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## Abstract

This paper reports high-temperature/pressure turbulent burning velocities and their correlation of expanding unity-Lewis-number methane/air turbulent flames, propagating in near-isotropic turbulence in a large dual-chamber, constant-pressure/temperature, fan-stirred 3D cruciform bomb. A novel heating method is used to ensure that the temperature variation in the domain of experimentation is less than 1 °C. Schlieren images of statistically spherical expanding turbulent flames are recorded to evaluate the mean flame radius 〈R(t)〉 and the observed flame speeds, d〈R〉/dt and S_{F} (the slope of 〈R(t)〉), where S_{F} is found to be equal to the average value of d〈R〉/dt within 25 mm ≤ 〈R(t)〉 ≤ 45 mm. Results show that the normalized turbulent flame speed scales as a turbulent flame Reynolds number Re_{T,flame}=(u'/S_{L})(〈R〉/δ_{L}) roughly to the one-half power: (S_{L}^{b})^{−1}d〈R〉/dt ≈ (S_{L}^{b})^{−1}S_{F} = 0.116Re_{T,flame}^{0.54} at 300 K and 0.168Re_{T,flame}^{0.46} at 423 K, where u′ is the rms turbulent fluctuating velocity, S_{L} and S_{L}^{b} are laminar flame speeds with respect to the unburned and burned gas, and δ_{L} is the laminar flame thickness. The former at 300 K agrees well with Chaudhuri et al. (2012) [16] except that the present pre-factor of 0.116 and Re_{T,flame} up to 10,000 are respectively 14% and four-fold higher. But the latter at 423 K shows that values of (S_{L}^{b})^{−1}d〈R〉/dt bend down at larger Re_{T,flame}. Using the density correction and Bradley's mean progress variable 〈c〉 converting factor for schlieren spherical flames, the turbulent burning velocity at 〈c〉=0.5, S_{T,c=0.5}≈ (ρ_{b}/ρ_{u})S_{F}(〈R〉_{c=0.1}/〈R〉_{c=0.5})^{2}, can be obtained, where the subscripts b and u indicate the burned and unburned gas. All scattering data at different temperatures for spherical flames can be represented by S_{T,c=0.5}/S_{L}=2.9[(u′/S_{L})(p/p_{0})]^{0.38}, first proposed by Kobayashi for Bunsen flames. Also, these scattering data can be better represented by (S_{T,c=0.5}-S_{L})/u' = 0.16Da^{0.39} with small variations, where the Damköhler number Da = (L_{I}/u′)(S_{L}/δ_{L}) and L_{I} is the integral length scale.

Original language | English |
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Pages (from-to) | 173-182 |

Number of pages | 10 |

Journal | Combustion and Flame |

Volume | 172 |

DOIs | |

State | Published - 1 Oct 2016 |

## Keywords

- Expanding turbulent flames
- General correlation
- High pressure
- High temperature
- Turbulent burning velocity

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