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

Effect of Centrifugal Force on Turbulent Premixed Flames

[+] Author and Article Information
Alejandro M. Briones

University of Dayton Research Institute,
300 College Park,
Dayton, OH 45469
e-mail: alejandro.briones.1.ctr@us.af.mil

Balu Sekar

AFRL/RQTC, Wright-Patterson AFB,
Dayton, OH 45433

Timothy Erdmann

Innovative Scientific Solutions, Inc.,
Dayton, OH 45459
e-mail: timothy.erdmann.3.ctr@us.af.mil

Flame propagation velocity is the observed flame velocity from a reference frame rotating in the same direction and angular speed as the tube, which is also located at the axis of rotation. In other words, flame propagation velocity is the summation of the local flow velocity and the turbulent flame speed.

In the Introduction we refer to a maximum of 3500 g because that is what Lewis et al. state in their papers. However, a careful examination of the data suggests that the maximum occurs at 2500 g. Consequently, there is a better agreement of the simulations with experiments (2000 g versus 2500 g).

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 26, 2014; final manuscript received July 8, 2014; published online August 5, 2014. Editor: David Wisler.

The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Eng. Gas Turbines Power 137(1), 011501 (Aug 05, 2014) (10 pages) Paper No: GTP-14-1309; doi: 10.1115/1.4028057 History: Received June 26, 2014; Revised July 08, 2014

The effect of centrifugal force on flame propagation velocity of stoichiometric propane–, kerosene–, and n-octane–air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional (2D) geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane–air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum, then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest that there are no distinct differences among the three mixtures in terms of the trends seen of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical model is set in a noninertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh–Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also generated from the ignition zone but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau–Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame–eddy interactions. Only at low centrifugal forces, the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultracompact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000 g range.

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Fig. 1

Schematics of the (a) TVC and (b) HGC concepts. The IGVs are not shown.

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Fig. 2

Schematic of computational domain. The black lines represent impermeable adiabatic walls, whereas the red lines represent the plane of symmetry. The center of the tube and the rotation direction are also indicated. The location of the probes to measure the averaged propagation velocity is indicated by the green solid circles. The units are in meters.

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Fig. 3

Instantaneous temperature contours for 1 g stoichiometric propane–air premixed flame at t = 2, 8, 14, 20, and 25 ms. The contour units are in Kelvin. Dimensions are in centimeters.

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Fig. 4

Instantaneous static gauge pressure contours for 1 g stoichiometric propane–air premixed flame at t = 2, 8, 14, 20, and 25 ms. The contour units are in Pascals. Dimensions are in centimeters.

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Fig. 5

Instantaneous temperature contours for 1 g, 395 g, 1000 g, 2000 g, and 3000 g stoichiometric propane–air premixed flame at t = 8 ms. The contour units are in Kelvin. Dimensions are in centimeters.

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Fig. 6

Measured [3] and predicted flame propagation velocity as a function of centrifugal force for propane–air mixtures at 1 atm and φ = 1.0. The dashed lines represent the trends.

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Fig. 7

Temporal flame surface area for the propane–air flames presented in Fig. 6

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Fig. 8

Turbulent flame speed as a function of time for propane–air premixed flames presented in Fig. 6

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Fig. 9

Instantaneous temperature contours for 2000 g stoichiometric kerosene–air and n-octane–air premixed flame at t = 2, 4, 6, 7, and 8 ms. The contour units are in Kelvin. Dimensions are in centimeters.

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Fig. 10

Flame propagation velocity as a function of centrifugal force for atmospheric, stoichiometric turbulent propane–, kerosene–, and n-octane–air premixed flames




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