishnan

GM R&D,
30500 Mound Road,
Warren, MI 48090

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 23, 2013; final manuscript received November 5, 2013; published online January 9, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(5), 051507 (Jan 09, 2014) (9 pages) Paper No: GTP-13-1384; doi: 10.1115/1.4026165 History: Received October 23, 2013; Revised November 05, 2013

A comparative cold flow analysis between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) cycle-averaged velocity and turbulence predictions is carried out for a single cylinder engine with a transparent combustion chamber (TCC) under motored conditions using high-speed particle image velocimetry (PIV) measurements as the reference data. Simulations are done using a commercial computationally fluid dynamics (CFD) code CONVERGE with the implementation of standard k-ε and RNG k-ε turbulent models for RANS and a one-equation eddy viscosity model for LES. The following aspects are analyzed in this study: The effects of computational domain geometry (with or without intake and exhaust plenums) on mean flow and turbulence predictions for both LES and RANS simulations. And comparison of LES versus RANS simulations in terms of their capability to predict mean flow and turbulence. Both RANS and LES full and partial geometry simulations are able to capture the overall mean flow trends qualitatively; but the intake jet structure, velocity magnitudes, turbulence magnitudes, and its distribution are more accurately predicted by LES full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) with a RNG k-ε turbulent model and one cycle or more are good enough for capturing overall qualitative flow trends for the engineering applications. However, if one is interested in getting reasonably accurate estimates of velocity magnitudes, flow structures, turbulence magnitudes, and its distribution, they must resort to LES simulations. Furthermore, to get the most accurate turbulence distributions, one must consider running LES full geometry simulations.

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Figures

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Fig. 2

Computational domain, measurement location, and measured and GT-power calculated pressure histories

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Fig. 3

Mesh arrangement for the fine mesh with in-cylinder mesh size of 1 mm

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Fig. 6

Line contours of Urms = 12 m/s (75% of the maximum value) overlaid on top of the mean velocity contours (except (f) where Urms = 10 m/s). The line contours enclose the regions with high turbulence velocities at 100 deg ATDCE: (a) PIV, (b) LES full, (c) LES partial, (d) RANS (k-ε) full, (e) RANS (k-ε) partial, (f) RANS (RNG) full, and (g) RANS (RNG) partial. Measured and calculated swirl torque for flow bench models A, B, and C.

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Fig. 7

2D contours of mean velocity (m/s) overlaid with velocity vectors at Y = 0 plane (300 deg ATDCE): (a) PIV, (b) LES full, (c) LES partial, (d) RANS (k-ε) full, (e) RANS (k-ε) partial, (f) RANS (RNG) full, and (g) RANS (RNG) partial

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Fig. 8

2D contours of turbulence velocity magnitude (m/s) at Y = 0 plane (300 deg ATDCE): (a) PIV, (b) LES full, (c) LES partial, (d) RANS (k-ε) full, (e) RANS (k-ε) partial, (f) RANS (RNG) full, and (g) RANS (RNG) partial. Comparison of volume-integrated TKE for flow bench models A, B, and C.

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Fig. 13

Mean velocity (m/s) distributions at selected cutting planes for full geometry RANS k-ε simulations at 100 deg ATDCE

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Fig. 12

Z-component velocity distributions at Z = 10 mm (right before intake) for (a) full geometry, and (b) partial geometry RANS k-ε simulations at 100 deg ATDCE

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Fig. 11

2D contour plots of Umean. Regions with velocity magnitudes less than 25 m/s have been eliminated to better capture the internal jet structure.

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Fig. 10

Line contours of Umean for different magnitudes; depicting the intake jet structure

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Fig. 9

Line contours of Urms = 3 m/s (dashed) and 2.5 m/s (solid) overlaid on top of the mean velocity contours at 300 deg ATDCE: (a) PIV, (b) LES full, (c) LES partial, (d) RANS (k-ε) full, (e) RANS (k-ε) partial, (f) RANS (RNG) full, and (g) RANS (RNG) partial

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Fig. 14

Pressure oscillations at intake port for an individual LES cycle and first two cycles for RANS k-ε simulations

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