Rotating Detonation Wave Direction and the Influence of Nozzle Guide Vane Inclination

Kurzfassung

This study describes a rotating detonation combustor (RDC) equipped with a set of nozzle guide vanes (NGVs) of variable number and inclination angle. Different instrumented guide vanes were manufactured and integrated for in situ measurements of static and stagnation pressure. It is shown that the mode progression and stagnation pressure gain of the device are not negatively affected by addition of the NGV stage. The positive effects of increasing mass flux, increasing NGV throat restriction, and decreasing air injector pressure drop are observed; however, no positive pressure gain is ultimately measured. A large number (N=680) of individual runs with a single detonation wave mode is statistically analyzed. In this analysis, the wave direction is automatically determined using a cross-correlation method, and binomial hypothesis testing is subsequently applied to the dataset. It is demonstrated that changing the vane inclination influences the preferential detonation wave direction such that the oblique shock is oriented at a less acute angle with respect to the vane´s axial chord. This results in less energy reflected back to the detonation wave and increases the ability of the vane stage to ingest the high-enthalpy flow, which also impacts a number of performance metrics. The combination of wave direction and vane inclination is categorized as either "aligned"or "misaligned" based on these observations. For the aligned configuration, the flow acceleration across the vane stage is larger, as is the static pressure difference between pressure and suction sides. The average flow Mach number at the NGV leading and trailing edges and the static pressure distribution in the converging-diverging vane section are shown to agree well with predicted values from isentropic relations. Pressure fluctuations are attenuated by some 80% across the NGV stage. The study demonstrates that for RDCs integrated into larger systems, it is imperative to know and control the wave direction, and that NGVs may be a useful tool to achieve this goal. It further underlines that a careful integration of turbomachinery with RDCs is key to harnessing the full potential of this promising technology.