Simultaneous High-Frequency Pressure and TDLAS Measurements in a Small-Scale Axisymmetric Isolator with Bleed

Abstract

In this experimental study, simultaneous high-frequency pressure and Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurements were made at seven locations within the isolator region of an axisymmetric direct-connect, hydrocarbon-fueled, scramjet research combustor. The two measurement techniques were co-located in the isolator region in order to detect potential unstart per-cursors. The research combustor was attached to a Mach 2 nozzle and downstream combustion was stabilized by a cavity with additional in- stream fueling. Preliminary results show power spectral densities from the two measurements are in agreement. Further analysis is needed to identify possible pre-cursors to gross shock train movements. Shock-train propagation velocities are on the order of 2 - 4 % of the incoming freestream velocity, which is slightly lower than values measured in rectangular combustors. The non-resonant portion of the TDLAS signals provides 20 -40 ms more lead time than for shock movement than either the resonant TDLAS signal or the high- frequency pressure measurements.