Simulations of freely propagating turbulent premixed flames

Transcription

1 Copyright 1996, American Institute of Aeronautics and Astronautics, Inc. AIAA Meeting Papers on Disc, July 1996 A , N J-4030, AIAA Paper Simulations of freely propagating turbulent premixed flames Thomas M. Smith Georgia Inst. of Technology, Atlanta S. Menon Georgia Inst. of Technology, Atlanta AIAA, ASME, SAE, and ASEE, Joint Propulsion Conference and Exhibit, 3nd, Lake Buena Vista, FL, July 1-3, 1996 The propagation rate and the structure of freely propagating premixed turbulent flames are investigated using one-dimensional simulations based on the Linear-Eddy Model (LEM) (Kerstein, 1991). Extensions to earlier models were carried out to include thermo-diffusive (Lewis number), finite-rate kinetic, and heat release effects. Reasonably good quantitative agreement in predictions of turbulent flame speed with fan-stirred bomb experiments of Abdel-Gayed et al. (1984) is obtained over most of the reported u-prime/sl range. The resulting propagation speeds are also in good agreement. Comparisons with weak-swirl burner experiments of stationary flames by Bedat and Cheng (1995) show that the model fails to predict the reported ut/sl with u-prime/sl. Reasons for the differences are discussed. (Author) Page 1

2 Simulations of Freely Propagating Turbulent Premixed Flames Thomas

3 be highly convoluted

4 diffusivity

5 diffusion of a marker particle due to the range of eddy sizes from / to rj based on "triplet mapping" (Kerstein, 1991) is given by: (3) Turbulent stirring is modeled as stochastic rearrangement events which interrupt

6 the future), a number of cells equal to the increase in the number of cells are truncated from the burnt side of

7 3 Results and Discussion

8 constant pressure, c p, the Lewis number of the deficient reactant, Le, and the Prandtl number, Pr, are all assumed

9

10 pre-exponential factor

11 one-dimensional simulations based

12 anisms for Nonpremixed Turbulent # -Air Jet Flames," Combust. Sci. Tech., Vol. national) on Combustion, The Combustion Institute,

13 Pope, S. B. and Anand, M. S. (1984) "Flamelet and Distributed Combustion in Premixed Turbulent Flames," Twentieth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, pp Pope,

14 Table I. Laminar Flame Properties. Flame Al A A3 A4 Bl B B3 B4 B5 B6 B7 B8 B9 BIO S L [m/sec:] $«ft xl0 4 [m] l/x!0 e [m /sec.] Le A [sec.- 1 ] 5.55e9 5.55e e8 4.55e6 3.01e8 3.01e8 3.01eS 3.01e8.736e5.641e eS 3c9 3.01e8 3.01e8 E a [cal/g mo/] Tf [K] T f [K] * Table II. Turbulent Flame Properties. Flame Al A A3 A4 Bl B B3 B4 B5 B6 B7 B8 B9 BIO Gl Re U 1 [m/sec.] L H u'/s L u t [m/sec.] WI/SL XLEM H # cells C\ tfj

15 MOVING OBSERVATION WINDOW Flame Center R INFLOW _u i OL IL L 3L 4L I Flame Brush Width - OUTFLOW 5Z, X Fig. la. Schematic diagram

16 le+00 le-04 0 Gr /Ti=1.0 Q QTi'/T =.0 <3 e>tf/t =5.0 A &rf/tl=10.0 r)'/tl=0.0 r('/ti=50.0 T1*/TI=100.0 le Fig. 3a. Normalized stirring rate parameter for different stirring rate constants, C^, as a function of N. Fig. 3b. Distribution function of eddy sizes chosen for stirring events. Yakhot's

17 YtkboCt RNG Model <r588) Andrews «al (1974). S,=.17.Crv. Andrews E a E

18 u i > ert ert J-J.\J 15.0 i,,, i,,,, l "8 q 5.0 &4 on