Fuel and Combustion

Fuel and Combustion

Numerical Investigation of the Effects of Blockage Ratio and Obstruction Geometry on Flame Acceleration and Overpressure of Gas Explosion

Authors
Sobhan Emami Koopaei
Kiumars Mazaheri
Department of Mechanical Engineering, Gas Dynamics Laboratory, Tarbiat Modares University, Tehran, Iran
Abstract
The aim of the present paper is to investigate the effects of obstacles with different blockage ratio and geometry on flame acceleration and overpressure of premixed flame propagation using large eddy simulation. The subgrid-scale reaction rate is represented by the Flame-wrinkling combustion model developed by Weller. For the purposes of this paper, three different obstacles with circular, triangular and square cross-sections are studied here covering blockage ratios ranging from 10% to 72%. It is found that square and circular obstacles, result the fastest and the slowest flame acceleration, respectively. Velocity of jet-like flow around the obstacles and the level of turbulence generated by obstacles are increased with increasing blockage ratio and caused an increase in flame speed. The amount of unburned mixture trapped behind the obstacles, that plays a significant role in the overpressure, is found to be the highest for triangular obstacles.The maximum overpressure increases with increasing blockage ratio, but the rate of increase depends on the obstacle geometry. The square obstacles lead to highest overpressures while the circular ones produce the lowest overpressure. The time needed to reach the maximum overpressure decreases with increasing blockage ratio and depends on the obstacle geometry.
Keywords
Turbulent premixed flame
Flame acceleration
Large eddy simulation
Explosion overpressure
Obstacles
1.     T. Poinsot and D. Veynante, Theoretical and Numerical Combustion. Second Edition, R.T. Edwards, Inc., Philadelphia, USA, 2005.
2.     A. R. Masri, S. S. Ibrahim, N. Nehzat and A. R. Green, “Experimental Study of Premixed Flame Propagation Over Various Solid Obstructions,” Experimental Thermal and Fluid Science, 21, 2000, pp. 109-116.
3.     S. S. Ibrahim and A. R. Masri, “The Effects of Obstructions on Overpressure Resulting from Premixed Flame Deflagration,” Journal of Loss Prevention in the Process Industries, 14, 2001, pp. 213-221.
4.     S. S. Ibrahim, G. K. Hargarve and T. C. Williams, “Experimental Investigation of Flame/Solid Interactions in Turbulent Premixed Combustion,” Experimental Thermal and Fluid Science, 24, 2001, pp. 99-106.
5.     G. K. Hargrave, S. Jarvis and T. C. Williams, “A Study of Transient Flow Turbulence Generation during Flame/Wall Interactions in Explosions,” Measurement Science and Technology, 13, 2002, pp. 1036-1042.
6.     S. Patel, S. Jarvis, S. S. Ibrahim and G. K. Hargrave, “An Experimental and Numerical Investigation of Premixed Flame Deflagration in a Semiconfined Explosion Chamber,” Proceedings of the Combustion Institute, 29, 2002, pp. 1849-1854.
7.     J. E. Kent, A. R. Masri and S. H. Starner, “A New Chamber to Study Premixed Fame Propagation Past Repeated Obstacles,” 5th Asia-Pacific Conference on Combustion, the University of Adelaide, Australia, July 2005.
8.     R. Hall, A. R. Masri, P. Yaroshchyk and S. S. Ibrahim, “Effects of Position and Frequency of Obstacles on Turbulent Premixed Propagating Flames,” Combustion and Flame, 156, 2009, pp. 439-446.
9.     D. J. Park, A. R. Green, Y. S. Lee and Y. Chen, “Experimental Studies on Interactions between a Freely Propagating Flame and Single Obstacles in a Rectangular Confinement,” Combustion and Flame, 150, 2007, pp. 27-39.
