Flow Measurements Using Particle Image Velocimetry in the Ultracompact Combustor

The potential for the ultracompact combustor (UCC) lie in future research to reduced fuel consumption and improved engine performance. Velocity measurements performed on the UCC test rig at the Air Force Institute of Technology revealed flow patterns and time-averaged turbulence statistics for data taken burning hydrogen fuel in a straight and a curved cavity vane configuration. Over an equivalence ratio from 0.7 to 1.5, the straight vane configuration showed spanwise velocity decreased linearly with distance from the cavity vane over the width of the main channel. Increasing the flow rates and holding the equivalence ratio and ratio of cavity to main airflow rates constant, flow velocities in the main channel showed an increase with the curved circumferential configuration but a decrease with the straight circumferential configuration. Turbulence intensity is expected to be a major contributing factor, specifically since measured at 15% and 21% in the main channel for the straight and curved configurations, respectively. The results also show how the radial vane cavity (RVC) created strong vorticity throughout the main flow supporting a recirculation zone for mixing. Peak vorticity occurred farthest from the cavity vane suggesting the angle of the radial vane cavity is effective in generating increasing flow rotation. 1. Introduction The concept of an ultracompact combustor (UCC) has been in development for over ten years, offering the potential advantages of increasing gas turbine engine (GTE) performance while decreasing overall length and weight as described in [1–3]. Enabled by its short axial length, a UCC could be used in a GTE in place of the conventional main burner, as an interturbine burner, or both. Instead of using the axial length between the compressor and turbine, the UCC uses a channel around the engine’s circumference for the primary combustion zone (Figure 1). The combustion reaction is cavity-stabilized using trapped vortex combustion (TVC) along the outer wall of the circumferential flow path. By utilizing the circumference of the engine to complete the primary combustion, studies have shown the combustor section of a GTE could be shortened by 66% while maintaining 99% combustion efficiency [4]. Figure 1: Cross-section of (a) UCC pictorial concept and (b) trapped vortex combustion [ 5]. Specific thrust, a measure of thrust per unit air mass flow, of modern GTEs, is primarily limited by the maximum allowable turbine inlet temperature [6]. As GTE main combustors operate lean overall, burning additional fuel will raise the turbine