Radial Swirlers and Mixing Tube Assembly Aerodynamics and Performance Parameters Evaluation: Part 1 - Hot-Wire Measurements in the Swirler Exit Plane

Swirling flows have been widely used to generate the suitable conditions for self substained flames inside modern aeroengine combustors, both for the recirculation generation capability and turbulence intensity. Nevertheless the recent attempt to employ lean premixed prevaporized burners, which can be affected by pressure and velocity fluctuations, requires a deep knowledge of the parameters influencing the swirlers aerodynamics. The purpose of this experimental work is to characterize the aerodynamics of the assembly composed by a centripetal swirler and a straight mixing tube as a function of basic geometrical design parameters. The typical geometrical configuration of the centripetal swirler - mixing tube assembly allows to identify a group of geometrical parameters which can influence the characteristics of the flow leaving both the swirler and the straight duct: the swirler geometrical angle, the vane pitch to chord ratio, and the swirler axial height to mixing tube diameter ratio. Their range of variation has been obtained through the analysis of existing prototypes. According to the range of variation analysis a minimum number of geometries (combinations of the fundamental geometrical parameters) has been defined and tested in order to obtain significant information on the relationships between geometrical parameters and aerodynamic performances. The complex aerodynamic phenomena, which take place both inside and downstream the swirler - mixing tube assembly, have been studied with different and complementary techniques in order to have a complete characterization of the effect of the geometrical parameters variation on many aspects of the flow. All the measuring campaign has been performed at fixed total pressure drop between the settling chamber and the mixing tube outlet section. Present work has been divided in two parts. In the first part, which is here presented, velocity components, turbulence intensity and the flow angle has been measured by means of a two-components crossed miniature hot-wire probe, which has been traversed circumferentially downstream of the swirler vanes. Results from the hot-wire anemometer measuring campaign allow basically to evaluate two main performance parameters which are the swirler velocity reduction coefficient and the mass averaged flow angle, that is actually the main indicator of the swirler capability to deflect the flow and consequently it influences largely the phenomena which can occur in the mixing tube or downstream of the discharge section.