A laser Doppler anemometer was used to measure the axial and
radial velocity components of hydrogen-air counterflow diffusion
flames (CFDF). An axisymmetric opposed jet burner (OJB) used seeded
air in one cylindrical tube, and a hydrogen-nitrogen mixture in the opposing
cylindrical tube. Velocity measurements were made at four different
operating flow rates, and were used to compute the associated
strain rate fields. The results were used to qualitatively assess current
CFDF modeling schemes, and to expand the knowledge of the fluid velocity
field behavior within these flames.
The data show behavior qualitatively consistent with most models
and experimental studies: the radial velocity is essentially linear with
radial position, and the velocity data collapse to functions of axial position
only for regions away from the stagnation plane. However, the
data also show a variable strain rate field and a relatively thick reaction
zone, which are both inconsistent with CFDF models. The axial velocity
fields also behaved unexpectedly as the operating flow rates were increased,
transitioning from the characteristic N -shaped profile to an
asymptotically-approaching profile.
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