10.  P. Naamansen, D. Baraldi, B. H. Hjertager, T. Solberg and S. Cant, “Solution Adaptive CFD Simulation of Premixed Flame Propagation Over Various Solid Obstructions,” Journal of Loss Prevention in the Process Industries, 15, 2002, pp. 189-197.
11.  S. Patel, S. S. Ibrahim, M. A. Yehia and G. K. Hargarve, “Investigation of Premixed Turbulent Combustion in a Semi-confined Explosion Chamber,” Experimental Thermal and Fluid Science, 27, 2003, pp. 355-361.
12.  M. P. Kirkpatrick, S. W. Armfield, A. R. Masri and S. S. Ibrahim, “Large Eddy Simulation of a Propagating Turbulent Premixed Flame,” Flow, Turbulence and Combustion, 70, 2003, pp. 1-19.
13.  A. R. Masri, S. S. Ibrahim and B. J. Cadwallader, “Measurements and Large Eddy Simulation of Propagating Premixed Flames,” Experimental Thermal and Fluid Science, 30, 2006, pp. 687-702.
14.  S. R. Gubba, S. S. Ibrahim, W. Malalasekera and A. R. Masri, “LES Modeling of Premixed Deflagrating Flames in a Small-scale Vented Explosion Chamber with a Series of Solid Obstructions,” Combustion Science and Technology, 180, 2008, pp. 1936-1955.
15.  S. R. Gubba, S. S. Ibrahim, W. Malalasekera and A. R. Masri, “An Assessment of Large Eddy Simulations of Premixed Flames Propagating Past Repeated Obstacles,” Combustion Theory and Modelling, 13, No. 3, 2009, pp. 513-540.
16.  S. S. Ibrahim, S. R. Gubba, A. R. Masri and W. Malalasekera, “Calculations of Explosion Deflagrating Flames using a Dynamic Flame Surface Density Model,” Journal of Loss Prevention in the Process Industries, 22, 2009, pp. 258-264.
17.  V. Di Sarli, A. Di Benedetto, G. Russo, S. Jarvis, E. J. Long and G. K. Hargrave, “Large Eddy Simulation and PIV Measurements of Unsteady Premixed Flames Accelerated by Obstacles,” Flow, Turbulence and Combustion, 83, 2009, pp. 227-250.
18.  V. Di Sarli, A. Di Benedetto and G. Russo, “Using Large Eddy Simulation for Understanding Vented Gas Explosions in the Presence of Obstacles,” Journal of Hazardous Materials, 169, 2009, pp. 435-442.
19.  V. Di Sarli, A. Di Benedetto and G. Russo, “Sub-grid Scale Combustion Models for Large Eddy Simulation of Unsteady Premixed Flame Propagation around Obstacles,” Journal of Hazardous Materials, 180, 2010, pp. 71-78.
20.  H. G. Weller, “The Development of a New Flame Area Combustion Model using Conditional Averaging,” Thermo-Fluids Section report TF/9307, Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, March 1993.
21.  A. Yoshizawa and K. Horiuti, “A Statistically-Derived Subgrid-Scale Kinetic Energy Model for the Large-Eddy Simulation of Turbulent Flows,” Journal of the Physical Society of Japan, 54, 1985, pp. 2834-2839.
22.  H. G. Weller, G. Tabor, A. D. Gosman and C. Fureby, “Application of a Flame-Wrinkling LES Combustion Model to a Turbulent Mixing Layer,” Proceedings of the Combustion Institute, 27, 1998, pp. 899-907.
23.  O. L. Gulder, “Turbulent Premixed Flame Propagation Models for Different Combustion Regimes,” Proceedings of the Combustion Institute, 23, 1990, pp. 743-750.
24.  I. K. Nwagwe, H. G. Weller, G. R. Tabor, A. D. Gosman, M. Lawes, C. G. W. Sheppard and R. Wooley, “Measurements and Large Eddy Simulations of Turbulent Premixed Flame Kernel Growth,” Proceedings of the Combustion Institute, 28, 2000, pp. 59-65.
25.  S. B. Pope, Turbulent Flows, First Edition, Cambridge University Press, Cambridge, UK, 2000.
26.  I. B. Celik, Z. N. Cehreli and I. Yavuz, “Index of Resolution Quality for Large Eddy Simulations,” Journal of Fluids Engineering, 127, 2005, pp. 949-958.
27.  A. Kempf, R. P. Lindstedt and J. Janicka, “Large-Eddy Simulation of a Bluff-body Stabilized Nonpremixed Flame,” Combustion and Flame, 144, 2006, pp. 170-189.