Effects of heat release and buoyancy on flow structure and entrainment in turbulent nonpremixed flames

Particle image velocimetry was used to examine the velocity fields in the near- and far-field of the axisymmetric jet in co-flow under nonreacting and reacting conditions. The jets studied include nonreacting jets at Re-o = 10,000 and 2,000 and flames at Re-o = 10,000 and 37,500. Qualitatively, heat release was seen to impact the instantaneous flow structure over the first third of the flame length by restricting the large-scale movement of the jet. The instantaneous flow structure over the remainder of the flame length was less affected by heat release, a possible consequence of the lower density gradients. Heat release was seen to impact the mean characteristics of the flow by reducing the local Reynolds number by a factor of 10 over the length of the flame and reducing the global entrainment rate by similar to 50%. In addition, heat release acted to narrow the jet width up to 20%. reduce the turbulence intensities up to 40%, and increase the centerline-velocities by factors of 2 to 3. The effects of buoyancy resulting from heat release were also examined and tended to counteract the effects of heat re;ease by promoting entrainment and increasing turbulence intensity. (C) 2001 by The Combustion Institute.