Uncertainty Quantification of Kiel Probes for RDC Applications

Abstract

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs). Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several interferences from the probe in unsteady trans- and supersonic flow. This work investigates the response of a Kiel probe to highly unsteady flow, similar to that in an RDC. The probe is subjected to an underexpanded starting jet behind an incident shock with Mach numbers of 1.6 to 2.7, emanating from a shock tube with a reservoir ratio of about 394. The incidence angle of the probe is varied between 0° and 90°, as is the probe’s axial location with respect to the tube’s exit plane. High-speed schlieren images reveal the Mach number of the moving shock wave and the structure of the detached bow shock at the Kiel head, which is similar to that of a bluff body. It is shown that the measured stagnation pressure signal is independent of inflow angle over a range of 45°, and that signal attenuation is caused by gas processing through the bow shock and viscous losses in the probe’s capillary. Moving the probe downstream of the shock tube’s exit plane causes a 7% reduction in the measured stagnation pressure, due to the expansion process. The frequency response of the Kiel probe to sinusoidal, small-amplitude pressure fluctuations is determined up to 5600 Hz, confirming that no unwanted Helmholtz resonance is present in the probe. A Berg-Tijdeman representation delivers amplitude ratio and phase lag of comparable magnitude.