Base Pressure Fluctuations on Typical Missile Configuration in Presence of Base Cavity

Abstract

Pressure fluctuations in the base region of a typical missile configuration at a freestream Mach number of 0.7 are examined experimentally in the presence and absence of a base cavity. The objective was to characterize the pressure fluctuations and explain the influence of base cavities on their behavior. Experiments include unsteady pressure measurements at six azimuthal locations. Substantial variation in the characteristics of pressure fluctuations is noticed along the azimuthal direction due to the asymmetry of the model. The base cavities are seen to enhance the base pressure and reduce the root mean square of the pressure fluctuations. Higher-order moments show diminishing trend as the length of the base cavity is increased. Spectra in the absence of cavity exhibit three types of narrow-band tones based on the Strouhal number. Type I tones disapper from the spectra for small-length cavities, whereas type II tones get suppressed. On the other hand, for the large-length cavities, type I tones get enhanced, whereas type II tones disappear. Autocorrelation and cross-correlation plots exhibit a large-amplitude, low-frequency oscillation that exists even after large separation times for the larger-length cavities, and virtually no such oscillations are visible for the small-length-cavity models.