Effect of geometry and Reynolds number on the flow field of low-swirl combustors

Flames within combustors can be stabilised by creating recirculation of hot products to act as a heat source for the continuous ignition of the fresh mixture. Swirling flows through sudden expansions is the most common solution adopted to induce recirculation zones. In addition to flame stabilisation, the swirling motion enhances the mixing between the fuel and the oxidant streams, promoting complete fuel combustion. Because of the close relation between flow field and combustor performance, swirling flows have been widely studied in the literature. Experimental analyses usually deal with high-swirling flows because they produce strong recirculation zones which provide a stable anchoring to the flame. By comparison, few studies in the literature focus on low-swirl flow fields. In this study, low-swirling flows generated by axial swirlers are analysed. Data taken from the literature of axial and tangential velocities measured on combustors of similar geometry and swirl number are compared in order to evaluate the effect of some design and operating parameters on the flow field. The literature database is extended considering original measurements performed by the authors on a laboratory combustor. The paper aims at providing a comprehensive insight of the flow field by considering the effect of parameters not yet systematically investigated in low-swirl combustors.