Particle image velocimetry studies of turbulent nonpremixed flames

Particle Image Velocimetry (PIV) is used to examine the velocity fields in two types of turbulent nonpremixed flame geometries, piloted and lifted. Piloted natural gas flames are studied to examine the effects of heat release on turbulent flow structure and entrainment. Velocity measurements at the base of lifted methane and ethylene flames are made to examine the nature of the stabilization region.; Qualitatively, heat release is 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 is less affected by heat release, a possible consequence of the lower density gradients. Quantitatively, heat release impacts 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 approximately 50%. Heat release also acts 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 are also examined and tend to counteract the effects of heat release by promoting entrainment and increasing turbulence intensity.; From the lifted flame study, the coflow is found to negatively impact flame stability as evidenced by a significant increase liftoff height in the presence of low coflow velocities. The PIV measurements in the region of the lifted flame base show that the instantaneous flame base is anchored primarily in the low velocity regions of the jet. The fluid velocity conditioned on the instantaneous flame base location is less than three times the laminar flame speed.