Nonlinear aspects of supersonic flow past a cavity

Abstract

Study of supersonic flow over wall-mounted cavities for two different length/depth (L/D) ratios is carried out experimentally. Unsteady pressure measurements were made on the front and aft walls of the cavity. Data analysis was performed on the experimental results so obtained. Spectra of the unsteady pressure data exhibit multiple tones. Higher-order spectral technique is implemented on the unsteady pressure data to ascertain whether these multiple tones are due to possible nonlinear interactions between the primary cavity modes (Rossiter modes) or not. Significant nonlinear interactions in the form of both sum and difference frequencies between the cavity modes are observed in both the cavities. The spectra of the cavity with L/D ratio 2 show distinct peaks due to nonlinear interactions while the cavity with L/D ratio 3 does not exhibit observable peaks in the spectra. The spectra of both the cavities show presence of low-frequency peaks of significant amplitudes. These low-frequency modes interact with the primary cavity modes to produce significant bicoherence values. The reasons for their existence could not be predicted. It is identified that the dominant mode in the spectra of the cavities is critical for most of the interactions observed.

On the modulating effect of three-dimensional instabilities in open cavity flows

“…This tool has been applied to the study of open cavity flows on many occasions, from Knisely & Rockwell (1982) and Isaacson & Marshall (1983) to Larchevêque et al (2004) and Gloerfelt (2006), but only a handful of works have focused the high-order spectral analysis on very low frequencies. Kegerise et al (2004) and recently Vikramaditya & Kurian (2012) highlighted the occurrence of nonlinear interactions between such low frequencies and the dominant frequencies of the shear layer in the compressible regime. The bispectrum of a temporal signal x(t) is the two-dimensional Fourier transform of the third-order cumulant, which is also written as…”

“…On the other hand, very low modulating frequencies -more than 10 times lower than locked-on frequencies -are generally disregarded. AMs at such very low frequencies have still been unambiguously identified in several studies (Neary & Stephanoff 1987;Kegerise et al 2004;Delprat 2006;Malone et al 2009;Delprat 2010;Vikramaditya & Kurian 2012). An illustration of such a phenomenon is given in figure 2.…”

Shock and shear layer interaction in a confined supersonic cavity flow

“…Cavity flows have been studied both experimentally [39][40][41] and computationally [42][43][44] in a variety of flow regimes from different points of view ranging from aeroacoustics [45][46][47][48] to heat transfer [49][50][51][52] . However, the majority of the outcomes from the computational analysis related to confined cavity flows assume clean flow in the freestream [53][54][55][56] i.e., flow without any shocks or compression waves (Mach waves).…”