The effect of nozzle contour on the vibroacoustic loads that form from high area ratio rocket nozzles during sea level launch

Abstract

An accurate assessment of the vibro-acoustic loads that form during startup of large area ratio rocket nozzles is important for sea-level launch vehicle design and certification. These loads are driven principally by various flow and shock patterns that form inside the nozzle, which are unique to the nozzle contour. This presentation will review a number of laboratory-scale measurements of different nozzle contours and configurations reported by Baars and Tinney, Exp. Fluids, (2013), Donald et al. AIAA Journal (2014), Canchero etal. AIAA Journal (2016), and Rojo et al. AIAA Journal (2016) as it relates to launch platforms of current interest. In particular are the various sources of noise pertaining to transonic resonance, broadband shock associated noise, and the end-effects-regime (EER). The latter of these is unique to the thrust-optimized parabolic contour nozzle as is used on the current Space Launch System vehicle. This EER event occurs when the annular flow structure is in a partial restricted-shock separated (RSS) flow state and is categorized by an onset of relatively low frequency energy driven by intermittent buffeting between RSS flow and partial free shock separated flow at the nozzle lip.