EXPERIMENTAL-STUDY OF PREMIXED TURBULENT COMBUSTION IN OPPOSED STREAMS .1. NONREACTING FLOW FIELD

To provide a fundamental fluid mechanical background for a broader study of premixed turbulent combustion in opposed streams, this work examines the flow field in the absence of combustion. This particular flow geometry is part of a class of stagnating flows used to study fundamental turbulent combustion processes because the flow symmetry does not require any surface near the flames. The range of conditions studied-in terms of mean velocities, turbulent intensities and length scales-is similar to those where combustion could exist in the flow. Two-component laser doppler velocimetry is used to measure the velocity statistics. The mean flow is found to be self-similar for all the conditions tested, and produces a region of plane straining which is homogeneous in the vicinity of the stagnation. This self-similar flow structure is shown to include flows stagnated by a flat plate. There is a strong interaction between the existing turbulence in the flow and the mean straining which can increase the rms velocity as the flow stagnates. The mechanism that increases the turbulence is difficult to identify with certainty, but the results are found to be consistent with the ideas of vortex stretching. The turbulence in the flow is uniform across the jets and therefore any flame in the flow will experience the same upstream conditions over much of its area.