Turbulent Structure of a Diffusion Flame in Grid Turbulence

Axial, radial and tangential velocities were measured using an LDV in a field in which a laminar hydrogen jet (6.0 m/s at the center of a burner exit) was injected into a co-flowing air stream (6.0 m/s) with or without grid turbulence. The conditional sampling based on the origin of the jet and the co-flowing stream was applied. The interaction between grid turbulence and the flame is discussed in detail. It is found from the radial profile of the mean velocity that with the grid the jet and the co-flowing stream are mixed intermittently. Inside the flame the jet flows inward and the co-flowing stream flows outward. The profiles of axial and radial turbulent intensities of the co-flowing stream have a peak near the flame and at this location the histograms of velocity are bimodal. This suggests wrinkled laminar flamelets; that is, the fuel, the air and the flamelets are mixed intermittently. Moreover, the mean axial/radial velocities of the air and the flamelets are different from each other but the mean tangential velocities are the same. Thus, the histograms and the profiles of the turbulent intensity depend on the direction.