Some Characteristics of Non-Reacting and Reacting Low Swirl Number Jets

Abstract

The paper considers low swirl turbulent number jets. Swirling jets are used to stabilize premixed flames in gas turbines. Normally, the swirl number is large enough to allow vortex break-down and thereby flame stabilization along the upstream edge of the back-flowbubble.With decreasing swirl the vortex-breakdown may disappear altogether. However, it has been found that under certain conditions the flame may be kept at a certain (mean) distance away from the nozzle even without vortex break-down. The mechanism for the flame holding under such conditions is discussed. The discussion is based upon LES results and some experimental data. We discuss also the precession of the central core both under non-reacting and reacting condition. LES and experimental results show that the precession of the central core is normally in the same direction as the swirl. However, for certain range of swirl numbers and at some axial distances one may find precession in the counter direction. The mechanism for this effect is discussed.