Experiments were conducted to improve the thermal performance of a tapered Hartmann–Sprenger tube of length-to-diameter ratio 11 by replacing its tapered end section with a cylindrical section. Three modified tapered cavities with cylindrical end sections, having length-to-diameter ratios of 4.1, 6, and 6.85, are studied along with the reference cavity for jet–cavity spacings of 2.19 and 2.58, and nozzle pressure ratios ranging from 8 to 20. Cavities are made of zirconium dioxide ( \({\text {ZrO}}_{{2}}\) ), which allows the local heat release location to be observed distinctly as a glowing spot. Results indicate that varying the end configuration of the tapered cavity primarily increases the amplitude of pressure pulsations, which helps to enhance their thermal performance. The best configuration is the one in which a cylindrical section is added immediately downstream of the heat release location of the original reference tapered cavity. A threefold increase in (i) the maximum end wall temperature and (ii) the rate of heat generation is achieved relative to the reference cavity. The latter is critical in designing a resonator ignitor with the enhanced response time. The jet–cavity resonance phenomenon is studied using a K-type thermocouple and a 1/4" (6.35-mm) microphone placed at 50 diameters from the jet nozzle exit plane.
