Non-stationary shock motion unsteadiness in an axisymmetric geometry with pressure gradient

Abstract

Shock wave / boundary layer interaction is studied in a large area ratio axisymmetric nozzle comprising a design exit Mach number of 5.58. Shock motion unsteadiness is captured by way of the dynamic wall pressure and is evaluated during overexpanded operations up to a nozzle pressure ratio of 65. Stationary SWBLI is first considered at a nozzle pressure ratio of 28.7 such that the internal flow structure is in a restricted-shock separated state; the mean position of the annular separation shock resides at a fixed position. Conditional averages of the wall pressure fluctuations show how the motion of the incipient separation shock is out of phase with pressure fluctuations measured in the separated region downstream of the shock; pressure decreases when the shock moves downstream and vice versa. This is indicative of a long intermittent region, in terms of the boundary layer thickness, as the observed phenomena can be explained by translating the static wall pressure profile along with the shock motion. Non-stationary SWBLI is then considered by increasing the nozzle pressure ratio over time (transient startup). Under these conditions, the shock pattern varies in strength and structure as it sweeps through the nozzle. A time-frequency analyses of the fluctuating wall

Wall Pressure and External Velocity Field Relation in Overexpanded Supersonic Jets

“…This peak seems similar to those previously reported in similar nozzle configurations [4,3,21,14]. Baars et al [4], Baars and Tinney [3], Georges-Picot et al [14] and Baars et al [5] attributed the emergence of such a peak to a transonic resonnance occurring in the nozzle whereas Nguyen [21] recognised these events to be screech tones, usually encountered in supersonic jets [32,33]. Before discussing this question, we aim at describing in more details the structure on the fluctuating pressure field in the separated region.…”

“…Continuing the work of Baars and Tinney [3] and Baars et al [5], this paper aims at providing insights on the behaviour of the pressure fluctuations and their associated azimuthal Fourier modes. We focus on the separated zone of the flow in a TIC nozzle (FSS regime) providing an analysis of different regimes that can be observed by finely varying the NPR.…”

“…In this figure, the grey circle represents the nozzle wall at a given axial position and the arrows represent the force induced by a specific pressure mode on a surface element. Hence, the decomposition of the pressure field in azimuthal Fourier modes is a necessary tool to identify the sources of side loads [9,4,3,5]. The PSD of each individual azimuthal mode can be obtained as the Fourier transform of their auto-correlation function:…”

“…Hence, they did not provide a fine description of the wall pressure fluctuation with respect to the NPR in this study. In more recent studies, the same group provided experimental investigation of pressure fluctuations using varying NPR conditions and time-frequency analysis [3,5]. They therefore were able to scan an entire range of NPR conditions in a single run.…”

Effect of Stagger on the Vibroacoustic Loads from Clustered Rockets

“…16 are the signatures corresponding to shocks in the annular RSS flow passing over the Kulite as NPR was increased. 23,34 At t = 18 s, the flow enters a long period of continuous EER where the annular RSS flow structure moves up-and downstream rapidly. The wall pressure alternates between 0.4 and 1.8 atmospheres as separation bubbles and shocks in the annular RSS flow pass back and forth over the transducer.…”