David J. Mee

This paper presents the noise levels generated inside a two-dimensional scramjet combustor at Mach 7.3 freestream using the focused laser differential interferometric (FLDI) technique. FLDI measurements were taken at the front, middle, and rear of the combustor’s center plane under unfueled, combustion-suppressed, and combustion-on conditions. Spectral analysis of the FLDI signal shows density fluctuations inside the scramjet combustor are almost two times higher than the freestream and confirms the capability of this technique for measuring the disturbances in a complex hypersonic flowfield. Though combustion-induced pressure rise is low, a trend in the increase in the normalized density fluctuations/noise levels due to supersonic combustion is observed across the measurement locations for the combustion-on condition. However, the overall increment in the noise level is modest between the three conditions and across the three probing locations. This infers that, for the current scramjet geometry, fueling rates, fuel–air mixing, and supersonic combustion are not the dominant noise sources in the scramjet combustor. Instead, the base hypersonic flowfield inside the scramjet combustor is the main contributor to the noise field. Noting that there is relatively large uncertainty in the measured noise levels and that the combustion-induced pressure rise is modest in the present study, further investigation is needed to check the applicability of these results to the scramjet engines with flow paths having more complex flowfields, fueling schemes, and fueling rates.