Effect of the precession Strouhal number on naturally precessing jet flames

Abstract

Jet precession is a rotational oscillatory motion of an entire jet with respect to an axis in space other than its own centre line. Under certain conditions, an initially non-swirling, round jet expanding into a large cylindrical chamber is self-excited to precess about the axis of chamber (Nathan et al. 1998, J. Fluid Mech. 370, p. 347). This study aims to examine the effect of the precession Strouhal number (Stp) on the precessing jet (PJ) flame. Images of the instantaneous flame produced by a fluidic PJ nozzle are presented for Stp= 0.033, 0.13 and 0.33, respectively. It is shown that the precession Strouhal number has dominant influence on the PJ flame characteristics. For instance, an increase in Stpresults in the flame growing in length (and also volume). Consequently, the global mixing and strain rates of the flame decrease significantly as Stpincreases. By comparison, the Reynolds number effect is negligible.