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The interaction of turbulence and pressure gradients in a baffle-stabilized premixed flame

Published online by Cambridge University Press:  21 April 2006

M. V. Heitor ,
A. M. K. P. Taylor  and
J. H. Whitelaw
M. V. Heitor
Affiliation:
Department of Mechanical Engineering, Imperial College, London SW7 2BX, UK
A. M. K. P. Taylor
Affiliation:
Department of Mechanical Engineering, Imperial College, London SW7 2BX, UK
J. H. Whitelaw
Affiliation:
Department of Mechanical Engineering, Imperial College, London SW7 2BX, UK
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Abstract

Simultaneous measurements of time-resolved velocity and temperature have been obtained by laser-Doppler anemometry and numerically compensated fine-wire thermocouples in the near wake of a premixed flame stabilized on a disk baffle located on the axis, and at the exit, of a confining pipe. The diameter of the disk was 0.056 m, the diameter of the pipe was 0.080 m, the volumetric equivalence ratio with natural gas as the fuel was 0.79 and the Reynolds number, based on pipe diameter and upstream pipe bulk velocity of 9 m/s, was 46 800. The purpose of the measurements is to quantify the relative magnitudes of terms involving the mean pressure gradient and Reynolds stresses in the balance of turbulent kinetic energy and heat flux in a strongly sheared, high-Reynolds-number, reacting flow. The latter term has been associated with non-gradient diffusion in other flows. Source terms involving the mean pressure gradient are large in the conservation of turbulent heat flux but not in the conservation of Reynolds stress. The ‘thin-flame’ model of burning suggests that the sign and magnitude of the heat flux is closely related to the conditioned mean velocities. The mean axial velocity of the reactants is larger (by up to 0.27 of the reference velocity) than that of the products on the low-velocity side of the shear layer that surrounds the recirculation bubble but the reverse is true on the high-velocity side. These observations are related to the sign of the axial pressure gradient, which is associated with the streamline curvature, and the consequent preferential acceleration of the low-density products. Generally, the Reynolds stresses of the products are higher than those of the reactants and, in contrast to previously reported measurements, the contribution to the unconditioned stresses by the difference in the mean velocity between products and reactants, the so-called ‘intermittent’ contribution, is small. This is a consequence of the high Reynolds number of our flow.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 181 , August 1987 , pp. 387 - 413
Copyright
© 1987 Cambridge University Press

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