Transient wall pressures in an overexpanded and large area ratio nozzle

Baars, W and Tinney, C 2013, 'Transient wall pressures in an overexpanded and large area ratio nozzle', Experiments in Fluids, vol. 54, no. 2, pp. 1-17.


Document type: Journal Article
Collection: Journal Articles

Title Transient wall pressures in an overexpanded and large area ratio nozzle
Author(s) Baars, W
Tinney, C
Year 2013
Journal name Experiments in Fluids
Volume number 54
Issue number 2
Start page 1
End page 17
Total pages 17
Publisher Springer
Abstract Surveys of the fluctuating wall pressure were conducted on a sub-scale parabolic-contour rocket nozzle to infer an understanding of the flow and shock structure pattern during fixed and transient operations of the nozzle. During start-up, the nozzle is highly overexpanded, which results in unsteady wall pressure signatures driven by shock foot unsteadiness. Wall pressure data are first analyzed using spatial Fourier transformations to extract the azimuthal modes during various operating states. A timefrequency analysis of the temporal azimuthal mode coefficients is then used to characterize the time-dependent spectral behavior of the wall pressure signatures during start-up. For both fixed and transient operations of the nozzle, the axisymmetric breathing mode (m = 0) comprises most of the resolved energy. As for the transient operations alone, slight deviations in ramp rate are shown to considerably influence the amount of unsteadiness that the nozzle wall is exposed to, even though the general spectral and temporal features remain similar. In particular, increased ramp rates result in increased wall pressure intensity. Secondly, three major low-frequency events (f less than or similar to 400 Hz) were observed during start-up and are attributed to: (1) FSS -> RSS transition, (2) the passing of the reattachment line from the first separation bubble, and (3) the ` end-effects regime'. The last of these refers to a condition where a trapped separation bubble opens intermittently to ambient at the nozzle lip.
Subject Aerodynamics (excl. Hypersonic Aerodynamics)
DOI - identifier 10.1007/s00348-013-1468-8
Copyright notice © Springer-Verlag Berlin Heidelberg 2013
ISSN 0723-4864
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