Wavelet Analysis of Wall-Pressure Fluctuations in a Supersonic Blunt-Fin Flow

Poggie, Jonathan; Smits, Alexander J.

doi:10.2514/2.18

Cited by 27 publications

(5 citation statements)

References 20 publications

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“…Camussi & Guj 1997;Guj & Camussi 1999;Camussi & Di Felice 2006). Wavelet analyses of wall pressure fluctuations have been carried out by Poggie & Smiths (1997) and Lee & Sung (2002). The latter authors showed interesting features of the propagation of the pressure perturbations and their phase velocity.…”

Section: Post-processing Methodsmentioning

confidence: 99%

Cross-wavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers

2008

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Pressure fluctuations measured at the wall of a turbulent boundary layer are analysed using a bi-variate continuous wavelet transform. Cross-wavelet analyses of pressure signals obtained from microphone pairs are performed and a novel post-processing technique aimed at selecting events with strong local-in-time coherence is applied. Probability density functions and conditionally averaged equivalents of Fourier spectral quantities, usually introduced for modelling purposes, are computed. The analysis is conducted for signals obtained at low Mach numbers from two different non-equilibrium turbulent boundary layer experiments. It is found that that the selected events, though statistically independent, exhibit bi-modal statistics while the conditional coherence function coincides with its non-conditional Fourier equivalent. The physical nature of the selected events has been further explored by the computation of ensemble-averaged pressure time signatures and the results have been physically interpreted with the aid of numerical and experimental results from the literature. In both experiments, it has been found that the major physical mechanisms responsible for the observed conditional statistics are represented by sweep-type events which can be ascribed to the effect of streamwise vortices in the near-wall region. More precisely, the wavelet analysis highlights the convection of the selected structures in both cases. Conversely, compressibilty effects could be related to these events only in one case.

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Section: Post-processing Methodsmentioning

confidence: 99%

Cross-wavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers

2008

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“…Among the various wavelets proposed so far, consideration is given to a real-valued 'Mexican hat' wavelet, which is defined as ψ(t) = (1 − t 2 ) exp(− 1 2 t 2 ). This wavelet is known to be effective in resolving highamplitude peaks in the signal (Addison 1999;Poggie & Smits 1997). Compared to the Morlet wavelet, the Mexican hat wavelet provides better temporal resolution at the expense of frequency resolution.…”

Section: Wavelet Transform Analysismentioning

confidence: 99%

Multiple-arrayed pressure measurement for investigation of the unsteady flow structure of a reattaching shear layer

2002

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Spatio-temporal characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated through an extensive pressure-velocity joint measurement with an array of microphones. The experiment was performed in a wind tunnel with a Reynolds number of 33 000 based on the step height and the free-stream velocity. Synchronized wavelet maps showed the evolutionary behaviour of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. To see the relationship between the flow field and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering, termed ‘spatial box filtering’ (SBF), was introduced and examined. The vortical flow field was reconstructed using every single-point velocity measurement by means of the conditional average based on the SBF second mode of pressure fluctuations. The flow field showed a well-organized spanwise vortical structure convected with a speed of 0.6U0 and a characteristic ‘sawtooth’ pattern of the unsteady trace of reattachment length. In addition to the coherent vortical structures, the periodic enlargement/shrinkage process of the recirculation region owing to apping motion was analysed. The recirculation region was found to undergo an enlargement/shrinkage cycle in accordance with the lowpass-filtered component of pressure fluctuations. In addition, such modulatory behaviour of the vortical structure as the global oscillation phase was discussed in connection with the conditionally averaged flow field.

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“…Before making a detailed comparison of Plotkin's model to the reattaching shear layer data, we will briefly compare the model to data obtained in a blunt fin flow, which was examined previously by Poggie & Smits (1997). We include this digression because the theoretical model has not, to the best of our knowledge, been compared to any experimental data since Plotkin's original paper.…”

Section: Comparison With Theoretical Modelmentioning

confidence: 99%

“…The experimental model used by Poggie & Smits (1997) was an unswept fin mounted normal to the wind tunnel floor at zero angle of attack. The leading edge was a semi-circular cylinder of diameter D = 19 mm, and the free-stream conditions were essentially the same as those described here for the reattaching shear layer flow.…”

Section: Comparison With Theoretical Modelmentioning

confidence: 99%

“…The shock motion has a broad spectral content, but appears to contain two characteristic scales: one because of perturbation of the shock by organized structures in the flow turbulence and the other because of relatively large-scale, low-frequency expansion and contraction of the separation bubble (Poggie & Smits 1997). The shock motion may be driven in part by cyclic vortex shedding analogous to that observed in low-speed separated flows (Eaton & Johnston 1982;Driver, Seegmiller & Marvin 1987;Thomas 1987;Visbal 1991), and also by turbulence in the separation bubble and in the incoming flow (Bogar 1986;Erengil & Dolling 1993;Brusniak & Dolling 1994).…”

Section: Introductionmentioning

confidence: 99%

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Shock unsteadiness in a reattaching shear layer

Poggie

Smits

2001

J. Fluid Mech.

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The origin of shock unsteadiness in a Mach 2.9 turbulent reattaching shear layer was investigated experimentally using temporally resolved flow visualization and measurements of wall pressure fluctuations. In this flow, the separation point of a turbulent boundary layer is essentially fixed at a backward-facing step, and the reattachment point is free to move along a ramp. In order to examine the influence of disturbances originating in the incoming shear layer, artificial disturbances were introduced into the flow through steady air injection in the vicinity of separation. The effect on the reattachment shock system was dramatic: the intensity of the pressure fluctuations and the amplitude of the shock motion increased substantially, and power spectra of the pressure fluctuations showed a distinct shift to lower frequency. The spectra collapsed onto a common curve in non-dimensional coordinates based on a length scale derived from two-point cross-correlations of the flow visualization data and a convection velocity derived from cross-correlations of the pressure measurements. The data were compared to a theory developed by Plotkin (1975), which is based on perturbation of a shock by random fluctuations in the incoming turbulent flow. Plotkin's model mimics the manner in which relatively broad-band perturbations in the incoming turbulent flow lead to relatively low-frequency motion of the separation bubble and its associated shock system. It is an excellent fit to separation shock motion, such as that generated in a blunt fin flow (briefly illustrated here). In the present shear layer flow, this low-frequency motion was detectable in the spectra near reattachment, but contained considerably less energy relative to the shock motions caused by direct perturbations by the incoming turbulent structures. These results indicate that the shock motion in the reattaching shear layer is primarily caused by organized structures in the incoming turbulent flow.

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Wavelet Analysis of Wall-Pressure Fluctuations in a Supersonic Blunt-Fin Flow

Cited by 27 publications

References 20 publications

Cross-wavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers

Cross-wavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers

Multiple-arrayed pressure measurement for investigation of the unsteady flow structure of a reattaching shear layer

Shock unsteadiness in a reattaching shear layer

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