Experimental Comparison of Different Pressure Gain Measurement Techniques for RDCs

Rotating Detonation Combustors (RDC) feature an inherently unsteady internal flow field with characteristic frequencies in the kHz range, which makes accurately quantifying the achieved pressure gain challenging. The present study therefore considers three methods to determine the stagnation pressure of the high-enthalpy outlet flow: Mach-corrected Capillary Tube Averaged Pressure (CTAP) measurements of pt4, direct Kiel probe measurements of pt8, and Equivalent Available Pressure (EAP) measurements using a thrust stand. The methods differ significantly in their relative accuracy and the amount of required instrumentation. A parametric study with all three approaches was conducted at TU Berlin over a range of configurations and operating conditions to compare the acquired data. To this end, a 5~kN class thrust stand was used along with a calibration method and base drag measurement setup. Further, a low Mach number correction was implemented for Mach-corrected CTAP and EAP data at conditions where the M8=1 assumption breaks down. The EAP data displays the highest amount of scattering due to the large number of calibration that need to be taken into account. The base drag pressure distribution on the outlet flanges, which can amount to 12.78% and more of EAP, varies significantly with the operating condition. All three methods generally agree well with one another, with EAP being the most conservative. Kiel probe measured stagnation pressure is on average about 5% higher than EAP and 3% higher than the Mach-corrected pt4. This underlines that methods with reduced instrumentation may be useful for pressure gain estimation. Nevertheless, it also shows that a standardized data reporting method may be required in the community to compare different experiments.